Hiroshi Masui / Univ. of Tsukuba Measurement of Centrality dependence of identified hadron Elliptic Flow in sNN = 200 GeV Au+Au collisions at RHIC - PHENIX Hiroshi Masui / Univ. of Tsukuba for the Collaboration JPS, 62nd Annual Meeting JPS, Sep/24/2007 Hiroshi Masui / Univ. of Tsukuba

Why Elliptic Flow ? Sensitive probe in the early stage of heavy ion collisions Initial geometry overlap (eccentricity) Initial density + EOS System size (number of collisions) Final momentum anisotropy (v2) Z Y X Reaction plane Py Pz Px JPS, Sep/24/2007 Hiroshi Masui / Univ. of Tsukuba

Universal Scaling of v2 ? Universal scaling of v2 suggest QM2006 A. Taranenko Universal scaling of v2 suggest v2 for a variety of particle species at RHIC are determined through (, KET/nq) Its magnitude is established in partonic level before hadronization At mid-rapidity JPS, Sep/24/2007 Hiroshi Masui / Univ. of Tsukuba

Motivation Universal scaling of v2 has been observed by assuming   v2 of non-identified charged hadrons v2  F(KET/nq) Questions Are these assumptions really correct ? The scaling of v2 is tested from central to mid-central. How about peripheral collisions ? Study the validity of the scaling of v2 in a wide range of centrality for identified hadrons JPS, Sep/24/2007 Hiroshi Masui / Univ. of Tsukuba

PHENIX Experiment Vertex, Centrality Event plane Tracking PID BBC, ZDC BBC (full azimuth, || = 3.0 - 3.9)  Large rapidity interval Tracking DC, PC PID TOF (||</4, ||<0.35), t ~ 120 ps , p : pT < 4 GeV/c, K : pT < 3 GeV/c JPS, Sep/24/2007 Hiroshi Masui / Univ. of Tsukuba

Centrality dependence of v2(pT) v2 increase with increasing centrality Similar mass ordering for all centrality JPS, Sep/24/2007 Hiroshi Masui / Univ. of Tsukuba

KET + NCQ scaling of v2 Scaling holds for all centrality ? Ratio of data to fit (next slide) JPS, Sep/24/2007 Hiroshi Masui / Univ. of Tsukuba

v2(Data)/v2(Fit) Scaling works within systematic errors, except for low KET Radial flow ? JPS, Sep/24/2007 Hiroshi Masui / Univ. of Tsukuba

Eccentricity Eccentricity () is estimated by Glauber MC simulation  value’s are not changed so much in b = 5 - 9 fm (10 - 50 % centrality). / ~ 10 % Quite different for different definitions of  at central and peripheral Systematic error on  ~ 10 - 20 % JPS, Sep/24/2007 Hiroshi Masui / Univ. of Tsukuba

Eccentricity scaling Scaled v2 with participant eccentricity Start to break even in mid-central at high KET Scaling works at low KET within systematic errors Clear difference between central and peripheral The difference of v2 is also observed for different eccentricity * Only statistical errors are shown * Systematic error on  ~ 10 - 20 % JPS, Sep/24/2007 Hiroshi Masui / Univ. of Tsukuba

Summary Study the scaling of v2(pT) for identified hadrons in a wide range of centrality KET + quark number scaling Scaling holds within systematic errors, except for low KET New RXNP detector could help us to reduce systematic errors add more statistics at peripheral events Eccentricity scaling Scaling breaks even in mid-central at high KET works for low KET within systematic errors Clear difference between central and peripheral Suggest that v2    v2    f(Npart) JPS, Sep/24/2007 Hiroshi Masui / Univ. of Tsukuba

Back up JPS, Sep/24/2007 Hiroshi Masui / Univ. of Tsukuba

Elliptic Flow at RHIC Substantial elliptic flow signals are observed for a variety of particle species at RHIC JPS, Sep/24/2007 Hiroshi Masui / Univ. of Tsukuba

Event plane resolution Event plane resolution is determined by multiplicity and v2 Maximum at mid-central High multiplicity, small v2 at central Low multiplicity, large v2 at peripheral JPS, Sep/24/2007 Hiroshi Masui / Univ. of Tsukuba

Terminology Definition of eccentricity Weighting Averaging std : Standard eccentricity var (participant eccentricity part) 2 (event plane eccentricity) : var, subtract auto-correlation event-by-event (an idea from ShinIchi) Weighting part (coll) Calculated by weighting with Npart (Ncoll) distribution Averaging {2}  2 Averaging of 2 over all events, then take square root More natural definition like measured v2 Total : 3  2  2 = 12 definitions JPS, Sep/24/2007 Hiroshi Masui / Univ. of Tsukuba

Eccentricity Estimated by Glauber MC simulation coll > part due to steeper Ncoll distributions compared to Npart JPS, Sep/24/2007 Hiroshi Masui / Univ. of Tsukuba