PHENIX Overview: Status of QGP

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PHENIX Overview Status of QGP

• Terry C. Awes
• Oak Ridge National Laboratory
• IX Workshop on High Energy Physics Phenomenology
• Jan. 3-14, 2006
• Bhubaneswar, India

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Quark Gluon Plasma
F. Karsch, Prog. Theor. Phys. Suppl. 153, 106
(2004)

• Lattice QCD predicts transition to deconfined
  Quark Gluon Plasma phase at 175MeV
• Goal of Relativistic Heavy Ion collisions - to
  produce and characterize QGP state.

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Central Relativistic Heavy Ion Collision
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Studying high density matter with Relativistic
Heavy Ion Collisions

• Does the produced matter in RHI reach local
  equilibrium - allowing a discussion of matter
  properties ?
• Is deconfined quark matter produced?
• What is the transition temperature?
• What are the characteristics of the quark matter?
• Opacity
• Viscosity
• Heat capacity - Degrees of freedom - quarks and
  gluons or more complicated colored objects?
• etc

What have we learned so far?
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PHENIX detector at RHIC

• Hadron measurement
• hlt0.35
• PID using TOF
• p/K/p separation up to 2 GeV/c (EMCAL)
  and 4 GeV/c (TOF)
• Electron measurement
• hlt0.35
• PID using RICH
• e/p separation up to pT 4.8 GeV/c
• Photon measurement
• hlt0.35
• Two different calorimeters PbSc and PbGl
• PID using TOF, shower shape, charged veto
• Muon measurements
• 1.2 lt h lt 2.4
• Two separate arms at forward and backward rapidity

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Centrality Nucleon Collisions Nucleon
Participants
Spectator neutrons
10-15
5-10
0-5
Peripheral
Central
Forward Mult.

• Centrality selection Sum of Beam-Beam Counter
• (BBC, h34) and energy of Zero-degree
  calorimeter (ZDC)
• Extracted Ncoll and Npart
• based on Glauber model.

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The Final State Particle Yields
Assuming Chemical Equillibrium (Chemical
Freeze-Out)
Braun-Munzinger, Maegestro, and Stachel

• Excellent description of relative yields of
  particles with only 2 parameters.

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QGP to Hadron Phase transition?

• Chemical Freeze-Out Temperature (at mB) is
  remarkably close to the Hadron to QGP phase
  boundary predicted by Lattice QCD.
• How can chemical equillibrium be attained so
  rapidly? (Hadronic rates/cross sections too small
  -- equilibrated in partonic phase?). Why is TChem
  so high?

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The Final State Thermal Freeze-Out
Particle Spectra Central AuAu T109MeV bT(Max)
0.77

• Particle Spectra p,K,p,f (low pT) can be
  described consistently with common Temperature
  and radial flow velocity profile (max. bT )

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The Final State Thermal Freeze-Out

• Particle Spectra (p,K,p,f) can be described
  consistently with common T and radial flow bT
  that depends on overlap volume.
• Increase in centrality (volume) gives longer
  lifetime - more rescattering allows transfer from
  thermal to collective motion, thus larger bT and
  lower T.
• Results suggest significant rescattering.
  Pressure? Thermalization?

Temperature
ltbTgt
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Anisotropic Flow aka Elliptic Flow

• For non-zero impact parameter, the nuclear
  overlap volume is f-asymmetric.
• If the matter interacts strongly, pressure
  gradients will result and the initial spatial
  asymmetry will be converted to a momentum
  asymmetry.

• Elliptic flow v2 2nd Fourier coefficient of
  azimuthal anisotropy

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Elliptic Flow via 2-particle correlation
2-particle correlation with trigger particle
selected according to event plane measured in
forward rapidity region (BBC).
R(f)
Azimuthal Correlations include elliptic flow and
di-jet contributions
f
More about jet component later
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Final State Elliptic Flow
PHENIX Preliminary
Observed large v2 implies strong interactions in
the produced matter.
From Hydro

• Observe v2 dependent on pT and particle mass
• Such dependences expected from hydro (flow)

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Final State Putting it together
One can obtain a consistent description of the
final state -- particle spectra, yields,
azimuthal asymmetries, and radii (from p-p HBT
analyses) using a hydro inspired Blastwave
model (F. Retiere, nucl-ex/0404024).
AuAu 200 GeV
T106 1 MeV ltbInPlanegt 0.571 0.004
c ltbOutOfPlanegt 0.540 0.004 c RInPlane 11.1
0.2 fm ROutOfPlane 12.1 0.2 fm Life time
(t) 8.4 0.2 fm/c Emission duration 1.9
0.2 fm/c c2/dof 120 / 86
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QGP to Hadron Phase transition?

• Particle Yields Chemical Freeze-Out at T175MeV
  and mB 30 MeV.

???

• Consistent description of final state indicates
  that system lives 10fm/c, with pion emission
  occurring in a final burst of 2fm/c duration at
  T100MeV

• Did system initially enter QGP phase? How far
  -what T?

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Probing the Early Phase Theory

• Ideal Hydrodynamics (11Dim) can describe the
  particle spectra and v2 if Equation of State
  includes QGP phase. EOS without QGP too hard.
• Parton Cascade (Boltz.Eq.) requires unphysically
  large cross sections (45mb). Why?
• Suggests initial matter of Quarks and Gluons is
  strongly interacting (sQGP) and non-viscous
  (Ideal Hydro). Perfect Liquid
• Large initial energy density ?15-25 GeV/fm3
  (?çrit1GeV/ fm3)

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Perfect Liquid h/s1/4p
h/s1/4p
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Press release based on RHIC White Papers
PHENIX (Nucl. Phys. A757, 2005 III) Model
comparisons show HydroChemEq doesnt work,
HydroHadronCascade is better.
p
p
elliptic flow
PHENIX white paper, NPA757,184(2005)
pT spectra
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State of the Art
CGC3D hydrohadron cascade (Hirano et al)
Reproduces all quite well including rapidity
dependence of v2 for non-peripheral collisions.
h shear viscosity, s entropy density
Its ratio to entropy density
Absolute value of viscosity
Its because h/s is small that Ideal Hydro works
so well. Hirano Gyulassy, nucl-th/0506049
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Probing the Early Phase Back to experiment

• If initial phase is thermalized it should radiate
  photons. Measure the initial temperature via the
  spectrum of thermal photon radiation. If you
  measure T0 much greater than TC one can be sure
  to have started in QG phase.
• Study production of hard probes produced early in
  the collision to deduce properties of the
  produced medium that they must traverse
• Jets, i.e. hard scattered partons. More
  particularly high pT particles from jet
  fragmentation.
• Charm production
• J/y production

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Photons Continum Spectrum with Many Sources
Rate
WeakEM decay gs (p0,h) Bkgd
Hadron Gas Thermal Tf
QGP Thermal Ti
Pre-Equilibrium
Jet Re-interaction
Turbide, Rapp, Gale
Final-state photons are the sum of emissions from
the entire history of a nuclear collision.
pQCD Prompt
Eg
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p0 and h - On the way to Measuring Direct g in
?s200 GeV/c AuAu collisions

• Measure p0 and h distributions-
• Input to MC to calculate decay g
• Compare measured g to decay g to extract direct
  g yield

Au-Au PRL 91 072301
h Spectra
Centrality
PHENIX Preliminary
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High-PT p0 spectra in pp collisions at 200 GeV/c
Spectra for p0 out to 12 GeV/c compared to NLO
pQCD predictions (by W.Vogelsang) pQCD works
very well!
p-p PRL 91(2003) 241803
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High-pT g in pp (dAu) Collisions at 200 GeV/c
As observed for p0 production, the direct photon
measurement in pp agrees with NLO pQCD
calculations. The preliminary dAu g yield also
agrees with ltNcollgt -scaled NLO pQCD
calculation. Baseline for comparison with AuAu g
results.
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First RHIC AuAu Direct Photon Results

• Direct g excess consistent with NLO pQCD pp
  predictions, scaled by the number of binary
  collisions.
• Fragmentation?, Bremsstrahlung?, Thermal?

PHENIX PRL 94, 232301 (2005)
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Centrality Dependence of Direct Photons

• Within errors ltNcollgt scaled NLO pQCD describes
  g yield even to low pT !
• Need to improve errors on pp and AuAu
  measurements to search for deviations from pQCD
  as evidence for other contributions, e.g. thermal
  g

PHENIX PRL 94, 232301 (2005)
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Thermal Photon Expectations?

• Hydrodynamical predictions for thermal g (HRG
  QGP) plus prompt NLO pQCD prediction yields.
• Consistent with thermal with QGP with T0 of
  590MeV.
• Measured g yield is consistent with NLO pQCD
  prediction with or without thermal contribution.
• NLO pQCD works too well!? Fragmentation g
  contributions are large (50 at 3 GeV/c, 35 at
  10 GeV/c). Why not modified?

Central AuAu
dEnterria and Peressounko nucl-th/0503054
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Thermal Photons Initial Temperature

• Preliminary result from higher statistics Run4
  data set. Different method.
• Can the errors on the data, pQCD and thermal
  model calculations be reduced sufficiently to
  deduce initial temperature? Probably not...
• Can deduce that the photon yield is consistent
  with various predictions with T0max
  500-600 MeV
• T0ave 300-400 MeV

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Hard Probes Nuclear Effects?
Nuclear Modification Factor
Compare AA to pp cross section
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Centrality Dependence RAA for p0 and charged
hadrons
Suppression increases with increasing nuclear
overlap volume. Increasing density and pathlength.
(Difference between p0 and charged hadrons due to
contributions from protons - more later)
PHENIX AuAu 200 GeV p0 data PRL 91 (2003)
072301. charged hadron PRC 69 (2004) 034909.
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Quenching of Hard Scattered Partons

• Hard parton scatterings in nucleon collisions
  produce jets of particles.

• In the presence of a dense strongly interacting
  medium, the scattered partons will suffer soft
  interactions losing energy (dE/dxGeV/fm).
• Softer fragmentation spectrum Jet Quenching

Alternatively, reduced hard scattering rate due
to initial state PDF modification? Gluon
Saturation
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Theoretical Interpretation of High-pT p0
Suppression
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A Closer Look at pT Dependence of Direct Photons
and p0 Production for Central AuAu

• High pT g yield consistent with binary scaled
  pQCD in contrast to factor of 5 suppression of p0
  h yields.

PHENIX PRL 94, 232301 (2005)

• Direct g are not suppressed - strong evidence
  that hadron suppression is due to final state,
  i.e. parton energy loss.

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Baryon Anomaly

• While p0 show strong high pT suppression, high
  pT protons seem not to be suppressed.
• Surprising result if p and pbar produced from
  fragmentation.
• f shows suppression similar to pions. Not a
  mass effect.

Can be explained as a quark recombination effect
(thermalfragmentation quarks) - strong evidence
that quark matter has been formed.
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Quark Scaling of Elliptic Flow (v2)

• Scale baryon/meson v2 and pT by number of quarks
  (nq 3, 2).
• Observe near universal scaling (better if
  account for decay contribution to pions).
• Strongly suggests that collective flow develops
  during the quark phase.

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Even heavy quarks flow

• Measure Charm via single electrons after
  subtracting photon conversion contribution.
• Recombination model indicates that the charm
  quark itself flows at low pT.
• Charm flow supports high parton density and
  strong coupling in the matter. It is not a weakly
  coupled gas.
• Drop of v2 at high pT perhaps due loss of
  collectivity or to b-quark contribution.

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Heavy Quarks also lose energy

• Measure Charm via single electrons after
  subtracting photon conversion contribution.
• Even heavy quark (charm) suffers substantial
  energy loss in the matter.
• The data suggest large c-quark-medium cross
  section evidence for strongly coupled QGP?
• The data provide a strong constraint on energy
  loss models.

Theory curves

(1-3) from N. Armesto, et al.,
hep-ph/0501225 (4) from M. Djordjevic, M.
Gyulassy, S.Wicks, PRL. 94, 112301
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J/y Suppression System Size Dependence

• Models that were successful to describe SPS data
  assuming disociation in QGP or by comovers fail
  to describe data at RHIC.
• Predict too much suppression!

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J/y Suppression System Size Dependence

• The preliminary data are in better agreement with
  models with the predicted suppression
  re-generation (quark recombination) at the energy
  density of RHIC collisions.
• Can be tested by measurement of v2(J/y)?

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Di-jet analyses just a taste

• Di-jet tomography is a powerful tool to probe the
  matter - study yields, widths, pT , and
  centrality dependence.
• The shapes of jets are modified by the matter.
• Mach cone?
• Cerenkov?
• Flow?
• Can the properties of the matter be measured from
  the shape?
• Sound velocity
• Dielectric constant

PHENIX preliminary
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Summary and Conclusions

• Although there is no smoking gun signature for
  deconfined (QGP) matter, there is now a large
  body of data that provides many model
  constraints. Were on the way towards development
  of a Standard Model of RHI collisions (eg.
  CGC3D Hydro Hadron Cascade).
• Some experimental observations and inferences at
  RHIC
• Produced matter is strongly interacting large
  collective flow and parton energy loss, including
  charm.
• Locally thermalized very likely because of
  above and success of Hydro interpretation.
• Quark Gluon phase very likely per success of
  quark recombination interpretation of baryon
  anomaly, flow.
• Much more to come