quark matter at high density/temperature

Quark Matter at High Density/Temperature James Dunlop ICHEP04 1

Quark Matter at High Density/Temperature

James C DunlopBrookhaven National Laboratory


QGP a (locally) thermally equilibrated state of matter in which quarks and gluons are deconfined from hadrons, so that color degrees of freedom become manifest over nuclear, rather than merely nucleonic, volumes.

M. Gyulassy & L. McLerran

Approximately thermalized matter at energy densities so large that the simple degrees of freedom are quarks and gluons. This energy density is that predicted by LGT for the existence of a QGP, 2 GeV/fm3.

Defining the question

Recent Definition from STAR for the Quark Gluon Plasma

Contrast with other recent definition:


RHIC Implementation

• Flexibility is key to understanding complicated systems– Polarized protons, sqrt(s) = 50-500 GeV– Nuclei from d to Au, sqrt(sNN) = 20-200 GeV

• Physics runs to date– Au+Au @20,62,130,200 GeV– Polarized p+p @200 GeV– d+Au @ 200 GeV

PHENIXBRAHMS &PP2PPPHOBOS

STAR 1.2 kmRHIC


RHIC Experiments

Four experiments, two large, two small:

STAR: Large acceptance (PHENIX: Electron/muon identification, high rate trigger, limited acceptance (central arm)

PHOBOS: Tabletop: limited tracking acceptance, largest multiplicity acceptance of all experimentsBRAHMS: Forward tracking in classical spectrometer


in entropy density, hence pressure

in heavy-quark screening mass

in chiral condensate

The most realistic calcs. no discontinuities in thermodynamic proper-ties @ RHIC conditions (i.e., no 1st- or 2nd-order phase transition), but still crossover transition with rapid evolution vs. temperature near Tc 160 – 170 MeV.

Lattice QCD Predicts a RAPID Transition


No exp’tal smoking gun! Rely on theory-exp’t comparison

Charged particle pseudo-rapidity density

HBT parameters

pT-integrated elliptic flow

pT-integrated elliptic flow, scaled by initial spatial eccentricity

But only smooth behavior is observed


pT-integrated yield ratios in central Au+Au collisions consistent with Grand Canonical stat. distribution @ Tch = (160 ± 10) MeV, B 25 MeV, across u, d and s sectors (s consistent with 1.0).

Inferred Tch consistent with Tcrit (LQCD) T0 =~ Tcrit .

Does result point to thermodynamic and chemical equilibration, and not just phase-space dominance? Also works in e+e-, p+p

Strangeness EnhancementResonances

STARO PHENIX

Chemical Equilibration? Hadron Yield Ratios


Collective Behavior: Azimuthal Anisotropy v2

)(tan,2cos 1222

22

x

y

pp

vxyxy

y

x

py

px

coordinate-space-anisotropy momentum-space-anisotropy

Pressure converts initial coordinate-space Anisotropy into final momentum-space anisotropy


Time evolution in Ideal Hydrodynamics

• Elliptic Flow reduces spatial anisotropy -> shuts itself off

• Sensitive to EARLY TIMES


Elliptic flow with ultracold trapped Li6 atoms, a=> infinity regimeThe system is extremely dilute, but can be put into a hydro regime, with an elliptic flow, if it is specially tuned into a strong coupling regime via the so called Feshbach resonance

Extremely cold system at T=10 nK or 10^(-12) eV can produce micro-bang

Analogy to Ultracold Atoms

Analogy pointed out by Shuryak


Hydro calculations: Kolb, Heinz and Huovinen

v2 vs. Ideal Hydrodynamics

• Ideal hydrodynamics reproduces v2 relatively well – Below pT~2 GeV, matches v2 and spectra to ~20-30%

• Appealing picture: – Nearly perfect fluid with local thermal equilibrium established at <~1

fm with a soft equation of state containing a QGP stage

STAR Preliminary


Score board: status of hydrodynamic models

• Hadronic + QGP hydro reproduces features of v2(pT) of , K, p

• Require early thermalization (therm<1fm/c) + high init > 10 GeV/fm3

• Detailed discrepancies between models and with experiment

Source average

Table courtesy of PHENIX


P. Kolb, J. Sollfrank, and U. Heinz, Phys. Rev. C. C62 054909 (2000).

Sharp freezeout dip

Hydro+RQMD no dip?

Teaney, Lauret & Shuryak

Hydro vs. STAR HBT Rout/Rside

How does sensitivity to EOS in hydro calcs. compare quantitatively to sensitiv-ity to other unknown features: e.g., freezeout treatment (compare figures at right), thermaliz’n time, longitudinal boost non-invariance, viscosity? What has to be changed to understand HBT (below), and what effect will that change have on soft EOS conclusion?

How unique and robust is hydro account in detail?


Partonic energy loss in dense matter:“Jet Tomography”

Multiple soft interactions:

Strong dependence of energy loss on gluon density gluemeasure color charge density at early hot, dense phase

Gluon bremsstrahlung

Opacity expansion:

glueSmediumT

SR

kq

LqCE

2

2

ˆ

ˆ4

L

ELogrdCCE jet

glueSaA 23 2

,

Bjorken, Baier, Dokshitzer, Mueller, Pegne, Schiff, Gyulassy, Levai, Vitev, Zhakarov, Wang, Wang, Salgado, Wiedemann,…


Partonic energy loss via leading hadrons

-

Energy loss softening of fragmentation suppression of leading hadron yield

ddpdTddpNdpRT

NNAA

TAA

TAA //)( 2

2

Binary collision scaling p+p reference


Control system: p+p collisions

p-p PRL 91 (2003) 241803

Good agreementwith NLO pQCD

2/ ( , )a Nf x Q

2/ ( , )ch aD z Q

Parton distribution functions Fragmentation functions

0

0 well described by pQCD and usual fragmentation functions

To generalize for nuclei:fa/N(xa,Q2,r) fa/N(xa,Q2) .

Sa/A(xa,r) .

tA(r)

Nuclear modification to structure function (shadowing, saturation, etc.)

Nuclear thickness function


Suppression of inclusive hadron yield

• central Au+Au collisions: factor ~4-5 suppression • pT>5 GeV/c: suppression ~ independent of pT

PRL 91, 172302

Au+Au relative to p+p Au+Au central/peripheralRAA RCP


pQCD in Au+Au? Direct photons

[w/ the real suppression]

( pQCD x Ncoll) / background Vogelsang/CTEQ6

[if there were no suppression]

( pQCD x Ncoll) / ( background x Ncoll)

Au+Au 200 GeV/A: 10% most central collisions

[]measured / []background = measured/background

Preliminary

Perturbative calculation for direct photons works in central Au+Au

pT (GeV/c)


0 RAA s Systematics

Cronin and parton energy loss at lower s

Vitev, nucl-th/0404052

Reasonable agreement with 62.4 GeV result.

larger Cronin effectgluon dN/dy = 850 (rather than 1100)

No large surprises in energy dependence

PHENIX Preliminary


Jets at RHIC

p+p jet+jet (STAR@RHIC)

Au+Au ??? (STAR@RHIC)

nucleon nucleonparton

jet

Find this……….in this


Jets and two-particle azimuthal distributions

p+p dijet • trigger: highest pT track, pT>4 GeV/c

• distribution: 2 GeV/c<pT<pTtrigger

• normalize to number of triggers

trigger

Phys Rev Lett 90, 082302


Azimuthal distributions in Au+Au

Au+Au peripheral Au+Au central

Near-side: peripheral and central Au+Au similar to p+p

Strong suppression of back-to-back correlations in central Au+Au

pedestal and flow subtracted

Phys Rev Lett 90, 082302

?


“Real” tomography: geometry of medium

Au+Au: Away-side suppression is larger in the out-of-plane direction compared to in-plane

Geometry of dense medium imprints itself on correlations

STAR Preliminary, nucl-ex/0407007

?


Inclusive hadron and away-side cor-relation suppression in central Au+Au, but not in d+Au, clearly establish jet quenching as final-state phenomenon, indicating very strong interactions of hard-scattered partons or their fragments with dense, dissipative medium produced in central Au+Au.

PHENIX

Hard Sector: Quantitative Indication of Early Gluon Density


pQCD parton energy loss fits to observed central suppression dNgluon/dy ~ 1000 at start of rapid expansion, i.e., ~30-50 times cold nuclear matter gluon density.Large extrapolation needed to take into account time-dependent expansion How sensitive is this result to:

assumptions of factorization in-medium and vacuum fragmentation following degradationtreatments of expansion and initial-state cold energy loss preceding hard collision?

Questions for Parton Energy Loss Models


sNN = 130 GeV Au+Au

Does the high initial gluon density inferred from parton E loss fits demand a deconfined initial state? Can QCD illuminate the initial conditions? Assuming initial state dominated by g+g below the saturation scale (con-strained by HERA e-p), Color Glass Condensate approaches ~account for RHIC bulk rapidity densities dNg/dy ~ consistent with parton E loss.

Rapidity dependence of RdA consistent, though questions about uniqueness

Remaining questions about robustness and uniqueness of approach

Gluon Saturation: a QCD Scale for Initial Gluon Density + Early Thermaliz’n Mechanism?

BRAHMS, nucl-ex/0403005

PHOBOS, PRC 65, 061901R


Unusual behavior in baryons

Large enhancement in baryons at intermediate pT

Not explainable in vacuum fragmentation framework


Intermediate pT: hints of relevant degrees of freedom

• Clear separation into two classes: baryons and mesons

• Apparent scaling with number of constituent quarks in final-state hadron

• Explained currently by recombination/coalescence of constituent quarks at hadronization

• If better established, direct evidence of the degrees of freedom relevant at hadronization, and the existence of collective flow at the constituent quark level

v 2/nq

STAR Preliminary, nucl-ex/0403032


jet partner equally likely for trigger baryons & mesons

Same side: slight decrease with centrality for baryonsLarger partner probability than pp, dAu

Away side: partner rate as in p+p confirms jet source of baryons!“disappearance” of away-side jet for both baryons and mesons

Jet-like correlations at intermediate pT

PHENIX Preliminary, nucl-ex/0408007


Can one account simultaneously for spectra, v2 and di-hadron correlations at intermediate pT with mixture of quark recombination and fragmentation contributions? Do observed jet-like near-side correlations arise from small vacuum fragmentation component, or from “fast-slow” recombination? Are thermal recomb., “fast-slow” recomb. and vacuum fragment-ation treatments compatible? Double-counting, mixing d.o.f., etc.?

Duke-model recomb. calcs.

Duke-model recomb. calcs.

Questions for Coalescence Models


…suggest appealing QGP-based picture of RHIC collision evolution, BUT invoke 5 distinct models, each with own ambiguities, to get there.

pQCD parton E loss

Ideal hydro

Quark recombination constituent q d.o.f.

CGC

Statistical modelEarly thermalization + soft EOS

Very high inferred initial gluon density

Very high anticipated initial gluon density

u, d, s equil-ibration near Tcrit

Five Observations


RHIC has made major advances in runs 1-3, leading to an appealing picture of bulk, dense, highly interacting matter.

1) Extended reach in energy density appears to reach simplifying conditions in central collisions -- ~ideal fluid expansion; approx. local thermal equilibrium.

2) Extended reach in pT gives probes for behavior difficult to access at lower energies – jet quenching; ~constituent quark scaling.

However: In the absence of a direct “smoking gun” signal of deconfinement revealed by experiment alone, a QGP discovery claim must rest on the comparison with a promising, but still not yet mature, theoretical framework. In this circumstance, clear predictive power with quantitative assessments of theoretical uncertainties are necessary for the present appealing picture to survive as a lasting one.

Summary

quark matter at high density/temperature

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