it's my great pleasure to introduce
today's speaker professor Anne Sickles
professor Sickles received her PhD in
physics from Stony Brook University
after doing research at Stony Brook
National Lab she joined the department
here in 2014
professor Sickles' research focus on an
exotic state of matter that existed only
at the beginning of the universe but
amazingly these days scientists can
actually recreate and study the matter
in in labs in colliders so this is what
Professor Sickles will tell us
let's welcome professor Sickles okay well
thanks for coming thanks for spending
part of your Saturday doing physics are
listening to physics I said what I'm
gonna tell you about is called the
quark-gluon plasma it's called the
hottest matter in the universe to me I
was saying now we're able to actually
recreate that in the lab and so that's
what I'm gonna tell you about today so I
say something is the hottest matter in
the universe that's an absolute scale
but how hard is it compared to things
that you might know about well today is
gonna be a nice day we don't have any
beaches but a nice day is 80 degrees
Fahrenheit right this is this is pretty
hot lava which I think we could all
agree is too hot to touch is about 2,000
degrees Fahrenheit so that's something
you really should be careful with an 80
degree day you're okay lava you should
take some more precautions it can really
mess up your day the center of the Sun
which we can all agree is really hot
it's 28 million degrees okay that's
pretty respectable it's the hottest
place in the solar system a supernova so
this is the collision ooh this is an
explosion exploding star so this is a
quite a bit hotter than the Sun but as
supernovae rings in at about
50 billion degrees Fahrenheit what I'm
gonna tell you about today is the core
glowing plasma and it's 5 trillion
degrees Fahrenheit and I can't download
a picture on YouTube so that what I'm
gonna do is I'm gonna try to explain to
you how we do this in the lab what we're
doing to try to build a picture of the
quark-gluon plasma so the way we do this
is I have to take a little bit of time
and explain to you what matter is made
out of the stuff that you see around you
so you see atoms you see atoms that are
formed into molecules and solids you
know the wood biomolecules that are
where in this tree at some point the
tables the chalkboard all of this is
made out of atoms and atoms are
interesting because they're mostly empty
this is just a picture I took off
Wikipedia and it shows an electrons
orbit so the electrons there's a few
electrons in every item-- it depends on
which atom you're talking about how many
electrons there are but they're very
small point like particles that circle
around what is the nucleus of the atom
and the thing about the nucleus is
that's where all the over 99% of the
mass of an atom is is this nucleus and
an atom is about 10 to the minus 10
meters angstrom and the nucleus is a few
Fermi's across and what the heck's of
Fermi a Fermi is 10 to the minus 15
meters and so that's how big the nucleus
is and so everything that you see around
you the mass is coming from the nucleus
and the nucleus is incredibly small most
the vast majority of the atom is really
empty space so what we're gonna do is
we're gonna take a close look inside the
nucleus and then we're gonna use the the
nucleus to create the core clon plasma
so nucleus 99% of the mass of normal
matter is in the nucleus and the nucleus
to vary in size from hydrogen which is
the lightest to uranium to all the
transionic elements that are created in
the lab so these are small to large it's
composed of protons and neutrons so
those are the building blocks
of the nucleus so the proton carries a
plus-one electric charge and the
neutrons they don't carry any electric
charge and that's what I've Illustrated
here I'm not sure this is just a
PowerPoint drawing if proton should be
red or blue
it doesn't particularly matter there's
two kinds of constituents in the nucleus
the nucleus what holds these things
together what holds together a bunch of
protons and in the nucleus
well it's something called the strong
force and the strong force is strong
it's incredibly strong and so what it
does is it keep to all these protons
together they all have the same electric
charge you might think that they should
blow up but they don't which is why
we're here and they're held together by
the strong force and there are four
fundamental forces of nature gravity
electromagnetism which one or the two
you're most familiar with but then
there's these two nuclear forces the
strong force and the weak force but this
is maybe you're not always the most
creative neighbors and I'm gonna tell
you about the strong force so it's very
strong and it's also very short-range so
it doesn't impact your daily life so
much except for the fact that it holds
the nucleus together and makes
everything else possible okay so what's
inside protons and neutrons they are not
point particles they have subscribers
and they're made out of these even more
exotic particles quarks and gluons and
these are the fundamental particles
which interact by the strong force or
quarks and gluons they were they were
derived in the or they were discovered
in the 70s so that's why they have
whimsical names the quarks they carry
electric charge this is really electric
charge of the proton comes from is from
the the quarks that make it up and the
gluons they exist to bind quarks
together more or less and hence they're
called gluons and so you might have
learned in high school chemistry as I
did that the proton is made up of three
quarks and so that's what I've drawn
here this is my proton is a PowerPoint
circle in three quarks as letters but
actually the proton is a quantum system
and it has an extremely rich structure
so there's a whole bunch and this is
just when I got bored of drawing these
circles or these letters here it has a
whole bunch of quarks and gluons inside
of these these are virtual particles
that flicker in and out
existence but that's really what the
what is made up of the protons and the
neutrons looks pretty much the same way
at least from this level what is
interesting about this the strong force
is that this this quark all by itself
the strong force does not like that it
has a property called confinement which
doesn't let you have that
so all quarks and gluons in nature in
the natural state of matter have to
carry no net charge according to these
strong floors the the charge in the
strong force is called color and
everything has to exist in these
colorless objects you can't have a quark
by itself and that's really a
fundamental property of the strong force
and because you have this confinement
property this is why you don't have an
intuitive feel for how the strong force
works because you have a feel for how
electronics works because you can plug
things into outlets it's very accessible
to you electrons are all over the place
you see lightning in the sky that's
electric discharges but confinement
makes that all those those things about
the strong force are really wrapped up
inside these protons and neutrons or to
10 to the minus 15 meters across so it's
really remote from your everyday
existence despite the fact that it makes
up you know a huge fraction of your
everyday existence so this is what makes
the strong force hard to study is the
property called confinement so you know
normal people might give up at this
point but physicists you know we like to
dig in so what happens what if I want to
have free quarks and gluons what if I
want to have a system that's made up of
quarks and gluons rather than protons
and neutrons which are then themselves
made up of quarks and gluons so what we
want is a system that is hot and dense
enough to essentially melt the protons
and neutrons that's what we want to do
just like I could melt my coffee cup if
I held it over something that was hot
enough
lava maybe if I held it over that I
could melt that well if I could find
enough energy maybe I could melt these
protons and neutrons and have a system
that's really made up of the fundamental
quarks and gluons
okay so what I need is I first need to
start with something that's made up of a
whole lot of quarks and gluons and for
that what we use is the lead nucleus and
it's not particularly important that
it's led it could be anything we want
something that's big letters a heavy
nucleus it's made up of many protons and
neutrons which are them themselves made
up in many quarks and go on and so this
is a good place to start then just like
with my coffee cup I want to add energy
I want to have something to heat it up I
can't use a Bunsen burner or lava or
anything like that because it's not hot
enough it doesn't provide enough energy
so what we do is we actually add another
nucleus and we smashed them into each
other and then that takes the kinetic
energy from these two nuclei coming at
each other which are going over 99.9
whatever at the speed of light and the
the kinetic energy that these two nuclei
bring when they smash into each other
liberate these quarks and gluons and
that is essentially what we're doing and
that is how we create the quark-gluon
plasma and this is interesting for two
reasons the first of all is because
there's only four fundamental forces of
nature and so studying how one of them
changes when you heat it up is
intrinsically interesting the other one
is that this is actually what the
universe looked like about a millionth
of a second after the Big Bang so this
is actually a window back in time so
we're not only doing something which is
intrinsically interesting but we're
talking us more for time or we're
learning more about where we came from
inhabitants of the universe so I can't
do this here for you today there's no
demonstration on this it would be
tremendously unsafe we'd all have to
take radiation training there's two
places in the world where you could do
this
there's particle accelerators this is
what you used to do it the first one
that I'm going to talk a lot about is
the Large Hadron Collider Collider which
is in Geneva CERN it's it's big it's
it's very huge it's something like 16
miles around
it's underground the collider actually
goes over these great French Swiss
border in a couple of places it
very high-energy collisions I'll come
back to that at the end and so that's
where the the Large Hadron Collider is
we also have a Collider in the US which
is called the relativistic heavy ion
collider it's on Long Island in New York
at Brookhaven National Lab it's a lower
energy Collider but there are reasons
that it's actually particularly
interesting which I'll talk about at the
end and so these are the only two places
in the world where you are where one can
do this as I'm involved in experiments
at both and I'm gonna tell you a little
bit about this but first I'd like to
show you a YouTube video because who
doesn't like YouTube videos this is one
that it was put out by CERN and it shows
you a little bit about how these
colliders work and what I want you to
take away is that these things are
incredibly complicated
so there's CERN in the middle of Europe
there's Lake Geneva
there's the LHC and what you see is
there's this whole complex I work at the
Atlas detector but what you do is you
start out in these small things which
are off the LHC first you have to have
something which provide you with the
nuclei and so that's what happens here
you accelerate it using electric fields
and then you put them in these circular
colliders for use electric and magnetic
fields to essentially speed up these
protons so that was the proton booster
and then after that you get it going
around in the proton synchrotron which
is a bigger higher energy machine these
things were used for research once and
now we just use them as warm-ups so when
they're going fast enough you put it
into the super proton synchrotron of
course which is bigger there are a Nobel
Prizes associated with these machines
these are amazing machines and then
finally you put the protons or the lead
nuclei whatever you're colliding into
the LHC and so this this is huge this is
the CMS experiment they're my
competitors and many of my friends
actually I work at the Atlas experiment
which is what's right here and so what
happens is in a few places around the
ring we bring these beams into collision
and then we measure the signals that
come out in our detectors here and the
rest of this video it goes on it's about
the computing challenges and I think you
can trust me that the computing
challenges of dealing with this data
our non-trivial but that's not why you
came all right so this is about how
colliders work there's more videos on
this you can certainly watch the whole
thing so this is what I want to do I
wouldn't take heavy nuclei I want to
smash them into each other and recreate
this hot matter that's from the the
earliest moments of the universe so just
to set the scale um it lasts for about
10 to the minus 23 seconds which is an
unfathomable short amount of time
it's a billionth of a trillionth of a
second if you want to count the
exponents so I can't do anything to it
once it happens it exists it goes on its
own trajectory but I and my detectors
and anything cannot respond to it fast
enough it's a billion times smaller than
the pixel on your iPhone display so it's
the size of this cork long plasma is
about the size of the nucleus and so the
lead nucleus is about kind of minus 14
meters across so that's about how big
this court glowing plasma is so that's
why there's no picture and and this
makes challenges for an experimentalist
I'm an experimentalist and physicists
use challenging when something sounds
impossible and it's just a way to make
sure that uh we can suitably impress
people when we finally do it so I work
with the eyeless detector and an acute
that's really the only way to say it
I've ever actually seen it it's deep
underground but many people do go down
there it's 25 meters tall so meters
about 3 feet so it's about 75 meters
tall these are people little artist's
rendering of people that's about the
size you would be if you were standing
on the Atlas detector 44 meters across
that's about 150 feet across ah the
collisions happen here in the very
center and the detectors built like an
onion it just keep going out more and
more detectors different ways of
measuring what comes out so just some
statistics there's a hundred million
electronics channels 3,000 kilometers of
cables 7,000 tons millions of lines of
code 3,000 people are needed to get
physics out of this thing from 38
countries
truly international collisions every
hundred nanoseconds most of time they
collide protons looking for new
particles but that's not really what I'm
gonna tell you about right now those
people are my friends but I'm gonna tell
you about the coracoid plasma so our
output so far is 800 science papers and
50 million emails hundreds of thousands
of doodle polls trying to schedule
meetings okay so what do we actually see
we see hundreds or thousands of new
particles creatively so we take this we
make this cork long plasma we turn
energy and then of course expands and it
cools off because it doesn't last very
long it's over really quick and so these
this energy that was in the cork lump
plasma has to go somewhere and so we
make particles this is an artist's
rendering of some of these particles and
this is exactly according to the most
famous physics equation e equals MC
squared we take this energy and we turn
it into massive new particles and since
we can't do anything to the court go on
plasma these particles really provide
the only window we have and into the
collision so you can think of it like
reconstructing a car accident from the
patterns in the glass right this is what
we have we have the remnants and we have
to sort through them and try to figure
out what happened in some particular
collision and we look at each collision
independently so a collision is the
result of two led nuclei smashing into
each other we look at that independently
but then we look at billions of these
collisions so they're all different and
we try to look for the pattern in in
what we see that's really what we do is
experimentalist so this is a slide that
I had up at the beginning so this is a
very head-on mudbud collision and this
is the the green and the blue here is a
model of what the Atlas detective looks
like and the orange lines each one of
those is a particle that was created in
a single collision and tracked through
our detector so really we can have up to
10,000 particles created in the most
head-on collisions so now I started to
talk about head-on collisions so maybe I
should we should get into G
so what actually nuclear collisions look
like and the nucleus is small I already
told you that I said we use big ones oh
but what a nuclear collisions actually
look like and they look kind of like
this the nucleus so this is gold but it
doesn't really matter gold and letter
both about we're both big and so these
two nuclei come in ones coming in from
the left ones coming in from the right
one is red and one is blue you can see
they're offset from each other
you can also see that these let these
gold nuclei have a hundred and ninety
seven protons and neutrons in them and
so these protons and neutrons they're
basically clumped into like a ball shape
but there's there's luck shoee shion's
the protons and neutrons can move around
this is a simulation of how one looks so
you see there's some that are you know
barely hanging on and then there's weird
structures each one's a little bit
different and these nuclei nobody makes
them come in exactly head-on right we
don't have the ability you have a
question yes yes they are fully stripped
so these are plus seventy nine so they
have a huge electric charge which is a
totally interesting field but not
anything I'm going to talk about here
but they have a huge electric charge at
this point so they come in and they can
they can hit at whatever impact
parameter they want to they can miss
each other and a lot of times they do
they can hit where they're totally head
on and then they can hit where they're
offset with each other as you can see
here so this one the nuclei are offset
the Centers are offset by from each
other by six Fermi's which is not a lot
to you or me it's a lot compared to this
nucleus size so here they come in and
what I've done is that the darker
protons and neutrons are those that
interact and the lighter ones are the
ones that that miss and because these
things are going pretty much the speed
of light they don't have they don't have
time to figure out that they missed
they come in they hit and the things
that miss just keep going down keep
going because they don't know that their
friends got into this massive collision
they missed out on that so we can rotate
this right of you
a little bit and so now I've just
rotated at 90 degrees so one of the
nuclei is coming in one of the nuclei is
going out to the screen and so what you
see is this region where they overlap
with each other
it's kind of like a football shape and
if you just you know draw two circles
you see exactly that that's probably
what should happen and the the football
shaped nests essentially of the region
where the collision happens depends on
how far offset these things were with
respect to each other so they all look
different so these are three different
ones with different impact parameters so
here the impact parameter the the nuclei
are offset a lot with respect to each
other here they're offset less and here
they're offset almost none at all so you
can see the nuclei have a little
different shapes in general though this
is more circular so how are what are we
going to do your question I know these
are inelastic we really blow things up
and create new particles so this is this
is just one of these collisions and the
first thing you can do is you can count
the directions that all these particles
come out all these orange tracks that I
showed you a few slides ago you can just
count where the particles are and this
is what we do in physics I teach the
freshmen we always have to define a
coordinate system you have to know what
you're doing all right so here's my
coordinate system it wouldn't be a
physics lecture unless I throw in a
Greek letter so we're gonna call the
angle Phi and we're just gonna count the
number of particles this is a relative
number of particles so we just put it at
1 this is the number of particles that
come out with respect to this angle Phi
it's in radians cuz for physicists
that's what we like to do so this is the
stuff that comes out this way is it zero
here pi is over here so that's there and
PI over 2 which is here is the stuff
that comes out the top on the bottom so
what you see is that the number of
particles varies a lot depending on how
you come out of this collision there is
you know 20 minus 20% ha that's kind of
interesting so we see less particles
that come out this way the top and the
bottom from the the ends of the football
and we see a lot more particles that
come out the long side and if you are
lucky enough to be making a measurement
and see a huge effect like this this is
great you take it and you ride it for
all it's worth right so that's what we
do because this gives us a lot of
physical insight what's going on if you
just imagine that in your football you
just had a few particles then the
density is very low and any particle no
matter say this particle here no matter
which way it tries to come out it's very
unlikely that it's gonna hit anything
else there's just not a lot of particles
most of it is free it's just like if you
try to walk across the street and
there's no cars it's 3:00 a.m. nobody's
around you know you're not gonna run
into anybody no matter which way you
walk but if you you know try to walk
around the quad at lunchtime or Green
Street at lunch times you're gonna run
into a lot of people right but if the
density is low you're not gonna run into
anybody if you increase the density now
this particle here it's easy for it to
come out this way any way it tries to go
that's inside it's gonna hit a lot of
particles and so what this variation and
the angles that the particles come out
is telling us is that the interactions
must be important that this must be
important in the collision because for
an order for you to have any sort of
variation and the angles that the
particles come out they have to know
that the other particles are there and
the only way they can know that they're
there is if they're interacting with
them in some way so we know the density
is high and actually working with our
theoretical colleagues what we have is
we have actually the limit of a lot of
interactions so what I've drawn here is
uh it's a rainbow-colored set of circles
right so this is high density these are
lower density and obviously not
obviously obviously to me maybe outside
the collision region is just vacuum
these beam pipes that there's nothing
else in the LHC except for the the
particles which are colliding so we know
the density is zero outside of our
football
it's very high in the middle and so what
we have is we have a steep pressure
change here and a very strong or gradual
pressure change here and so one thing
you can think of this as is think of
this like a topological map right this
is the top of the mountain this is the
equivalent of jumping off a cliff right
it's a very steep decline down this way
is more like going down the garden path
this is a very slow side down and so
what happens to the court glowing plasma
is it explodes outward because there's a
huge pressure change just like falling
off a cliff it explodes outwards in this
direction and it does not explode
outward in this direction as much and
that's why you see more particles coming
out in this way then you see this way
because it's really exploding outward
and this this is characteristic of how a
liquid works it's the limit of huge
amounts of interactions this is how a
liquid works this is what happens in in
water like what's in your daily
experience so how do you characterize a
liquid um there's lots of different ways
we can characterize a liquid I'm gonna
talk about viscosity so you have an
intuitive feel for viscosity right ah
water right you can support waves in
water you can have ripples and water all
of these things water is a very low
viscosity it's generally a very good
like wood you can describe it well the
theory of how you describe liquids is
hydrodynamics because water is very good
liquid honey is it is a much worse
liquid it has a higher viscosity you
know this see the ripples that you see
in the waves in this nice picture from a
family vacation to Hawaii they have a
lot of structure this jar of honey has
no structure you know that you could not
get that kind of structure with
something that with the viscosity of
honey so it by looking at these
variations we know that the course on
plasma is actually supporting a lot of
ripples and what we can do is we can use
models to actually take these ripples
and try to figure out what the viscosity
of the quark-gluon plasma
and that is something that we've spent a
long time doing in this field so
viscosity we typically write it in terms
of this funny quantity ada over us it is
the viscosity s is related to the
disorder in the system so if we write it
in these units now I've got a lot of
Greek letters right I have Ada and I
have pi here so it's 25 in units of 1
over 4 pi and these are funny units and
I'll get to it in a second this is the
viscosity of water so we already know
water is a very good liquid if we
measure the viscosity of the quark-gluon
plasma it has a viscosity in these same
units of less than 5 so water is
actually about a 5 times better liquid
no other way the quark-gluon plasma is
about a 5 times better liquid even than
water and we already said that water was
really the prototypical liquid so
interestingly why is this important why
do I use these units because there's a
calculation in string theory 11
dimensional black holes and a theory
theory that was kind of like the real
theory of the strong force but not quite
and there's a conjecture that there's a
universal quantum minimum the how good
of a liquid you could have and that is
it this one over 4 pockets so it's
possible that if we are able to quantify
the viscosity of the quark-gluon plasma
we would actually be testing a
calculation that has to do with string
theory and string theory I don't know
how much you know about it but one that
one thing about it is it's not readily
experimentally testable so there's a lot
of interest and being able to see how
these two things fit together
bringing down this bound here and trying
to understand if this bound is violated
or not so this is a this is a very
important question to us determining
what the viscosity is however there's
another question and that's why why
should the viscosity of the quarks and
gluons a very high 5 trillion degrees
why should that be so big what about the
strong force leads to this fluid
behavior and this is actually the
question that I want to answer
because it's really it's inherent and in
these explaining understanding where
this comes from and to answer that
question we need a picture of really
what's happening inside the core clone
plasma we need to zoom in you think
about all right you know that water is
h2o that's the chemical formula for a
water molecule that doesn't tell you why
water at room temperature is a liquid
and why water at 32 degrees freezes so
we have a descriptive understanding of
the court glowing plasma but we then
want to get at an understanding of why
and so that's what I want to talk about
here we need a microscope so this is now
my cartoon quark-gluon plasma it's right
there
this is exactly what it looks like if I
draw it on my computer and I want to do
something like an x-ray of the
quark-gluon plasma
all right you break your button your arm
the doctor wants to take a picture so he
takes x-rays and he shoots them at your
arm and looks at what comes out this is
exactly what I want to do here I want to
shoot something through the quark-gluon
plasma look at what comes out I don't
want to use x-rays so I want to use
something that interacts by the strong
force so what I'd really like to have is
a beam of quarks and gluons and shoot
them through my quark-gluon plasma and
look at what comes out now I don't have
such a thing so again this is an
experimental challenge and so I'm going
to talk to you about how we're trying to
do that well actually I told you that a
proton is made up of quarks and gluons
right so if I have two protons that are
coming at each other this is kind of
like two beams of quarks and gluons
shining right at each other isn't it and
sometimes if you get lucky and wait long
enough a quark from one proton really
hits a quark from another proton head-on
and when that happens they exchange a
lot of momentum and you get a cork
coming out this way and a cork coming
out this way so now I have taken my beam
of quarks and gluons from these two
incoming protons and I scattered two of
them one coming out this way one coming
out the other way because of course we
have to conserve momentum
to come in pairs and they have to be
back-to-back and of course confinement
kicks in nature does not like my freak
works scattering out at high-energy and
so I'll talk a little bit about this but
of course in the end what we observe is
a bunch of particles and those are
represented by those nerves here these
are just a bunch of particles things
like protons and neutrons that come out
at the end so we observe this this is an
event display from Atlas so this is a
real event a proton proton collision and
there's a lot of details on these plots
this is the view where one proton is
going into the screen and one proton is
coming out and these yellow spots here
and the green are proportional to the
amount of energy that was deposited in
the Atlas detector and so you see that
there's a lot of energy this way and
there's a lot of energy that way so
those are your back to back
we call them Jets so this is a pair of
Jets they're back to back to conserve
momentum if you imagine cutting the
detector and unrolling it like you would
with a paper towel tube and then looking
at the energy which is what's shown here
you can see these are these two energy
deposits they're really the only thing
that happened in the event so this is
what you see these are the Jets so if I
take my beam of protons and then I just
cover them up with a whole bunch of
other protons and neutrons well this is
just like using my lead my lead
collisions right so there are certainly
protons in this led niklas protons in
this one the same idea works with
neutrons as well so if I just take a two
giant nuclei and I run them into each
other I will create a quark-gluon plasma
and sometimes these core gluon plasmas
will have going through it these two
Jets just like I was showing you before
so that's what we're going to use as our
microscope we're gonna use these fast
quarks and gluons that are created when
a quark from one proton or neutron hits
head on a quark from another one and so
that's how we're gonna use it that's
what we're gonna use for our microscope
so it can happen anywhere within the
court glumly plasma I've had it happen
here at this place where the star
so you have one coming out this way one
coming out this way it could have
happened anywhere this is just where I
drew it and then of course it turns into
a bunch of particles that's what I've
shown here again by these arrows these
are the particles from one jet and these
are the particles from the other Jets so
the question is I can show you
PowerPoint drawings all day but what
about the data this is but this has got
to be better and so we did this and holy
mackerel I don't see a pair of Jets here
this is the equivalent plot of the
unrolled detector that I was just
showing you I see one jet and I don't
know if I squint I may be able to
convince myself there's a little
something extra here where the other jet
should be but but I certainly don't see
the same visual clarity that I did
before and that's troubling right
because physicists I believe a few
things and one of them is very deeply I
believe in momentum conservation
tell me something doesn't violate
momentum or violates momentum
conservation I get very upset and I
generally don't want to be upset so all
right let's take a look the energy of
these Jets I mean this is just one event
anybody can wiggle their way out of one
event this is not statistics this is
just some Annika right so we did this
measurement which I've shown here so
this is a plot of the energy of one jet
over the identity of the other Jen I
called one jet to and one jet one it
doesn't particularly matter they're both
the same and what's shown in the blue
points is proton-proton collisions this
is where we have these beautifully
balanced Jets that I showed you first
what's shown in the red points is
collisions between two led nuclei and so
if the Jets are perfectly balanced
you should be at one the ratio of these
should be one if the Jets are are
imbalanced you should be away from that
you can see the blue points are not
actually perfectly at one the one is the
most probable value and that's because
the strong force is really complicated
and there's great stories and why this
is a distribution not a not just a spike
at one but the light collisions are
troubling because really it does seem
like the most probable value here is the
second jet has half the energy of the
first jet and so this event display that
I showed you here is not a fluke this is
really what's going on and so there it
is you know in platform with error bars
that are shown here there's really no
getting around this we're seeing
something that's totally different
and loud loud collisions than we are and
as an experimentalist this is fantastic
when I first saw this plot I almost fell
off my chair I mean it was amazing I
remember the day I could tell you about
it
this is amazing so we've got a lot of
energy that's removed from debt - this
is great this tells us that our
microscope is interacting if the Jets
just went totally through the
quark-gluon plasma and they changed
nothing then that's what's the point
it's not gonna work
but since they do change this tells us
that we have the opportunity to learn
something so now I've revised my picture
so we've got this one jet here and this
jet doesn't seem very much of the
quark-gluon plasma its path as it is
rather short but then I have this poor
jet that has a long path through this
very hot matter and so the energy of the
particles is reduced and what I've shown
here in these blue arrows is a lot of
stuff that comes from the other
particles that come from the
interactions of the jet with the
quark-gluon plasma as it's going through
these are the lower energy particles so
the arrows are shorter so what how do we
understand that I do that I have to tell
you a little bit about how a jet is made
I just had arrows that went to more
arrows I kind of waved my hands but this
is how a jet is made I said that nature
doesn't want you to have a free quark
and I said that Jets come from a quark
which had hit another quark and then
scattered like a billiard ball so how do
we reconcile these statements well you
start out here this is my quark
represented by this arrow that's going
along here and it tries to progress
forward in time going this way this is
it going along and nature starts to
impose confinement the strong force says
no you cannot just be a bear quark and
so this is a gluon
of course Nature doesn't like a bear
glue on either and so it starts to make
more and more particles and we call this
dressing essentially that's what's
happening
nature is dressing up the quirk with
more and more quarks and gluons and
eventually these things become lower and
lower energy and they become the
particles that we observe in our
detector so it's like a shower process
you start with one thing that makes two
things makes four things and eventually
what you have at long times is you have
the the particles that we expect to see
and this is what we measure in our
detector and it's really the process of
dressing up these quarks and gluons the
quark-gluon plasma changes that so what
I've shown here are more gluons these
are the gluons from the court glowing
plasma and again it's just a cartoon but
there's more interactions and so this
dressing process happens differently in
the quark-gluon plasma than it does when
there's no core clump plasma and this is
really the key this is what allows us to
have information so if we can take the
measurement the Jets that we observe and
sort of go back to how they must have
interacted what these interactions that
are shown here in red must have looked
like that's how we find things out and
that's how he is the check as a
microscope so essentially we get more
particles they have different energy and
it's because of these red interactions
here and so that's what explains the
blue the blue particles here ah it's not
just a cartoon I measured it so this is
a plot that was made by my group myself
actually much blood sweat and tears so
this is the number of particles in a jet
we like to pick ratios a lot of things
help experimentally when you take ratios
this is the number of particles in a jet
divided in blood lead collisions divided
by the number of particles in a jet in
proton-proton collisions as a function
here on the the x axis is the particle
energy and you can see at higher
energies there's not so much difference
at lower energies there's this huge
excess it's a 50% excess for all of
these jets
and that really is these blue particles
these extra low energy particles that we
see in LED collisions compared to those
in proton-proton collisions so I've told
you about what we see this is a paper
that came out in the beginning of the
summer what are we doing next well
there's two things that are really you
know I put a lot of my time into one
thing is that we work with theorists to
build models which tell us how to turn
this cartoon into these measurements so
they do calculations and predict
measurements and we make measurements
and try to compare them to their theory
and we work together to try to determine
what are the most useful measurements to
make so I have three thousand
collaborators on Atlas there's two other
collaborations that do a lot of these
sorts of measurements CMS and Elise at
the LHC and then there are lots of
groups of theorists that make these
models so this is very interactive field
hence all the doodle polls all the
emails we have to talk to each other
this is there's no there's no simple
road map the other thing is this an
experimentalist we're kind of crazy
obsessive people oh I try to figure out
how I can everything I can about this
process so how this depends on the size
of the core clone plasma the energy of
the jet type of quark the temperature of
the core complements whatever and so I
get graduate students and postdocs and
you just we go at it right this is this
is what we do this is what makes us
happy so I want to tell you a little bit
about what we're doing to try to
understand how this depends on the
temperature of the core klom plasma now
so I told you there were two colliders I
told you a lot about the LHC I should do
a video didn't tell you about this
relativistic heavy ion collider in New
York so you don't know what a TeV is
probably but at the LHC the collisions
happen at five TV a trick they happen at
point two TV there's this factor of 25
difference and the interesting thing is
that the collision energy sets the
temperature of the quark-gluon plasma
this is the key it's how fast they're
going that tells you how hot your
quark-gluon plasma is and it's not like
your stove where you can just turn it
down the elate see does not run well at
point two TV it's like you know trying
to drive a sports car and traffic you're
just gonna get upset so this runs very
well there so what we do is it's
actually much more efficient to use two
machines and so that's what we do we
vary the energy of the we look at we use
both machines to vary the temperature of
the quark-gluon plasma because anything
if you want to study it and you don't
know how it depends on temperature
you're missing a huge a huge slice of
the pie here right if you didn't know
how water depended on temperature ice
and water vapor
you'd miss you miss all sorts of things
so in order to do this we have to build
a new detector so Ric has been running
since 2001 and people weren't asking
these questions in the 90s when those
detectors were designed but now
especially driven by the LHC we're
asking these questions and so we want to
go back and look at Rick again but the
detectors are not the right detectors
for it and so we're building this
detector called s Phoenix and so it's
currently under construction as a new
detector a trick which is optimized for
these jet measurements and so this is a
long time work going up and I was there
in the room when it was first brought up
we've been working on it for I think six
years now we expect to take data in 2023
this is an engineering drawing of it
there's the person you can see this is
considerably smaller than Atlas as I
showed you earlier and the reason it's
smaller is because we're at twenty five
times lower collision energy so we don't
have to detect this energetic of
particles so that that makes things a
little easier
we built our detector around a
superconducting solenoidal magnet and if
that sounds complicated it is there's a
decent chance that you buy one and you
try to turn it on it doesn't quite work
so we stole ours from the Stanford
Linear Accelerator in the dead of night
no no it was the Department of Energy
they were a lot of there was a lot of
paperwork but they had one that had been
used for an experiment which was
decommissioned and so we put it on a
truck there it is on the truck at the
Stanford Linear Accelerator complex in
the Bay Area and we drove it across the
country to New York
the people who with this tracking
tracking company did and so that's
really what we're building our detector
around
I mean think building a detector it's
gonna be in New York well actually we're
making a big chunk of it here I in my
lab I was gonna say our Bannock but
actually the labs in Champaign over by
the stadium and we're building these
blocks and these blocks you can come up
and see them afterwards these are
they're heavy they're made out of
tungsten powder and they're you know
this bag and they have which maybe you
can see they're filled with plastic
scintillating fibers so we're gonna
build 6,000 of these blocks and these
are really an essential component of the
jet measurement at s Phoenix so what
happens is electrons or photons they
come in this way this is really the last
thing that they see this is what the
front of the detector will look like or
looks like this is just a photo of this
which you probably can't see a blow-up
that I took with my phone so they hit
the tungsten and just like what would
happen to you when you hit a block of
tungsten they stuck and they start to
create more particles they have a
showering process which is very similar
what I told you about jets only this is
driven by the electromagnetic force and
this showering process creates a lot of
light and these scintillating fibers
take the light and they pass it to the
front of the calorimeter oh this is it
it's a calorimeter it pass it to the
front where we read it out on photo
sensors and so our job at Illinois is to
build these bricks we're brick builders
I'm the blockhead that's what I get to
be so this is really an essential
component of this measurement there's a
nice picture of one these are a couple
of my undergrads working in a tent it's
it's party tent and the reason it's a
party tent is because these fibers are
hard to see they're a half millimeter
across so we needed we have a high bay
but we needed something that brings the
light down lower so they don't ruin
their eyes too much so they are working
on it they're happy trust me so that's
what we're doing here to try to learn
more about the quark-gluon plasma we
work at the LHC we also building
for the future as well so really what
we're doing is we're using fast quarks
and gluons as a microscope to study the
inner workings a trillion degree matter
we're doing this at two places at CERN
and Brookhaven
really this is a new window into one of
the four fundamental forces of nature
and we'll look back at the early
universe what I'm spending a lot of time
on right now is getting ready for this
new data that we're gonna have a PhD in
November again a lot of doodle polls and
emails but we're very excited about this
I'm really looking forward to it
we're also working hard towards a new
detector to be able to understand the
temperature dependence of this core klom
plasma thanks a lot
so that's a really interesting question
and we we don't know the answer to it so
we we we can't we can't compress it in
the way that you could try to compress
water but we do look at it's this dude I
talked about the viscosity which is
assuring viscosity but there's also a
bulk viscosity which is the viscosity
against expansion and that's something
that we're we're trying to study a lot
right now actually
yes I think that the more that you can
understand about it going this way which
is the way that is accessible from us
now then you can then feed that into
models which take into account that the
early universe started from very
different initial conditions so that's
something that you have to exactly what
am I trying to get why should that and I
don't know the answer to that I don't
have an intuitive picture I'd love to be
able to give a talk in five years or I
did have an intuitive picture but this
is really this is something we don't
understand yet this is where we said
yeah oh sorry
so that's just some fee so they asked
about the corresponding cemetery for
color chart so what nature required the
fundamental theory of the strong force
is called quantum chromodynamics
and so that enforces the color charge
conservation so we can talk about that
in more detail later if you want yes so
parts of it do get activated
we haven't cooled to vary how cold you
need it depends on the various
technology that detector components we
have a silicon detector which is quite
cold other parts of our color we also
have a liquid argon calorimeter so you
have to keep that at a constant
temperature the activated parts actually
I was talking remember about the parts
of the nuclei that get sheared off and
they don't know their friends had the
collision those goes straight down the
beam pipe and so they end up very angle
angles that are very close to the beam
pipe and that's where a lot of the
activation happens in the detector
itself it's generally safe to go down
there and less the obviously and less
the accelerator is on that stuff is not
so activated so those are the the normal
particles of particle physics soap ions
cans protons neutrons B hadrons D
hydrants yes that is essentially what's
happening in this dressing process is
going from quarks to going to the normal
stuff that people who take particle
physics classes hear about
oh no no this this will not the lead
nucleus is remarkably stable and we
don't keep it around long enough to be
able to make constraints on anything
like that yes
you
