Directed flow of identified particles from Au+Au Collisions at RHIC

Directed flow of identified particles from Au+Au Collisions at RHIC Jiayun Chen (for the STAR Collaboration) Institute of Particle Physics, Wuhan, P.R. China

Outline • Motivation • Data sample, Proton selections, & V0reconstruction • Event plane reconstruction • v1 results • Discussion and Summary 第十届全国粒子物理学术会议 2008年4月26日-4月29日南京

In the forward region +z, the leading participating nucleon will interact with many other nucleons in the “almond”, they will go to +x direction. <px> or directed flow rapidity pt Motivation Directed flow (v1) Anisotropic flow Elliptic flow (v2) Higher harmonics 第十届全国粒子物理学术会议 2008年4月26日-4月29日南京

flow antiflow Motivation Anti-flow/3rd flow component, with QGP  v1 flat at middle rapidity. Directed flow (v1) and phase transition Brachmann, Soff, Dumitru, et. al. , PRC 61 (2000) 024909. L.P. Csernai, D. Roehrich PLB 458, 454 (1999) M.Bleicher and H.Stocker, PLB 526,309(2002) 第十届全国粒子物理学术会议 2008年4月26日-4月29日南京

Common cut: |Primary Vertex| < 30cm No. Dedx Points > 10 No. fit Points > 20 No. fit Points/No. Max [0.52,1.05] Global DCA < 1.0cm nSigma [-2.5,2.5] Proton: 0.4 < pT <1.0 (GeV/c) Antiproton: 0.15< pT <1.0 (GeV/c) DataSet: 62GeV Au+Au Minimum Bias 3M 200GeV Au+Au Minimum Bias 7M Proton & Antiproton Selection STAR Preliminary 第十届全国粒子物理学术会议 2008年4月26日-4月29日南京

cuts: Distance of closest approach(DCA) between daughters < 0.8cm DCA of V0 to Primary Vertex (PV) < 0.5cm Daugter’s DCA to PV > 0.8 cm decay length > 6.0cm daughter’s Tpc Hits > 15 V0sreconstruction 1.11<mass<1.12 0.48<mass<0.51 1.11<mass<1.12 第十届全国粒子物理学术会议 2008年4月26日-4月29日南京

Event Planereconstruction the event plane vector and the event plane angle from the nth harmonic of the particle’s azimuthal distribution are defined by the equations: -- the azimuthal angle of the ith particle in the event plane determination -- weights 第十届全国粒子物理学术会议 2008年4月26日-4月29日南京

Rapidity gaps -1.3 1.3 2.5 4. -4 -2.5 ZDC-SMD FTPC FTPC ZDC-SMD TPC Combined Event Plane Reduced non-flow effects 第十届全国粒子物理学术会议 2008年4月26日-4月29日南京

Flattening Event Plane FTPC Raw Phi distribution Principle of shifting: Make corrections to the event plane angle itself, & flatten the event plane distribution. The corrected event plane angle is FTPC weighed Psi distribution E877 Collaboration, J. Bareeette et al, Phys.Rev.Lett.70,2996(1993) 第十届全国粒子物理学术会议 2008年4月26日-4月29日南京

Sub-Event Plane FTPC Event Plane distribution ZDCSMD Event Plane distribution 第十届全国粒子物理学术会议 2008年4月26日-4月29日南京

Combined Event Plane • After the flattening of YFTPC & YZDCSMD Full EP. The final event plane used is defined by the sum of Where • or weight is from resolution 第十届全国粒子物理学术会议 2008年4月26日-4月29日南京

STAR Preliminary STAR Preliminary Resolution of FTPC,ZDCSMD,Combined • The event plane resolution(62 GeV) is enhanced by combining EP of FTPC & ZDC-SMD with proper weight. • Because the directed flow moves to larger pseudo-rapidity at the higher beam energy, the FTPC is less useful. • No obvious improvement for combined event plane at 200GeV. 第十届全国粒子物理学术会议 2008年4月26日-4月29日南京

Proton & Antiproton v1vs. Rapidity Proton 0.4<pT<1.0 (GeV/c) Antiproton 0.15<pT<1.0 (GeV/c) • For 62.4GeV, we use combined reaction plane while for 200GeV, use {ZDC-SMDs} as reaction plane. • Proton and Anti-Proton v1: • For 62.4GeV: Proton v1 is less than 1%,antiproton v1 is less than 2%. • For 200GeV: Proton & anit-Proton v1 is less than 0.5%. 第十届全国粒子物理学术会议 2008年4月26日-4月29日南京

Proton & Antiproton v1vs. Centrality • From the 10%-60%(central to peripheral)in 200GeV，v1(Anti-Proton) shows a weak centrality dependence. 第十届全国粒子物理学术会议 2008年4月26日-4月29日南京

Ks.L &L v1vs. Rapidity • For 200GeV, v1(Ks. L &L)is less than 2%. • Ks v1 seems different in 200GeV & 62.4GeV • L v1 is flat in the mid-rapidity in 200GeV & 62.4GeV with the errors • L v1 • In 200GeV: Also is flat in the mid-rapidity with the errors • In 62.4GeV: Seems to show a interested curve • |y|<0.5: the Ks and L seem in the same direction. • The error bar needs to be reduced. 第十届全国粒子物理学术会议 2008年4月26日-4月29日南京

Summary • The event plane resolution is enhanced by combining EP of FTPC & ZDC-SMD with proper weight; • Au+Au at 62.4GeV • Proton v1 is less than 1%. • AntiProton v1 is less than 2%. • Au+Au at 200GeV • Proton, AntiProton v1 is less than 0.5%. • Weak centrality dependence at 200GeV. • Made an attempt to studydirected flow of K0S & L, L. To do list: • analysis run VII’s data (~60M MB events). 第十届全国粒子物理学术会议 2008年4月26日-4月29日南京

Backup

STAR ZDC-SMD ZDC side view SMD is 8 horizontal slats & 7 vertical slats located at 1/3 of the depth of the ZDC Transverse plane of ZDC Scintillator slats ofShower Max Detector • New knowledge of the direction of the impact parameter vector • Minimal, if any, non-flow effects • Worse resolution than from TPC, but that disadvantage is minor 第十届全国粒子物理学术会议 2008年4月26日-4月29日南京

第十届全国粒子物理学术会议 2008年4月26日-4月29日南京

Directed flow of identified particles from Au+Au Collisions at RHIC

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