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**PID v2 and v4 from Au+Au Collisions at √sNN = 200 GeV at RHIC**

N. Li for the STAR Collaboration Lawrence Berkeley National Laboratory, Berkeley Institute of Particle Physics, Wuhan, China

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**Outline Motivation Analysis Results Summary**

Na Li th Winter Workshop on Nuclear Dynamics

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**Motivation Formation of QGP in high-energy nuclear collisions:**

De-confinement Collectivity Local thermalization Important questions We study with dataset of highest statistics Na Li th Winter Workshop on Nuclear Dynamics

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**Anisotropy Parameters**

spatial space anisotropy Azimuthal correlation with the reaction plane. Built up in the early stage, therefore supplies the early information of matter generated in the collision. momentum space anisotropy Na Li th Winter Workshop on Nuclear Dynamics

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**Motivation (cont.) Study the PID dependence of v2 and v4.**

Study Number-of-Quark scaling. Range? v4/v22 : a probe of ideal hydro behavior. STAR: Phys. Rev. C 77 (2008) 54901 pQCD ReCo & Coalescence Hydro R. S. Bhalerao et.al PLB 627, 49; Borghini and Ollitrault, PLB 642, 227 Na Li th Winter Workshop on Nuclear Dynamics

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**Anisotropy Parameter v2**

STAR: Phys. Rev. C 77 (2008) 54901 How about the higher order anisotropic flow such as v4? Baryon and meson elliptic flow follow the number of quark ( Nq ) scaling. Indicates that partonic flow builds up at RHIC. Na Li th Winter Workshop on Nuclear Dynamics

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**Anisotropy Parameter v2 v4**

STAR: Aihong Tang, Proc. 24th Winter Workshop on Nuclear Dynamics Peter Kolb, PRC 68, Hydro, Boltzmann calculations: J. –Y. Ollitrault v4 : 4th harmonic If system reaches local thermal equilibrium, according to ideal hydro dynamic calculation, v4/v22 approaches 0.5 at high pT region. Directly related to the degree of thermalization of the medium. Na Li th Winter Workshop on Nuclear Dynamics

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**Dataset and Cuts System: Au+Au collision Energy : sNN = 200 GeV**

Event sample : ~60 M events Year: 2007 Pseudorapidity range: TPC : < η < 1 FTPC : < η < -2.5 (east) 2.5 < η < 4.0 (west) Tracks used for TPC event plane: No. of fit hits > 15 No. of fit hits/No. of possible hits >0.52 0.1 < pT < 2.0 GeV/c | η | < 1.0 Tracks used for FTPC event plane: 6 =< No. of fit hits < 12 No. of fit hits/No. of possible hits > 0.52 0.1 < pT < 2.0 GeV/c 2.5< | η | < 4.0 Na Li th Winter Workshop on Nuclear Dynamics

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**TPC Event Plane 2nd harmonic event plane (a) (c) (b)**

STAR preliminary (a) 2nd harmonic event plane Event plane angle (Rad) (c) STAR preliminary (b) Detector bias is removed by applying phi weights to the tracks. Phi weights are generated by inverting the normalized phi distributions of detected tracks for a large event sample. Na Li th Winter Workshop on Nuclear Dynamics

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**FTPC Event Plane The event plane distribution is**

J.Barrette et al. Phys. Rev. C56 (1997)3254 Phi weight + Shift Phi weight Event plane angle (Rad) STAR preliminary The event plane distribution is not flat after phi weight correction due to several acceptance effect of FTPC. Add additional shift correction. Large η gap is used to reduce the non-flow effect. Na Li th Winter Workshop on Nuclear Dynamics

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**Invariant Mass Method Assume KS0**

STAR preliminary STAR preliminary KS0 Assume Borghini et al. Phys. Rev. C70 (2006)4905 Na Li th Winter Workshop on Nuclear Dynamics

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**Pion and Proton Identification**

TPC: pi/K ~ 0.7 GeV/c pi+K/p ~1.1 GeV/c pi/p ~ > 3GeV/c relativistic rise Cuts used for identification: No. of fit hits > 15 No. of fit hits/No. of possible hits >0.52 pT < 1 (GeV/c) < nσπ (p) < 2 pT > 2.5 (GeV/c) 0 < nσπ < 1 -1 < nσp < 0 M. Shao, et al., Nuclear Instruments and Methods in Physics Research A 558 (2006) pion purity: over 95% proton purity: 70% The effect on proton v2 will be about 10%. Using Run 4 data result Na Li th Winter Workshop on Nuclear Dynamics

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**v2 {TPC} and v2 {FTPC} v2(pT) have been measured for , p, KS0 and .**

Au+Au 200GeV (minibias) STAR preliminary STAR preliminary v2(pT) have been measured for , p, KS0 and . Non-flow effect reduced considerably by using the FTPC event plane. minibais result for centrality 0-80% Na Li th Winter Workshop on Nuclear Dynamics

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**Number of Quark (Nq) Scaling**

STAR preliminary STAR preliminary The number of quark scaling for , KS0 and holds up to (mT – m)/nq ~ 1 GeV/c2. Protons seem to deviate from the scaling at lower pT. Na Li th Winter Workshop on Nuclear Dynamics

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**v4 {TPC} v4(pT) has been measured for , KS0 and .**

STAR preliminary STAR preliminary v4(pT) has been measured for , KS0 and . The Nq scaling for v4 is observed at (mT - m)/nq < 1 GeV/c2, similar to that of v2. Na Li th Winter Workshop on Nuclear Dynamics

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**Test of Ideal Hydro Predictions**

STAR preliminary v4 /v22 is about 1 at pT ~ 2 GeV/c, larger than the value 0.5 expected from ideal fluid calculations. Na Li th Winter Workshop on Nuclear Dynamics

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**Summary FTPC event plane is used in STAR in order to reduce the**

non-flow effect. Run 7 high statistics data used in this analysis. Proton and anti-proton seems to deviate from the number of quark scaling at (mT - m)/nq ~ 1 GeV/c2 . The number of quark scaling has been observed for v4 at (mT - m)/nq < 1 GeV/c2. Mesons and baryons (, KS0 and ) have similar v4/(v2)2 ratios. It is close to unity at pT > 1 GeV/c, higher than ideal hydrodynamic model predictions. Na Li th Winter Workshop on Nuclear Dynamics

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BACK UP Na Li th Winter Workshop on Nuclear Dynamics

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**Number of Quark (Nq) Scaling**

STAR preliminary STAR preliminary Na Li th Winter Workshop on Nuclear Dynamics

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