Elliptic Flow in PHENIX Hiroshi Masui for the PHENIX collaboration CIPANP 2006, Westin Rio Mar Beach Puerto Rico May 30 – Jun 3, 2006

Why Elliptic Flow ? Study the properties of matter created at RHIC Z Study the properties of matter created at RHIC The probe for early time The dense nuclear overlap is ellipsoid at the beginning of heavy ion collisions Pressure gradient is largest in the shortest direction of the ellipsoid Spatial anisotropy  Momentum anisotropy Signal is self-quenching with time Elliptic flow (v2) is defined by the 2nd coefficient of Fourier expansion Reaction plane Y X Py Pz Px Hiroshi Masui / University of Tsukuba

Outline direct  D Elliptic Flow, v2 , K, p Elliptic Flow, v2 partonic hadronic direct  D Elliptic Flow, v2 , K, p time Partonic degrees of freedom, Thermalization, .. Elliptic Flow, v2 Bulk, early probe Charged hadrons give us a base line  Meson Small interaction cross section, long lived life time (~40 fm/c) Penetrating probes Heavy flavor electrons (charm) Direct  Hiroshi Masui / University of Tsukuba

Baseline : charged hadrons Charged hadrons, v2 vs pT PHENIX : PRL 91, 182301 (2003) v2 ~ k   Large elliptic flow at RHIC Consistent with hydrodynamics with rapid thermalization,  ~ 1 fm/c v2 scales initial eccentricity () of reaction zone Hiroshi Masui / University of Tsukuba

Hydro scaling Scaling holds up to KET = 1 GeV Meson/Baryon v2 M. Issah, A. Taranenko, nucl-ex/0604011 Hydro scaling of v2 K0S,  (STAR) : PRL 92, 052302 (2004)  (STAR) : PRL 95, 122301 (2005) , K, p (PHENIX) : preliminary Meson v2 Baryon v2 * KET ~ mT – m0 at y ~ 0 Scaling holds up to KET = 1 GeV Meson/Baryon v2 Possible hint of partonic degrees of freedom Hiroshi Masui / University of Tsukuba

1.  meson v2 Hiroshi Masui / University of Tsukuba

Clear  signal  reconstruction via K+K- decay channel S/N ~ 0.3 Centrality 20 – 60 % S/N is good Event plane resolution is good Separation between meson/baryon v2 is good v2 do not be varied too much. Before subtraction Signal + Background Background After subtraction Hiroshi Masui / University of Tsukuba

“Meson” type flow !  v2 vs pT Hydro. mass ordering for pT < 2 GeV/c v2() ~ v2(), v2(K) for pT > 2 GeV/c Mass Number of constituent quarks Consistent with the description by quark coalescence, recombination models Hiroshi Masui / University of Tsukuba

Hint of partonic d.o.f Hydro scaling of v2 Hydro + Nquark scaling K0S,  (STAR) : PR 92, 052302 (2004)  (STAR) : PRL 95, 122301 (2005)  (STAR) : preliminary , K, p, 0, d (PHENIX) : preliminary Hydro + Nquark scaling Works for a broad range of KET  meson also follow the scaling Partonic degrees of freedom WWND 2006, M. Issah Hiroshi Masui / University of Tsukuba

2. Heavy flavor electron v2 Hiroshi Masui / University of Tsukuba

Clean heavy flavor electron Cocktail subtraction Converter subtraction Signal / Background ratio Run4 Run2 Two different techniques show an excess heavy flavor electron signal Signal/Background > 1 for pT > 1 GeV/c Hiroshi Masui / University of Tsukuba

Hint of Charm flow e v2 vs pT Data indicate finite v2 of charm quark V. Greco, C. M. Ko, R. Rapp: PL B 595, 202 (2004) e v2 vs pT Data indicate finite v2 of charm quark Suggest thermalization of c quark as well as light quarks What is the origin of high pT drop ? Hiroshi Masui / University of Tsukuba

b quark contribution ? H. Hees, V. Greco, R. Rapp: PRC 73, 034913 (2006) e v2 vs pT (1) input D or B meson v2 decrease, (2) flat at high pT (2) v2 D  e output B  e (1) Simulation B  e (2) SQM 2006, S. Sakai pT (GeV/c) High pT drop might be explained by B meson contribution Hiroshi Masui / University of Tsukuba

3. Direct  v2 Hiroshi Masui / University of Tsukuba

Clear Direct  signal Large direct  excess PRL 94, 232301 (2005) Large direct  excess 0 is suppressed but direct  not Both results are consistent with pQCD Hiroshi Masui / University of Tsukuba

Possible 3 different scenarios  v2 vs pT PRL 96, 032302 (2006) Direct  v2 1. Hard scattering v2 = 0 2. Parton fragmentation v2 > 0 3. Bremsstrahlung v2 < 0 Inclusive  Consistent with expected  v2 from hadron decays Hiroshi Masui / University of Tsukuba

v2direct = 0 ?  v2 vs pT Direct  v2 PRL 96, 032302 (2006) Direct  v2 Direct  excess ratio is consistent with v2BG/v2inclusive, suggest v2direct = 0 Favors prompt photon production for dominant source of direct  Hiroshi Masui / University of Tsukuba

Conclusions Elliptic Flow is powerful tool to study hot and dense matter at RHIC  meson  Partonic degrees of freedom Hydro. mass ordering for pT < 2 GeV/c For pT > 2 GeV/c, v2() prefer quark composition not mass Hydro + Nquark scaling works for  meson as well as other hadrons Heavy flavor electron  Thermalization Consistent with non-zero charm flow, suggest thermalization of c quark as well as light quarks Bottom contribution at high pT need to be studied experimentally Direct   Coming soon … v2direct = 0, consistent with the scenario of direct  production from initial hard scattering Year-4 data may enable us to reduce statistical error bars, and extend pT reach, and to measure thermal  v2 Hiroshi Masui / University of Tsukuba

Thank you Hiroshi Masui / University of Tsukuba

Back up Hiroshi Masui / University of Tsukuba

Converter Subtraction method Ne 0.8% 1.1% ? % 1.7% With converter Photonic electron W/o converter Photon Converter (Brass 1.7 % X0) around beam pipe Conversion from beam pipe Dalitz : 0.8 % X0 equivalent Non-photonic electron X0 Source of background electrons Photon conversion 0     e+e- Dalitz decay (0 ee,  ee, etc) Di-electron decays of , ,  Kaon decays Conversion of direct photons Hiroshi Masui / University of Tsukuba

Inclusive electron v2 (w., w/o. converter) Converter subtraction method Inclusive electron v2 w. and w/o. converter. Clear difference between them. Electron v2 with converter include large photonic component. Hiroshi Masui / University of Tsukuba

Inclusive & photonic electron v2 pT < 1 GeV/c  Converter method pT > 1 GeV/c Simulation v2(inclusive) < v2 (photonic)  v2(non-photonic) < v2(photonic) photonic e v2 inclusive e v2 (w/o. converter) Inclusive electron v2 Hiroshi Masui / University of Tsukuba

Centrality dependence Non zero heavy flavor electron v2 ! Hiroshi Masui / University of Tsukuba

Run4 inclusive  v2 v2 pT 0 inclusive  Hiroshi Masui / University of Tsukuba

Independent on system size Eccentricity scaling Eccentricity scaling A wide range of centrality Independent of system size Integrated v2  eccentricity Reduce systematic error from eccentricity calculation Cancel systematic error by the ratio of v2(pT) / (integrated v2) Hiroshi Masui / University of Tsukuba

Hadron identification Time-of-flight || < /4, || < 0.35 Timing resolution ~ 120 ps /K separation ~ 2 GeV/c K/p separation ~ 4 GeV/c EM Calorimeter || < /2, || < 0.35 Timing resolution ~ 400 ps /K separation ~ 1 GeV/c K/p separation ~ 2 GeV/c Hiroshi Masui / University of Tsukuba

The PHENIX experiment Acceptance Centrality Event plane Tracking Central arm: || < , || < 0.35 Centrality Beam-Beam Counter, Zero Degree Calorimeter. Event plane BBC Tracking Drift chamber, Pad chambers. Particle identification Electron Electro-Magnetic Calorimeter Hadron Time-of-Flight, Aerogel Cherenkov Counter, EMCal Hiroshi Masui / University of Tsukuba