Evidence for a new phase of matter measured with the STAR experiment at

RHICRene Bellwied

Wayne State University

International Nuclear Physics ConferenceGoteborg, Sweden, June 27- July 2, 2004

The compelling global questions

Could there be evidence for a different phase of matter at even lower x ?

Are the quarks and gluons weakly interacting, as expected from a plasma, or strongly interacting as

expected from an ideal fluid description ?

Is this phase thermally and chemically equilibrated ?

Is there evidence for a phase transition to a deconfined and chirally symmetric phase of quarks and gluons at

high T ?

Different types of RHIC measurements

(producing probe and medium in the same collision)• We are producing ‘soft’ and ‘hard’ matter. An arbitrary distinction is coming from the applicability of pQCD which is generally set to pT > 2 GeV/c (hard). Below 2 GeV/c we expect thermal bulk matter production.– Medium: The bulk of the particles; dominantly soft

production and possibly exhibiting some phase.– Probe: Particles whose production is calculable,

measurable, and thermally incompatible with (distinct from) the medium (hard production)

• Measure bulk matter properties to determine global properties (collectivity, equilibration, timescales)

• Measure the modification of high pt probes to determine specific properties of the matter produced

Behavior of hard probes when traversing an opaque medium

coneRFragmentation:

z hadron

parton

p

p

Jets from hard scattered quarks observed via fast leading particles orazimuthal correlations between the leadingparticles

However, before they create jets, the scattered quarks radiate energy (~ GeV/fm) in the colored medium: decreases their momentum (fewer high pT particles) “kills” jet partner on other side

Understanding ‘bulk properties’

99.5%

Dominant feature: order of magnitude increase at high pT

Elliptic (anisotropic) Flow for a mid-peripheral

collision – a strong indicator of collectivity

Dashed lines: hard sphere radii of nuclei

Reactionplane

In-planeOu

t-o

f-p

lan

e

Y

X

Re-interactions FLOW Re-interactions of hadrons or partons or both ?

Flow

Flo

w

...) φ) ( v ) (φ v (dy dpN d

dφ dy dpN d

t t

2 2 2 121

2 1

2 3

cos cosπ

Directed flow Elliptic flow

PHOBOS: Phys. Rev. Lett. 89, 222301 (2002)  STAR: Phys. Rev. Lett. 86, 402 (2001)

Hydrodynamic limit

STAR

PHOBOS

Hydrodynamic limit

STAR

PHOBOS

Figure from Masashi Kaneta (BNL)

RQMD

v2 (anisotropy, squeeze-out) measurements

First time in Heavy-Ion Collisions a system created which, at low pt ,is in quantitative agreement with ideal hydrodynamic model predictions for v2 up to mid-central collisions

System deformation confirmed in HBT

• Final state eccentricity from

– v2

– HBT with respect to reaction plane

• Conclusions:– System was still

deformed at freezeout– System froze out

EARLY

Y

XTime

22

22

xy

xy

Tim

e

Elliptic flow v2 scaling at intermediate to high-pt • two groups,

baryons and mesons

• suggesting relevance of constituent quarks in hadron production

S.A. Voloshin, Nucl. Phys. A715, 379 (2003).

D. Molnar and S.A. Voloshin, PRL 91, 092301(2003).

Further tests: , 0, K*, pentaquarks

scaling could be seen as a signature of deconfinement !

Another sign of deconfinement: energy and particle production at RHIC

dNg/dy ~ 200 (HIJING)

dNg/dy ~ 1000 (CGC)

Gluon density in proper modelEquals final state hadron density:dNch/dy ~ 1000 (measured)

Parton – hadron duality ??

Radial expansion: Identified particle spectra in Au-Au

BRAHMS: 10% centralPHOBOS: 10%PHENIX: 5%STAR: 5%

• The spectral shape gives us:

– Kinetic freeze-out temperatures

– Transverse flow• The stronger the flow the

less appropriate are simple exponential fits:

– Hydrodynamic models (e.g. Heinz et al., Shuryak et al.)

– Hydro-like parameters (Blastwave)

• Blastwave parameterization e.g.:

– Ref. : E.Schnedermann et al, PRC48 (1993) 2462

Hydromodels Yield common freeze out T & radial expansion velocity

Blastwave vs. Hydrodynamics

Tdec = 100 MeV

Kolb and Rapp,PRC 67 (2003)

044903.

If blastwave is correct this might be an indication for early development of radial flow i.e. collectivity at the partonic level

,

,K,P,

STAR preliminary

The Ultimate test of parton collectivity:

D-meson expansion

D0, D, D* spectra from d+Au

Cover range 0.2 < pT < 11 GeV/c

Necessary baseline for Au+Au

Electrons from TPC,TOF & EMC

STAR Preliminary

Beauty

Charm

Particle production ‘chemistry’: beautiful agreement with statistical

chemical equilibration model for non-resonant particles

Does the thermal model always work ?

Resonance ratios not well described Reaction dynamics

Dat

a –

Fit

()

Rat

io

Strange resonances in medium

Short life time [fm/c] K* < *< (1520) < 4 < 6 < 13 < 40

Red: before chemical freeze outBlue: after chemical freeze out

Medium effects on resonance and their decay products before (inelastic) and after chemical freeze out (elastic).

Rescattering vs. Regeneration ?

Lifetime and centrality dependence from (1520) / and K(892)/K

Model includes: • Temperature at chemical freeze-out• Lifetime between chemical and thermal freeze-out• By comparing two particle ratios (no regeneration)

results between : T= 160 MeV => > 4 fm/c (lower limit !!!) in agreement with T and dt fromStable particle analysis

G. Torrieri and J. Rafelski, Phys. Lett. B509 (2001) 239

Life time:K(892) = 4 fm/c (1520) = 13 fm/c

Time scales according to STAR data

hadronization

initial state

pre-equilibrium

QGP andhydrodynamic expansion

hadronic phaseand freeze-out

PCM & clust. hadronization

NFD

NFD & hadronic TM

PCM & hadronic TM

CYM & LGT

string & hadronic TM

dN/dt

1 fm/c 5 fm/c 10 fm/c 20 fm/ctimeChemical freeze out

Kinetic freeze out

Balance function (require flow)Resonance survival

Rlong (and HBT wrt reaction plane)

Rout, Rside

How to test the matter with high pt probes

Is jet quenching an initial or final state effect ?

We measure two predicted ‘QGP signatures’

• The ‘quenching’ of high pt particles due to radiative partonic energy loss

• The disappearance of the away-side jet in dijet events traversing the apparently opaque medium

?

Is suppression of high pt particles in RHIC AA collisions an initial state (due to gluon

saturation) or final state (due to jet

quenching) effect? Initial state?

Final state?

partonic energy loss in dense medium generated in collision

strong modification of Au wavefunction (gluon saturation)

Ultimate test: dA collisions

Nuclear suppression factors (AA/pp) vs (dA/pp)

• Striking difference of d+Au and Au+Au results. Enhancement vs. suppression. (Cronin effect in cold nuclear matter).

• Final state effect confirmed by back-to-back correlations• Energy loss depends on the size of medium traversed

Cronin Effect:

Multiple Collisions broaden high PT

spectrumPedestal&flow subtracted

Hadron suppression prevails at 62 GeV

• 2 bins, driven by p+p– = 0: pT <~6 GeV– = 0.7: pT <~10 GeV

• Significant suppression seen at 62 and 200 GeV

• 1/3 of dataset: quantitative treatment awaits full analysis

RC

P

Where does the energy go?• On the away side:

energy loss in medium has been converted to lower pt particles

Leading hadrons

Medium

Away

syst. error

Near

STAR Preliminary

pTrigger = 4 -6GeV/c

<pt> in cone is still higher than in medium but is approaching equilibration with medium• Statistical distribution of momentum conservation describes the correlation function at all centralities

(1/N

trig)

dN/d

()

STAR Preliminary

p+ptrig4 6 GeV/c

0.15 4 GeV/cT

T

p

p

stat. mom. conserv.Borghini et al.

Au+Au 5%

stat. mom. conserv.Borghini et al.(1

/Ntr

ig)

dN/d

()

Identified particles at intermediate to high-pt

• Two groups, baryons and mesons, which seem to approach each otheraround 5 GeV/c

• Suggesting relevance of constituent quarks for hadron production • Coalescence/recombination provides a description ~1.5 - 5 GeV/c

Recombination + Fragmentation at mid pt Recombination at moderate PT

Parton pt shifts to higher hadron pt.

Fragmentation at high PT:

Parton pt shifts to lower hadron pT

recombining partons:p1+p2=ph

fragmenting parton:ph = z p, z<1

Recomb.

Frag.

Summary of experimental observations

• At RHIC we showed that Au+Au collisions create a medium that is dense, dissipative and exhibits strong collective behavior– We observe suppression phenomena in

single particle observables and very importantly also in the correlations (large acceptance)

– We observe constituent quark scaling in v2

and Rcp at ~ 2-5 GeV/c and gluon density scaling in the energy production

– We observe strong collective behavior (flow) in all bulk matter observables

(nucl-th/0403032)

A few thoughts for your way home

The matter produced is an almost perfect fluid ! A strongly interacting parton liquid is not what we expected. (sQGP is the new theory label)

Maximum opacity (Gyulassy 01) Navier-Stokes (Teaney 03)

Where is the weakly interacting plasma ?

Shuryak, QM04

deconfinement

restoration

partonfluid(pre-hadrons)

Cassing, priv.comm.

England: University of Birmingham

France: Institut de Recherches Subatomiques Strasbourg, SUBATECH - Nantes

Germany: Max Planck Institute – Munich University of Frankfurt

India:Bhubaneswar, Jammu, IIT-Mumbai, Panjab, Rajasthan, VECC

Netherlands:

NIKHEFPoland:

Warsaw University of TechnologyRussia:

MEPHI – Moscow, LPP/LHE JINR – Dubna, IHEP – Protvino

Switzerland:University of Bern

U.S. Labs: Argonne, Lawrence Berkeley, and Brookhaven National Labs

U.S. Universities: UC Berkeley, UC Davis, UCLA, Caltech, Carnegie Mellon, Creighton, Indiana, Kent State, MIT, MSU, CCNY, Ohio State, Penn State, Purdue, Rice, Texas A&M, UT Austin, Washington, Wayne State, Valparaiso, Yale

Brazil: Universidade de Sao Paolo

China: IHEP - Beijing, IPP - Wuhan, USTC,Tsinghua, SINR, IMP Lanzhou

Croatia: Zagreb University

Czech Republic: Nuclear Physics Institute

STAR: 51 Institutions, ~ 500 People

Consequences of a strong v2 and final state jet quenching at RHIC

1.) v2 is strong and has to come from very early time after collision. Hadronic v2 is not sufficient in terms of magnitude and timescale2.) v2 is very well described by hydrodynamics (fluid dynamics). 3.) if the phase producing the flow is partonic then we have partonic fluid (dissipative, strongly interacting, small correlation length) rather than a plasma (large correlation length, weakly interacting quasi-particle gas).

Discovery of the suppression phenomena at RHIC

• The observed strong suppression can be described efficiently by parton energy loss in matter starting with large energy and gluon densities

• Does the magnitude of parton energy loss inferred from these observations demand an explanation in terms of traversal through deconfined matter?

• Can we prove from the inferred densities that deconfined matter has been created?

Is the system in approximate local thermal equilibrium?

• The unprecedented success of hydrodynamics calculations assuming ideal relativistic fluid behavior in accounting for RHIC elliptic flow results has been interpreted as evidence for both early attainment of local thermal equilibrium and softening of the equation of state, characteristic of the predicted phase transition.

• How do we know that the observed elliptic flow can not result alternatively from a harder EOS coupled with incomplete thermalization? (D. Teaney, J. Lauret, E.V. Shuryak; Phys. Rev. Lett 86, 4783 (2001))

Nuclear modifications in dAu at = 3.2!

Physics at RHIC II in an LHC-era

BRAHMS, R. Debbe (DNP2003)

BRAHMS, R. Debbe (DNP2003)

LHC ions saturated (ycm)?

LHC ycm ?

RHIC in unique region!

ycm final state effects

forward initial state RHIC ycm

Saturation at low x (10-3)?

RHIC forward?

PT is balanced by many gluons

“Mono-jet”

Dilute parton system

(deuteron)

Dense gluon field (Au)

• E > 25 GeV• 4

Beam View Top View

Statistical errors only

25<E<35GeV

35<E<45GeVSTAR

Preliminary

dAu Correlations: probing low x

Fixed as

E & pT grows

Large 0+h± correlations

• Suppressed at small <xF> , <pT,>

Consistent with CGC picture

•Consistent in d+Au and p+p at larger <xF> and <pT,>

as expected by HIJING

Gluon transport: molnar,gyuallasy (01) navier-stokes: teaney (03)

The QGP is almost a perfect fluid

opacity

V2 in Au+Au 62GeV

0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5-0.1

0.0

0.1

0.2

0.3 Au+Au 62GeV (TOFr) k(TOFr) p(TOFr)

K*0

V2

PT(GeV/c)

Momentum conservation

Particle yields

• Chemical freeze-out 160 +/- 10 MeV, close to expected critical temperature, particle ratios similar in pp for most abundant species

• Deviations of the resonance yields compared to thermal model predictions indicative of hadronic phase after chemical freeze-out

STARO PHENIX

Strangeness Enhancement Resonances