Download Quark Gluon Plasma: the Hottest Matter on Earth

Quark Gluon Plasma:
the Hottest Matter on Earth
John Chin-Hao Chen (陳勁豪)
RIKEN Brookhaven Research Center
Brookhaven National Laboratory
03/21/2012
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Once upon a time…
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The universe startsfrom a big bang
As time goes by, big fireball starts to cool off
13 billion years later, it is where we are now
What is the very beginning of the universe looks like?
Quark Soup?
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Outline
• What is quark gluon plasma (QGP)?
• Some properties of QGP
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Part I: What is QGP
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Quarks are confined
• Quarks are confined
in protons and
neutrons
• The further quarks
apart, the stronger the
force; the closer the
quarks, the weaker
the interaction
• What will happen if
we increase the
energy “high enough”?
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The Idea of Quark-Gluon Plasma
• Typical nucleon energy density (energy inside the
nucleon) is about 0.13 GeV/fm3.
• Higher temperature → higher energy density →
create more new particles (by E = mc2)
• When the energy density exceeds 1GeV/fm3, many
new particles are made → packed close together
• matter will exist not as hadrons (protons, neutrons…),
but as independent quarks and gluons.
• In this medium, the quarks and gluons are
deconfined.
• It is called “Quark–Gluon Plasma ”
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How do we melt the nucleon?
But how hot
do we need?
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Energy density / T4
How hot do we need?
Hadrons
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• At critical temperature, TC,
the energy density
increases rapidly due to
Gas
the increase of degrees
of freedom. (dp -> dQGP)
Plasma
• TC ~ 175MeV. The energy
density e~1GeV/fm3.
• TC ~ Trillion (1012) K
• Temperature of the core
of Sun: T~107 K
Temperature
Phase
transition
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Where in the universe can we
achieve the extreme condition?
• T~1012 K: 1 micro second
after the big bang?
• Super high pressure:
maybe inside the neutron
star?
• Where else?
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The Hottest Matter is on Long Island!
Collides p+p, Au+Au and other species at various energies!!
Maximum energy: Au+Au at s = 200 GeV per nucleon pair
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What happens in heavy ion collisions
• The beams travel at 99.995% the speed of light.
• The two ions look flat as a pancake due to Relativity. (g~106 at
full energy collision @ RHIC).
• The two ions collide and smash through each other for 10-23 s
• The collision “melts” protons and neutrons, and liberates the
quark and gluons.
• Thousands of particles are created and fly out from the collision
area; plasma cools off.
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Two General Purpose Detectors
STAR
specialty: large acceptance
measurement of hadrons
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PHENIX
specialty: rare probes, leptons,
and photons
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Events viewed by detectors
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PHENIX: Pioneering High Energy
Nuclear Interaction eXperiment
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A even hotter matter at LHC
• The Large Heavy Ion Collider
• Three experiments: ATLAS, CMS, ALICE (dedicated HI
experiment)
• Collides Pb+Pb @ √sNN = 2.76/5.5 TeV, and p+p at √s =
2.76 TeV for reference
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Part II: Some properties of QGP
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Some properties of QGP will be
discussed
• Is it hot enough?
– Temperature
• How does the bulk behave?
– Collective flow
• How do we probe the QGP
– Hard probes
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How do we understand the
properties of QGP?
• We collide heavy ions (Au/Pb) which
creates QGP
• We have most simple system p+p as a
baseline measurement
• We compare what we see in pp (no QGP)
and AuAu (with QGP), see what happened
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Some useful terminology
• Central collision: the two nuclei
collide “head on” (0-10% centrality)
• Peripheral collision: the two nuclei
touch by edge (70-92% centrality)
• Npart: Number of nucleons
participating the collision
• Ncoll : Number of binary collisions
• pT : transverse momentum
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Number of photons
How do we measure the
temperature of QGP?
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• We measured the direct
photons from pp and
AuAu collisions
• We see enhancement of
photon yield in AuAu
enhancement
AuAu
pp
– Similar to black body
radiation from QGP!!
– T ~ 220 MeV
– Tc ~175MeV
– Or 4 trillion degrees
Celsius
– Or 250000 times hotter
than the center of the Sun
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Low pT Direct Photon vs different
system
rg = (# of direct g) / (# of inclusive g)
• Low pT direct photon ratio in various collision systems are
measured in PHENIX
• large enhancement above pQCD calculations (lines) in AA
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What is the initial temperature?
Tc ~170 MeV
• Various theory calculations to describe the data
• Tini ~ 300-600 MeV (initial state dependent)
• All above Tc (~170 MeV from lattice QCD)
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How do the particles move?
• Collision area has “almond”
shape due to overlap
geometry of the nuclei.
• Almond shape leads to ununiform momentum
distribution.
• Pressure gradient pushes the
“almond” harder in the short
direction.
• This is a “hydrodynamic”
effect.
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We can also measure the shape
fluctuations
• The nuclear is not perfect in
shape
• Nucleon distribution is not
smooth
• Azimuthal symmetry of the
colliding area no longer
available
• dN/df  1+S(2vncos n(f-Fn))
• vodd is possible, which is due to
shape fluctuations
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vn(Fn) vs pT
• All vn increases with pT
• v3 is independent from centrality
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What is viscosity
• Viscosity is the
resistivity of the fluid
• Low viscosity: milk
• High viscosity: honey
• Low viscosity means
the energy can
transfer through the
fluid very fast
• no viscosity = “ideal
fluid”
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New Tool to Calculate the QGP
Properties: String Theory
QGP
AdS/CFT
space
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• Through Ads/CFT
correspondence, some
strongly coupled 4
dimension quantum field
theory situation can be
transformed in to a black
hole in 5 dimensions
• By solving the relatively
“easy” black hole
properties in 5-dim space,
we can calculate many
properties for strongly
coupled system, such as
QGP
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v2 and Viscosity
• String theory predicts there is
a universal minimum on
viscosity for strongly coupled
system (h/s = 1/4p ~0.08)
• QGP: tiny viscosity per
particle (h/s ~0.08 in
hydrodynamics and under
Glauber initial state
conditions)
• The most perfect fluid in the
world!!
Phys. Rev. Lett 99, 172301 (2007)
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vn vs theory
• All theory predicts v2 well
• v3 adds in additional discrimination power
• Data favors Glauber + h/s = 1/4p
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Other perfect fluid?
• Cold atomic gas
• T ~ 10-9 K
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• Electrons in graphene
(2010 Nobel Physics)
• T ~ room temperature
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How do the particle flow?
• In higher pT, the v2 is saturated
• v2 is particle type dependent
• The matter is strongly coupled!
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• v2,M(pT)~2v2,q(pT/2)
v2,B(pT)~3v2,q(pT/3)
• The quarks have collective motion.
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Beam energy dependence of vn
• Various beam energy: 39, 62, 200 GeV
• vn does not have significant beam energy dependence
• Hydro dynamical behavior down to 39 GeV
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Hard probes on QGP
• Hard probes
–
–
–
–
–
Jets,
Heavy flavor (c, b)
Quarkoniums (J/y, U)
direct photons,
Z/W (LHC)
• Usually produced at the beginning to the
collision
• Probes live through out the whole formation
stages
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What is jet?
• When 2 quarks collide,
back-to-back jets are
produced
• Jet is a narrow cone of
hadrons and other particles
resulting from a fast quark
or gluon
• In heavy ion collision, the
colliding area has high
energy and particle density,
which will modify the jet
passing through this hot
and dense medium.
• Also called Jet Tomography
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Jet tomography in daily life– P. E. T.
• PET - Position Emission
Tomography
• Physiologic images
based on the detection of
radiation from the
emission of positronelectron annihilation.
PET scan of human brain. Picture from Wikipedia.
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Jets in the plasma
p+p @ 200 GeV
STAR
Au+Au @ 200 GeV
p-p di-jet Event
What happened to the
jets in the medium ?
Where is the jet?
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How do we study jets?
• Best way:
– Direct jet measurement (difficult at RHIC)
– g-jet (also difficult)
• We can also study
– High pT single particles (coming from jet
fragmentations)
– Two particle correlations (leading high pT particles
from jet fragmentations, correlated with another lower
pT particle)
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p0 spectra in Au+Au vs. p+p
• in central Au+Au
collision, less p0 is
produced than
expected yield from
scaled p+p
• The yield in Au+Au is
suppressed
central
Ncoll = 975  94
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High pT hadrons are suppressed!
R AA
Yield AuAu

 N binary  AuAu  Yield pp
•RAA : nuclear modification
factor
•If no “effects”:
•RAA = 1 at high-pT where
hard scattering dominates
• Suppression:
•RAA < 1 at high-pT
Phys. Rev. Lett. 91, 072301 (2003)
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The matter is DENSE.
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Summary of particle suppression @ RHIC
• Hadrons (made of quarks) lose energy in the medium
• Photons don’t feel strong interactions, so loss no
energy in the plasma
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arXiv:1202.2554
RAA @ LHC
• Similar suppression trend till 20 GeV/c
• RAA increases with pT when pT > 20 GeV/c
• No suppression in photon, Z
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Awayside jet is suppressed in HI collision!
same
away
Same side, no
modification
away side, jet is
absorbed in the medium
Phys. Rev. Lett. 91, 072304 (2003)
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Jet suppression @ LHC
Pb+Pb @ √sNN = 2.76 TeV
• Jets are “visible”
• Di-jet suppression!
• Consistent with RHIC
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Dijet energy imbalance
• AJ=(pT1-pT2)/(pT1+pT2)
AJ = 0 means no suppression
• Significant suppression in central Pb+Pb collisions
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g-jet
(g-hadron correlation)
Low zT
High zT
zT = pTa/pTt
zT ~ -ln(zT)
• Use direct photon to tag jet energy to study the energy loss
• Jet energy is lost in AA collisions!
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The shape of the Correlation
• Jet shape depends on
particle energy
• Jet shape is modified
by the plasma
Phys. Rev. C 78 014901 (2008)
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Do we see the Mach cone in QGP?
D
• The far side peak
moved to ~ 1200 in
central collisions!
• “Mach Cone” like shape
• Sound wave propagate
through QGP?
• If so, it can be used to
estimate the speed of
sound in QGP
Phys. Rev. Lett. 98, 232302 (2007)
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Two particle Dh-Df correlations
Peripheral Au+Au
Dh
Central Au+Au
Df rad
Dh
Both near and away side
are modified!
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Df
shoulder ridge
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v3, reason for ridge and shoulder?
• Ridge sits at Df ~ 0,
shoulder sits at
Df~2p/3, 4p/3
– A 3-peak structure!
• v3 (Fourier Coefficient
of the cos3Df term)
gives a natural 3-peak
structure
• Is v3 the explanation?
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Jet shape with higher vn modulated
background subtraction
200GeV Au+Au
0-20%, inc. g-had.
• When v3 modulation is included in the
background subtraction, the double peak
structure in away-side disappears.
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Some properties of QGP will be
discussed
• Temperature: it is hot!
• Collective flow: it flows like a perfect fluid!
• Jet quenching: it is dense, and opaque to
fast quarks
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Why QGP is so interesting?
• highest energy density frontier
• It was last seen when the universe is
0.000001 second old
• A test ground for string theory
• It is a hottest perfect fluid, what about the
coldest end, the atomic gas? In solids?
• A lot more…
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Connection with other area of
physics
Nuclear
physics
Particle
physics
Cosmology
QGP
String
theory
Theoretical
physics
Condensed
matter
Atomic
physics
QGP is highly active!!
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Summary
• A hot dense matter, quark gluon plasma, is
created in heavy ion collisions
• It has the lowest h/s ~ 1/4p, which is the
most perfect fluid in the world
• Partons lose energy in the medium
• A highly active field, many questions need
to be answered! (and to be found!)
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