Measurement of low mass vector mesons by e + e - pairs in s NN =200GeV d+Au collision at PHENIX

Measurementof low mass vector mesonsby e+e- pairsin sNN=200GeV d+Au collision at PHENIX 槌本裕二 Yuji Tsuchimoto for PHENIX collaboration tsuchimoto@bnl.gov Experimental Quark Physics group Hiroshima University, Japan - Yuji Tsuchimoto - QM2004 - (refer talk by R.Seto in parallel2 on Jan.13)

Motivation Quark mass in vacuum mu ~ md ~ 5 MeV/c2 ms ~ 100 MeV/c2 • The chiral symmetry is partially restored at normal nuclear density. • Mass modification of vector mesons is expected. (partial) chiral symmetry breaking Effective quark mass in hadron mu ~ md ~ 300 MeV/c2 ms ~ 500 MeV/c2 T.Hatsuda and S.Lee QCD sum rules for vector mesons in the nuclear medium (Phys.Rev.C46-1 1992) - Yuji Tsuchimoto - QM2004 -

previous experiments • Vector meson mass may be modified in dense matter. • What happened in hot matter at RHIC? (refer talks by A.Cherlin(CERES) and R.Muto(E325) in parallel2on Jan.13) KEK E325 K.Ozawa et al. Observation of r/v Meson Modification in Nuclear Matter (Phys.Rev.Lett 86-22) G. Agakichiev et al. Low-mass e+e− pair production in 158A GeV Pb-Au collisions at the CERN SPS, its dependence on multiplicity and transverse Momentum (Phys.Lett.B422:405-412,1998 ) - Yuji Tsuchimoto - QM2004 -

low-mass mesons • w : mass 782 MeV/c2, G = 8.4 MeV/c2 • r : mass 769 MeV/c2, G = 150 MeV/c2 • Mass modification will be larger than f • f : mass 1019 MeV/c2, G = 4.2 MeV/c2 • Branching ratio of f→KK to f→e+e- may be changed by mass modification. • We expect no large modification at d+Au collision for each. - Yuji Tsuchimoto - QM2004 -

PHENIX detector • RHIC : p+p, d+Au, Au+Au sNN = 200GeV (500GeV for p+p) • BBC → trigger/centrality/vertex • PHENIX Central Arms can detect electrons, photons, hadrons within the same h region, |h| < 0.35 (|h|<0.38 for g) • Drift Chamber → pT • EMC → energy • RICH → electron ID - Yuji Tsuchimoto - QM2004 -

Energy/momentum Matching select Electron identification We used the following cuts. EMC matching • EMC matching < 4s • 0.5 < E/p < 1.5 • n0>=2 • Ghost track cut • reject worse matching track If dz<1 and df<0.1 in the DC position. • RICH ring sharing cut • reject one track if dz<10 and df<0.1 in the RICH position randomly. Cut - Yuji Tsuchimoto - QM2004 -

Ghost track rejection • Ghost tracks share a close hit position in the drift chamber. We rejected one of the tracks randomly if dz<1cm and df<0.1 rad. • We also cut ring shared tracks if dz<10cm and df<0.1 rad in RICH. We choose better E/p track. Z difference on DC [cm] - Yuji Tsuchimoto - QM2004 - f difference on DC [rad]

Conversion Rejection by invariant mass and PhiV • e+e- pair from photon conversion has small phiv and small mass.we cut those pairs at low-background region • Kill all tracks if PhiV<0.1 for mass<400MeV • PhiV is angular orientation between pair tracks’ surface and magnet field. Conversion pair has 0 PhiV in principle. • Kill all tracks if mass<100MeV PhiV ( 100<mass<400MeV ) Cut Cut PhiV Mixing - Yuji Tsuchimoto - QM2004 -

ERT electron trigger &Event selection Minimum bias triggered • Front-end electronics and data storage limit trigger and recording rate. • Give priority for electron events to record. • ERT electron trigger by RICH & EMC online ERT triggered see poster by F.Kajihara(Instr4) about ERT trigger • Analyzed 31M of ERT-electron Triggered Events. • Corresponds to 1.9G minimum bias (raw trigger) • 50% of total data taken during run3 - Yuji Tsuchimoto - QM2004 -

Invariant Mass Spectra • Background estimated by event mixing with offline ERT-electron trigger emulation • Use 500-600,1100-1200 MeV region for normalization of Opposite arm. • Use 850-950,1100-1200 MeV region for normalization of Same arm. - Yuji Tsuchimoto - QM2004 -

Invariant mass spectra • Fit is to relativistic B-W convoluted with gaussian • M=1.0177  0.0023 GeV/c2 • =4.46 MeV/c2 (fixed) • exp=8.1  2.1MeV/c2 • 2/DOF=13.6/13 - Yuji Tsuchimoto - QM2004 -

MB acceptance Acceptance With ERT Acceptance Correctionwith ERT trigger efficiency • Throw 2M of single f decay into e+e- with slope 440MeV • Use GEANT for response • Use the efficiency to get corrected mT spectra - Yuji Tsuchimoto - QM2004 -

mT spectrum • dN/dy=.056 .015(stat) 50%(syst) • T=326 94(stat) 53%(syst) MeV PHENIX Preliminary - Yuji Tsuchimoto - QM2004 -

mT spectra comparison with KK results • Those points are agreed within error bars • ee channel • dN/dy=.056.015(stat) 50%(syst) • T=32694(stat)53%(syst) MeV • KK channel • dN/dy = 0.04230.0063(stat) (+0.0076,-0.0073) (syst.) • T (MeV) = 429  27 (stat)  35 (syst) PHENIX Preliminary - Yuji Tsuchimoto - QM2004 - see poster by D.Pal(Spectra9) for KK data

dN/dy / Nparticipant PHENIX Preliminary (d+Au) PHENIX Final (Au+Au) • dN/dydAuee=.056.015(stat) 50%(syst) • f increases from dAu to AuAu by factor ~2 • this behavior is same as inclusive K yield at Au+Au - Yuji Tsuchimoto - QM2004 - see posters by D.Pal(Spectra9) and C.F.Maguire(Strange14) for KK data

Slope PHENIX Preliminary (d+Au) PHENIX Final (Au+Au) • T=326 94(stat) 53%(syst) MeV • Those are agreed within error - Yuji Tsuchimoto - QM2004 - see posters by D.Pal(Spectra9) and C.F.Maguire(Strange14) for KK data

Summary • I obtained • dN/dy=.056.015(stat) 50%(syst) and • T=326 94(stat) 53%(syst) MeV of f in e+e- mode at sNN = 200GeV d+Au collisions • Those are consistent with results of K+K- mode within error bars. • f increases from dAu to AuAu by factor ~2. - Yuji Tsuchimoto - QM2004 -

Next step • Merge remain statistics ( ~50% ) • Tune electron ID finely • Analyze w/r • These will show at JPS (March) - Yuji Tsuchimoto - QM2004 -

Measurement of low mass vector mesons by e + e - pairs in s NN =200GeV d+Au collision at PHENIX