4. Nuclear Matter and Deconfined Quarks and Gluonsuwer/lectures/... · freeze-out (the earliest in...
Transcript of 4. Nuclear Matter and Deconfined Quarks and Gluonsuwer/lectures/... · freeze-out (the earliest in...
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4. Nuclear Matter and Deconfined Quarks and Gluons
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The Standard Model of particle physics predicts a cosmological, QCD–
related smooth transition between an early high-temperature phase
dominated by quarks and gluons (~12 ps after Big Bang) and a low-
temperature phase dominated by hadrons.
The very large energy densities at the high temperatures of the early
universe have essentially disappeared through expansion and cooling.
Nevertheless, a fraction of this energy is carried today by quarks and gluons,
which are confined into protons and neutrons.
According to the mass-energy equivalence E = mc2, we experience this
energy as mass. More than 99% of the mass of ordinary matter comes from
protons and neutrons, and in turn about 95% of their mass comes from this
confined energy.
Dürr et al., Science, 322 , 1224-1227 (2008).
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Melting Nuclear Matter: Quark Gluon Plasma
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According to today’s understanding such a phase existed
10 ps after the big-bang and lasted for about 10 s.
• Can we produce the QGP phase
in the lab?
• What are the properties?
• Phase transition?
http://www-
linux.gsi.de/~andronic/intro_rhic/
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Quark Gluon Plasma – A new state of matter
Shortly after the property of asymptotic
freedom has been discovered the
transformation of nuclear matter into a
deconfined phase has been discussed.
If temperature and/or nuclear
densities are high enough strongly
interacting quarks become free:
Quark Gluon Plasma:
• Ignoring interactions between quarks
and gluons: ideal gas
• Significant interaction between quarks
and gluons: liquid (hydrodynamic
system)
Remark: 100 MeV 1.16 1012 K
Phase diagram in ~1980
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Thermo-dynamical phase transition:
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Gibbs free energy:
j
jjdnSdTVdpdG
TSpVUTpG ),(
Change of #particle of jth chemical
component. is the chemical potential
of this component:
jinpTj
jn
G
,,
Phase boundary (equilibrium):
0jjpT dndG ,
2-phase system (1,2):
),(),( TpTp 21
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Phase diagram of QCD
49= Change of energy when adding additional baryon
= net baryon density
Sufficiently high baryon density:
Cooper pairing of quarks near the
Fermi surface (neutron starts):
Color superconductor
Chiral symmetry broken
Chiral symmetry restored
RHIC
LHC
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Phase Transition & Critical Temperature & Order Parameter
hadrons quark/gluon
at large T
(ignoring masses)
Degrees of freedom
QGP:
Hadronic gas phase (only pions): N = 3
Lattice QCD predicts phase transitionEnergy density of hadron gas
(ideal gas)
Critical temperature: TC = 173 MeV(zero net-baryon density)
Critical density: c ~ 0.7 GeV fm-3
nuclear density: = 0.15 GeV fm-3
Inside nucleon: = 0.5 GeV fm-3
)32(4
782 fNN
(ud+ heavy s)
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Time development of Heavy Ion Collision
= ideal way to get conditions of
extremely high T and .
Formation time τ0 = 1 fm/c = 3,3*10-24s
QGP in thermal / chem. Equilibrium.
Cool down: hadronization
Temperature O(1012K)
Lifetime 10 fm/c = 3,3*10-23s
Lorentz contratcion: 100 (RHIC), 2700
(LHC)
Critical temp. corresponds to
energy densities of ~ 1 GeV/fm3
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1. Chemical freeze-out: inelastic collisions cease.
(Close to phase boundary?). Yields are frozen.
Temperature: Tch
2. Kinetic freeze-out: elastic collisions cease.
Spectra are frozen ( t+ = 3…5 fm/c).
Temperature: Tfo
Critical temperature: Tc
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Heavy Ion Colliders
Facility Location System Energy (CMS)
AGS BNL, New York Au+Au 2.6-4.3 GeV
SPS CERN, Geneva Pb+Pb 8.6-17.2 GeV
RHIC BNL, New York Au+Au 200 GeV
LHC CERN, Geneva Pb+Pb 5.5 TeV
Brookhaven National Lab:
Relativistic Heavy Ion Collider
(RHIC)
Experiments: STAR, PHENIX,
PHOBOS, BRAHMS
sNN
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First Pb+Pb collisions in ALICE
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Geometry of AA collisions – Impact parameter
Participants
Spectators
Spectators
“Glauber” model of AA
b
Binary Collisions
Participants
b (fm)
Np
art, N
co
ll
Binary Collisions:
1. Jet Production
2. Heavy Flavor
Cannot directly measure the impact parameter:
Use total number of produced particles and
detected “spectators” as a measure for the
“centrality” of the heavy ion collision.
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Centrality measurement
“peripheral”
“central”
ALICEALICE
Two variables:
• zero degree calorimeter
• charged track multiplicity
TPC multiplicityZero degree calorimeter
VZero detector
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• In hadronic collisions most particles have only small transverse momentum
• Observable particles carry only small fraction of (anti)protons longitudinal momentum (x = pz/pz,max)
• “Rapidity” variable “increases dynamic range” (x < 0.1)
• Rapidity not easy to measure. Use pseudo-rapidity instead:
• Particle density dN/d related to dN/dy:
(Pseudo) Rapidity
)ln(~ln2
1x
pE
pEy
z
z
2tanlnBeam axis
TT dyd
dN
dd
dN
pp
=v/c
small deviations
for slow particles 57
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Experimental probes for QGP
Global
Observables
Is initial state dense
enough?
• Particle Multiplicities
• Energy Density
Collective
Behavior
Is QGP a
thermalized state?
• Hadron Yields
• Elliptic Flow
Hard ProbesFormed early,
probe medium
• Energy loss of jets
• Charm production
Why What
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Charged particle density
6% most central collisions
(grey band: syst. error)
Particle density at mid rapidity is a measure of energy density:
At mid rapidity particles have <pT> ~ 500 MeV
RHIC
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Energy density - Bjorken Estimate
crit~1 GeV/fm3 at critical temperature
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Hadron yields at mid-rapidity
Analysis of hadron yields provides a “snapshot” of AA collision at chemical
freeze-out (the earliest in the collision timeline we can look with hadronic
observables).
• Large amount of newly
created particles.
• Large variety of species
• Mass hierarchy in production:
u,d quarks are remnants from
incoming nuclei
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Thermal model for yields
Grand canonical partition function for specie i:
)/T-(E-exp1ln2
lnZ ii0
2
2i dppVgi
12 ii Jg
22
ii mpE
iCiSiIiBi CSIB ,33
Spin degeneracy factor
total energy
chemical potential
ensures (on average) conservation of quantum numbers:
iiB BnVNBaryon number
iitot InVI ,, 33Isospin
iiii CnVSnV0Strangeness, charm
+ = fermions,
- = bosons
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0 3
2
2
1exp2
),(
3
T
ISBE
dppgTn
iiSiBi
iBi
I
Fit of particle multiplicites
with TCh and B as free
parameter:
TCh = 174 MeV
B = 46 MeV
Hadron yields are well described by thermal model.
TCh agrees well with the
theoretical calculation of
Tc for phase transition
P.Braun-Munzinger et al., hep-ph/0105229
Phys.Lett. B518 (2001) 41
sNN = 200 GeV
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Elliptical flow - properties of QGP
Anisotropy and elliptical flow:
• Gradients of almond-shape surface will lead to
preferential expansion in the reactions plane.
• Anisotropy of emission is quantified by 2nd
Fourier coefficient of angular distribution: v2
• Supports idea of collective expanding medium
in thermal equilibrium
y
y
p
ptan
Highly compressed,
very asymmetric fireball
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Elliptical flow measured at RHIC
agrees well with hydrodynamic
models assuming an ideal liquid
(i.e. no viscosity): Expanding
medium behaves like an ideal
liquid.
Bulk evolution described by
relativistic hydrodynamics and an
equation of state determined by
weakly interacting quarks and
gluons: confirms the idea that
fireball reaches equilibrium
quickly.
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Effect of QGP on hard (early) particlesEnergy loss in dens medium
Calculation assuming very dens gluon gas
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ALICE
Clear effect of a opaque
nuclear medium confirmed
at LHC.
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J/ Suppression in QGP
2. Charm
Production
1. Colliding
Ions
QGP
3. Charm
Destruction
4. Freeze out
Early signature
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Catherine Silvestre – CMS
Confirms the large
suppression seen at
RHIC.
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QGP
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• Clear evidence of a new phase of matter in thermal quilibirium in
the early stage of the Heavy Ion collision.
• Predictions of clear experimental signatures not easy:
QCD + Thermodynamics + relativistic Hydrodynamics needed to
describe the observables. Modeling involved.
• Exciting time: Huge set of measurements expected in the next
year will unreveal the properties of this phase of matter.