Anisotropic flow at RHIC: How unique is the NCQ scaling ? 2018/11/12 Anisotropic flow at RHIC: 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. Zhu J. Phys. G32, 1121(2006) Quark Matter 2006, Shanghai China

Quark Matter 2006, Shanghai China Outline Motivation Model study v2 dependent on centrality, pT and time of freeze-out Summary Quark Matter 2006, Shanghai China

High-energy Nuclear Collisions 2018/11/12 High-energy Nuclear Collisions time Initial conditions and interactions Hot and Dense Cooling down freezing out Experimental probes: 1) Energy loss 2) Elliptic flow, radial flow … Quark Matter 2006, Shanghai China

Anisotropy parameter v2 2018/11/12 Anisotropy parameter v2 Sensitive to initial/final conditions and equation of state (EOS) ! coordinate-space-anisotropy  momentum-space-anisotropy y x py px v2 : a probe of the dynamics governing the system’s evolution Flow : represents the collective motion of particles. Quark Matter 2006, Shanghai China

Identified particle v2 at 200 GeV PRL 92(04) 052302 v2 appears to saturate at ~0.13 for KS and ~0.20 for  with the saturation setting in at different pT. Quark Matter 2006, Shanghai China

Number of constituent quark scaling Scaling works with kaons, protons, lambdas and cascade. Pions differ from scaling may due to resonance decays. X. Dong et al, PLB597 328 Quark Matter 2006, Shanghai China

NCQ-scaling: Partonic flow In this scenario we can infer the value of the parton v2 in the relevant pT region (~7%). Quark Matter 2006, Shanghai China

Quark Matter 2006, Shanghai China 2018/11/12 coalescence Produced particles are hadronized via coalescence v2 follows the scaling with Number of Constituent Quarks(NCQ): (n=2), (n=3) 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

Quark Matter 2006, Shanghai China 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 at the hadronic stage? Quark Matter 2006, Shanghai China

Quark Matter 2006, Shanghai China 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

Quark Matter 2006, Shanghai China 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. 1 Re-scatterings are necessary. 2 Re-scatterings at partonic level are essential. Originates from at partonic stage? Quark Matter 2006, Shanghai China

Temporal Structure of the v2’s development 2018/11/12 Temporal Structure of the v2’s development early late Flow originates in the model with re-scatterings. Strong correlation between freez-out time and v2 v2 decrease with pressure gradient( time) Quark Matter 2006, Shanghai China

correlation between freeze-out time and elliptic flow 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 more frequent re-scatterings among partons at very early stage lead to saturate at higher pT. Quark Matter 2006, Shanghai China

Quark Matter 2006, Shanghai China Identified elliptic flow pT dependence of v2 Compared to data, main features are reproduced low pT hydrod behaviour intermediate pT hadron-type dependence v2 increases with pT and then saturates(or decrease) NCQ is not unique hadronic interactions predicted hadron-type dependence. Quark Matter 2006, Shanghai China

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

pT dependence of identified v2 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 Quark Matter 2006, Shanghai China

pT dependence of identified v2 pT>1.5 GeV/c lack of development of hydrodynamics σ are most important; 2:3 scaling for M-B distinguishable differences between two NCQ Coalescence: 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) Quark Matter 2006, Shanghai China

Quark Matter 2006, Shanghai China 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

Quark Matter 2006, Shanghai China Cross sections: AQM Quark Matter 2006, Shanghai China