1. 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

2. 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

3. 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

4. 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

5. 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

6. 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, PLB
Quark Matter 2006, Shanghai China

7. 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

8. 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, (03)
Coalescence hinting system is partonic, hadrons are formed at the boundary of parton and hadron
Quark Matter 2006, Shanghai China

9. 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

10. 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

11. 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

12. 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

13. 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

14. 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

15. 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

16. 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

17. 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

18. 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

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