Quark Matter 2006, Shanghai China 1Feng Liu

Anisotropic flow at RHIC:Anisotropic flow at RHIC: How unique is the NCQ scaling ?How unique is the NCQ scaling ?

Feng Liu Yan Lu

Institute Of Particle Physics CCNU , Wuhan

M. Bleicher, P. Sorensen, H. Stöcker, N. Xu, X. ZhuJ. Phys. G32, 1121(2006)

Quark Matter 2006, Shanghai China 2Feng Liu

OutlineOutline

• Motivation

• Model study

v2 dependent on

centrality, pT and time of freeze-out

• Summary

Quark Matter 2006, Shanghai China 3Feng Liu

High-energy Nuclear CollisionsHigh-energy Nuclear Collisions

time

Initial conditionsand interactions

Cooling down freezing out

Hot and DenseHot and Dense

Experimental probes:1) Energy loss2) Elliptic flow, radial flow …

Quark Matter 2006, Shanghai China 4Feng Liu

Anisotropy parameter vAnisotropy parameter v22

Sensitive to initial/final conditions and equation of state (EOS) ! coordinate-space-anisotropy momentum-space-anisotropy

y

x

py

px

22

22

xy

xy )(tan,2cos 12

x

y

p

pv

v2 : a probe of the dynamics governing the system’s evolution

Flow : represents the collective motion of particles.

Quark Matter 2006, Shanghai China 5Feng Liu

Identified particle v2 at 200 GeV

• v2 appears to saturate at ~0.13 for K0.13 for KSS and ~0.20 for 0.20 for with the saturation setting in at different pT.

PRL 92(04) 052302

Quark Matter 2006, Shanghai China 6Feng Liu

Scaling works with kaons, protons, lambdas and cascade. Pions differ from scaling may due to resonance decays. X. Dong et al, PLB597 328

Number of constituent quark scaling

Quark Matter 2006, Shanghai China 7Feng Liu

In this scenario we can infer the value of the parton v2 in the relevant pT region (~7%).

)3(3)(

)2(2)(

22

22

Tquark

Tbaryon

Tquark

Tmeson

pvpv

pvpv

partons moving-co of ecoalescenc

by formation hadronFor

NCQ-scaling: Partonic flow

Quark Matter 2006, Shanghai China 8Feng Liu

coalescence

Produced particles arehadronized via coalescence v2 follows the scaling with Number of Constituent Quarks(NCQ): (n=2), (n=3)K S

0

Models: R. Fries et al, PRC68, 044902(03)

Coalescence hinting system is partonic, hadrons are formed at the boundary of parton and hadron

Quark Matter 2006, Shanghai China 9Feng Liu

Motivation

measure v2 and RAA,RCP for PID particles hadrons formed via the coalescence of quarks

cornerstone: observed NCQ scaling of v2

interpretation addresses key issues systematic study other possible explanations Questions:• Is this a unique ?• What is v2 in the hadronic model ?• How about the contributions of re-scatterings a

t the hadronic stage?

Quark Matter 2006, Shanghai China 10Feng Liu

hadron-string transport Model study of v2

UrQMD(v2.2), RQMD (v2.4): successful in predicting most of observed features of integrated bulk property

Model features and utilization

1 Switch on/off re-scattering among particles to study whether re-scattering is important ?

2 With hadronic but without partonic re-scattering. to study influence on the results without partonic re-scattering.

Quark Matter 2006, Shanghai China 11Feng Liu

2 Re-scatterings at partonic level are essential.

1 Re-scatterings are necessary.

Originates from at partonic stage?Originates from at partonic stage?

Almost zero.Even though initial space anisotropy exists,momentum anisotropy can’t be converted into.

Reproduce the trend of experiment but have smaller value than experiment’s.

Quark Matter 2006, Shanghai China 12Feng Liu

early late

Flow originates in the model with re-scatterings.

Strong correlation between freez-out time and v2

v2 decrease with pressure gradient( time)

Temporal Structure of the v2’s development

Quark Matter 2006, Shanghai China 13Feng Liu

1 Decrease with pressure gra- dient(time).2 re-scattering resists the trend of decrease.

The higher- pT particle ‘s v2 decreases more slowlier.earlier stage of the collision more strongly

Balance of the two effect(saturation)

At RHIC,the stronger and morefrequent re-scatterings amongpartons at very early stage leadto saturate at higher pT.

correlation between freeze-out time and elliptic flow

Quark Matter 2006, Shanghai China 14Feng Liu

Identified elliptic flow pT dependence of v2

Compared to data, main features are reproducedlow pT hydrod behaviour intermediate pT

hadron-type dependence

v2 increases with pT and then saturates(or decrease)

NCQ is not uniquehadronic interactions predicted hadron-type dependence.

Quark Matter 2006, Shanghai China 15Feng Liu

pT dependence of identified v2

Low pT mass ordering, hadronic interactions contribute to collective motion.higher pT, hardon type dependence pT > 2.5 GeV/c, v2 decrease. NCQ scalling

Quark Matter 2006, Shanghai China 16Feng Liu

angular-dependent matter density gradient. push matter move outwards collective flow

Σ super-surface where hadrons are emitted σinteraction cross section ~ additive quark model

low pT re-scattering → hydro-like mass ordering

pT dependence of identified v2

dtyxAdpyxtppv TThT ),(),,,(),()(2

Quark Matter 2006, Shanghai China 17Feng Liu

pT>1.5 GeV/c lack of development of hydrodynamics σ are most important; 2:3 scaling for M-Bdistinguishable differences between two NCQCoalescence: identical elliptic flow of all baryons AQM scaling ordering of the elliptic flow at fixed pT according to the strangeness content. v2(N) > v2(Λ) > v2(Ξ) > v2(Ω)

pT dependence of identified v2

Quark Matter 2006, Shanghai China 18Feng Liu

Summary

• v2 dependent on centrality,pT and t are studied. • re-scatterings are necessary for development of collective elliptic flow• model has smaller v2 than experiment partonic collective motion are important at RHIC• at intermediate pT ,hadron-type dependence is produce by hadronic transport model NCQ scaling isn’t a unique deconfinement mechanism high precision v2 measurement are necessary

Quark Matter 2006, Shanghai China 19Feng Liu

Cross sections: AQM