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PID v 2 and v 4 from Au+Au Collisions at √s NN = 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 2 Na Li 25th Winter Workshop on Nuclear Dynamics Motivation Analysis Results Summary

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Na Li 25th Winter Workshop on Nuclear Dynamics 3 Motivation Formation of QGP in high-energy nuclear collisions: De-confinement Collectivity Local thermalization Important questions We study with dataset of highest statistics

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Na Li 25th Winter Workshop on Nuclear Dynamics 4 Anisotropy Parameters spatial space anisotropy momentum 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.

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pQCD ReCo & Coalescence Hydro Motivation (cont.) 5 Na Li 25th Winter Workshop on Nuclear Dynamics Study the PID dependence of v 2 and v 4. R. S. Bhalerao et.al PLB 627, 49; Borghini and Ollitrault, PLB 642, 227 Study Number-of- Quark scaling. Range? v 4 /v 2 2 : a probe of ideal hydro behavior. STAR: Phys. Rev. C 77 (2008) 54901

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Na Li 25th Winter Workshop on Nuclear Dynamics 6 Anisotropy Parameter v 2 Baryon and meson elliptic flow follow the number of quark ( N q ) scaling. Indicates that partonic flow builds up at RHIC. STAR: Phys. Rev. C 77 (2008) How about the higher order anisotropic flow such as v 4 ?

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Na Li 25th Winter Workshop on Nuclear Dynamics 7 Anisotropy Parameter v 2 v 4 Peter Kolb, PRC 68, STAR: Aihong Tang, Proc. 24 th Winter Workshop on Nuclear Dynamics v 4 : 4 th harmonic If system reaches local thermal equilibrium, according to ideal hydro dynamic calculation, v 4 /v 2 2 approaches 0.5 at high p T region. Directly related to the degree of thermalization of the medium. Hydro, Boltzmann calculations: J. –Y. Ollitrault

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Dataset and Cuts 8 Na Li 25th Winter Workshop on Nuclear Dynamics Tracks used for TPC event plane: No. of fit hits > 15 No. of fit hits/No. of possible hits > < p T < 2.0 GeV/c | η | < 1.0 System: Au+Au collision Energy : s NN = 200 GeV Event sample : ~60 M events Year: 2007 Pseudorapidity range: TPC : -1.0 < η < 1 FTPC : -4.0 < η < -2.5 (east) 2.5 < η < 4.0 (west) Tracks used for FTPC event plane: 6 =< No. of fit hits < 12 No. of fit hits/No. of possible hits > < p T < 2.0 GeV/c 2.5< | η | < 4.0

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Event plane angle (Rad) TPC Event Plane 9 Na Li 25th Winter Workshop on Nuclear Dynamics 2 nd harmonic event plane 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. STAR preliminary (a) STAR preliminary (b) (c)

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Na Li 25th Winter Workshop on Nuclear Dynamics 10 FTPC Event Plane J.Barrette et al. Phys. Rev. C56 (1997)3254 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. Phi weight + Shift Phi weight Event plane angle (Rad) STAR preliminary

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Invariant Mass Method 11 Na Li 25th Winter Workshop on Nuclear Dynamics Borghini et al. Phys. Rev. C70 (2006)4905 Assume KS0KS0 STAR preliminary

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Pion and Proton Identification 12 Na Li 25th Winter Workshop on Nuclear Dynamics 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 p T < 1 (GeV/c) -2 < n σ π (p) < 2 p T > 2.5 (GeV/c) 0 < nσ π < 1 -1 < nσ p < 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 v 2 will be about 10%. Using Run 4 data result

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Na Li 25th Winter Workshop on Nuclear Dynamics 13 v 2 {TPC} and v 2 {FTPC} v 2 (p T ) have been measured for , p, K S 0 and . Non-flow effect reduced considerably by using the FTPC event plane. STAR preliminary Au+Au 200GeV (minibias)

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Na Li 25th Winter Workshop on Nuclear Dynamics 14 Number of Quark (N q ) Scaling STAR preliminary The number of quark scaling for , K S 0 and holds up to (m T – m)/n q ~ 1 GeV/c 2. Protons seem to deviate from the scaling at lower p T.

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Na Li 25th Winter Workshop on Nuclear Dynamics 15 v 4 {TPC} v 4 (p T ) has been measured for , K S 0 and . The N q scaling for v 4 is observed at (m T - m)/n q < 1 GeV/c 2, similar to that of v 2. STAR preliminary

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Na Li 25th Winter Workshop on Nuclear Dynamics 16 Test of Ideal Hydro Predictions v 4 /v 2 2 is about 1 at p T ~ 2 GeV/c, larger than the value 0.5 expected from ideal fluid calculations.

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Na Li 25th Winter Workshop on Nuclear Dynamics 17 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 (m T - m)/n q ~ 1 GeV/c 2. The number of quark scaling has been observed for v 4 at (m T - m)/n q < 1 GeV/c 2. Mesons and baryons ( , K S 0 and ) have similar v 4 /(v 2 ) 2 ratios. It is close to unity at p T > 1 GeV/c, higher than ideal hydrodynamic model predictions.

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Na Li 25th Winter Workshop on Nuclear Dynamics 18 BACK UP

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Na Li 25th Winter Workshop on Nuclear Dynamics 19 Number of Quark (N q ) Scaling STAR preliminary

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