Good evening everyone.  Can you hear me?
I'm assuming you can.
Welcome to the Royal Society.   I'm Alok Jha.
I'm going to be Chairing this event for you
this evening.
It's fantastic to see so many people here
to hear several talks about the future
of particle physics - one of the most
abstract of abstract subjects.
But as we've seen over the last few years,
the subject of the Large Hadron Collider,
theoretical physics and the Higgs boson
- these things seem to get an inordinate
amounts of coverage,
even more than main medical stories,
I think they talk to something within us all
about where we all come from,
how we do this complex stuff
and today we're going to be talking about
what happens after all of this.
So cast your mind back to July 2012.
This is a quote from Rolf Heuer,
the CERN Director General.
On 4 July 2012 he said,
after several presentations by the teams
at CERN he said,
"We have a discovery.  We've observed
a new particle consistent with the Higgs boson.
It's a milestone.  I think we can all be proud".
These aren't things that scientists say very often
in public scenarios but really it was
one of those things the whole world was watching,
even if the CERN web feed did
fall apart at certain points.
That's another story...
Now, this was a groundbreaking
moment in particle physics and it arrived
after a search of almost fifty years.
It was for something called, well nicknamed,
for better or worse, the elusive God particle.
I'm going to ask one of the Scientists on today
to tell you why that's a terrible name
for that particle, but...
I think what we're going to discuss here
is what this discovery means.
You know, what does the future look like?
Where do we go next?
Is the Higgs boson the end?
Does the Large Hadron Collider pack up and go?
The answer I will tell you is no, obviously.
There is plenty more to do
and there are many, many open questions in physics
and our Panel is here to go through all of those
and you'll get a chance to ask as many questions
as you like in as much complex detail
please as you like as well.
These are... you know,
we've got the real crème
of the physics community here so make sure...
if you can stump then,
that would be a great thing wouldn't it?
Think of a new question.
Alright, well let me introduce the Panel
to you very briefly
and then they will give 10-minute talks each.
After that, we're going to have
a 15-20 minute discussion on stage
where some of the Panel will talk...
will respond to each other's presentations,
and then we'll open the questions out to you.
So speaking first will be Professor John Ellis.
He's an FRS and Clark Maxwell Professor
of Theoretical Physics at King's College,
London and has worked at CERN since 1978
and is one of the founding fathers
of many of the theoretical ideas that we are
going to be discussing this evening,
including supersymmetry which someone should
ask him about at some point.
Then, Tara Shears,
who is an Experimental Physicist
and Professor of Physics
at the University of Liverpool,
she will hopefully tell us how
the Higgs was found;
what you do to collect all that data
and how you know you've really got a signal.
Speaking next will be Ben Allanach.
He's a Theoretical Physicist
and Principal Investigator
for Theoretical High-Energy Physics
at the University of Cambridge,
and he'll be talking about where we go next;
what are we looking for after the Higgs
has been found.
And last but not least, Terry Wyatt, also an FRS.
He is a Professor of Physics
at the School of Physics and Astronomy
in the University of Manchester.
And we're going to hopefully get him to wind up
and tell us a lot more about the measurements
of the Higgs itself.
So we found the Higgs two years ago,
but that's not the end of the story
for Higgs itself.
We need to find out how it works;
whether it's just one Higgs, many Higgs,
what does it actually do as a particle.
As a Physicist you need to understand more than
just the fact that it's there,
you need to understand how it behaves.
So, without further ado, Professor John Ellis...
Okay, thanks very much for the introduction.
Good evening everybody.
So, the theme of this evening
is the Higgs boson and beyond
and I'm somehow going to sort of take you up to,
but not quite to the discovery of the Higgs boson.
So, here you see the outline
of the Large Hadron Collider at CERN.
You can tells it's large because
that's Geneva Airport over there
on the right-hand side,
so the runway's about 4 kilometres long
and I remind you that the Large Hadron Collider
has a circumference of about 27 kilometres.
Of course, from the aeroplane you don't see
very much because its' buried about
100 metres underground.
So, our story is about how this man's predication
came to be verified by experiment.
This is a picture of Peter Higgs in 1965,
shortly after he proposed his ideas
and when he was trying to work out
some of the detail,
so if you look very carefully at his desk there,
you might spot some of his little secrets.
So, the Higgs boson is somehow the culmination
of a quest that's being going on for well,
more than a century to uncover the
fundamental constituents of matter,
and I always like to emphasise that you know,
we're talking about you know,
real matter, the sort of stuff that you,
even I, am made of right?
We're not talking about some airy-fairy stuff
that only exists in accelerators.
So, we know that all of the visible matter
in the universe is made up of
the same limited number of constituents,
so everybody knows that we're made of atoms.
Atoms have electrons orbiting around nuclei.
In the first half of the 20th century,
physicists figured out that inside those nuclei,
there are things called protons and neutrons
and you know, for a generation or so
it was thought that those might be
truly elementary particles.
Now we know better and in the second half
of the 20th century we figured out that
inside those protons and neutrons
there were things called quarks and those quarks
are currently the limits of our understanding
of nuclear matter.
So what we're trying to do now
is to understand better these fundamental
constituents of matter, the electrons,
the quarks in related particles,
and of course, also the forces between them.
So we have what we call somewhat prosaically,
the Standard Model of particle physics
which describes all the visible stuff
in the universe and it was proposed
in the 1960s by Abdus Salam
whom you see here,
originally from Pakistan although he did much
of his famous work at Imperial College
just up the road,
it was also proposed by Sheldon Glashow
and Steven Weinberg,
a couple of American theorists and they made
really essential use of the ideas of Peter Higgs
and his colleagues that we're going to
come to in a moment.
So the whole edifice of the Standard Model
rests on Peter Higgs' foundations.
So, this theory was proposed in the 1960s.
The first experimental verifications
of key predictions of the Model
came in the 1970s and if you come and visit CERN,
you're going to see the piece of apparatus
where the first evidence for the
Standard Model emerged.
I can't promise you're going to see anybody
in Lab coats like that;
you don't see many of those around
at CERN at the moment but anyway...
You can see the apparatus.
So that was followed in the 1980s and 1990s
by many different experiments that verified
details of the predictions of the Standard Model.
So what does this Standard Model consist of?
So I mentioned quarks,
so we know that there are
six different types of quark.
I mentioned the electron,
so we know that there are two, heavier objects,
very much like the electron,
apparently identical except for the fact
they just weigh more.
And then there are the neutrinos;
I won't say very much about the neutrinos,
they were very much in the news
a couple of years ago but unfortunately
for all the wrong reasons.
So these are the fundamental building blocks
of matter and between them we have
four fundamental interactions.
So two of them of course are familiar
from everyday life;
there's gravity that keeps even
Theoretical Physicists' feet firmly on the ground,
electricity and magnetism,
so the basis of light, radio etc.
And then inside the nucleus we've got
two fundamental forces,
the strong nuclear force that holds
nuclei together and the weak nuclear force
that is responsible for radioactive decay.
So I like to think of what you see on this slide,
as being in some sense the cosmic DNA.
That these particles they have properties somehow
to encode all the information you need
to make all the visible stuff in the universe
- almost all the invisible stuff in the universe,
because there is just one little thing missing
from what's on this slide and that is
where particle masses come from.
So the electron has to have a mass
- that's what determines the size of an atom.
The weak force is carried by a very
massive particle.
That particle the W was not massive.
Then only radioactivity would be as strong as
electricity and magnetism and not only would
we glow in the dark,
life would just be impossible.
So it's important to understand where
particle masses come from.
So let me just provide a little bit
more detail on that.
So one of the first elementary particles
to be discovered was the photon;
the photon is the quantum of light
and it was postulated by Einstein in order to
understand how light interacts with matter,
in particular, metals and it was actually
for that that he got the Nobel Prize
not for his much better known work,
at least to the lay public on special
and general relatively.
So, photon, particle of light and it is mass-less
so it always travels at the speed of light.
So I contrast that with the particles responsible
for those weak nuclear interactions
that I mentioned a moment ago.
So these were first postulated back in the 1930s
by Hideki Yukawa and they were discovered
actually at CERN in 1983 by Carlo Rubbia
whom you see here,
together with a large collaboration...
a little bit like a sort of action pre-play
of the Higgs discovery.
The big mystery about this particle
is that it is as heavy as a medium-sized nucleus.
So, particles have to have mass,
of course Newton told us
weight is proportional mass,
Einstein told us that energy is related to mass
but they didn't explain where the masses
come from,
and that's where Peter Higgs comes in;
that's his formula on the blackboard
and if you want more details,
it's on my t-shirt!
Now, according to his theory just as there's
a photon which is a quantum of light,
there is a particle called the Higgs boson
which is the quantum of his theory.
I should mention that there's an
Alumnus of King's College, London.
So this theory...
I mentioned Peter Higgs but he was just one
of several Theoretical Physicists who proposed
this idea back in 1964,
so it's 50 years ago already and I would like to
mention also a couple of young Russian physicists
who proposed the idea simultaneously
the following year.
These guys were 19 years old when they
came up with this theory,
so any of you who are older than 19,
sorry you're already over the hill.
So of all these, Peter Higgs was the only one
who mentioned the existence of this boson
and that's why it's called the Higgs boson.
So, I'd like to give you a little analogy
for thinking about the way this thing works.
So, the Higgs idea is that empty space
is actually a medium,
and it's full of something that we call a field
- think of electromagnetic fields,
think of gravitation fields...
but think of a universal isotropic field
that fills the whole of space,
much like Siberia is covered with an infinite
isotropic field of snow.
So what happens when you try to go through
this snowfield?
Well if you're a skier, you skim across the top,
you go very fast;
that's like a particle that travels at
the speed of light that does not interact with
that Higgs snowfield.
On the other hand,
if you are wearing snowshoes,
then you sink into the snow,
you interact with that Higgs field;
you go slower than the skier
- that's like a particle with a mass that travels
at less than the speed of light,
an electron maybe.
And then finally,
if you try to walk through Siberia,
you're going to sink very deeply into the snow.
You're going to interact very strongly
with that Higgs snowfield.
That's like a particle that travels much less
than the speed of light,
maybe a W particle for example.
So to complete the analogy, snow...
what is the fundamental particle of snow?
It's the snowflake.
So you can think of the Higgs boson as
correspondingly in a far more flaky way,
being the quantum of this Higgs snowfield.
So, this idea was proposed back in 1964.
My own involvement in it started in 1975,
a mere 39 years ago,
and with a couple of colleagues we wrote a Paper
previewing what this particle might look like.
At that time, these ideas were very speculative
and people thought it was
probably all bullshit...
Anyway, so for these reasons we wrote,
"We do not want to encourage big experimental
searches for the Higgs boson".
Fortunately, our esteemed experimental
colleagues didn't take our advice.
Anyway, I just want to take you up to
the situation just before the Higgs boson
was discovered and various other experiments
indicated that probably something rather like
the Higgs boson might exist and this is
a somewhat technical curve,
don't worry about the details
look at the bottom there.
This was the preferred value for the mass
of the Higgs boson and the prediction
was 125 ± 10, roughly speaking times the mass
of the proton and in the next talk,
you'll hear about what happened next.
Thank you.
Thanks John.
So John's explained to us what the Higgs theory is
and why it's so important
and he's also shown us that it's an integral part
of our Standard Model of particle physics,
an integral part of our understanding
and so if we want to confirm that the
Standard Model is correct,
we needed to find that Higgs boson
that's predicted to exist
and the theory helps us here,
because as John says,
it tells us how the Higgs boson behaves
experimentally, how it decays to other particles
and so that tells us what to look for
experimentally.
But the only catch is it tells us how the
Higgs does this as a function of its' mass
and it just didn't tell us what the
Higgs mass was,
so despite John's warnings in his paper,
it didn't stop experimentalists going off
and searching for it for years...
for years without success.
And so when the LHC was planned,
it was designed to be able to explore
the entire range of masses that
a Higgs boson could have if the theory
was correct and John alluded to that
in his last slide,
and Terry is going to tell us a little bit
more about how the Standard Model
could predict those masses or at least
the allowed range of them later on.
Now, before I show you how the
LHC discovered the Higgs,
I want to give you an idea and a feeling
for how it is that we do our business,
how we do our research at the LHC
and make that discovery.
John has already reminded us
that the LHC is a huge,
enormous particle accelerator,
the most powerful particle accelerator that
we've ever built and if you go and visit it,
which you can do at the moment by the way,
it's a good time, you can actually stand
next to it and you can see that
it's formed of a long, continuous chain
of blue superconducting magnets.
These make up beams of particles that circulate
in the accelerator, go around in a circle,
and these are interspersed by radiofrequency
cavities that accelerate those particles
and make them go faster.
And what the LHC does when it operates,
is to take two beams of protons,
that's a nuclei of hydrogen atoms,
circulate them in opposite directions
and it designs spec, get them going at
just 20 kilometres an hour less than the
speed of light and then when that's done,
the beams are brought into collision,
not just once or twice, but 40 million
times a second, and what's of relevance
in our search for the Higgs,
is that in every one of these proton/proton
collisions in a tiny, tiny area of space
for a tiny instance of time,
what we're actually doing is recreating
the very high temperatures of the very early
universe.
It's a regime where matter doesn't consist of
atoms or molecules;
it consists of fundamental particles.
It's a regime where we can expect
the Higgs boson, if it exists,
to momentarily come into existence
before it disappears again.
Now by early, I do mean early
and we're talking about billionths of a second
after the big bang.
Now, collisions happen at four points around
the ring and around every point,
we build an experiment which essentially
behaves like a gigantic three-dimensional
digital camera.
It takes a snapshot of the particles that are
produced in a collision and records them,
so that we can analyse that information later.
And two of the four experiments have
a particular role to play
in the search for the Higgs.
There's the ATLAS experiment first of all,
and this is a very early picture of the
ATLAS experiment that was taken
during construction.
I just want to put it up here to show you
that just as the LHC is incredibly large,
so our experiments are no less large.
The ATLAS experiment is 20 metres high
and this really is a real person standing
in front of it, to give you that sense of scale.
And the other experiment participating
in the search for the Higgs is the sister
experiment located on the opposite side
with the LHC ring.
It's called CMS.
The C in this case stands for compact,
believe it or not,
because this is only 15 metres high,
instead of 20 metres high,
even if it weighs twice as much as the
ATLAS experiment.
Now although these two experiments
look very different, they...
they behave and we use them
in exactly the same way.
So if you were to cut these experiments in two
and look at them in cross-section from the
collision of the protons on the left to the
outer-most layer of the experiment on the right,
you'd see that they're constructed as a series
of layers of precision particle detection devices,
each with a different job to do;
each telling us different information about
the particles that are produced in the collisions
that helps us identify them.
So, if we record this information and we
analyse it using computers,
we can actually identify the particles that are
produced in collisions by how far they penetrate
into the experiment before they're absorbed
and by the specific patterns of energy deposition
they leave behind.
And in that way, when the LHC operates,
we can record event snapshots like this;
we can identify each of these particles
and then we can match it back to our theory
of how we expect Higgs to behave,
how we expect it to manifest itself
in our detectors.
We can identify the signature which is...
which signifies the Higgs and then test our
hypothesis to see how well it matches.
And this is a sort of way that
our Higgs search goes on.
We analyse as many of these snapshots
as possible.
We look for evidence of Higgs production,
we match it to our hypothesis,
we see how well it fits,
and we let the evidence mount up and up and up
as well analyse more data.
Now the LHC has been operating for some years
and already by 2011 we started seeing
the first hints that there might be something new
there in the data, something unexpected,
and by 2012...
July 2012, CERN had a public seminar
where they announced the latest results from
the CMS and ATLAS experiments and this was
based on the analysis of about
300 trillion proton/proton collisions,
just to give you an idea of the vast amount
of data involved in this exercise.
Now this was incredibly exciting for us because
we all had an inkling that something amazing
was going to come out of it.
If you were on CMS, you knew what you'd seen...
well at least in the two days or so leading up to
the seminar you knew what you'd seen,
but if were on the ATLAS experiment,
you had no idea, and vice versa.
And if you weren't on either of the
experiments like me,
you had no idea what anyone had seen
and thus it was all extremely interesting
and exciting.
So, for the seminar, CMS went first.
They showed their evidence and they summarised
with this slide,
and they demonstrated to us in 25 minutes
that they had indeed seen something genuinely new;
a new particle, we knew it was new
because it had a mass unlike anything
that had been seen before,
that 125 times the proton mass that John
had predicted a few moments ago,
and we'd seen it at a very significant level.
This is an extremely exciting statement if you're
a particle physicist,
probably not if you're not.
I should just explain it -
in particle physics we have a threshold
to define when something is discovered or not
in terms of the significance that you've reached.
Unfortunately it's at 5 standard deviations,
not 4.9.
5 standard deviations just corresponds to
a chance of one in 1.7 million that background
fluctuations have mimicked your signal.
It's a very safe level to be certain
that you've actually seen something new.
Because CMS hadn't quite reached that level,
the word discovery does not appear on this slide.
Next, ATLAS went up and showed their evidence
and remarkably, they saw the same phenomena.
They also saw evidence of a new particle
with the same mass and with the same sort of
level of significance.
And this is extremely strong in physics;
two independent experiments with independent data,
independent people analysing it
in independent ways, seeing the same thing.
And it was at that point that we realised
that something really big was happening.
It was at that point that Rolf announced
we thought we had it,
and indeed we did.
We thought we'd made a discovery,
we knew we had moved physics on.
We knew that this indeed as The Economist said,
was a giant leap for science.
Now CERN that an inkling that something big
was going to come out of this so they'd actually
invited as many of the theorists involved
in the Higgs predictions to attend the seminar
as possible.
So here's a photograph of two of
the most famous, François Englert on the left
and Peter Higgs on the right.
You might recognise one of our esteemed
Panel colleagues in the VIP seats at the front.
Remarkably, this I believe was the first time
that these two theorists had ever met in person,
although they subsequently went on to meet again
last year during the Nobel Prize.
Now, as John has said,
it's taken almost fifty years to discover
this particle and confirm its' existence
and I want to spend a moment before I stop
just telling you why that is.
There are two things you need in
an experimental facility to make this discovery
as we have now realised.
One is you need sufficient energy available to you
in order to bring this particle into existence
because it's very massive.
The other thing, the other vital ingredient
is to be able to generate the huge amounts of data
that you need to sift through to see it,
because the Higgs is produced very, very,
very rarely and only the LHC has had
that particular combination of features out of any
of our facilities and that's why we've only
just been able to find it.
Now let me give you idea of just how rare
the Higgs is.
I'm going to show you a time-lapse animation
of how the data has built up in one of the
discovery channels from the
ATLAS experiment.
So what you're seeing here;
the points are data accumulating for events
passing our selection as a function of the mass
at which they're happening,
to be compared to this red histogram that
shows you what background processes
we expect to contribute.
Now to make a discovery, we need an accumulation
of data that's not predicted by a background
and you can see, it's only where the entire
datasets and a thousand trillion
proton/proton collisions,
that you can be sure you're seeing something new
and it's only by comparing that to what you...
how a Higgs should behave that has that mass,
seeing it matching that gives you confidence that
not only have you discovered something new,
but you have discovered something consistent
with the Higgs.
You have discovered something that's most likely
a Higgs boson.
And since then, we've analysed more properties
of these particles and that's lent credence
to the hypothesis that they are a Higgs.
Now there are very few candidates there
and ATLAS and CMS have each only identified
about a thousand of these Higgs bosons each
and that forms us some level of our knowledge
experimentally about these particles
so although now we're confident
we've discovered a Higgs,
we still don't know if it's THE Higgs
that we expect from the Standard Model
and our tests to distinguish this rely upon things
like counting how often we see a Higgs boson
manifested in our experiments,
to specific experimental signatures.
We count how often we see it,
we count how often we expect to see it
if its' a Standard Model version.
If you see it as often as you expect,
then all of these points should line up at one.
This is the state of the art.
You see, there's a bit of fluctuation,
you see there's not very much precision
in our knowledge yet.
So, to move further and to explore
the question of whether we've seen
the Standard Model Higgs
or something even more exciting,
demands more data which we'll get when we
restart an LHC or possibly new facilities
and Terry will tell us more about that.
But already this wiggle room is still causing
immense excitement theoretically.
There are some twenty five papers that come out
each week onto our archive
with Higgs in the title,
that try to explain its' behaviour in terms of
something more exciting.
And now I'll hand over to my colleague Ben,
who will tell you what some of those
potential things might be.
Thanks a lot Tara.
It's going to take a little while for this
to load up.
Can you hear me at the back?
Yeah, okay.
I see my visitors made it at the back, good.
I'm glad you made it!
Okay so Higgs boson.
What an amazing discovery and how exciting
that was for all of us.
I remember in our Department,
I'm the one sort of most closely related
to that kind of physics so when they...
we heard that the webcast was going to come on,
I organised a projection of it in one of our rooms
and got everyone to come and I explained to them
beforehand what, you know what we might see
and what we might not see and then of course
the webcast didn't bloody work
and it was really embarrassing!
But still, when we managed to...
we still managed to find out what the news was
and you really feel like you're, you know,
part of something bigger than yourself
and it was quite a feeling.
It's brings shivers up the back of my neck
just thinking about it.
But what I want to talk about now,
is kind of slightly raining on that bonfire,
because it seems theoretically, there's a problem
with the Higgs boson.
There's a problem with the theory that
we don't understand and I want to talk to you
about that problem and how we might
resolve the problem,
by going beyond the Standard Model in our theory.
So the problem with the Higgs boson
is a problem with its' mass.
It's too light.
If we use Standard theory and we calculate what
its' mass should be,
you get an answer that's a billion
billion times heavier than it was measured to be.
Okay?
The reason it comes out to be really heavy
is because of the vacuum.
Okay, so the vacuum doesn't really exist.
Space-time has little particles popping in and out
of existence all the time.
This has predictions which you can measure
and indeed some of the experiments at CERN,
you know, some of the measurements at CERN verify
that this is the case and what they do is they
alter the mass of the particle that you produce.
This seething of the vacuum alters the mass.
Other particles that we know about,
they feel the effect of this seething vacuum
but they're masses are protected by
a mathematical symmetry in the theory
which means that they get small corrections
to their mass, no big great shakes...
but the Higgs, the Higgs has a problem.
It has no mathematical symmetry
and the corrections to its' mass tend to be huge;
and so much bigger than was measured.
So how do we resolve this problem?
Well, when you look into it in a bit more detail,
you realise that the particles that are popping in
and out of existence actually affect
the Higgs mass differently. So to explain this,
it depends on the spin of the particles
that are popping in and out of existence.
Particles, it turns out spin.
They have something that is akin to the...
they're like little spinning tops.
But unlike little spinning tops,
they can't spin at any rate.
They have certain amounts of spin.
They can have a zero units, half a unit,
one unit, three halves of a unit and so on...
And it turns out that all the ones
with whole units of spin,
they make the Higgs heavier when they pop in
and out of existence around it and the ones with
half units of spin, they make the Higgs lighter.
So this is a clue that if you can impose
a mathematical symmetry on your theory
that says okay, so...
that relates the spin of half particles and
the whole number spin particles,
maybe you can get the two contributions
to cancel exactly, or almost exactly,
and keep the Higgs light.
And this would explain why it's not
got a huge mass.
And indeed, this theory is called supersymmetry
and it's something that we all work on...
we're all familiar with
and John and I work on a lot.
And so this relates particles of
the different spins, half into just spin
and whole spin,
so if the rest of these properties
of the particles are similar between these
different spins,
then these large quantum corrections from
the seething of the vacuum,
they cancel each other.
So okay, that's all well and good.
This is a nice theoretical set-up,
you can make it all work with the mathematics,
but how do you tell...
you know, what's the signal?
What's the snowflake?
the quantum of this theory that you can measure
in an experiment because at the moment
it's just a speculative theory.
It explains the mystery about the Higgs boson
but we don't know whether it's right or not.
You want to be able to measure something
experimentally to tell whether it's correct.
So John already introduced these particles.
These are all but one of the particles
in the Standard Model and if you say okay,
I'm going to take this supersymmetric
theory seriously, what happens to this picture?
What happens is each of these particles gets
a copy of a different spin with all the other
properties being the same,
so on the left-hand side,
these are matter particles so we have up and down
quarks in our protons and neutrons for instance.
They're spinner half-particles.
These particles on the right-hand side,
those are particles that carry forces,
so for example, the photon,
the particle of light, those are all spin-one.
So if you impose supersymmetry on this theory,
you get a doubling of the number of
possible particles that can exist
and so if we looked at this up quark here
spinner-half,
that gets a supersymmetric copy,
that's called the squark, strangely, it feels
the same forces in the same strength
as this guy only it's spin differs by zero units
and its' heavier.
And so that happens for all of these particles
and so we get this kind of doubling
of the spectrum and so now you've got
your snowflake.
What you want to do is produce any of these
in the Large Hadron Collider
and measure them,
measure their properties and check they are
what you think they are,
and then you've verified this supersymmetry
theory.
Now, there's another interesting case...
another interesting thing about these guys here.
In here for example,
the supersymmetric copy of light,
the photino, that's a candidate for the
dark matter of the universe.
Galaxies go round too fast on the outside
to compare to what you predict using
in neutronium gravity and so we infer
the existence of tiny, invisible particles
which make up a lot of the mass of the galaxy
and so the question...
there are no particles in here in the
Standard Model that have the right properties
to be the dark matter, but when we put
supersymmetry down on the theory,
indeed we get candidates here that have
all the right properties;
they are electrically neutral,
they don't interact with light,
but they're heavy, so they make
the galaxies rotate in a certain way
which agrees with observations.
So okay, so we want to find these,
we want to collide protons at the LHC,
we want to turn the energy of the beams
through Einstein's E=mc² into mass,
these heavy...
the mass of these heavy particles.
They'll then decay very quickly,
they're predicted to decay within
in a fraction of a second, well within...
and like Tara's video showed,
you get a kind of spray of other particles
coming out, ordinary particles,
and so you have got to do
a bit of detective work and measure those tracks,
measure all the properties and you know,
kind of reverse time in your calculations
back down to the instant when the protons hit
and verify using the maths that indeed you produce
some of these particles.
So what would that look like?
Well here you have a mock-up,
a cartoon of one of the detectors,
ATLAS actually,
we've cut away the front quarter so you can see
what's happening.
So the proton has come in from
the right and the left,
those are these red arrows.
Now they have equal and opposite momentum,
these protons and school physics will tell you
that total momentum is always all-conserved.
So because the momentum is equal and opposite,
the total momentum is zero.
So after the collision when you produce
these fiery tracks,
the total momentum will also be zero.
If you've got tracks coming out one side
of the detector...
particles coming out one side,
they should be balanced by particles coming out of
the other side.
Now, if you see...
if you see collisions like this
where the particles all come out on one side
of the detector that seems to disagree with what
I just said, right?
So what you infer from this is that
an invisible particle was going in the opposite...
at least one...
was going in the opposite direction.
So you have to do this many times,
these collisions, many times.
You have to measure lots of these events,
do the maths and calculate how often
you know you miss particles down cracks
for instance in the detector or they just don't
trigger the electronics or whatever,
that's your background in this case, and then...
but the point is that this signal of you know,
this missing momentum in this direction,
that's precisely what you'd expect if you produced
some supersymmetric particles which then decayed
to dark matter;
the dark matter supersymmetric particle.
The dark matter interacts only very weakly
gravitationally but only very weakly
with ordinary matter so the prediction is that
it would go straight through this detector
and in fact probably through the Jura Mountains
just behind CERN,
without interacting with anything
and so it acts like a thief,
stealing momentum off from this collision
and so the momentum that you see in the tracks
doesn't really balance.
And so this is like the smoking gun signature
actually for production of dark matter
but it's been applied to supersymmetry
which has the dark matter in it.
Okay.
Now, of course the Large Hadron Collider
isn't the end of the story, we hope.
There are...
sorry I should point out actually
before I go onto that,
this is a speculative theory.
We don't know if this is right.
I mentioned this before and the LHC is shut down
at the moment and is going to start up
next year with double the energy
and so the idea is that it hasn't found
unambiguously any supersymmetric particles yet
but the idea is that they are too heavy...
they were too heavy really
for it to have seen them but the energy
of the beams is going up
by almost factor of two next year,
and so we hope...
we've got great hopes that within the first year
or two, they'll be a discovery
because you can now make the heavier
supersymmetric particles,
measure events like this, do your analysis,
and say okay we've got a signal for something new
that's beyond the Standard Model.
So now, Terry I think is going to talk about
what could happen after the LHC
with future colliders.
Perhaps we can do collisions
at higher energies and so on.
Thank you.
Yes, so I'd like to talk in
a little bit more detail about some of the physics
of Higgs bosons that we would like to study
and some of the accelerators that we might build
in order to make these studies.
So as we've heard, we've found a Higgs boson
but in order to see whether this is really
THE Higgs boson of the Standard Model,
we have to make much more precise measurements
of its' properties so when the LHC turns back on,
we're going to be measuring many more...
collecting many more Higgs bosons,
measuring their mass,
measuring the way in which Higgs bosons decay,
as Tara has already said,
by looking at the number of different Higgs bosons
that we see in different possible ways
in which the Higgs boson can decay,
we can measure the strength with which
the Higgs boson couples to all of the other
different particles of the Standard Model
and indeed itself,
which is an important part of the Standard Model.
And so we are going to be making measurements
like this and we will expect everything to lie
on a nice straight line like this,
if this is really the Higgs boson.
And in some sense, this mass of 125 GeV
is very serendipitous.
It means that the Higgs boson whose properties,
now know that we know its' mass are completely
predicted by the Standard Model.
It should decay into many different possible types
of other Standard Model particles with rates
which are observable at our accelerators.
And there are actually many possible
future accelerators that we might build
in order to make more precise studies.
But in fact, it's not just looking at
the Higgs bosons themselves that we want to do.
We also want to look at this question,
how did we know the Higgs boson was there,
even before we had found it?
Or how did we have such strong evidence
that it was likely to be there?
And this is related to this seething vacuum
that Ben was talking about.
Even before we'd managed to produce Higgs bosons
and see them in these pictures from ATLAS and CMS,
we have seen the indirect effects of Higgs bosons
that have sort of just popped out of the vacuum
and then, for example,
if we produce a W boson, a Higgs boson could
sort of pop out of the vacuum and then get
reabsorbed by the W boson before it decayed.
This leads to subtle...
as Ben was saying
for the Standard Model particles,
subtle effects but ones that are nevertheless
observable and this is sort of summarised
in this picture here.
What this shows is that there are
these green bars here;
these show the actual measured values of
the mass of the W particle in these units
that John introduced as being about the mass
of the proton,
that's the mass of the W,
and this is the mass of the top quark.
Okay.
Those are there...
those are the observed measured values.
By looking at those kinds of processes
that I just saw whether Higgs boson was produced
inside a vacuum fluctuation,
then we could look at various different
measurements and come up with indirect evidence
that the Higgs existed,
for the Standard Model to be consistent with
all of those measurements,
and that gave us this grey ellipse here.
And the fact that that grey ellipse overlapped
with that cross there,
which is the direct measurement,
was already a very, very strong indication
that the Standard Model was correct
and that the Higgs boson had to exist.
Now we now the Higgs boson exists,
and we know its' mass,
that gives us a band in this direction here,
and if we combine the measurement
of the Higgs mass with this indirect information,
we get this little blue ellipse here.
And the fact that this blue ellipse overlaps
with that cross is even more strong evidence
that the Standard Model looks to be correct.
But what we would like to do as well as
measuring the properties of the Higgs boson,
we would like to shrink down
these uncertainties here;
repeat all of these measurements to be much more
precise so that we can test whether
the Standard Model is really right,
or whether you know,
if we shrink these error bars down,
maybe that cross and that ellipse will no longer
overlap.
That would be one indication that there is
new physics of the kind that Ben
was talking about.
In order to do that part of the programme,
we're going to back to colliding electrons
and positrons and I'll explain a little bit
about that later on.
Okay.
Another thing which is important to test,
which again relates to this...
what goes on at very high energies,
is to study...
when two of these Vector bosons
collide with one another and the fact
that they can have a Higgs produced here,
is an essential part in making
the Standard Model behave itself
when the collision energy of these W or Z bosons
gets to be very, very large
and that's another part of the thing
that we want to measure.
And one thing that comes out of these
supersymmetric theories for example,
is the prediction that there shouldn't just be
one Higgs boson, there should be
a number of Higgs bosons and so we're going to be
trying to look to see are there any more
Higgs bosons,
for examples ones that are at higher masses
than we've been able to explore.
Now there are lots of different possible
future accelerators that you could dream up
that you'd love to have if you were
a particle physicist and if money were no object,
or if the Government just thought that
giving money to particle physicists was better
than giving it to banks for example...
So, and when we think about the future,
we have to remember that the LHC has so far
collected 1% of the expected total amount of data
and at half of the centre of mass energy
that it was originally designed to deliver.
So the LHC has a lot still to go for it.
In fact, it's likely to be running
until about 2035,
before we finally give up on that machine,
and so there's lots and lots of potential
to discover particles of the kind
that Ben was talking about.
But looking then into the future,
we would love to be able to build
an electron/positron collider
in order to study this Higgs boson.
There are some advantages of doing that.
We have much cleaner events,
because electrons and positrons are fundamental
particles whereas as John has told us,
the protons are sort of...
they're messy,
sort of conglomerations of particles
which are much more difficult to understand
what's going on when we collide them.
And so one possibility is to build something
that's called that International Linear Collider;
I'll say a little bit more about some of
these things in a minute,
but I just wanted to give you an overview first.
So this could collide electrons and positrons
and might get up to an energy
of about 1,000 GeV.
Another possibility that people are starting
to think about seriously,
after the LHC is finished,
to build an even bigger circular tunnel
near to Geneva,
something like 100 kilometre tunnel,
and the idea there would be to sort of repeat
the history of the LHC tunnel,
first of all to have an electron/positron collider
that we could use to study the Higgs
and then to build an even more energetic
proton/proton collider.
Another way of doing electron/positron machines
would be to build this thing called
the Compact Linear Collider
which is a different technology that might
get us up to an electron/positron centre
of mass energy of around 3 tera-electron volts
and people even dream of being able to
collide muons, which are highly unstable particles
but do have some advantages if you want to
build a very, very high-energy collider.
Muons are fundamental particles
as John explained,
that are like electrons only more massive.
These dates here you should take with
a certain punch of salt and if
history is anything to go by,
they'll turn out to be wildly over-optimistic.
Okay.
So roughly what might this new collider
at CERN look like?
Well, you've seen...
this tiny little insignificant white circle there.
Well that's the LHC tunnel,
27 kilometres in circumference,
and people have started to look at the geology
around Geneva.
They've worked out you really don't want to go
under the Jura Mountains because it's limestone
and there's all sorts of underground river
and things like that,
and there's some more mountains over here,
so the best thing to do is to build something
that's big enough to go all the way round
the mountain so you don't actually have to
go under it.
This...
actually digging the tunnel is the easy bit.
The difficult bit is building magnets
which are two or three times as high field
as the ones which are currently in the LHC
in order to be able to bend these extremely
energetic particles round into a curved path.
And so, that's a difficult problem in principle,
it's a difficult problem to build...
then to put these things out to industry
so that industry could build them on the
sort of vast scale you'd need to fill
a 100 kilometre tunnel with them.
But there's R and D going on now
that maybe will solve some of these problems.
And there are other places
in the world for example,
China where people are thinking along
similar lines.
So I want to say a few words about these
electron/positron colliders.
The ILC, the International Linear Collider...
the idea here is to build two linear colliders
and one accelerates electrons and one accelerates
positrons and they collide in the middle.
It's actually fairly established technology.
You need to achieve extremely high
accelerating fields for these particles;
something like 40 million volts per metre,
so in one metre of this accelerator
you can accelerate a particle through
40 million volts and then you have
something like 30 kilometres of this
in order to get up to the
kinds of energies that you want.
It's...
it is established technology but it's
a huge facility in order to get up to what
is then in the end a relatively modest energy.
But you know,
it is certainly a possible way to go.
Another way, making use of this
100 kilometre tunnel if it were ever dug,
would be to build a ring collider
for electrons and positrons.
In fact, you actually have to build two rings.
The collision rate is so fast
that the particles would...
in the beams, you fill the beams
and then they would just decay away very quickly,
so you have to have another ring in which
you accelerate the particles up to
the desired energy and then you sort of
feed them in in a continuous fashion
into your main collider ring.
This has the advantage that you could probably
deliver a lot more collisions this way
than this way.
So that would be a good thing
if you build this tunnel.
There's another thing which I mentioned before,
the Compact Linear Collider.
So this is compact in the sense that CMS
is the Compact Muon Solenoid or the
Small Magellanic Cloud's are small, you know...
it's compact in a certain sense,
but it's still sort of 50 kilometres long
in order to accelerate... it has...
it achieves even higher accelerating fields
due to a very, very novel technology
that I don't really have time to go into.
I wanted to mention a few of the things
that we would want to study and a little bit
of why electron/positron collider is so useful.
So, these are the different kinds of processes
in the electron/positron collisions
that can produce Higgs's.
This first one is relatively easy to achieve
and this was the one that nearly led to
the discovery of the Higgs at the LEP accelerator
which was in the tunnel before
the LHC was built,
and if the LEP accelerator had just been
10GeV higher centre of mass energy
we would have found the Higgs at LEP.
And the advantage here is you collide electrons
and positrons, you know the energy
of electrons and positrons,
you then see as Z-zero boson which decays
so along the lines of conservation of
energy momentum that Ben was talking about,
you see this Z-zero,
you know what the centre of mass energy
and momentum was beforehand
and so even without seeing the Higgs at all,
you can reconstruct what the mass of the
particle was that would be recoiling against
this Z-zero that you see
and that's what's sort of plotted here.
So even if the Higgs was to decay to some of
these dark matter particles that Ben was
talking about that would be completely invisible
in the detector,
you would be able to see those particles
and learn a lot...
quite a bit about them.
That's something which is extraordinarily
difficult to do at the LHC because
the events are just so messy because the protons
lead to all sorts of rubbish that's flying around
which make it very difficult to see the Higgs.
It's difficult enough,
as Tara was saying to see the Higgs
when it decays into something you can see,
so when it decays into something
you can't see it's almost impossible because
of all the backgrounds which are there.
There are lots of other things that we would
like to study about the Higgs,
maybe I will just mention one more.
The Higgs has a mass,
and because it gets its' mass by
sort of interacting with itself,
this diagram here where we produce a Higgs
and then it produces...
it couples with another Higgs,
that's an essential part of the Standard Model
that we have to be able to verify.
It turns out that's extraordinarily difficult
to do both at the LHC and even in these
electron/positron colliders,
so this will be one of the most difficult
to achieve challenges and maybe when
you come back to The Royal Society in 2050,
people will still be talking about whether or not
we've seen this or not.
Okay, so just to wrap up...
From the discovery of W and Z bosons in 1983,
it took nearly 30 years to find the Higgs boson
and it may well be another 30 years before
we've fully understood all of its' properties,
so this is a long-term programme that
we're involved in.
We're all looking forward to the LHC turning on
and having higher energy
and a larger number of collisions.
Who knows what we'll see.
You know some people have
their favourite theories
like John and Ben, who knows...
maybe we'll find something completely different.
Maybe we'll find nothing at all
other than the sort of boring Standard Model
- we just don't know.
Because of that uncertainty,
we don't really yet know what would be
the next machine that we would want to build.
Hopefully when the LHC turns on,
it will just tell us,
it will just jump out of the data and say
build CLIC or build a 100 kilometre ring.
But at the moment we don't really know.
What we have to do now is
to do all of the R & D on the magnets
and the superconducting radiofrequency cavities
and do lots of design studies for detectors
and accelerators and things,
so that when the physics jumps out at us,
as we sort of hope it will,
we'll know which of these machines
we should build next.
And so... I'll end there.
Thank you.
Okay, I'll sit in the middle then!
Right, well thank you very much
everyone for your talks.
I'm just going to take some water...
I'm going speak...
we'll have a conversation on the stage
for just 15 or so minutes and then we will
turn over to you for questions.
John, I'd like to invite you maybe to respond to
some of these questions and things that are raised
by the other Panellists because you spoke first
and you didn't get a chance in your speech
to say any of that.
But before you do,
I'd like to ask you a question which is that,
we are talking here all the time
about July 4th 2012,
all the excitement that everyone went through
on that day,
I want to take you back to
the day before July 4th 2012,
I believe you were having rumours...
if the rumours are correct,
you were having champagne with Peter Higgs.
Now... did you know something at that time?
Well, no,
we knew that there was going to be
some exciting data but we did not know that
the two experiments would discover this new
particle independently.
Anyway, a few days beforehand I thought
it would be a really good idea if
Peter Higgs was there on the day,
so I tried to get in touch with him and you know,
persuade him that he really should come.
So he came the day before and so in fact,
yeah it's true we opened a bottle of champagne
with my wife who's sitting there and Peter,
and also Chris Llewellyn Smith
who was the Director General who got
the LHC approved.
But at that time, we didn't know
what the answer was going to be
but anyway...
we thought it'd be a good idea
to bottle of champagne either to celebrate
or to drown our sorrows, as the case may be.
So it was you that invited him up there wasn't it?
And by the way this bottle of champagne
is now a historic artefact;
it's in the exhibition that's touring right now
by the Science Museum.
This is correct;
you've donated it for the sake of history?
That's right,
as well as the page from my notebook
from the famous discovery seminar.
We had dinner with him like a week before,
because Cambridge gave him an Honorary Degree
and I managed to sort of buttonhole him and said,
are you going to CERN next week?
And he said, yeah,
and I said you know are you excited?
And we were both kind of jumping up and down
and he said he was excited.
He said he was excited?
This must have been after you'd contacted him.
I'm surprised CERN hadn't given him out
an invite anyway.
But fortunately he was there.
Well, they had but he wasn't too sure.
He was in Sicily at the time,
and you know, he doesn't like to travel too much
and so on and so forth
but I really put the squeeze on him.
Okay.  Well I'm glad you did.
Well let me ask about the theory that
you are associated with,
and Ben you mentioned as well...
supersymmetry.
This is the idea of going beyond the Higgs boson.
Now Ben you mentioned in your talk
that there is no physical evidence of it yet
and they were looking for it.
When can we expect there to be one of these
supersymmetric particles,
if it happens?
We've already pre-empted...
Yeah that's right!
What are we looking at because the LCH will
start up again next year going to full energy,
it's only at half energy up until now.
It's going to full energy...
when can we expect?
If we're reasonably lucky
then you know the LCH switches on early next year
with full energy and they'll start producing
supersymmetric particles from the word go,
so if we're in that lucky scenario...
I mean it's already there in the data
now it takes time to analyse, to collect you know,
a bit of data, make sure you know what's going on
with it,
you know people like Terry and Tara will be
sifting it and analysing it so that'll take
a good few months.
I mean it could be the end of next year.
You know, that will be a bottle of champagne
and John'll be having a good night.
We'll come back to the experimentalists
in just a second,
but John you've worked with supersymmetry
for decades and it's the big next idea
for the LCH to start working on...
It has been the big next idea for quite
a long while.
So tell me what, sort of, your thoughts are now...
this is the verge of some of your life's work
that's about to maybe come true or not?
Yeah.
Maybe I'll discover I've been wasting my time
for all of the 30 years or whatever...
I would like to comment,
perhaps building on something that Ben said
so there's this seething vacuum idea
which you know, you somehow tame
with supersymmetry and that means that
you're able to actually calculate the mass
of the Higgs boson and actually you know
we did some of those calculations
about 20-25 years ago and they predicted
that the mass of the Higgs boson should way
in the range where it's been discovered.
And Tara showed the properties of this Higgs boson
that's been discovered are quite similar to those
of the Standard Model and that is exactly what
you would expect in a supersymmetric model.
So it's true that we haven't found supersymmetric
particles yet, but the next best thing,
this Higgs really looks like what a supersymmetric
Higgs should look like.
Tara?
John, I have a question for you.
Actually for you as well Ben,
so let's say we start up the LHC in 2015,
we search, we search, we search...
Three years later there's still nothing.
How confident then are you both
that supersymmetry is still valid?
We'll give different answers
- slightly different answers to this.
You first John...
No, you go first.
Alright I'd say...
I'd start to get very worried after a few years
of LHC data.
The problem is, there's no strict cut off
where you can say okay,
it's definitely out now.
It gets more and more...
the higher you go up in mass in mass space,
which is what happens when you search for it,
the more and more uncomfortable you get.
The more accidental cancellations that you require
in the theory, and so there's no...
it's a bit subjective as to when you say okay,
I've had enough now.
You know, I don't believe in it anymore
and I'm going to look at alternatives.
I'd say that it's the best...
it's easily the best alternative
that anyone's thought of.
Hopefully there's something that we haven't
thought of that's even...
that you know solves it,
that would be great so we can tear up
the supersymmetry textbooks,
but I mean we must say that
we know that dark matter...
we're pretty sure, there are great indirect...
indications that dark matter particles exist
and so that's something beyond the Standard Model
and you know, so that's kind of there
independently of whether supersymmetry or...
exists or not.
So over to you, over to you John.
Well I'd like to say that over the
last couple of years I have been looking into
some of the alternatives precisely because
you know there was this Higgs boson
and there was no supersymmetry detected.
But eventually I concluded that in the centenary
of the Great War, I don't know of
a better haul so I've gone back to supersymmetry
and now I'm kind of thinking well how far
out there could supersymmetry be with this
100 TeV collider that Terry was discussing.
Would that be able to finally answer the question?
So this is what I'm thinking about at the moment.
So let me work that out
and then maybe I can answer the question.
Terry, can I ask you,
when thinking about the next generation of
collider,
and these things take decades to plan, build...
the LHC was you know,
in people's minds from the 80s...
How much do you...
what proportion of the decision-making happens
on people like Ben and John who come up with
theories and you want to test those theories
and they have to have particular predictions.
And how much is it just, well we need a detector,
let's find out what there is,
almost agnostic to what the theory might be.
I think we would,
before we make the next big decision,
we would love to have some direct evidence
for supersymmetry or for some
other new kinds of particles.
As Ben says, we sort of know there have to be
other particles beyond the Standard Model
particles out there because otherwise galaxies
and cluster of galaxies just wouldn't behave
the way that we see.
And of course we hope that those particles
will be of a mass which is small enough
for us to be able to see them when the LHC
turns back on.
So we would love,
and particularly I think as sort of
pragmatic experimentalists,
we would love to have sort of hard
incontrovertible evidence to tell us,
oh we should build CLIC or we should build
this 100 kilometre tunnel.
Maybe we won't have that luxury and you know,
you have to say, when...
in the middle of the 1960s when people
came up with these theories to explain
this incredibly esoteric-sounding problem
with the fundamental understanding
of elementary particles at the time,
that somehow the theories didn't seem to
quite work because the particles were
supposed to be mass-less and we knew they
had masses.
It sounded...
you know I wasn't around,
well I was around but I wasn't
a particle physicist at the time,
but you know,
looking back on it,
you're sort of amazed at the sort of vision
of those people and the fact that,
on these very esoteric grounds
and with a huge amount of sort of faith
in the beauty of the theory
and preserving the beauty of the theory,
this whole edifice was built up
and then 50 years later,
this particle was finally found.
You know, who knows...
maybe these sort of sceptical,
pragmatic experimentalists ought to listen
to our theoretical colleagues a little bit more
and share in their sort of vision and dreams
that supersymmetry is so beautiful
it has to exist.  I don't know...
John obviously has sort of...
his career has been sort of based on this idea
and sort of sceptical engineers you know,
like me, sort of don't believe him.
I think that it's actually very complicated
and difficult to discuss interaction between
theory and experiment because it's...
I mean of course what you want to do
is make model, independent measurements,
but you know these things are smaller
than we can see and you always end up with
some kind of modelling of what's going on
in order to be able to extract a measurement
and tell if you've got backgrounds or you know,
something new.
So it's actually very difficult to do
but of course you don't want to just listen to us
because, you know usually we're wrong, right?
I mean we make thousands of predictions,
you only need to right once though.
There are many more theories than there are
actual facts aren't there I suppose out there?
Let me just step back a little bit to explain
where we're at then with the physics.
Tara, can you just explain what it is
that's missing from the Standard Model?
So we've completed the Standard Model,
that's what everyone says,
but why is that not...
clearly not the whole picture?
Why do we even need to think about
supersymmetry or AN OTHERS theory?
The problem with the Standard Model is that
although it's incredibly successful as a theory
and so successful in fact,
that we haven't managed to find any discrepancies
between its' predictions and what we see
experimentally,
is that it's an incomplete theory.
We know it doesn't describe everything
that we know about in the universe.
John mentioned the forces that we know about.
Well only three of them are described
in the Standard Model, gravity is not contained,
so that's a pretty big thing to miss out of a
fundamental theory of the universe.
There's the dark matter that we've been
talking about as well.
The Standard Model doesn't tell us anything
about that,
it's completely unaware of it and yet,
the visible matter that the
Standard Model describes,
is just some 5% of the universe's whole
energy balance and then there are
other things as well,
I mean I could go on all night...
There's dark energy,
there's antimatter and the nature of antimatter.
Where the latter came from in the universe right?
Yes...
You're working on experiments
particularly looking at that and in the
Standard Model you don't understand how it is that
the universe produced matter in the universe
but no observable amount of antimatter.
Guys, you've had more than 70 years,
pull your fingers out seriously.
How much more have you got to do?
But the other thing that past accelerators
do of course, we hear about this in
the media a lot,
is as they get higher and higher in energy
they take you further and further back
into these questions of where matter from,
as in closer and closer to the energies
that were created just after the Big Bang,
and then you get things like cosmology
and particle physics sort of coming together
as the same thing.
How big can particle accelerators get?
If you wanted to go right back to
the beginning of the Big Bang to answer some
of these questions John,
do you have to build a universe essentially?
The cost is astronomical.
But I mean in all seriousness,
is there a limit to how far we can go
just experimentally?
I think, at the moment people have certain ideas
about how to accelerate particles.
So this Compact Linear Collider for example,
it's based on the idea that you can
achieve much...
you know something like two and a half times
the strength of the accelerating fields
to make your particles get closer and closer
to the speed of light.
That's a very novel technology.
As I say, you know compact is a relative term;
it's still 50 kilometres long which is quite large
and quite expensive.
People do have crazy ideas
of other ways of accelerating particles
that will produce even higher fields,
you know the idea is for example for...
in a hospital,
it would be great to be able to build
a little accelerator that was...
that was this big,
that your doctor could carry around in his pocket
that you could use for doing the kind of things
that you want accelerators in hospitals for.
And it would be great for particle physics
to be able to build something,
the sort of size of CERN that could reach
these tens or hundreds of TeVs.
So, who knows;
people have ideas and people are doing R and D.
It's hard to say at the moment
and it's hard to look into the crystal ball
and say what would be the highest possible energy
that you could achieve,
I just don't think we could say at the moment.
Yeah, I think there are plenty of
historical examples of distinguished
old physicists who said you know,
après nous le déluge,
you know nobody could imagine building
the next accelerator but somehow it's happened.
Somebody has come along with a new idea.
You know for example, back in the bad old days,
people used to bang particles into fixed targets
and now we realise it's a lot more efficient
to bang particles into each other.
It's trickier to do but if you can work the trick
then you get to much higher energies
and as Terry was saying,
there's all sorts of ideas out there
for bending particles more sharply,
and accelerating them to higher energies,
so you know,
I think there's life in the old dog yet.
If you go...
if you extrapolate out and really ask the question
what's the highest you could possibly go,
people do write papers on...
you try and accelerate particles by
doing a slingshot round a spinning black hole
to ridiculously high energies.
But I mean it's a bit tricky
to get hold of a big black hole.
- You need a black hole somewhere nearby,
don't you?
I'm going to ask one more question before
coming to the audience,
but let me see where the microphones need to go
so when we ask the...
do the questions from the audience
there's microphones going around
so wait till they come along.
So please put your hands up
if you want to ask something.
There we are,
let's go over there first and then,
wherever the microphone is closest,
there and then just here.
Keep your hands up.
And whilst the microphones are
going over to there,
one more question from me,
Tara let me ask you this,
we talked about the Higgs being the reason that
things have mass and this is what goes around
all over the place and is probably the one thing
that everybody knows about the Higgs now,
but in fact Higgs doesn't account for most of
the mass matter at all does it?
No, that's right.
It only accounts for the mass of fundamental
particles so particles like quarks,
like electrons, like these carriers of the forces,
the W and the Z bosons.
In fact, most of our mass that we have
in our bodies, in our atoms is a consequence
of the binding energy of the atoms
which comes from the strong force.
So I think the Higgs is possibly responsible for
about a fingernails' worth of your body weight,
if it comes down to it.
It's a very small fraction.
Keep that in your mind before going on about
the Higgs being the source of all mass everywhere.
I think it's always instructive to know that,
and it also tells you how much more we have
to understand about all of this mass
and matter come from.
Right, questions from the audience...
Did you have your hand up over here?
There you are.
Yes, we hear about bosons being force-carriers
and bosons mediating force,
but what actually do the boson do?
If the photon is the boson which carries
the electromagnetic force,
how does it work?
And also, do you need a boson to create
electric charge,
like you've got a boson for creating mass?
Have you got someone you specifically want
to answer that because I reckon
any of these guys can answer the question but...
John, do you want to give it a go?
I'll give it a go.
So you have a number of different,
interesting questions there so first of all,
how do these particles mediate the force?
So, you've got a particle going along like this,
it flashes off for example the photon.
Now that is going to carry some energy
and momentum.
So if it hits another particle,
it's going to give it a kick and that kick is what
we interpret as a force.
Now, you might say well why boson?
Couldn't I do that with particles that
aren't bosons, particles that we call fermions?
The trouble then is that they wouldn't add up
in a coherent way so you know,
one photon gives you a little bit of a kick,
another one gives you a bit more of a kick
and so on.
That builds up into what we think of as
the electromagnetic potential,
or what we think of as the gravitational potential
of the earth or in that case the gravitance
all adding up together.
So that was one part of your question,
I think the other part was could you imagine that
there is some particle that generates charge
in the same way that the Higgs generates mass.
And, yeah it's possible. And that is
in some sense what happens in string theory.
But that...
that's beyond, beyond the Standard Model.
Does anyone else want to add anything to that
before we go on?
Okay, there's a question here.
I wonder if you could explain what...
how this relates in a bit more detail,
how this relates to God?
Right, who wants to tackle that?
That's a question for them!
Do you mean God as in capital G, or small G?
Tara?
Are you referring to the phrase
the God particle by any chance?
Yeah.
Right. It's a phrase that none of us
are particularly keen on.
To put it mildly.
And I believe it came from Leon Lederman,
a Nobel Prize Winner in America
who wrote a book about his fruitless search
for the Higgs boson and...
The story is a little bit more
complicated in fact...
he was apt to call it that Goddam particle
and supposedly his editor said
well you can't say that
but you can call it a God particle.
But as you say, it's deeply...
deeply embarrassing and...
So in the interests of increased book sales
it's become known as the God particle.
Does that answer your question?
I don't think there is anything particularly
spiritual about the Higgs boson.
One good question about this, why is it...
you mention that only because Peter Higgs
mentioned the scale of Boson in his paper
and no one else did,
but if you speak to...
I've interviewed Tom Kibble
who was one of the other authors
around the time who came up with one of
the same ideas;
he might have been lying to me
but I don't think he was,
I said did you think there was a scale of Boson?
And he said yeah of course,
it was obvious that there must have been
but only Peter Higgs wrote it in his paper,
hence it's the Higgs boson.
Should it be called something else?
Is that a question that comes up ever
in physics meetings?
It comes up, but I think that you know,
too much water has you know,
gone under the bridge by now.
So I think, when we're very careful,
we refer to some of the other guys
when we're talking about the basic idea
for how you give masses to particles
but as say, you know,
Peter Higgs was the only one who commented
explicitly in his paper that you know,
this particle should exist and so on.
If you've got any names, do shout them out,
maybe there'll be a vote one day for a new name
for the Higgs particle.
Over here...
There was a question over here, other side?
So you outlined two benefits of supersymmetry
The accidental cancellations to bring
the Higgs mass back to what we measure it at
and then secondly the candidate for dark matter.
Does it have any costs?
So clashes with existing ideas or models
or internal contradictions?
Yeah, as usual supersymmetry comes with
a few problems which you need to solve
but we always see problems as opportunities
just like we did with the Higgs boson
mass problem;
that's an opportunity to discover some new physics
and you know increase our knowledge.
So, one thing that needs to be understood
with supersymmetry is called,
they're called flavour measurements,
but they're really about how the different
particles mix with each other and you can
make measurements of the way that some of the
particles decay and constrain that mixing
and you know that's something to be understood
with more detailed model-building
in supersymmetry certainly.
And there are competitors.
I don't think they do very well compared to
supersymmetry but there are other ideas,
people work with extra dimensions,
so-called composite Higgs models where perhaps
the Higgs isn't the fundamental particle,
it's made of smaller particles.
All of these things you know,
you need to consider and test them against current
and future data.
Perhaps if I could follow up on that...
you mention this problem of flavour,
which is how the various different types of
quark change into each other and in fact,
Tara's experiment, is studying that in
great detail and maybe a LHCb Collaboration
have stopped doing it now,
but there was a period where every few months
there would be a press release from the
LHCb Collaboration saying we've
killed supersymmetry.   Again!!!
And I remember one time I was
in some conference in Beijing and something
appeared on the BBC website
saying supersymmetry killed again.
So I wrote to the journalist saying
well you know I don't think it's really quite true
and so on and so forth.
So he said, may I quote you as saying that
you're not losing any sleep over it?
And I said yes you may.
And of course I was losing sleep,
because I had jetlag and I was in Beijing
in the middle of the night,
but I wasn't so worried about supersymmetry.
Okay, yeah?
I think this is one for the
theoretical physicists.
We talked about fizzing vacuums and
these particles that we can't see or detect
at the moment.
Are we started to see evidence of particles
that might have existed before the Big Bang?
Any evidence of particles before the Big Bang?
Now... there are many multiple questions there.
Well okay.
I missed something out that I meant to say
which was that these supersymmetric particles,
they decay really quickly
so just after the Big Bang,
they would have been around in the thermal plasma
if the theory is correct but they decay away
very quickly so there's none of them,
apart from the dark matter ones which are stable
hanging around in the universe today.
I don't know, my view is you can't...
currently we can't say anything about
before the Big Bang.
At the Big Bang, space and time cease to exist
and you're really lost in terms of theory
then because you've lost conservation
of momentum and energy,
you need space and time in variants
with respect to space and time in order to
define those things,
so I think it's unknowing...
I'd say it's unknowing.
I don't know if you've got any
views on that John?
Yeah, I think I would agree with you.
In fact precisely we think the concepts of space
and time didn't make any sense
if you go back that far,
you can't even talk about before the Big Bang.
Does the multi-verse theory take it anywhere?
Does that help in any way
or just complicate everything?
Is it even not real?
Well, you're talking here to a bunch of
fuddy-duddy old conservatives yeah.
I therefore feel we're not...
at least I'm not real big on the multi-verse.
My problem with it is its'...
in nearly all variants of it,
you can't test it.
So the multi-verse theory for those that
don't know is that you know there are
many different, perhaps infinite
but there are many different universes
and we just happen to be in one of them
where planets and human life can exist
and maybe in some of the others,
the laws of physics are different,
somewhat different but in most of the variants,
you can't test the existence of
these other universes so it's kind of fun
to think about it and it could even be right,
but how can you tell,
that's the important question.
Previous Presidents of this Society are now into
multi-verse theory of course,
so it's not THAT crazy.
Okay, down here.
Hello Panel.
Yeah I just wanted to ask,
can the Panel confirm that there is symmetry
between the Higgs boson theory,
Einstein's relativity and the multi-verse theory.
Is there symmetry between these theories?
Is there symmetry between those three theories?
They're big theories.
I'm not sure how you would answer that question
to be honest with you.
Does anyone want to tackle it?
There are some ideas about how you could
link many of these ideas together
and I'm thinking particularly of
string theory okay?
And, so string theory would put together
the Higgs boson and related particles,
it would put together the graviton and you know,
it could provide a framework where you could
put gravity along with all the other interactions
and string theory is actually one of
these theories that suggests that there might be
a multi-verse but so far it's very speculative
and we're always up against this problem
that Ben mentioned,
how do you test these ideas,
and you're talking to a bunch of people
who are really obsessed with actually
experimentally verifying these speculations.
Supersymmetry is difficult to test
and the string theory is even further
down the line, which could explain everything.
Let's go over to this side, does anyone...
Over this side, there we go.
A question for Professor Wyatt,
in terms of future possible colliders,
if they're based on the same model as the LHC.
Could you explain what is needed
in terms of the magnets to increase
the acceleration,
I mean are we talking about more
or just greater forceful magnets?
So for an accelerator like the LHC
where you are accelerating protons,
the thing that limits the energy
of the machine is the strength of the
magnetic fields that you have to bend them
into a circular path okay,
so at the LHC the magnets are about 7 Tesla
and with a ring of 27 kilometres,
you can work out that you can only accelerate
the particles up to about 7 TeV of energy.
So if you want to get to higher energies,
you either have to get more power...
more magnets that produce a higher field strength
so that you can bend more energetic particles
around in the same ring,
that's one possibility that people have discussed,
at some point throwing away the LHC
and putting a new accelerator
with even higher field magnets.
The other thing you do is to build
a bigger tunnel which then you don't have to
bend the particles as much because
they go round a bigger tunnel.
Or, the ideal is of course to do both,
so you have stronger magnets and also
a bigger tunnel and if you do that,
then you could,
with these kind of ideas that I was showing you,
you could get up to something like 100 TeV
in the centre of mass of your colliding protons
and so that would be a lot...
so the LHC is 14 TeV,
so let's say we don't find anything
and we still believe John and Ben
that supersymmetric particles exist,
then maybe we would find them
if we could build an even bigger accelerator.
Terry is that...
just a really quick thing here.
Is this the idea of building a bigger accelerator
and bigger magnets or whatever else;
is it a physics problem
or is it a money problem?
It's both.
It's an extremely challenging thing
to do to build...
you know the LHC magnets
were both an engineering,
but also a manufacturing feat at the time,
you know these magnets,
they started off as tiny little R and D projects
in labs at CERN,
building tiny little magnets that were this big,
that could produce these kinds of fields.
Then they build slightly bigger prototypes
and then they started putting some of this
prototyping out to industry
and eventually they managed to put this sort of
technology into three different companies
in three different European countries
that were able to build these huge magnets
on this huge industrial scale that you needed
to fill a 27 kilometre tunnel, so that was...
that was a small R and D project at CERN
which blossomed into this huge industrial process
with huge spin-off benefits it has to be said
for all of those companies.
But it was also a big financial thing.
It took the CERN budget,
which is of order a billion Swiss francs,
ten years or more to build this accelerator
so it is also a big money problem.
And that will be true for this new accelerator.
Now everyone wants to build these magnets;
people have these dreams to get to
20 Tesla magnets and in order to do that,
the kind of super-conducting,
very low temperature magnets
that we have in the LHC, just...
we know they couldn't possibly work at 20 Tesla.
You have to actually start building warm
super-conducting magnet elements
which are very, very expensive
and very, very difficult and you put those
in the centre of the magnet
and then you surround it with possibly
a sort of onion of other different technologies
and at the outside you'd have this
sort of old-fashioned LHC-type technology.
These are incredibly complex magnets
which don't even exist yet,
they exist in people's minds
but they don't exist even as small
little working prototypes at the moment
so it's a long challenge.
You raise a really good point Terry,
because I'd really like to emphasise
the long-term nature of researching
how to build a facility like this.
You've heard that the LHC...
it really started off its' design in the 1980s
and as Terry said,
at that point the technology didn't exist
to realise it.
It took years of R and D to get the magnets
to the stage where they could be manufactured
to the quality that is needed
and it's why we have to plan already.
It's why Terry has shown you this huge long list
of future accelerators,
because it's going to take us time to get there
and realise it,
and if we want to understand the answers
to these big physics questions
that are so fundamental,
then that's the sort of process we have to
go through and as Terry said,
it does have also the benefit of
yielding spin-offs along the way that benefit lots
of other industries too.
It is a money problem.
Clearly we're talking about extremely large,
extremely technically challenging projects.
These things cost lots of money.
You know, many millions of whatever
your favourite currency unit is,
but you have to put it a little bit in context.
When you think of what humankind spends money on,
you know...
not just the completely destructive things
that it spends money on,
but also a lot of the things that you know,
building bridges from nowhere to nowhere
just to satisfy some politician
or a motorway that nobody needs
or twenty international airports
built in a country just because it's got
so much money it doesn't know
what to do with it all,
and if you think of at least what we would maybe
somewhat over-grandiosely call
the sort of benefits to mankind of doing
this kind of work,
the number of people who get inspired
by hearing this kind of physics
and seeing the kind of...
the success following the successes
of these groups of people.
At least we would like to think
that this would be a good way of mankind
investing a very small fraction of
the kind of money that it spends
doing at best useless,
if not totally destructive things.
Can I just make one quick comment?
The...
actually the technology that's used
in the LHC for accelerating the protons
is now being used for treatment
of certain kinds of cancers with much smaller
proton accelerators.
I think there are five in the UK now,
is that..?
No, there are actually two going to be built.
That's right, that's right.
But there's one at UCL right?
Anyway, so CERN now is engaging
with this trying to get the cost and the size of
these things down so you get these
technologic spin-offs which are...
you know useful for health applications
and all sorts of other things.
Okay.
Let's have two more questions.
I think we're going to run out of time,
we're coming to the end.
There's one at the back,
and then we'll come back to the front here.
We'll get them both the same time
and then we can ask you to choose between
which one to answer. Just keep your hand up.
This is a question not unrelated to what
you are talking about now about the spend
and what you get back,
and what I'm interested to know is like
you obviously have a whole list of particles
to look for,
you've got a whole list of equipment
you want to build,
but like to the person on the street,
are there scientists and engineers going
please make it true because I'm waiting
for your theory so that I can make a...
whatever it is.
Like, does this theory enable you to put anything
into practice that people could interface with
anytime soon?
So say it just happens,
like you woke up and it's here now,
is there anyone downstream waiting for you?
- Great question,
hold that thought Panel.
There's a question here, just here.
If you could put your hand up,
and then...
This is a bit more for the theoretical physicists.
You have to point out if I've
got it wrong anywhere,
so graviton dictates how mass will interact
with other mass, so dictating how gravity works.
A Higgs boson gives things mass,
it dictates how much mass something has.
So how would those two bosons interact
if you've got something that defines the mass
but something defines how those masses interact?
Are they going to be sort of really similar
or really kind of opposite
or are they sort of the same thing?
What an interesting question.
I think there's a gentleman here who's been
asking right from the beginning,
we'll have you as well.
Why don't we start answering those questions?
You've kind of answered some of those Terry.
Could you stick your hand up, just here.
There you are, it's you.
You've answered some of those questions about
what happens if you discover the Higgs boson and,
What pratical use...
Yeah, what practical use is it?
So it's hard to imagine a practical use
for the Higgs boson itself.
As we've heard,
we haven't managed to produce very many of them
and the amount of energy we've had to expend
to produce them and then they only hang around
for a rather short amount of time, before...
you know you don't get long to make use of it
before it's decayed away,
but I hope we've given you at least a flavour
for the things that you do on the way
to finding the Higgs boson,
can lead to all sorts of totally unforeseen
consequences,
so for example, when a computer scientist
working at CERN thought it would be a good idea
for a physicist to be able to exchange information
with one another,
that would be convenient to be able to do
and a few particle physicists got together
and they, they sort of thought
oh that's actually quite useful.
Nobody imagined that the world wide web
as it then became,
would completely transform the lives,
I don't think that's too exaggerated a way of
talking about it,
this was just some spin-off of
a few computer scientists
and a few particle physicists getting together
and thinking wouldn't it be nice if I could
get access to some information on your computer
without you having to give me a password
so I could log into it and so,
some of these industrial applications
of things that Ben was talking about,
these proton accelerators for cancer therapy,
the kind of detectors we have to develop
to see these amazing pictures of these events
at the LHC have all sorts of spin-offs
for medical imaging,
for monitoring that people aren't
doing naughty things with their
nuclear power programmes.
There are huge numbers of spin-offs
but unfortunately if I tried to sell you
a practical application of the Higgs boson
I don't think you should buy shares
in that particular enterprise.
It's worthwhile just saying though
that when the electron was found,
no one had any idea what
the electron would do and...
Yes.
Or antimatter.
Or antimatter.
Antimatter is used routinely in medical diagnosis
when Dirac postulated back in the 1920s.
I think maybe buying shares
in the Higgs boson company might...
I fall into John's old farts trap, yes.
If I might just add one more thing
to what Terry was saying,
another thing that is really important
is the whole inspirational nature
of this type of science.
There's a great dearth of students,
school students going into stem subjects
and studies have been carried out of
physics undergraduates who always cite,
it's the big science that
attracts their attention;
it's astrophysics,
it's particle physics.
Now the Government have shown that
there's a stem shortfall.
If you want to rebalance the economy away from
financial services towards a more nuanced
and sustainable economy,
you need greater stem skills,
you need more engineers and it's through...
in a way,
our esoteric subjects that are so interesting
that attract children into studying them
who then go on to degree courses
who then go out and also benefit the economy
in other ways.
So there are all these intangible ways that
this type of research has a knock-on effect.
Now, I've not forgotten your question
but let's get yours as well
and we'll get the Panel to answer both
at the same time.
Thank you.
Can you explain if and or how
the gravitational waves breakthrough
has had any effect in the light of
what you've been talking about?
You're talking about BICEP2 and all of that?
Okay.
Well look, there's two very interesting questions,
about the graviton and how that interacts
with the Higgs boson,
the graviton if that exists, first of all.
And also the recent BICEP result
which showed that gravitational waves,
Einstein's gravitational waves,
are likely to be true,
or likely to be detected.
Who would like to tackle either of those?
Let me go for BICEP and I think
I would like to strike a somewhat
cautionary note...
Would you mind explaining John,
just for the rest of the audience,
what the result was and what it means.
Right, so the universe is kind of big
and old right?
And there's a theory called cosmological inflation
that provides a...
Let me call it an explanation of this
which is that very early in the history
of the universe it underwent a very dramatic
and rapid period of expansion.
and there have been various experiments,
satellites that have found pieces of evidence
for this,
in particular I would mention the Planck satellite
last year which verified one of the
key predictions of this theory.
But the real excitement came in March
when this other experiment, called BICEP,
found evidence for another key prediction of this
inflationary theory which is vibrations in the
fabric of space time and these would be
gravitational waves.
It is thought that these would have had
a quantum origin so they'd actually be
quantum gravitational radiation
so this was a big deal,
written in very big font.
Okay, but their interpretation of their data
is very much contested at the moment
by other experts in the field,
who say that they underestimated some of the
possible pollution of their signal and you know
it's possible that they are right
but I think the consensus is at the moment
that it has not yet been proven.
But if it were true,
then this would be fantastic,
because you would be seeing quantum fluctuations
in space time, they would have...
they would be in some sense gravitons,
so this would be as big a deal as the Higgs boson,
but let's wait and see.
Tara or Ben,
would you like to tackle the
graviton / Higgs boson question?
Okay, so gravity actually couples to energy really
and so it comes to mass as well
because mass is a form of energy,
so graviton couples to light for instance
which has no mass, but it has energy,
so light will bend when it's going round the sun
as was famously seen during the eclipse
in you know 1919,
that's right, by Eddington & Co.,
whereas the Higgs boson really is...
the particle itself isn't really the thing
that's responsible for generating mass.
It's this snowfield that John was talking about,
and it's really ripples on the snowfield
that we see as a particle.
So now, I'm getting kind of technical on you.
I realise...
So, it's not like the...
it's the particles really that give you mass,
it's this field that suffuses
throughout the whole universe
- you can think of it as a jelly or something
you know, that you know,
like the snowfield, that some things
you have to push through so they've got inertia
and therefore mass.
So they would interact.
The Higgs has...
Higgs bosons have energy and so it would be...
they would be affected a little bit by gravity
but they tend to decay before the gravity
can move them much.
That's the answer.
Alright.
Well we're going to have to
leave the questions there.
Thank you very much for all your questions
and thank you for coming
and can I just get you to put your hands together
for our Panel.
