It's a great pleasure to be here.
I'm delighted to see you all here.
I have to confess,
when Glenn asked me to do this with him,
I think we both enormously underestimated
the task of taking five or
six decades of work by thousands and
thousands of people and
compressing it down into three
hours without the use of equations.
In any case, what I want to talk
about tonight as Glenn indicated,
was the standard model
of particle physics.
And in particular,
talking about fundamental forces and
culminating in our understanding
of the origin of all mass.
So it's heavy stuff.
So the clock is in three parts.
First is terms that you will learn
along the way, fundamental forces and
gague bosons.
Then the second act will be to
answer the question, how do we know?
And then the third will be to
tackle the question of how we
understand mass is generated.
And to sort of advertise that we
are on the verge of knowing whether or
not this is right.
So what I want to start
off with is actually,
reviewing where Glenn left off last time.
Then we'll talk about
interactions between those and
then some mixing and matching of it.
So last time Glenn told you that
basically all matter that we know,
we first realized was made out of atoms.
Then that the atoms
are composed of electrons,
negatively charged particles circling
around a much much smaller nucleus.
The nucleus held together by
a force called the strong force,
composed of protons and neutrons.
And that those protons and neutrons
in turn were made out of quarks and
antiquarks.
Specifically up quarks and down quarks.
So almost everything that we know of,
that we see that were made of,
is in this first column.
Up and down quarks making up protons and
neutrons and the electrons orbiting them.
However, in the course of the 30s and
40s and so on, as physicists
began to explore the world further
additional particles were discovered.
First was the muon which looks
like a heavy copy of the electron.
It's about 200 times as heavy.
When it was first discovered,
Wolfgang Pauli,
the famous physicist's
response was who ordered that?
This was basically repeated over and
over again.
After the up and down quark, I think
Glenn told you about the strange quark.
Then subsequently, in the early 70s,
the charm quark was discovered and
then quarks called top and bottom.
Physicists, as you may have gathered,
tend to use somewhat facetious naming
schemes, not always very imaginative.
Now Glenn also told you I think
that the electrons are held
in orbit around the nucleus
by the electric force.
Which we've understood since Einstein and
the early days of the 20th century is
carried by particles called photons or
white quanta.
And then what I had probably only
vaguely alluded to, I think,
was that the strong forces is carried
by particles that look like eight
copies of the photon in first
approximation also have no mass.
And then the weak force responsible for
decay of nuclei
in radioactivity is now understood
to be carried by sort of
things that look similar to the photon but
weigh about as much as a rubidium atom.
And so the question is is how
to make sense of all this.
Now one thing that I did want to call
your attention to is the neutrino.
You know it has a close connection
with Case Western Reserve history.
Fred Reines,
who won the 1995 Nobel prize for
the detection of the neutrino
this very lightweight particle
with no charge that interacts
only exceedingly weakly,
was in fact chair of the Case physics
department from 1959 to 1966.
Now in actually working out this theory,
there's a formidable
amount of mathematical heavy
lifting that has to be done.
And in the 1930s as the theory was
being developed, the computations
that were developed were just long,
tedious, and prone to errors.
In the late 40s, a then young physicist
Richard Feynman came along and
realized that you could compress all that
mathematics into a series of pictures.
And the pictures basically could
be reduced to a couple of things.
You have lines with arrows
on them that represent
mathematical expressions covering
electrons or things similar to electrons.
And squiggly lines representing photons or
things similar to that.
And they can interact, basically at
a point, and so they bounce off.
Now this represents a very well
defined mathematical equation.
I'm not going to write it down.
We don't need that for what we're doing.
What I want to do is point out
some of the qualitative pictures
that you could get from it which will be
important for what we're doing today.
But every picture that I draw represents
a very precise mathematical formula.
So if we introduce the notion of time, and
ask what does that
particular symbol represent?
Well, it can represent several
things depending on the ordering.
You can have an electron coming along and
that a quant of light, say this
bounces off an electron in the room.
You would represent that
process by a diagram like this.
The electron gets hit with the photon and
the electron goes off in another
direction because it's been hit.
And so this is sort of a way of
understanding the electric and
magnetic force.
You can also have a situation in
which the electron is going along and
it emits a photon and
the electron recoils in another direction.
But you can also do things like this.
You have an electron going forward
in time emitting a photon and
scattering backwards in time.
And Feynman basically recognized
that you could think of
an electron going backwards in time
as an anti-electron or a positron.
Which I think Glenn was briefly
able to do going forward in time.
So what this represents is an electron
going forward in time colliding with
a positron moving forward in time and
emitting a photon.
So this is matter antimatter annihilation.
And you can have the inverse process, in
which you have a photon coming along and
then designing to turn into
an electron and a positron.
And where again, in some sense you can
think of the positron as the electron
moving backwards in time.
But all of these different processes
are represented by that same initial
diagram that I drew.
So how would you actually know
if this makes any sense at all?
Well, so how do we measure it?
First thing is is how do you tell the
charge of a particle that's moving along?
Well, there's basically
two things you can do.
You can send a charged particle
through an electric field.
In which case, from combing your
hair in the winter and so on,
that static electricity will
attract other charged things.
So you can bend things that way.
You can also,
if you've got a magnetic field and
send a charged particle through it,
it will also bend.
And so for a given magnetic field,
the positive particle will move in one
direction and the negative particle
will move in the other direction.
But how do you see the particles at all?
Well, in early technology that originally
what was called Cloud Chambers.
The next generation technology
were called Bubble Chambers.
And what you see here is a famous
Bubble Chamber called the big
European Bubble Chamber because
it was big and in Europe.
For size, you can see my son
here standing underneath.
And so this was one which was
commissioned in the late 1960s.
It was filled with liquid hydrogen.
It had a big plunger that dumped
some particles through it.
Pulled the plunger down just before that,
and when the particles went through,
they would cause the hydrogen
to boil along the trajectory.
Everywhere that the charged
particles ionized,
and then they'd take a picture of it.
And during the history of this, I think,
this chamber was used for something
like 23 million photographs in 22
experiments over about a 20 year lifetime.
And then someone had to go in and scan
every single one of those photographs.
Again, I point out the CWRU connection.
The Bubble Chamber was invented by
Don Glaser who was CIT class of '46 and
won the Nobel Prize for this in 1960.
So here is
a nice bubble chamber photograph,
and what I call attention to,
this curve coming along here is a positron
and you see it disappears right there.
It's hidden electron in one of
the orbiting, one of the hydrogen atoms,
and so you don't see anything, but there's
a photon, a gamma ray, that comes across.
And then about here, that interacts and
creates an electron positron pair.
And so you see the positron
turning around this way and
the electron coming around this way.
And so what you see in that part of
this photograph is both an antiparticle,
a piece of antimatter annihilating.
And then the creation of antimatter
together with ordinary matter here.
And so before your eyes,
these processes that we just
talked about being played out.
And so again, in terms of diagrams, what
happened is you have a positron colliding
with an electron giving
rise to a gamma ray.
And then a newly electron
positron pair being created.
And basically almost everything
I do in this talk is going to be
variations on this theme.
So if we go back to the standard model,
we were looking basically at
interactions of this with this, but
you could equally well work with muons.
So that you could collide an electron with
a positron to make a photon that would
create a muon, anti-muon pair,
and we'd see examples of that.
You could, since it's also neutral,
rather than have the photon, you can have
the Z boson as an intermediate state.
And we'll see how that's used to
discover a total later on in the talk.
Rather than it being and
electron or a muon, or
something like that,
you could create a quark, anti-quark pair.
And we'll talk about examples of that, and
see pictures of that,
later on in the talk as well.
And indeed, if you don't want to collide,
for technical reasons.
Sometimes it's easier rather than
colliding the electrons with positrons,
it's easier to collide
protons with anti-protons.
And since the protons
are made of quarks and
the anti-protons are made of anti-quarks.
What you're really doing is
colliding quarks with anti-quarks.
You can again,
have the same intermediate process.
And then that can fall apart
into electrons and positrons or
muons or more quarks or anti-quarks, or
just generically stuff and anti-stuff.
And so we will see examples
of all that as we go forward.
Actually this is a really convenient
point to call it quits for this stage.
The basic idea is, again, that we've
got simple diagrams that represent
complicated mathematics but the underlying
processes are easy to visualize.
And it's not abstract stuff.
We can actually see it happening.
And so we're gonna use this over and over
again to explore what the world is made
out of at the very,
very smallest distances.
>> I would have to assume that this
is the same no matter where it is.
It's not what we can see
just on earth, but that it would be
the same anywhere in the universe.
>> The answer is yes.
We believe,
and in many areas can check, that the laws
of physics are essentially the same.
We know that the laws of a comic
physics work the same everywhere.
It's basically, we wouldn't understand the
large scale structure of the universe if
that wasn't basically true.
So now, the one caveat is in
the very very early universe.
And this will be something
that you can come back and
ask the question again
after the third part.
In the very, very early universe, when the
universe was very, very hot, for reasons
that I'll allude to later or at least set
up for you to ask the question again.
The laws of physics could be somewhat
different, and we'll talk about that but
only in a very well understood way.
>> So the quarks, are they detectable or
observable anywhere, like in a collider?
I hear they got this forces,
if you send him apart there
the binding force increases.
>> So Glen told you that protons and
neutrons, other particles, pions.
I think he showed you a table which
probably your eyes rolled up into the back
of your head when you saw the hundreds
of strongly interacting particles.
All are believed to be made of quarks
and/or anti-quarks, but we've never
seen a free quark or free anti-quark,
and we don't actually expect to.
And the reason is is while I said
the gluons are very similar to photons,
there's a key difference,
they interact with each other.
And it turns out that because
they interact with each other,
if you imagine having a quark and
an anti-quark that you could hold onto and
try pulling them apart.
The force,
if you do that with an electron and
a proton, the force eventually
falls off as you pull it apart.
It doesn't fall off with quarks and
anti-quarks.
And so instead, I brought along my
handy prop, it's like a rubber band.
And so, in fact, the origin of the string
theory was rooted in just this,
something we'll talk about next week.
So imagine you've got a quark at this
end and an anti-quark at this end.
You pull it apart, and
as you know from pulling a rubber band,
the force doesn't drop.
But if you pull hard enough what happens
is, is it becomes energetically favorable
to pop a new quark,
anti-quark pair out of the vacuum.
So that this quark is now
connected to a new anti-quark.
And this antiquark is now
paired to a new quark.
And what you've done is taken what
was one meson and created two mesons.
And so when you smash a proton into a
proton, you know the quarks all interact,
some of them will go out.
And then you have these forces
between them that sequentially
split them into more and more particles.
So when you try smashing a quark out
of a proton or something like that
what you end up getting is a jet
of particles strongly interacting.
And this will be key in terms of what we
talk about in terms of particle detectors
and how you see them.
But at the fundamental level anytime that
you smash a quark out of a proton or
anything of that sort, what you expect to
see in your detector is a jet of particles
going off in the direction that
the cork was originally heading.
Part two.
So we had the nice,
the late 20th, early 21st century
periodic table of fundamental
particles that I just showed.
How actually have we deduced that?
Glenn told you how we
figured out the electron and
some of the quarks, but
how do we figure out the rest?
So there's three parts to it.
The story in terms of how we
understand this experimentally.
So one is I have to tell you a little
bit about particle accelerators.
Second, I have to tell you a little
it about particle detectors,
because we've advanced far
beyond the bubble chamber days.
And then I'm gonna to show
you a series of events that
again basically illustrate the kinds of
things that I've just been talking about.
So the the world's premier
particle accelerator these days is
the Large Hadron Collider, which is
located just outside Geneva, Switzerland.
This is the yellow shows the tunnel.
It's about on average about 300
feet underground for scale.
You see the Geneva airport here.
This is Lake Geneva, Lake Leman here.
These are the Jura Mountains in
the foreground here and in the distance.
It's 17 miles in circumference and
uses, when it's operating,
about as much power as the entire canton
as Geneva does when it's not operating.
And the border between Switzerland and
France runs along here so
the particles travel internationally
with great frequency.
Now one of the things that noted here is
a couple of locations around the ring.
Here underground are large caverns
dug out for the detectors,
that I'll show you a little bit about,
are located.
The other thing I'd point out is in its
current operation, there are two sets of
magnets around here, because it
collides protons on protons and so
you need separate beams,
because protons are the same charge.
Though the ring was
originally dug in the 1980s,
late 1980s, for
any electron positron collider.
So many of the results will show from that
phase where they were colliding electrons
and positrons.
Then to do to higher energies they
installed much more powerful super
conducting magnets and
now we're colliding protons on protons.
Now, just to show you,
the yellow was this big ring here.
And you see the locations for
the two big detectors, ATLAS and CMS.
You can't directly send protons into that.
You need to sort of accelerate
it in stages to get it up there.
And so
there's a series of smaller accelerators.
This one, the SPS, super proton
synchrotron, was built in the 1970s and
at that time was the highest
energy accelerator.
Now it's just use as an injector
into the larger one.
But we'll see some results from this.
This also was the first accelerator.
It was originally just protons,
and then in the early 1980s,
they developed techniques to store
large quantities of anti-protons.
And so they had protons going in
one direction around the ring and
antiprotons going around the other
direction in the ring and
studied proton, antiproton collisions.
And then there's a series of
smaller accelerators that
basically raised the energy of the beam
up to be able to inject it into that.
It's a big operation.
So this is what it looks
like down in the tunnel.
I'm actually a member of the smallest
of the collaborations of
the Large Hadron Collider called TOTEM,
and I won't say very much about it.
The main thing is you can see
how big the tunnel is, and
also note the bicycles here.
Much of it is wide enough that
you can get a cart through, but
there's several sections where
there's a bypass for the carts, and
the only way to go great distances
is actually to ride bicycles.
And then this is actually
the reason I was down there.
You can't see that as well as I'd like.
We've got a series of detectors,
basically silicon detectors,
that we move to within about a millimeter
of the beam so that we can look at very,
very small scattering angles, and as I've
said measure the size of the proton.
And it turns out the size of the proton
depends on the energy at which you
measure it with.
And so
it's a number that actually is needed so
that you understand how to calibrate
everything else the machine does.
Now our experiment is on either side of
one of the large detectors called CMS for
Compact Muon Solenoid, and
we'll see more about this.
This is just me setting the scale for
the central part of the detector
there that you see in the background.
And here's,
from a slightly different viewpoint,
a sort of a fish-eye view, so you can see,
you can see in the last photo,
was only a small portion
of this entire detector.
And again, you see the person down here,
to set the scale.
So this is big.
I should mention,
it's not only physically big.
It's a collaboration of
about 2,500 PhD physicists
at about 180 institutes and
universities in 38 countries.
Planning for it started in 1988,
I think, and
effectively it only started to
operate about two years ago.
So it's a major, major enterprise.
So what's actually going on?
So this is sort of the proton beams
come into or out of and collide in
the center of this detector here.
What you're seeing in this section
is sort of a cross sectional area of
this octant so
there's a series of detectors.
In the inner three feet or so are a series
of planes of silicon that are very thin.
So when a charged particle goes through,
it records what the location of that
charged particle is going through.
And because you have a series of them,
you can basically piece together
the tracks of individuals particles.
Then you've got a layer which is
about three feet thick of lead.
And when an electron or a gamma ray hits
the lead, it causes a shower of electrons.
It interacts electromagnetically and
you just get this big shower of the
electrons which is contained within it.
And if you drill a holes in the lead and
and put in glass fibers that have
been doped with suitable chemicals,
when one of those electrons hits
the fiber, it gives off a pulse of light.
And if you collect all the light,
the intensity of that pulse of light is
proportional to the energy
of the particle that hit it.
And so that's called a calorimeter, but
it's basically a way of measuring how
much energy that particle deposited.
Now, behind that is about
another ten feet of, I think,
depleted uranium in this case,
but again, very heavy.
If you have a strongly interacting
particle like a proton or a neutron or
a pion, it'll be stopped in here and
will also cause showering.
You again drill holes and put in fibers or
something like that, collect the light.
And that gives you a measurement
of the energy of that particle.
Then since they wanted to directly
measure the energy of charged particles
magnetically, cuz then a giant, at about
10 to 12 feet out, there's a giant
super conducting solenoid to create
a magnetic field within this whole thing.
So this is just an enormously intense,
huge, huge,
magnetic field with an enormous
amount of energy stored.
Now if you remember sort of
the field lines on the Earth or
something like that,
magnetic field lines like to go out and
then they have to go somewhere and
come back again.
And since you don't want
these strong straight fields,
you don't wanna know where they're going.
They then have a series of
iron return yokes that have
the field coming back through them.
But in between them, they place more
chambers to track charge particles.
And a way this can be used is as follows.
If you see a charge track going through
the inner chamber and depositing energy in
the electromagnetic calorimeter,
you know that's in the electron.
If you don't see any charge tracks, but
you see energy in the electromagnetic
calorimeter, you know that's a photon.
If you see a charge track depositing
energy in the Hadron Calorimeter,
you know that's a proton or
maybe a charged pion, something like that.
If you see no tracks in the inner part and
energy in the Hadron Calorimeter,
you know that's a neutron or
some other neutral hedron.
And if you see a charge track in the
interior, no energy deposited there, but
see the tracks out here again,
that's a nuon.
So depending on what you see where,
you know what the particle is that
you're observing, and you've got multiple
measurements of what the energy of it is.
And the reason for the size of the whole
thing is the laws of physics say, if you
wanna stop the hadrons, you need ten feet
of lead or uranium surrounding everything.
Then you've gotta have your magnet.
Then you've gotta have your return yoke.
So this whole thing is what
about seven meters in diameter.
So about twenty-five feet halfway so
the whole thing's the size
of a five story building.
>> Seven meter radius?
>> Seven meter radius.
Yes, yes.
So that's why, now, so how does this work?
This actually is going back to a much
earlier experiment of the SPS,
this is in a 1983.
This was an experiment called UA1.
There was a proton beam coming in here,
antiproton beam coming in here,
it collided, and what you see coming out
here is charge tracks in the inner part.
This is their way of displaying
that energy was deposited in
the electromagnetic calorimeter and
then the dotted lines here just
show you where it would have gone.
And you don't see any energy
deposited further out.
So, this is a new electron,
this is a new electron.
And the energies of those two electrons
sum up to the mass of a Z boson.
And the rest of this, remember when you're
colliding a proton and an antiproton,
you're colliding a quark and
an antiquark, well,
something has to happen to the quarks and
antiquarks in that.
They basically just go in the forward
direction through that process of rubber
band splitting that I talked about.
And so these are completely
uninteresting tracks here.
But what this is is actually the picture
of the first Z-boson that was ever seen.
And so it was kind of cool.
When it first appeared, right, you know,
everyone got terribly excited because
this had been predicted for you know,
well over a decade, and then actually
to build a machine, turn it on and
see it right where it was expected
to be was sort of quite amazing.
Now, you wanna have lots of cross checks.
One of them is,
if the Z is doing what you'd expect it to,
in addition to turning into electrons,
it should turn into muons.
And so, this doesn't show up as well as
I'd like, but this is the same detector.
Proton coming in, anti-proton coming in,
you'll see the remnants of the two, and
then what you see here is a charge track.
No energy deposited in the calorimeters.
And then out here in the muon chambers,
you see tracks again.
And the same thing with this
one going in this direction.
So this is a muon, this is a muon, and
the energies of the two add
up the mass of the z-bosons.
So this is the creation of a z-boson
ddecaying into a muon and an anti-muon.
Now, just one event, there's any
variety of things that could fake it.
What you really need to do
is a large number of them.
So when they built the electron
positron collider, what they could do
was change the energy of the beams and
slowly ramp it up.
One energy one day, and
then take it to a higher energy.
You sit at one energy,
you count how many Zs do you see?
And this is essentially what's
being plotted here at 88.
You saw 5 and some unit time interval,
89 you saw 7 or so,
you ramp it up to, what's that,
about 87 or so, you see about 17.
All the way up to
the central energy of it.
You're seeing about six times as
many events as when it was there.
And ramps back down.
Now the other thing that was
important about doing that is,
remember that our periodic
table of the standard model,
particles had three generations,
three columns, the electron, muon, and
the tau neutrino, the up and down quarks.
Charmed and strange, top and bottom.
So the question was, were there more?
And that's actually something that
the calculations go beyond what I can draw
pictures of at the moment.
But if there had only
been two generations,
the peak would have looked like this.
And if there were four generations,
that is that we had more quarks
to discover at this point,
it would have looked like this.
And instead, it's sitting right here.
And so this is a strong confirmation
that we shouldn't expect
anymore copies beyond what
we already know about.
And in some sense it's
kind of disappointing but-
>> [LAUGH]
>> Now, this of course also went to
Nobel Prize, Carlo Rubbia who,
at that time was a professor of Harvard,
later went on to be the director
general at Sern, put together UA1.
And Simon van der Meer is the one
who figured out how you could create
anti-protons, collect them, cool them
down, store them, put them into a ring in
large enough industrial quantities to
be able to make this whole thing work.
Now, just very quickly, you can make
half a Z go to a quark, anti-quark pair.
It throw off a gluon,
like what we talked about earlier.
In that case, you have a quark,
gluon, antiquark.
You should expect three jets.
And lo and behold, this is from
the electron positron collider.
Electron coming in, positron coming in,
you see, jet, jet, jet.
So each of these, you see the energy being
deposited in the Hadron Calorimeter so
that you know that these are jets of
strongly and correcting particles.
And so
this was the discovery of the gluon.
Same thing with Z goes to, they ramped it
up to where you could create pairs of Ws.
The Ws can decay for
example into quark, antiquark pairs.
In that case you would see four jets, and
this was the first
discovery of the creation.
Electron positron goes to W, anti W.
With four jets.
>> Who supports the CERN Program and
is this information proprietary, or
is it just shared with everyone?
I think of atomic energy
before the Manhattan Project.
>> The answer to the first question is
CERN was created as a treaty organization.
And their budget is incredibly
stable because the contributions
are fixed by treaty, to change it,
you have to renegotiate the treaty.
That's very different from supporting
particle physics in the United States
where Congress has to
pass new appropriations,
or one hopes they pass new
appropriations every year.
So that's actually enabled
them to carry out long
term planning in a way
that we really can't.
They're also an international
organization, so
they're actually exempt from
a number of regulations that would
affect any national
agency which helps a lot.
Now the other part, and I'm actually gonna
close my talk in terms of openness of it,
but particle physics is
probably the most collaborative
community of scientists that exists.
Collaboration like CMS with 2,200 people,
2500 people, there has to be
an incredible degree of openness.
The author Webster alphabetical
by name of institution,
then alphabetical by person so
that there's no fighting over who's
first author, who's priority?
And great effort is made to get
the information into the public
domain very quickly.
And you saw an example of this how
many of you saw the press release,
or the press reports last
fall about the supposed
neutrinos going faster
than the speed of light?
Okay, so that was my example, this was
an experiment that was doing an experiment
and discovered something that they just
could not understand, it made no sense.
Now, they could have sat on it.
But instead what they did was release
essentially all the information
into the pubic domain, saying here's
something that we don't understand.
I personally think they should have beat
on it a little harder before they did
that, but in this case they actually
erred in the side of probably greater and
earlier dissemination.
Now what's happened since then
is other experiments have been
able to carry out comparable analysis and
found no effect.
Neutrinos don't move faster than the speed
of light and the original experiment and
people were breathing down their
neck discovered two problems.
One was a cable that was not
well plugged in and well,
I mean, think of the complexity
of these detectors, right?
There is a lot of cables there and
you can't get to all of them very easily.
And then the other part was there was
actually an error in the interpolation
algorithm that they used to
take basically GPS reading of
the surface down below and so
that I think is an example.
Now as a side,
I would say there is an issue
with data retention because
it's all stored electronically.
One of the great challenges is that
technology changes very quickly.
And so that for example experiments
that were done at Fermi Lab, say
in the mid 90s, like one of the ones I ran
then, all wrote our data to magnetic tape.
There's no reader in the world now
that can read those data tapes.
And there's some in museums that might be
able to be resuscitated, but there doesn't
exist a place you can just put it on and
so there are challenges like that.
But that's not an issue
of being proprietor.
I'll come back to the proprietary issue in
a big way at the very end of my talk cuz
I think it's very important.
>> With all the institutions and
people involved,
who is the one that actually makes the
decision as to which chairman goes when.
>> So
that's also a really complicated process.
So the, CERN has an organization
called the CERN Council,
which each of the members has
representatives to in the US,
which is not a member, has an observer to.
They setup a series of committees.
So for example,
with the experiment that I'm involve in,
the process was first a group of
people got together in the mid 90s and
said we wanted to do this experiment and
issued an expression of interest.
That was then reviewed by relevant
committees to indicate whether they
thought it was interesting enough to
pursue further or not and it got the nod.
So then it was advanced to and
simultaneously discussions have to be held
with each of the national funding
agencies to see if they're
willing to support people from
their country to work on it or not.
Which is one of the key things that
way then to a letter of intent,
which the there were then
referees that were appointed
that asked all sorts of
questions about that.
There were responses to
the letter of intent.
Then it advanced to the stage of a series
of technical design reports to make sure
that you can actually build everything
the way that you think it can.
Meanwhile, again, further conversations
with the funding agencies with each of
the nations that have scientist involved
as to how much money they're going to put
in to it to make sure that you can
actually finance the whole thing.
And so the real answer is that
it's a very very collaborative
process involving oversight
by scientists from many
countries over literally
a span of two decades.
So there is not one person
that finally does it.
I would say there's one exception to that,
that I know of, and
that's the experiment that I went
at Fermilab with BJP BOK Kang.
Where we hadn't the idea for
it in the first week of July 1992, and
we had to install
the first week of May 1993.
And there's a committee whose approval
we needed that only meets in the second
week of June.
So in that instance the director
approved it on his own recognizance,
[LAUGH] but it's a rare issue.
Part III, the Higgs Boson's spontaneous
symmetry breaking and the origin of mass.
This section also is in three parts.
First is on symmetry, broken symmetry,
and spontaneously broken symmetry.
The second is on the question
what is the vacuum?
And the third is the search for
the Higgs Boson.
So Glenn was at CERN a couple weeks ago
and brought back a coffee mug for me.
It doesn't show up to well,
maybe it shows up better for you.
It's not worth it, I'll skip it.
>> [LAUGH]
>> You can't see it there,
we're doing a commentary on this
part of the talk on the bottom line.
So again, to remind you of the standard
model, I've said several times before
that there's three generations.
There's also other a pointed out the
similarity between the W and Z except for
the mass.
If you also worked at the W, I means,
it's charged and the Z is neutral.
But in fact, any time where Z can go
to something quark antiquark pair.
A W can go to something like
an electron neutrino, or
a different quark antiquark pair, so
the charge is suitably conserved.
So there's the suggestion here that
there's sort of an approximate symmetry
involving the photon,
the z, and the w Boson.
And similarly the quarks and leptons.
That is that in some sense,
if you replaced one with another,
it looks more or less but
not quite the same.
Now, the first efforts in the 60s of
building a model was to basically say,
okay, it's approximately right, but
we just put in different numbers in the
equation to represent the actual values.
And turns out when you do that,
the theory is nonsense, you can't
calculate a thing that's not consistent.
And where else what I'm going
to describe is actually
the most accurate theory
ever devised by man.
Can make predictions accurate to
one part and ten to the eighth and
you can check it.
Experimentally, in some cases,
to 1 part in 10 to the 8th,
that's 10 parts in a billion.
So how does this work?
Incidentally, the Higgs boson,
why is it called the Higgs boson?
This is Peter Higgs.
He is the person that gets the credit for
suggesting what we're gonna
be talking about in the rest.
He's not the only one that did the work,
but he's the one that,
I think, first really got the publicity.
I show this picture because
it's got to be kind of heady to
have someone build a machine
that's 17 miles in circumference,
detectors that are five stories high,
spend billions of dollars all to look for
a particle named after you.
[LAUGH]
So it's conventional when giving talks
at this stage to introduce what's called
the Mexican Hat Potential and symmetry.
I decided rather than do that,
I would actually bring a Mexican hat.
So the point is this is
rotationally symmetric.
Suppose this direction in some sense were
Z and this were photon in some ur-world.
Then if you rotated it, it'd still more or
less look the same, right.
And so there's a rotational symmetry.
Now, what we're gonna do is talk
about how that can be broken.
And rather than trying demonstrate
it as hard as this is,
I actually,
through the wonders of the iPhone and
the ability to take photos quickly,
thought I would show you.
So in this image, you see the hat.
We're looking at it from above.
And the grapefruit here represents
sort of the state of the Higgs field.
And so you can have a situation
where it's symmetric.
If I rotate it, and again think of one
direction sort of loosely being Z and
the other being photon.
In this state, if I rotate it,
you know it looks the same.
The laws of physics wouldn't
care how you did it.
On the other hand,
you can have a state of broken symmetry.
If the Higgs boson lives here,
that direction's different
than the other direction.
And so if you have a mechanism for picking
out one, it turns out you can couple it to
particles and give rise to mass and
everything else and distinguish.
Even if the fundamental laws are
symmetric, the actual realization of it in
the lowest energy state can be different,
can be asymmetric.
Now, I told you if you just put this
in by hand it doesn't work, but
if you do it dynamically.
So imagine you create the universe and you
have the Higgs field being at the center.
Well, it doesn't wanna live there, right,
because it wants to roll down
the hill of the hat, and it does.
And so with the iPhone,
I actually waited til it fell and
managed to get a series of photos and
took those.
And so that's a situation of
spontaneously broken symmetry.
It's something where it's not
something you put in by hand.
The dynamics come out.
It landed here, it could have landed here,
it could have landed there.
All of them were equivalent, but
each of these would pick out a different
direction which would get mass.
So it would be a different combination of
the original photon and Z that got mass.
So this trick, right?
It's kind of a sleight of hand and
was treated in such way.
So much so
that when the original model for
the standard model was written down in
the late 60s by Weinberg and Salam,
they didn't have any faith that it was any
more consistent than the hand version.
And in fact,
no one referenced Weinberg's paper for
the first three years after he wrote it.
And then a young guy named Gerard 't Hooft
came along as a graduate student and
showed that, in fact,
it was all sensible quantum
mechanically if you did it this way.
Weinberg and
Salam picked up Nobel Prizes for it and
't Hooft later picked up a Nobel Prize for
his contribution.
And so this quirky idea of spontaneous
symmetry breaking, in fact, it turns
out to be the key to making everything
work and indeed is the origin for mass.
So how does that work?
So if you're like me, before I got
infected with quantum field theory,
I thought of the vacuum as a state
with nothing in it, just empty space.
But that's not the way that, once we turn
on quantum mechanics, we think about it.
The vacuum is a very busy
place with particles and
anti-particles popping out and
annihilating all the time.
What spontaneous symmetry breaking does
and what the idea there is to say at each
point in space, you've got a Higgs
field that can take some value.
And if the value of
the Higgs field was zero,
if it were at the top of the hat,
the universe would be symmetric.
But there's a potential associated with
it and so it wants to roll down that
potential and pick one of
the directions that it corresponds to.
And so that's happened, early in
the universe, picked out a direction.
And so all of space is filled with
this condensate of Higgs particles.
We don't see them directly,
but as electrons or Ws,
or quarks go toodling along,
they feel the Higgs field.
They bounce off it, back and forth, and
that's actually what gives rise
to the mass for those particles.
And so in some sense, it's kind of
ironic here at Case Western Reserve.
We abolished the ether in the late 1800s,
but
it's come back through the backdoor in
a relativistically consistent fashion
though the mechanism of
spontaneous symmetry breaking.
So one of the things is
just as the Cheshire cat is disappearing,
leaves his grin,
this doesn't just give masses to
the particles and break the symmetry.
The story doesn't end there.
It leaves with a prediction of one more
particle that wasn't on the table that I
showed earlier, and
that's what we call the Higgs boson.
It's not electron, it's not a quark,
it's not a gauge boson.
Its mass is unknown or
which from the point of view of theory,
you can't predict what it is.
It couples to all the known
particles with strength proportional
to the mass of those particles,
because it's what gives rise to that mass.
So we know how it couples to everything,
we just don't know how heavy it is.
So much of the work of the last 20 years
has effectively been looking for it.
And at this point, there's only a very
narrow window that hasn't been ruled out.
And actually, it turns out to be the
window where it's absolutely the hardest
experimentally to look for.
When I was first getting into
this business 20 years ago, 1989,
you knew it was heavier than ten
times the mass of the proton and
lighter than a thousand times the mass
of the proton, and that's all we knew.
But the hardest range is to find
experimentally just because of
issues of backgrounds and
ways you can look for it.
There's between about 120 times
the mass of the proton and
130 times the mass of the proton.
And it looks like it's right smack
in the middle of that range.
So if it's in that range,
how do you find it?
Well, we're colliding at CERN,
protons on protons.
Now at the kind of
energies you have there,
quarks don't actually matter very much.
At those kind of energies, remember I told
you that quarks can spit off gluons and
gluons can, in fact, spit off more gluons.
When you're looking at
those kinds of energies,
the proton is mostly composed of gluons.
The quarks are sort of
a perturbation to it.
So what the OHC really is
is a gluon-gluon collider,
and the rest of the stuff
is just along for the ride.
Now gluons are massless.
So the Higgs can't
couple to them directly.
But the gluons can couple to the top quark
which is the heaviest of the quarks.
And so you could have a gluon from
one of the beams give rise to a top,
anti-top pair.
One of the tops bounce off
a gluon from the other one.
And then the top from one and
the anti-top that you created from
the other could annihilate,
leading to a Higgs boson.
Which then can decay the same way,
but rather than giving off
gluons gives off photons.
So one of the easiest channels to
see in this range is basically two
photons coming out.
And then just the remnants of the rest
of the protons going down the beam pipe.
Now it doesn't have to be top, any heavy
particle that couples to it would do.
You could also have the Higgs
decay into a W plus/W minus pair.
And again you've got this loop of Ws.
And then since the Ws are charged,
they can also give rise to photons.
So, what the experiments are looking for
at the moment, are events in which they
collide, proton on proton, and
see two gamma rays coming out,
two photons coming out, and
not much else in the event.
And where the energy of the two
photons adds up to the energy of
the Higgs in a very well-defined bump.
So this is one of the candidate
events that's been announced, so
you've got proton coming in here,
proton coming in here.
The yellow is,
remember the inner tracking chambers,
with all the fine detail of a build
to track charge particles, so
this is all those little mesons coming
out from the the remnants of the proton.
They don't have very much energy,
they don't go very far.
It's basically uninteresting junk.
You see no tracks, and then energy
deposited in the electromagnetic
calorimeter sort of back to back,
and then nothing out further.
This basically just shows
how it would traverse so
that if there were anything out
in the hadron calorimeter, or
in the muon chambers, you'd know
that it was associated with that.
So what you see here is a photon,
very high energy photon going in this
direction, very high energy
photon going in this direction.
And in this case,
the energy of the two adds up to 125 GeV.
So this is one of the events that
they've identified as a candidate for
the decay of a Higgs boson to two photons.
Where are we at the moment?
So about a month ago CERN
issued a press release.
And basically the bottom line is one of
the experiments just basically said it
has to be between 116 and 131.
The other one between 115 and 127.
If you combine the two,
basically both experiments
are seeing events of
the sort that we just saw,
in the regime between about 125 GeV,
plus or minus 1.
There's not quite enough data yet
to say that it couldn't,
that a few percent probability level would
just be a statistical fluctuation, but
it is tantalizingly close.
So the expectation is our standard model
Higgs analysis with data collected so
far leaves us in a very
exciting position for 2012.
With the data we collect this year,
the machine just started
running again last week,
we will definitely be able to confirm or
rule out a standard model Higgs.
So a year from now the expectation
is it'll be either the thumbs up or
thumbs down, and
I know which way I'm betting.
So now, this is sort of the punch line,
namely we're on the verge of finishing
off all of standard particle physics.
That wasn't an entirely
satisfactory point to end the talk.
So the question about
proprietary nature of the data,
anticipating that,
I'm often asked what good is it?
There's an enormous amount
of effort going into this,
an enormous amount of money going into it.
And there's a couple of answers,
one is that we never know.
Maxwell, when he wrote down the equations
of electromagnetism in the 1860s,
it was decades before that bore
fruit in the form of radio.
The work on quantum mechanics in the 20s,
again,
it was decades before
the birth of the transistor.
And yet, of course,
all of our modern society depends
on those fundamental innovations.
So the real answer is we
won't know whether or
not something from this fundamental
physics is going to be a building block
for civilization really for
a couple decades.
However in the course of putting
together this immense project and
making it work, there's been one
major practical implication.
In order for people to collaborate,
CERN invented the world wide web.
And what you see here is the first
web server, specifically for
the Large Hadron Collider.
And then in the spring of 1993,
they basically released it to the world
claiming no rights, no royalties or
anything whatsoever.
And, as you know,
it has changed our lives.
And if nothing else comes out of it,
I'd venture to say that one
was worth the entire project.
Hey guys, thank you very, very much.
I'm told I have to end.
>> [APPLAUSE]
