v 2 and v 4 centrality, p t and particle-type dependence in Au+Au collisions at RHIC Yuting Bai for the STAR Collaboration

Yuting Bai2 Outline  Introduction  v 2  v 4  v 4 /v 2 2  Conclusion

Yuting Bai3 Anisotropic Flow  Anisotropic flow ≡ azimuthal correlation with the reaction plane  established early, self- quenching, therefore sensitive to the early stage of the collisions

Yuting Bai4 Charged particle v 2 as function of p t at 200GeV and 62GeV  Charged particle v 2 from four particle cumulant are measured up to ~ 10 GeV at 200GeV. For Au+Au at 200 GeV still significant v 2 above 6 GeV/c -1.3 <  < 1.3 Star Preliminary v 2 {4}: v 2 from 4-particle cumulant method.

Yuting Bai5  The centrality dependence of v 2 changes from low-p t to intermediate p t.  At intermediate p t the maximum v 2 is for the 30-40% centrality bin around 3 GeV/c. Charged particle v 2 as function of p t at 200GeV and 62GeV Star Preliminary

Yuting Bai6 Charged particle v 2 as function of pseudorapidity at 200GeV and 62GeV Star Preliminary  v 2 increases from 62 to 200 GeV

Yuting Bai7  The increase in v 2 from 62 GeV to 200 GeV is larger at forward rapidity could be understood as a result of v 2 ~ dN/d v 2 {200}/v 2 {62} as function of pseudorapidity at 200GeV and 62GeV Star Preliminary

Yuting Bai8 Charged particle v 2 as a function of -y beam at 200GeV and 62GeV  Longitudinal scaling approximately holds Star Preliminary Only particles with positive  are shown

Yuting Bai9 Centrality dependence: (m T – m) scaling  At low-p t m T -scaling: indicative for a common velocity for the different particles  At intermediate p t meson- baryon grouping: indicative for coalescence mechanism  m T -scaling and baryon meson grouping holds for all centralities! Star Preliminary event plane method

Yuting Bai10 Centrality dependence: NQ scaling  NQ scaling holds for all centralities.   is systematically lower than other particles in central collisions. Star Preliminary

Yuting Bai11 Star Preliminary NQ scaling at 62.4GeV  At 62.4 and 200 GeV the same scaling is observed! minbias data (0-80%)

Yuting Bai12 Higher Harmonics  Higher harmonics are expected to be present. For smooth azimuthal distributions they will be small, v n ~ v 2 n/2  v 4 /v 2 2 a probe of ideal hydro behavior and related to degree of thermalization! Peter Kolb, PRC 68, R.S.Bhalerao et.al PLB 627,49; Borghini and Ollitrault, arXiv:nucl-th/

Yuting Bai13 Charged particle v 4 as function of p t at 200GeV and 62GeV  Charged particle v 4 are measured up to ~ 7 GeV at 200GeV. Star Preliminary -1.3 < eta < 1.3 Relative to the 2nd order event plane

Yuting Bai14  As for v 2, v 4 increases from 62 to 200 GeV Charge particle v 4 as function of pseudorapidity at 200GeV and 62GeV Star Preliminary

Yuting Bai15  Same as v 2, for v 4 longitudinal scaling approximately holds Charged particle v 4 as function of -y beam at 200GeV and 62GeV Star Preliminary

Yuting Bai16 v 4 systematic uncertainty estimate  Uncertainties on are small, however they quickly become significant at larger p t

Yuting Bai17 v 4 /v 2 2 for charged particles at 200GeV  v 4 /v 2 2 a detailed probe of ideal hydro behavior and related to the degree of thermalization!  Data points are above the model predictions, however due to the systematic uncertainty from non-flow we can not exclude the models yet Star Preliminary

Yuting Bai18 Conclusions  v 2 from four particle cumulant is measured up to 10 GeV/c Still significant v 2 observed above 6 GeV/c  v 2 for identified particles shows m T scaling at low-p t and NQ scaling at intermediate p t For all centralities  The energy dependence of v 2 and v 4 is approximately described by longitudinal scaling  The observed ratio of v 4 /v 2 2 is above the ideal hydro predictions and close to AMPT, however the systematic uncertainties from non-flow do not allow us to contradict ideal hydrodynamics

Yuting Bai19 v 4 /v 2 2 for charged particle as a function of p t at 200GeV and 62GeV Star Preliminary

Yuting Bai20 v 4 /v 2 2 for charged particles as function of pseudorapidity at 200GeV and 62GeV Star Preliminary

Yuting Bai21  Systematic errors are shown at mid-rapidity only. At forward rapidity, the non-flow effects are expected to be small.  at mid-rapidity, the ratios are above 1, which is compatible with those at forward rapidity. v 4 /v 2 2 for charged particles as a function of pseudorapidity at 200GeV Star Preliminary

Yuting Bai22 non-flow effect on v 4 /v 2 2 For v 4 /v 2 2 :