Electron and identified hadron v 2 to look for hadronic or partonic origin of elliptic flow Shingo Sakai for the PHENIX Collaboration Univ. of Tsukuba

Outline  Introduction - motivation - method - overview of PHENIX detctor  Hadron v 2 (  /K/p/d) - comparison with hydro model - quark coalescence model (n quark scaled v 2 )  Electron v 2 - comparison with hadron v 2 page1

Introduction

Why identified v 2 ? ｘ ｙ pｘpｘ pｙpｙ Initial spatial anisotropy Momentum space anisotropy of particle emission -> Low p t - pressure gradient of early stage of collision - hydrodynamical behavior -> High p t - parton energy loss in hot & dense medium The azimuthal anisotropy of particle emission reflects Measurement of identified particle v2 gives us much more information of the collision dynamics page2

Measurement of v 2 > dN/d(  -  ) = N (1 + 2v 2 obs cos(2(  -  )))  : azimuthal angle of reaction plane  : azimuthal angle of particle v 2 obs : strength of azimuthal anisotropy (fitting of dn/d (  -  ) or v 2 = ) v 2 = v 2 obs / σ σ= = { } 1/2 Reaction Plane X Y  w i *sin(2  i ) tan2  rp =  w i *cos(2  i ) Measure azimuthal angle of each particle with respect to the reaction plane r.p -- e page3

Over view of PHENIX detector Charged Particle Tracking: Drift Chamber Pad Chamber Time Expansion Chamber Particle ID: Time of Flight Ring Imaging Cerenkov Counter TEC Muon ID (PDT’s) Calorimetry: Pb Scintillator Pb Glass Event Characterization Beam-Beam Counter Zero Degree Calorimeter page4

hadron v 2

Phenix (East-Arm) Hadron PHENIX -  TOF ~ 115 ps –  : 0.2 < p T < 3.0 GeV/c –K : 0.4 < p T < 3.0 GeV/c –P : 0.6 < p T < 4.0 GeV/c The PHENIX experiment has the high timing resolution TOF counter. page5

Particle ID π K mass 2 [(GeV/c 2 ) 2 ] P d Momentum [GeV/c] Clear signal peaks PID : m 2 = p 2 {(TOF/L) 2 -1} page6

Reaction plane r.p resolution = { } 1/2 Correlation r.p BBC_north & r.p BBC_south Centrality [%] v 2 =v 2 obs / resolution centralperipheral Determine r.p using BBC north and south Page 7

Comparison with hydro model p T < 2.0 GeV/c –Clear mass dependence v 2 (  ) > v 2 (K) > v 2 (p) Consistent with hydrodynamical model. p T > 2.0 GeV/c –v 2 (p) > v 2 (  ) –Clear departure from hydrodynamical behavior is observed. –Saturation at intermediate p T. page8

Quark coalescence model Quark coalescence model does well explain the meson and hadron v 2 behavior v 2 ( ｂ ) > v 2 ( ｍ high p t D. Molnar, S.A. Voloshin, nucl-th/ nucl-ex/ (PHENIX) page9

How about heavier particle ? (deuteron v 2 ) Clear mass dependence at low pt ; deuteron v 2 is smaller than proton v 2 v 2 of d+d-bar is estimated by subtracting backgrounds. m 2 distribution(1.0<p t (GeV/c)<2.0) mass 2 [(GeV/c 2 ) 2 ] Background under exponential d+d-bar candidate m 2 |<1.5σ(p) Fit:Gauss+exp | Minimum bias  s NN = 200 GeV PHENIX PRELIMINARY page10

p-n coalescence model v 2 d (p t ) = 2v 2 p (p t /2) Deuteron production ->final state coalescence of p(p-bar) and n(n-bar). - p,n coalescence prediction d-bar/d ratio vs. p t at Au+Au collision at sqrt(S NN )=200GeV (quark matter 2002 Anuj K. Purwar and Rickard du Rietz ) Minimum bias  s NN = 200 GeV v2v2 p t [GeV/c] page11

hadron or quark flow ? Minimum bias  s NN = 200 GeV Deuteron : coalescence of proton and neutron. But if it’s scaled with quark numbers ・・・ hadron mass dependence seems to be remaining even after n quark scaling. It might suggest that there are two different flows (quark flow and hadron flow) before and after phase-transition or chemical freeze- out. page12

Upgrade for identified particle v 2 at higher p T  Aerogel together with TOF can extend the PID capability up to 10 GeV/c !. Integration Volume PMT Aerogel (11x22x11 cm^3) for run4 Au+Au 80 box page13

electron v 2

Why electron v 2 ?  conversion  0   ee    ee, 3  0   ee,  0 ee   ee,  ee   ee  ’   ee inclusive electron / hadronic cocktail Clear excess above 1 GeV/c with respect to photon conversion and light hadron decay. The subtracted electron single spectra is consistent with charm decay (binary scaled). “ The high p t electron v 2 can carry information about the anisotropy of the parent charmed mesons. “ direct  (J. Alam et al. PRC 63(2001)021901) b c (PHENIX: PRL 88(2002)192303) From Run1 result page14

Electron measurement at PHENIX Electrons are identified as Cherenkov right in RICH - p t 0.2~4.9 GeV/c Number of hit PMT Ring shape E,p matching Cerenkov photons from e + or e - are detected by array of PMTs mirror Most hadrons do not emit Cerenkov light Electrons emit Cerenkov photons in RICH. Central Magnet ＲＩＣＨ PMT array page15

dn/d  distribution ptpt Miss ID e+(e-) dn/d  of after subtract Miss ID e+(e-) v 2 e is corrected by subtracting miss ID of electrons e+(e-) candidate cand --- dn/dphi of candidate (detected RICH) e+(e-) miss ID --- dn/dphi of miss ID e+(e-) dn/d  (dn/d  )/N 0 -  -  page16

P t dependence of v 2(e) (M.B) p t [GeV/c] v2v2 electron v 2 (“inclusive”) Dalitz decays Di-electron decays Photon conversions Kaon decays Thermal dileptons charm decay beauty decay Minimum bias  s NN = 200 GeV page17

Comparison with v 2 of hadrons v 2 (proton) v 2 (pion) v 2(e) v 2 pion & v 2 proton : nucl-ex/ (PHENIX) p t [GeV/c] v2v2 (M.B) > v 2(e) is larger than v 2(pion) & v 2 (proton) -> dominant pi0 decay - small decay angle - decay from higher p t 2.0GeV/c)>> v 2(e) seems to be smaller than v 2 (pion) particular interest because of the contributions from heavy-quark (c/b) decays !(but the data include another sources now) higher statistics needed. x30 statistics expected in run4. page18

What is needed to estimate charmed electron v 2 ? –Charm yield relative to inclusive electron yield at  s NN = 200 GeV (r= N p /N e ) –v 2 (p) – flow of electrons originating photonic source –Study v 2 D->eX (due to large Q value) page19

Summary Elliptic flow (v 2 ) of identified hadrons (  /K/p/d/e) has been measured at PHENIX. + hadron v2 –clear mass dependence observed at low p t region. –consistent with hydrodynamical model (p T < 2.0 GeV/c).  /K/p –deviate hydro. and saturation (p T > 2.0 GeV/c).  /K/p –consistent with quark coalescence model (more or less). –hadron mass dependence seem to be remaining after n quark scaling. + electron v2 - v 2(e) is larger than v 2 (pion) & v 2 (proton) at low p t. - v 2(e) seems to be smaller than v 2 (pion) at high p t. (indication) + higher p T data (high statistics) will be available in the next Run. –detailed identifed hadron v2 study at intermediate to high p T region. –high statistics v 2(e) to determine charmed electron v2. page20