[ Music ]
>> All right welcome everyone.
I'm excited to introduce
our speaker today.
Our speaker is Dr. Katherine
Grimm of CSU East Bay.
She has her Bachelor's Degree
in Physics from UCLA and her PhD
in particle physics from
Stony Brook University.
It's there where she
started working on DZero
at Fermilab in particle physics.
And then she took a post doc,
oh I didn't write
it down here, but -
>> Lancaster.
>> Lancaster in England, but all
of that time was actually spent
in Geneva at CERN, working
on the large hadron collider;
so that's why the turnout is so
good, everyone is here to hear
about the LHC and
the Higgs Boson.
She was on part of the team
that found the Higgs Boson,
the experimental
evidence of it of course.
And as a member of the
Atlas Collaboration,
one of the two main
instruments there,
that's getting it right, right?
>> Exactly.
>> She continues
to work on Atlas
from her now nearby
institution of CSU East Bay.
Let's give a warm
welcome to Dr. Grimm?
>> Thank you.
Thank you very much.
It's great to be here.
I'm going to try to talk loud,
but if you can't hear me just
give a little - raise your hand
and I'll try to talk
louder again.
Okay so yes, I'm going to
talk today about my work
at the large hadron
collider and specifically
about the Higgs Boson.
So first of all I'll
show a picture
of the large hadron collider.
So this is Geneva Switzerland.
This is with the Alps
in the background.
And this is an outline
above ground
of where the accelerator is.
So it's a tunnel underground,
100 meters underground
and it collides protons
together.
And the protons are collided
at these four places
along the circle
and at those places we
have huge detectors.
And so the detector where I
collect data is called Atlas,
it's over here.
It takes a long time to cross,
25 minutes if you want to go
to the other experiment
on the other side.
So it's really a gigantic ring.
Much bigger than
the one I did my PhD
on in Chicago for instance.
And the reason that we have
it so big is because we want
to get it going really,
really fast.
And I'll talk about that in a
little bit, about how that helps
to get going really fast.
I'll also say one
word about CERN.
So CERN is the name of
the lab that is in Geneva,
just under the map here.
So CERN was created
just after World War II
to bring people back
together in Europe,
especially particle
physicist working on the bomb.
So they created this lab
that was only for peace.
It was a peaceful
scientific endeavor
to bring people together
from different countries.
And so initially
here's an old picture,
it was just some European
countries and now it's really,
really a global collaboration of
people from all over the world
who come together to
do science at CERN.
And that's partially a nice
thing to be able to work
with people from around the
world, but also to be able
to build something this
big, you need resources
from many, many countries.
And you need people, a lot
of people so it's helpful
for the people, helpful to bring
people together and helpful
to bring people together
and helpful for the science.
I thought that was a cool
thing to work with old people
from around the world.
Okay so what I'm going to talk
about today is first
an introduction
to particle physics.
So what are elementary
particles?
Then I'll talk about
the main questions
that we have in particle
physics?
So what are we trying to answer
with an accelerator
for instance?
And specifically because
I work on the Higgs Boson,
I'm going to talk about
what the Higgs Boson is
and how we're trying to answer
these questions using the Higgs
Boson or by studying
the Higgs Boson.
And to be able to
answer that I'll talk
about specifically what we
do on a day to day basis
to study the Higgs Boson.
So I'll talk about
how the detector works
and how we get the
signal out of the data.
And then I'll show you where our
latest stuff that we published.
Okay so first what are
elementary particles?
So this is the question
that people have
always had basically,
what is the smallest thing?
What is everything made of down
to the very, very
smallest thing?
Where can you say
that we've gotten
to something that's indivisible?
So people have always wondered
this, the term atom comes
from Ancient Greece,
but even before
that people were wondering
what's inside of everything?
And so this is a
question that has evolved
at one point we thought
atoms were it,
that's what everything
is made of.
And everything is made of atoms
but now we've gotten inside
of the atom, so we think
that we have now the set
of elementary particles.
We think that the
entire universe is made
of these particles, so it's
six quarks, six leptons,
four force carrying
bosons and the Higgs boson.
So just - what is that
12 plus - 17 particles.
17 particles to make
up the entire universe.
And in fact, it's even less than
that for most of the universe.
So here I've circled the
quarks and the leptons that are
in our everyday matter.
So in everyday matter we
have protons and neutrons
and those are made of the
up quark and the down quark
as sort of illustrated here.
The proton has three quarks and
the neutron has three quarks.
And the atom of course
has electrons in it.
So we're familiar with
electrons and electricity,
and any time there's
radioactive decay or fusion
in the sun there's
electron neutrinos.
So a lot of our everyday life
is made up of these particles.
So really we've gotten down
to not very many particles
that make up everything.
And the other pieces of the -
of the elementary particle
table are heavier versions.
So these are the up and down
quark here and then the charm
and strange and the
top and the bottom,
those are heavier versions
of the up and the down.
So any time you have an
up, sorry a top quark
or a bottom quark mixed together
in some heavy conglomerate
of particles, it will
eventually decay back
down into our known matter.
So we live in a stable
universe for the most part.
And that's why we're over
here on the lightest side
of the quarks and the leptons.
The heavier ones
here are not stable
and so they always just
decay back down to electrons.
So the only place to find these
is where you have extra energy
that allows them to exist
in a semi-stable state
for a fraction of a second.
So that means inside of a
particle detector or inside
of like super high energy
astrophysical event.
So you can get new ones
for sure from cosmic rays,
really high cosmic rays
hitting the atmosphere or inside
of Super Novas or
early in the universe.
So let me go to the picture I
have of early in the universe.
Oh, and I should just say
we consider this the rules
that govern all of
these particles
to be the standard model
of particle physics.
So not only this list of 17
particles, but also the mass
that dictates how something
decays into something else
or how does radioactive
decay work?
Those rules are called the
standard model, so I'm going
to talk a little
bit more about that.
Okay so I was saying that the
- those heavier particles,
can they exist when
there's more energy present?
So there's more energy,
that's what we're trying to do
in the accelerator, or if you
just go back in time the energy
that exists now in the universe
was in a much smaller area,
so there was a high
concentration of high energy
and that allowed for some
of these heavier
particles to exist.
So in going higher in energy
and accelerator you're
in some sense going
back further in time
to when you had a hotter denser
environment in the universe.
And by studying what happens
in those high energy
environments we can understand a
little bit about the
evolution of the universe
or at least what was happening
in those environments
when it was so hot.
Here's another picture
that shows specifically
- here's atoms.
Before atoms the protons
and electrons weren't
going around each other.
Before that there was
free quarks, they weren't
yet coalesced into atoms.
So there was a cooling
that condensed everything
and eventually led to planets.
And then you go back in time
and you get heavier things
and you also get things
that are broken apart.
So what do we know?
I said that we know what
visible matter is made of.
So we think that all visible
matter is made of quarks
and leptons and we know about
the heavier rarer particles.
We think we know all of them,
but of course we're still
looking to make sure.
We also know how
elementary particles interact
with each other.
So how do you put
particles together
to make composite particles?
How is the proton work,
what's inside of it.
And how do heavier
particles decay?
We know the rules, we
can predict the lifetime
that heavier particle will
have before it decays.
We also know that
the electricity
and magnetism are really the
same force and also electricity
and magnetism can be written
as the same force
as the weak force.
So we now say that it is
the electro weak force.
So I'm going to talk a little
bit more about how people want
to then continue with
this unification.
We have electro weak, can we
bring in the strong force?
Can we bring in gravity?
That's a goal people have.
We also know why
particles have mass?
So this is related
to the Higgs Boson
and I'm going to
talk about this.
But these things certainly
immediately leave you
to say what do we not know?
So we don't know whether we
can unify the forces further.
Can we make the strong force,
written in the same equation
as the electro weak force.
Can we consider that one
force that just applies
in different situations?
And can we bring in gravity?
Why is gravity so much
weaker than the other forces?
You compare the strengths
in gravity, it's many,
many times weaker
than the other forces.
And why would that be?
We also have a question
about matter and anti-matter,
so I didn't talk about
it in the picture
of the elementary particles
but each particle
has an anti-particle.
So for every - go back.
For every one of these quarks,
there's an anti-matter partner.
And for every lepton there's
also an anti-matter partner.
But there is way,
way more matter
than anti-matter
in the universe.
And if you trace back,
if you understand the early
universe there's no reason
that it shouldn't be just equal
parts matter and anti-matter.
And so we're trying
to understand there must have
been something that happened,
some rule that makes it so
that in the end you're left
with more matter and
not so much anti-matter
because here we all are with
more matter and not smashing
into our anti-matter selves.
We also I'm sure you have
heard that a lot of the energy
in the universe we think is
dark matter and dark energy.
And so that's a big question.
So where is that on our table?
We say we know about visible
matter, what about all
that other matter
in the universe?
Is that somehow a piece
of the standard model?
Is there another column
that we're missing
that doesn't interact
with our matter?
So that's a question that
people try to get to at CERN,
can we understand where
these other particles are?
Can we create some?
And now we do have this
evidence for the Higgs Boson,
this brand new particle that was
discovered so the 17 of our -
we had this model that
there were 16 particles.
And then four years ago
we discovered one more.
So are we sure that we know
what we're dealing with,
with this new particle?
So that's a big question that
is still - people are working on
and specifically I'm working on,
so I'm going to talk about that.
And how even in studying the
Higgs Boson, how you can sort
of bring in some of
these other questions.
We're always interested
in coming up with a theory
that might encompass some
of these other answers.
Okay so let me try to tell
you about the Higgs Boson.
I have to say that the Higgs
Boson is not easy to explain.
So I'm going to give it a try.
Just to get a sense for
what it is we found.
So the way I like to think
of it is to first think
about the equation that
is the standard model.
So you can write down the
standard model in the same way
that you can write down like the
energy equation for a pendulum
or for something falling.
You can write down a kinetic
energy and a potential energy.
So this thing is moving and
so it has kinetic energy
and it's interacting
with gravity
and so it has some
potential energy.
If you take quantum
mechanics you can write
down a similar equation
for some particle.
So here's a particle with
sort of some kinetic energy
and interacting with
a potential;
so it could be gravity
or it could be one
of the other forces.
So you can write it down
in the same way you would
for something falling.
You could write down or a
quantum mechanical particle.
So just adding a little
something with this interaction
of your particle with a
potential, you can write
down the interaction real
small if you're at the bottom.
Between everyone of those
elementary particles.
So we said we know how
quarks and leptons interact.
You can write that down as
one term in your equation.
We know how quarks
interact with the bosons;
we know how the bosons
interact together.
Each one of those becomes
a term in your equation.
And you just have this energy
equation or the lagrangian
for each one of those -
the combinators of each
of the elementary particles
interacting with each other.
And luckily there's
not that many.
So you can just - you write
down each one of these
and then you have the lagrangian
that really describes the
entire standard model.
And [Inaudible].
So you can write it down in
this super, super short hand
of like all of the
particles interacting
and the Higgs particles
interacting and those correspond
to these are little diagrams
of the W, Boson interacting
with the Z boson or the gluons
interacting with each other.
The gluons [Inaudible] that's
the strong force carrier,
so the weak force is associated
with the W and Z bosons.
And the strong force is
associated with the gluons
and the electromagnetic force
is associated with the photon,
which I think is here.
It's also written on a T-shirt.
Here I wanted to
emphasize that this top part
which is very condensed in
this notation, but this is most
of the interactions
of the particles
and then there's
new part here is -
has to do really with the Higgs.
There's a big portion
of the lagrangian
that has this interaction
with the Higgs,
but okay let's get to that now.
So okay one of the criteria
for this lagrangian,
so that just means this
energy equation is that it has
to work all the time, and it
has to be gaged in variant.
So in a sense that
means it has to work
in all locations in all time.
It can't - or like if you think
of a potential difference,
it can't depend on the actual
potential you're dealing with,
just care about the difference,
sort of a gage in variance.
So this is a fundamental
requirement that if you have a -
if you really want to describe
exactly how all those particles
interact it better work at
all times and at all places.
It's supposed to be the entire
universe we're describing.
But they tried to ask - add
- there was a thing missing
from the standard model.
So when they unified the
electromagnetic force
with the weak force they saw
that there should be force
carriers for the weak force
and for the electromagnetic
part.
There should be three
that have mass and one
that doesn't have mass.
And the ones with mass or
the W and the Z, the W plus,
the W minus and the Z.
So the W is a charged one
and the Z is neutral, there's
two W and one Z. Those have mass
and when the weak force
interacts you can write it
down as the exchange
of one of these bosons.
And then there was
a fourth piece
and that was photon
with no mass.
And so they could
write out one equation
that represented
electroweak force either
with a massive boson or
with a massless photon.
Okay so that was a great
triumph and we were able
to predict a lot of things.
We could predict the W
and the Z would be found
at CERN and they were.
We predict a lot about
radioactive decay
so the working piece
of the standard model.
But then when they put in
those masses it broke the gage
and variance of the Lagrangian.
So the Lagrangian for
the entire standard model
that we thought we
understood of all the part
that was interacting
no longer worked.
It became non-invariant.
So then everybody questioned
[Inaudible] maybe everything
is broken.
Is the standard model not true.
How do we account for all of
the success of this model,
but also account for this fact
that we know the particles have
mass, not just the W and the Z,
but all the particles have
mass except the photons.
And none of them could be
added to the Lagrangian.
Okay so Peter Higgs
had this idea,
this is him having an idea.
Yes?
>> I'm wondering of
a simple way to think
about the gage in
variance breaking.
You've got this model that says
hey we have all these different
forces in nature and this
is going to simplify it
down into one [Inaudible]
electroweak.
Does the gage in variance -
the thing - it was beautiful
and then it broke this
thing, and it broke the idea
that I should be able to
look at - I want to say it
in a really broad way, but
look at it from any angle
or from any perspective and
the laws should be the same.
And then it says oh no it's not.
Is it simply that there was this
massless and massive particles
in those force carriers?
Like I'm just wondering if it's
as simple as that going oh,
you notice that you have
massless ones and massive ones
and that can't be a
variant in this way.
>> Basically yes.
If they were all massless I
believe it would all continue
to work, but we - there's
one way to do the formula
and it comes out that you
get three massive ones
and one massless one.
But then you put it
into the entire piece
and those terms are no
longer gage and variant.
And so if they - if you had
just put them in and massless,
all the bosons are massless,
then it would still work.
So it was working for one way
and then not from the other way.
And then we discovered those
bosons when they do have mass.
>> So actually the
discovery of those leading
up to the Higgs Boson was
the same that said there has
to be a Higgs Boson because now
we found these force carrying
particles isolated and the first
time they have mass and while
that wild idea that somebody had
comes forward that's the way the
universe works and now
we better hunt for a way
to make the laws simple again.
>> Exactly.
And especially the simple again
because of course people
had different ideas,
but Higgs had the
most simple idea.
So Higgs and Englert at
the same time had this idea
that you don't write in
the - you'll just write
in the mass basically and
that's what breaks everything.
Instead you write
in another field.
So if you write in that the
universe comes with it just
like sort of space time
there's also a field
that goes throughout
the universe.
And every single particle
interacts with that field,
so then the term
in the Lagrangian is
instead the interaction
of your particle
with the Higgs field.
And then it works gage in
variant works at all space
and time, so here's some
people playing on a mat
that represents the Higgs field
and this particle is interacting
more with the Higgs field
and this particle is interacting
less with the Higgs field.
And what that comes out to is
that this particle has more mass
and this particle has less mass.
So the W and the Z both have
a lot of mass, the up quark
and the down quark have a little
bit of mass and that comes
out as their interaction
with the Higgs field.
Okay so this was the idea
and then we said how
can we prove that?
That seems to work
and then the answer is
if there's a Higgs field there's
also a particle associated
with that field and
that's the thing
that we're going to try to find.
And if that exists then it seems
like the whole thing is true.
So this is - we got to look for
this, to show that it all works.
Okay so how do they do that?
How do you look for
a new particle?
So if the Higgs existed,
which we now found,
it lasts for only a fraction of
a second and so then it decays
into the known particles.
So just like I was saying,
the heavy particles are always
decaying into lighter particles.
The Higgs Boson will just last
for a fraction of a second
in an environment where
there's enough energy
and then it will decay
to lighter particles
to a lower energy state.
And you can calculate
what it should decay into.
It should decay into
more heavy particle
because it has the
association with mass.
So into W and Z bosons,
I drew it in real little.
It goes into the top
quark for just a second,
which then decays into photons.
It decays into the Tau particle,
which is like a heavy electron
in the bottom quark, which
is another heavy quark.
This is a graph that shows -
it's based on what the mass
of this new Higgs Boson particle
is, what it should decay into
and these are the rates.
So if the Higgs initially
when we were looking
for the Higgs Boson we had
no idea what its mass was.
That's not predicted
in the theory.
So we were first of course
looking at lower energies
because that's easier to
make in an accelerator.
And then eventually
those were ruled out
and we finally found the Higgs
at 125 GEV and so you can look
at what the rates are
that it should decay into.
If for a mass of 125 GEV mostly
it decays into bottom quarks.
And measuring now that we have
the Higgs, measuring the rates
that it does decay
into these things,
tells us if our theory
is correct, there's a lot
of calculation that goes
into doing these .And
if we can measure and make sure
that we get back what we
predict, that tells us
that we have the correct theory.
I'm going to say one more
thing that is confusing,
but this is part of the
results will show at the end.
So here's, we said
the Higgs is decaying
into these other
lighter particles
and that does tell us
something about the Higgs
that we've understood the way it
interacts with other particles.
It also can interact
with itself so very,
very occasionally the Higgs
Boson decays into Higgs Bosons,
and that tells us about
this - those fields.
The potential in the universe.
If the way it's often stated is
if this is the Higgs potential
it looks like a sombrero.
It's got a high point
in the middle at zero
and then it's got these two dips
which then become
a stable minima.
And at some point in the early
universe the universe was
at this unstable maxima and then
there was some little quantum
fluctuation and the universe
fell into one of the other side
of this well, and that's called
electroweak symmetry breaking
because you're no
longer symmetric.
And then all the
particles got mass,
so before that they
didn't have mass.
But then they thought
there was some little bump
and now we're in this dip.
And some people say well
we better measure this dip
because what if it
isn't the shape.
What if it's like another
unstable maximum, minimum
and then at some point
the fluctuation will bump
into another little thing
and everything will
have a different mass.
Okay I will talk a little bit
more about this but what I would
like to emphasize is that we
are measuring the Higgs decaying
into these particles, which
tells us how the Higgs interacts
with matter and bosons.
And then we will also
want to try to look
for the Higgs interacting
with itself
and then we'll understand
a little bit
about the whole field.
Okay. So that's sort
of the theory,
which is so hard,
but interesting.
Now we can - let's
go measure it.
So we look to the accelerator.
Here's the accelerator
again, right?
So we're smashing together the
particles, what do we want?
We want to create a really
high energy environment,
similar to some environment
at the start of the universe.
And we're going to do it
just in a really tiny space
and so we're going to have to
make that environment really,
really frequently, so the large
hadron collider collides protons
every 25 nanoseconds; so
that's 40,000 times a second.
And it runs about six
months a year continuously;
so this is from this year.
It turns off in the winter
when the electricity
is really expensive
and then they turn on in May.
And this is measure of the
amount of data that's collected;
so they start right in.
There's little stopping
points where they fix things,
but for the most part
they run continuously.
They're going to stop at the
beginning of [Inaudible].
So the data is measured in
femtobarns which is related
to the cross section
of the crossing
of the protons we've
collected so far.
This year 60 femtobarns and
it's really, really impressive.
A lot of successful running
because the last two years
we collected 80 femtobarns,
so it really - people
are super excited
that we crossed the hundreds.
We have tons and tons
of data which is great.
Okay and so where
would we like these?
We would like the collision
to happen exactly right here.
Because we have build this
gigantic detector in order
to measure exactly what
happens when the protons cross.
So when they cross, right
in this spot this is
a cross section view.
Tons and tons of new
particles spill out
and we measure the
trajectories and the energies
of all of those particles.
So I'm going to try to
show you this video.
So this is a zoom in of
the atlas experiment.
So they showed in the video
that it's underground.
It's 100 meters underground
and that's both
to protect the detector
from cosmic rays
and to prevent the
people from radiation.
So you have to take an
elevator down 100 meters
if you want to go and visit it.
And the detector is built,
again the protons hit
together right here
and it's built like an onion.
So there is many layers and
the middle layer is the most
sensitive and then they get
like trainer as you go out,
bigger pixels as you move
out and the whole thing,
it's about - here's
a person right here.
It's like four stories
high and the precision
at the inner layers is like
smaller micrometers, so really,
really highly precise
and really,
really big so that's
why it takes so,
so many people to build these.
It takes many, many years.
This is the middle
part of the detector,
so the very center of the onion.
So the protons hit right here
and you've got layers of silicon
and also tubes, so these
tubes that are filled with gas
and the charged particle
goes through.
It makes them electrons.
>> Is that outside?
That's not the video playing?
>> It's possible.
>> Yeah okay.
>> That's probably the next one.
[Inaudible].
Okay so you have a proton
or some particle here that's
being shown going through
and it hits each of these
layers and then we get a mark
that we can reconstruct
the track.
And we also get a measure
of how much energy came out.
So some of them are tubes.
This is a tube where
the particle goes in
and releases some ionizes the
gas and then that is a current
that slows down the wire,
down the middle of the tube
and then we read it out; so we
know the position and then based
on the number of the
charge we know the energy.
And that whole thing
is in a magnetic field.
What happens when a
charged particle goes
through a magnetic field?
It turns. And we know
that it turns the radius
of the turn is based
on the momentum,
and we know that the direction
of the turn is based on whether
or not the thing is
plus one or minus one.
So if it's a positron
it will turn one way,
if it's an electron it
will turn the other way.
So that rule that things turn
in a magnetic field is
really the basis of a lot
of particle physics or at least
of the detector is figuring
out whether you had a positive
or a negative particle,
and then what the momentum
of that particle was.
Here's a picture of a whole
bunch of particles going
into this - this is an
old fashioned detector
like a cloud - a cloud chamber
where you get a little tiny
bubble or a piece of vapor
where the particle has
gone through and then
because of the magnetic field
you get things turning either
one way or the other,
depending on the charge.
So I won't go through
each piece of the detector
but here's the part that I
showed the tracking part.
So this really - if you
want to get the trajectory
of the particle, you want
to measure the momentum.
Then there's a series of
calorimeters that are designed
to stop particles,
so the measure of all
of the energy that they had.
And you can distinguish
between particles based
on how much energy they had
and how they disperse their
energy in the calorimeter.
So a really heavy quark makes
it through a lot of material
and then makes it
a scattering jet.
So, this one says proton,
this is a proton going in
and when it hits matter,
so it hits other atoms,
it releases electrons and
moves around the neutrons
or the atoms, excuse me
and the material, it hits
and makes these shower shapes.
And you can distinguish
the shower shapes
between different types
of quark particles.
You can also distinguish
between electrons and photons
and between electrons and muons.
Muons may get out really, really
far, all the way to the end.
And so in that way you
smash together your protons
and then you can
distinguish the particles
that are coming out
of the collision.
Muons - hadrons,
which is the name
for particles make of quarks.
Energy from electrons
and atoms and photons,
those are stopped
in this first layer.
And then the trajectory of
anything that has a charge.
And then so the thing
that we are measuring,
it's not very many quantities.
We measure the charge, you
measure the pass, so the way -
the direction it went, the
momentum and the energy.
And basically all the
physics has to come
from those four quantities.
Okay I'm going to spend just
a moment talking about some
of the tricky ways of
identifying specific particles
because this is really what
people are working on a day
to day basis, and it's cool.
So okay b Quarks.
These are called b-jets so
this means that anything
that has a bottom quark in it.
So we said that the Higgs
decays into bottom quark.
So this was especially important
to study how bottom
quarks can be identified
in the particle detector.
So for the most part any
quark particle will come
through this tracking part
and leave a little trail,
go through the electromagnetic
calorimeter
and it will be stopped
in this big calorimeter,
the hadronic calorimeter
and leave a shower.
But it's a little bit
hard to distinguish
between the different
types of quarks.
But luckily with a b-quark
when it is initially created;
so here it's initially created
with this primary vertex,
that's where the two
protons hit each other.
It will form together
with another quark;
so quarks never like
to be alone.
This is part of the
strong force;
the strong force gets stronger
as you move away; so that means
that particles always
stick together even
if it means taking
a new particle
out of the quantum vacuum.
It will pull a new particle
out and put it with it,
so that it doesn't
have to be alone.
That's one of the
rules of quarks.
So if a b-quark is created
it will immediately bond
with another quark.
And that quark will have
some little lifetime.
It will travel little ways
and then it will decay
into lighter things.
And this property allows us
to look for a primary vertex
and then a secondary vertex.
So you look for particles
that are coming
out of the initial place where
the protons hit each other
and then you look
for a second place
where particles are coming out.
And this distinguishing
between the primary vertex
and the secondary vertex allows
you to say that was a b-quark.
So other quarks also
bond with particles right
when they're created, but
they don't have this lifetime.
It's a special characteristic
of B mesons or particles
that have a b-quark in them that
they last a little bit of time,
and so they have time to travel
in a detector before they decay.
So that identification
of a b-quark is dependent
on this traveling a little ways
and creating a secondary vertex.
Okay so that's the first one
and the second one I wanted
to talk about is the Tau.
So that's another particle
that the Higgs decays into.
The Tau is a heavy electron.
It decays into electrons
and also muons and quarks.
And we know exactly
the way that it decays.
It decays via the weak force
and it releases a neutrino.
And we can calculate exactly
how often it should decay
into these different muon
or electron or a quark.
And then we can identify the way
that that should
look in the detector.
So for the most part the problem
is that when a Tau decays,
it looks a lot like
a quark decaying.
So when the two protons
hit each other
for the most part there's a lot
of light quarks that come out
and so the background to every
signal you want to see is tons
of quarks coming
out of the detector.
So everything is
about distinguishing
between these random
quarks coming out
and something you're
really looking for;
so you're really
looking for this Tau
and instead you're seeing
all these other quarks.
And the way that you can
distinguish it is primarily
because the Tau decays
very particularly
into three little pions or
sometimes five little pions,
but they're close together.
Compared with quarks that
are spread apart more
and so this is super hard,
but you make a lot of models
of how quarks are looking
when they're coming
out of the collision
and how Tau's look
when they come out
of the collision.
So I've written down some
distinguishing characteristics.
The number of tracks
outside of this blue cone;
so you make a little
cone around your decay
and you count the number
of tracks that are in there
and you do that for
a simulation of taus
and a simulation of quarks.
And then you can write it
down and they look different.
And there's - you can
also measure the momentum
that is inside that close place
compared with the whole thing.
You come up with a whole lot of
different variables that talk
about how these two
shapes are different
and then you can either
say okay if I want
to distinguish the taus
then I'm only going
to take collision events that
exist where most of the taus lie
in each of these variables.
Then you cut out a lot of
data, so instead we train,
we do artificial intelligence
and train boosted decision trees
to make these cuts for us.
So they - you show a
boosted decision tree,
all of these different
variables and then it figures
out the best cuts to make and
then it creates a discriminate;
so this is a label
that's attached
to every collision event saying
whether it's more like a tau
or more like a regular quark.
So you can see that the
red ones, you plug back
in what you know to be taus and
it calls most of those taus.
Not everyone, but most of them.
And you plug back in what
you know to be a quark
and it correctly identifies
those as more quark like.
So then you can make
a cut that's here
and have a huge signal
compared to background.
Yes?
>> I forget this
is very advanced,
but it's also remarkably clear
job that diagram of showing -
say the spray looks like
this, we're looking for sprays
that spray out like this.
I just want to mention one of
our students did their project
and they were looking for
the [Inaudible] seen your
diagram before.
He was looking at b-bvar -
>> Yes.
>> So he was looking for those
and of course you showed us
why someone would do that;
that's the most likely
for the Higgs Boson.
It's mass, it's most
likely going to divide
into those two things.
And you told us about the
number of data events happening,
right 25 nanoseconds so you
have to have this in place
to even decide, is that right?
You have to have this in place
to even decide what to keep
to look later and say what can
we find out about the physics
of very small of
the Higgs Boson.
>> That's right.
After you spend a long time
making sure you've done this
right, you can apply
it really early
on in the data filtering
process and get rid of events
that are no good, that
are uninteresting to you.
>> So can I ask, I don't
want to monopolize your time,
but so you - when you were
talking you were [Inaudible] the
total sum luminosity or you know
of all the events study, right?
But the events study is that
part of why the slope is steeper
or maybe that was just
total integrated number
of events you're keeping?
Your [Inaudible] rate let's say
of getting Higgs Boson events,
like much better now
than it was in the past
because people have
developed these tools?
>> That graph was just
what we collected.
So it doesn't show what
has been thrown away.
The throwing away,
the efficiency
of collecting Higgs Boson events
has gotten better and better.
We're also taking in way
more and we're able to take
in more data at a time,
so we throw away more
but we also keep more.
So that's a set of cuts
that's gotten better.
So yeah, and then we're going to
upgrade again to get more data
and then we're going to -
everybody has to figure out how
to deal with that and throw
away more and keep more.
>> Get it, thank you.
>> Okay another reason that this
is cool is that this is used
in a lot of industry
now and it used to be
that particle physics was
sort of at the beginning
and now we're not
at the forefront
of this machine learning, but
it still works really well.
And now particle physics is
trying to learn from industry;
so you know you go to Google
and they're doing boosted
decision trees just like crazy.
And so you can learn from there
algorithms, there's an example
where you're trying to decide
if you're looking at a picture
of the sky or a building
and you sort
of decide is it [Inaudible],
is it green, is it long,
so these types of
decisions can go
into not just particle
physics but really a lot
of machine algorithms.
Okay so let's say that
we now have decided
that we have a collision
that has two -
let's do the B's and the taus.
This one is - we'll
do this one first.
This one is someone
else made the algorithm
to distinguish what
an electron looks like
or what a muon looks
like, which is way easier
than the B's and the taus.
This is the first place they
discovered the Higgs Boson.
The Higgs decays into a 2Z
boson and those in turn decay
into light particles, electrons
and muons and it's fairly easy
to see electrons and
muons in the detector
and you take those energies
of those four particles
and you add them up and that
should give you the energy
of the initial Higgs Boson.
And it should in principle,
I mean actually what it
gives you is the mass
of the initial Higgs
Boson, it's E=MC2.
This had some mass and
that went into energy
that was given to
these particles.
So on the histogram here
you have the combined mass
of the four leptons,
the four particles
that have finally decayed into
and then you make a little count
every time you got that mass,
and you see that you get a
big spike in counts at 90.
And that's the mass of the
Z Boson, so that's good.
We know that the Z Boson does
have some mass and so we see
that and then they also got
another bump at 125 and that was
from the mass of the new
particle, the Higgs Boson.
So we're always making
these graphs of the mass
and looking for a bump.
They call bump hunting.
So this is for Higgs
decaying into 2Z's,
which is a low rate,
but easy to see.
This is a picture of that so you
can see if the particle goes way
to the outside of the detector
that means it's a muon.
And so that's why it's
really easy to detect a muon.
It's also fairly easy
to detect an electron
because they're just clean and
not spread out like the quarks.
Here's the same graph of
the mass on the bottom,
but this time it's two Tau's,
so you have the Higgs Boson
decaying to two Tau's,
you identified them with
your boosted decision tree.
And then add up all of the
energies you get the mass,
and here you can see
that you have a lot
of different colors added on
top of each other and that's
because there's a lot of
background still that look
like Tau's, that
really are tau's.
You have the Z Boson decaying
into taus and that's in blue.
You have green, which is random
quarks that you've misidentified
with your boosted decision tree,
you need to model how
many you misidentified.
And then the data is
shown on top in black;
so the red is the predicted
Higgs Boson stacked on top,
so you get a little bit
of extra and that shows
that you saw not
just the background
but the background
plus a signal.
And you can see just
the fact that there's
so many other things in this
[Inaudible] it was a harder -
a harder job to find the
Higgs Boson in this channel,
decaying into two Taus.
Here's a second boosted
decision tree that's used even
to identify which particles
are more like the Higgs
and which are more
like the background,
so boosted decision trees
on boosted decision trees.
I won't go into the statistics,
there's some very fun statistics
to decide how likely it is
that you got a significant -
statistically significant
answer.
I'm going to go back to the idea
of studying what the
Higgs is decaying into.
So I just said we looked
at the - at the Tau.
Only just this past summer
they finally found evidence
of the Higgs decaying into
the 2B's in the B-bvar
so that's initial discovery
of the Higgs Boson was in 2012
and it took six years before
they could really understand the
b-jet, this process of the B's
coming together, flying away,
making a secondary
vertex and decaying again.
Using that technique to find
tow B's coming out of the Higgs
and adding them back together
and then having enough data
to show those came from the
Higgs; so again you have a lot
of background here
that look like b-jets
or have b-jets in them.
And then stacked on top
is the Higgs in red,
so you can see it's
really contending
with a lot of other backgrounds.
But finally in July they
found 5 sigma evidence,
so that means really
statistically significant
evidence of the Higgs
decays into B's.
Go forward, the quick plot
of the mass of the particle
that the Higgs decays into, and
the strengths of its coupling.
So it decays more often into
heavy things and we can plot
that and see it decays more
often into the top quark
and the W and the Z boson and
into the B quarks and the Tau.
It's not quite the rate;
it's the strength
of the interactions.
So the rate is the highest of
the B quarks, but the strength
of the interaction is higher
for the W and the Z. Yes?
>> Isn't that a sense
of that idea
of the Higgs feel being
the origin of mass?
The fact that mass
as a discriminate
for how the Higgs Boson is
becoming these other particles
and it follows this very clear
and I'm sure there's some
analytic function that fits
that really well that says yes
this is Higgs is the origin
of mass.
>> Yes, yes or at least
something that behaves exactly
as we have predicted the Higgs
to decay or interact, yes.
This is the - this plot
shows the prediction
from the standard model
Higgs Boson compared
to what has been measured,
so one is the standard
model prediction.
And here's how we measured the
b-quark connection, the taus,
each of the five big channels.
So it's really lining up
with what was predicted;
so it seems to be -
Higgs Boson as predicted.
But I still want
to talk one moment
about the Higgs interacting
with itself.
So this again is the
piece of the Lagrangian.
A piece of the description of
the standard model has to do
with the Higgs interacting
with itself.
And here's a little diagram
showing this is the Higgs
decaying into two more
Higgs and so we want
to measure how often
that happens.
The most common way that we said
the Higgs decays is to b-quarks
and this interaction the Higgs
decaying into itself happens
so rarely that you want
to choose something
that happens fairly
often; so we're looking
at the Higgs decaying into
four essentially four b-quarks
and also into two
b-quarks and two taus.
So basically we saw the
Higgs decaying into taus,
we saw the Higgs decaying
into B's now all we have
to do is look for both of
those at the same time.
So easy peasy.
We can use the same techniques
it's just the problem is it's
super rare; so here's a
picture of the decay where -
we're sure the decay happened in
here and there' two jets coming
out of the circle and turquoise.
And then two taus that
have also come out.
So we want an event
that looks like that,
a collision that
looks like that.
And so I have to show because
this is what I've been working
on but we just finished this
paper that is showing the search
for 2B's and 2 taus
at the same time
and we haven't seen
anything yet.
We just a couple
months ago only saw
for the first time the Higgs
decaying into the 2B's.
So to look for the
2B's and the two taus
at the same time is we're a
little ahead of ourselves.
But we're planning it because
the detector will be upgraded.
The whole [Inaudible]
collider will be updated
and when we have more data we're
going to do this analysis again
and then we're going to look
for the Higgs decaying
into two Higgs.
As of now it's just very
exciting to say that we've ruled
out that the Higgs does
not decay into two Higgs.
12 times more than
predicted, which is the type
of results you get
[Inaudible] over and over
when you're looking
for something
and you don't yet
have enough data.
You can only rule out some
extraordinary high deviation
from what's expected.
And we can also combine
that result with looking
at the four B's as the
BB and the tau tau.
You can also look at
2B's and two photons,
so these are all the normal
channels, but then put together.
And then when they're
put together we can rule
out the Higgs decaying
into two Higgs, 12 -
or 6.5 times more
than is predicted.
So sort of the current
state of affairs and then
when we get more and more
data we'll be able to see
if it is actually as predicted
by the standard model.
And along the way we will
also look for other things.
So I can go into another
whole talk about other things
that decay into two Higgs.
There are many, many
theories that try
to answer those other questions,
so what is dark matter,
why is gravity so weak?
Can we unify the forces?
So super symmetry is one of
the names of the other theories
that answer those questions
and some super symmetry,
all super symmetry theories
say that there have to be more
than one Higgs Boson,
there have to be five,
there has to be a heavy one
and a light one for instance.
And the heavy one would decay
into the lighter versions
of itself; so as we're
looking for the Higgs decaying
into two Higgs we're
also looking
for a large heavy Higgs
decaying into two Higgs.
So this is a plot showing
what that would look
like on our mass blast.
So now instead of going up to
125, we're going up to 1,400 GB.
So really high mass, do we see
some new particle out there,
like we saw the Higgs?
So we look both for a heavy
Higgs, we're also looking
for the theory about
little gravitons,
so they say maybe there's
a compactified dimension;
don't ask me what that means.
But has gravity in
another dimension
and we only see little
bits of gravity
and that's why gravity
is so weak for us,
but we could see
little gravitize them
and they would decay
into Higgs Bosons.
So we looked, we
didn't see that.
But you can make a ruling, this
is a plot that shows some theory
for the gravitons
and we have ruled
out that there can be no
gravitons above this amount.
So there may still
be a small number
of gravitons, but not so many.
So we ruled out that out
with this same analysis.
Okay I will end there because
I know it is 5:00 and just say
that we are producing now
enough Higgs Bosons at the LHC
that we can start to do
precision measurements.
We can measure how they
decay, how often they decay
and what types of
things they decay into.
And we can also use
those decays to look
for other types of [Inaudible].
Thank you.
[ Applause ]
>> You have such a large
amount of data that you need
to have artificial intelligence
program filter out most
of the results [Inaudible].
Is there a possibility
that you're already getting
information on new kinds
of particles and it's
being filtered out?
>> Yes, sure.
And that is a constant
worry; yes.
So always you basically if you
have some theory that you want
to test, you have to
do a million tests
to see what would be needed to
- what you would need to say
to see that theory and then
everybody has their theories
that they want to test.
And those get put
into the trigger
and [Inaudible] cuts out data.
And then in addition to that we
try to save a random selection,
that's just nobody decided
what it should be this random
selection, or something
really generic like the two -
the majority of the
protons hit each other
and then some little -
nothing much happens.
But they hit each other and
then the energy all goes
in the transfer direction,
that means that really
it was converted to mass,
something happened and
that particle decayed.
So something really happened; so
then you don't say I'm looking
for something with
2B's and two Taus.
You can say I'm just looking for
something where a huge amount
of energy came the
other direction
and that should be sort of
agnostic to specific theories,
but yes that is exactly the
problem and people spend tons
and tons of time
trying to make sure
that we're not throwing
away [Inaudible]
that we're hoping to find.
>> In fact, one of the first
cuts must have been to not want
to have two events that occurred
at the same time, right?
And yet the thing that you're
just describing wanting to find
in the later part was
something that looks
like two events at
some level, right?
>> Yes, we want to make sure
that we're not seeing two sets
of protons hitting each other
or even just two
quarks and four quarks.
You want just two quarks or
two muons hitting each other
and those decay into one
[Inaudible] in fact we have
to distinguish that from
multiple [Inaudible] hitting
each other.
It actually happens less than -
because of how often it
happens it's not very often.
>> I heard something
that it was describing.
I mean there were well-separated
in that sense okay,
the individual let's say protons
interacting with each other.
They're well separated
from the other ones.
>> It's - there's also a
whole lot of low energy stuff
that comes out when the other
particles interact a little bit
and then they send out just a
little bit of excess particles
that come in and that's
also very [Inaudible].
>> Yes?
>> My science blog off the
internet, so it must be true,
five new particles have
already been discovered at the -
>> Right, right s we have
discovered particles -
I don't know if I have any
particular graph showing it.
We have in the same way that
you can combine often the
down to make a proton.
You can combine the other quarks
and they make a stable particle
that lasts for some amount
of time and then decays.
And when particle physics was
first happening all they were
doing was shooting
together protons
or shooting together
electrons and looking
for these resonances,
so some bump in the data
and then they learned about
how the quarks interacted
with each other.
So there's like 30 known
particles that are interactions
of those quarks that
stick together
for just a moment
and then decay.
And already at the LHD
we discovered something
like five new ones, and
so that's very exciting
but it's not as exciting
as discovering something
that's not in this table.
So another - a new particle.
It's just another combination.
You say, okay they can
combine in this other way
and it helps us to learn more
about how quarks interact.
>> Thank you that clarifies.
>> In the old days there
were random coincidences
and if you have a 25
second window you worried
about [Inaudible], can
you narrow this window
or [Inaudible] limited
in the time it takes
them to [Inaudible]
>> They would like to
narrow the window, yes.
It used to be every 50
nanoseconds and then we went
down to 25, yes and I believe
that the new - not this coming,
so we're going to shut down
for two years and fix things
that are radiation damaged and
then run a little bit longer
and shut down for five years.
And then they're going to
upgrade the entire detector
and have a higher
luminosity and I believe
with that comes a
smaller window.
I don't have the number
in mind right now,
but the detector can do it.
It's more the - for
the trigger it's hard,
the trigger decisions.
They're trying to put boosted
decision trees into hardware
to get the trigger
because that's faster
than an offline software
trigger.
So that's a big challenge.
But it's also how
you get the more -
I believe the detector
components themselves do not
have a problem with going
a little bit quicker.
>> Out of curiosity I
think you hinted at early
in the presentation, what's the
implication of the [Inaudible]
of the Higgs for
vacuum stability?
>> Vacuum expectation?
>> Yes.
>> Yeah so that is a
component in the description
of the Higgs potential, if I can
find my Higgs potential picture.
So the terms that
describe this potential,
so that go into the
Lagrangian depend on this lamda
or here five that depends on the
vacuum [Inaudible] value and -
no the coupling of
the Higgs to itself.
So those two things together
and so if it's not the mass
of the Higgs, it is the
vacuum expectation value
that is measured
separately by someone else,
but that is a key component
that needs to go in to be able
to understand whether - when we
do measure the Higgs Coupling,
if we are in the standard model.
>> Okay.
>> I was wondering
on the [Inaudible] becoming
discouraged, will this upgrade
in the future broaden their
chances of [Inaudible].
>> Yes and yes.
There's - there was
a lot of hope
that the super-symmetric theory
is - seems simple and it seems
to answer a lot of questions.
It allows you to
beautify the strong force
in most versions
of super symmetry.
It often creates a particle
that could be dark matter,
which would be great and people
- a lot of people thought
that as the LHD turned
on you find the Higgs
and find the first
evidence of super symmetry.
And so far no other targets
[Inaudible] besides the Higgs
but when we go to
higher energy and we go
to higher [Inaudible] people
say that not only in the -
we can look always for a
new bump and a higher mass,
for a new particle that way.
But you can also look for the
rates of something like this
that depends on all - any
time you do this calculation
of how often this
should happen you have
to consider the possibility
that some other particle
interacted in here.
So in a sense you have
to include every other
of those 17 particles in your
calculation and if you get
down to a really, really precise
measurement you can tell whether
it's just those 17 or that
it's something else also.
And so people say if you measure
that really precisely you'll
know whether we've got all the
particles or there is some
extra piece that we're missing.
And so that's the way
that you can do it
if it was a really high
energy particle that we need
to discover, super symmetry,
we can do it indirectly,
discover that there's some
new particle indirectly.
>> A final question.
>> You mentioned earlier
about how it created mass
in transfer mass and
I was just curious how
that [Inaudible] relation
if it's interacting itself,
does that make sense?
>> I think that's getting at
some deeper, hard understanding.
So you're saying how
does it have mass itself
if it's creating mass.
Yes, it is interacting
with itself so in the fact
that it has mass, it's also -
yeah I think that's
the way to submit that.
It's when you - when a particle
has mass you can say it couples
[Inaudible], so the photon
travels through the Higgs field
and doesn't see it at all.
The Higgs travels through the
Higgs field and it does interact
with itself, and so
it does give mass
from interaction
with the Higgs field.
It's a good question.
>> Let's thank our speaker.
[ Applause ]
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