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Measurement of J/ y ->e + e - in Au+Au collisions at sqrt(s NN )=200 GeV at RHIC-PHENIX

Measurement of J/ y ->e + e - in Au+Au collisions at sqrt(s NN )=200 GeV at RHIC-PHENIX. Takashi Matsumoto, Univ. Tokyo For PHENIX collaboration at JPS meeting. Physics motivation. Search the new state of matter, Quark Gluon Plasma (QGP) J/ y suppression

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Measurement of J/ y ->e + e - in Au+Au collisions at sqrt(s NN )=200 GeV at RHIC-PHENIX

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  1. Measurement of J/y ->e+e- in Au+Au collisions at sqrt(sNN)=200 GeV at RHIC-PHENIX Takashi Matsumoto, Univ. Tokyo For PHENIX collaboration at JPS meeting

  2. Physics motivation • Search the new state of matter, Quark Gluon Plasma (QGP) • J/y suppression • is one of the possible signal when QGP is formed in the heavy ion collision (screening due to plasma) • Therefore, measuring the yield of J/y -> e+e- give us knowledge of the matter produced in early stage of the collision • There is alternative prediction that J/y yield will be enhanced by coalescence at RHIC energy (recombination of charm in the matter)

  3. PHENIX Experiment • Measurement of Vertex and Collision timing • Beam-Beam counter • Z-vertex<30 cm required • Zero degree Calorimeter • Coincidence between BBC and ZDC produce minimum bias trigger • Tracking detectors • Drift chamber • Pad chamber • Electron identification • Ring Imaging Cherenkov Detector • Electro-Magnetic Calorimeter

  4. Electron Identification Distance between track and ring • Ring Image Cherenkov counter • Track - Ring association • 3PMT hits • Ring shape cut phi direction [cm] All charged tracks z direction [cm] • Electron Magnetic Calorimeter • Energy – Momentum matching • Track – EMC position matching • EMC timing matching e+e- candidate net e+e- Background E/P Energy / momentum

  5. Analysis • 25M minimum bias events -> Nevent • Provided by BBC and ZDC correlation • Centrality selection (BBC,ZDC correlation) • 0%-20% (central), 20%-40%, 40%-92% (peripheral) • Invariant mass distribution -> NJ/y • Electron identification • Combinatorial background • B dN/dy for J/y ->e+e- in 3 centrality bin • where B is branching fraction (5.93 x 10-2) • Efficiency and acceptance corrected using data and simulation • Tracking and electron identification -> eacc x eeff,eemct • Run dependence (fluctuation of electron yield) -> erun-run • Centrality dependence of parameters (embedding) -> eembed

  6. Number of J/y • Invariant mass calculated from the electron candidate • NJ/y in Minimum Bias event • 10.8  3.2 +3.8-2.8 • Systematic error of N J/y is estimated by using several kind of fitting models • Fit with 50, 100 MeV/c2 mass bins • Fitting over the range • 2.0 – 3.5 GeV • 2.5 – 3.5 GeV • Fitting with constrained mass width : 60 MeV/c2

  7. J/y in 3 centrality bins 00-20 % : central 20-40 % : mid-central 40-92 % : peripheral PHENIX Preliminary PHENIX Preliminary PHENIX Preliminary invariant mass [GeV/c2] invariant mass [GeV/c2] invariant mass [GeV/c2] NJ/y =3.5  1.9  0.5 NJ/y =4.5  2.1  0.5 NJ/y =5.9  2.4  0.7

  8. Single J/y Efficiency • J/y Efficiency is calculated by simulation • Calculation was done with flat pt distribution. • one dead map is considered. • Relative difference is estimated using the electron yield (see next transparency) • Two pt distribution models of J/y were considered (systematic error estimation) • Total acceptance and efficiency: eacc x eeff • 0.0061  0.0011

  9. Other efficiency and yield calculation • Run dependence of acceptance:erun-run • Evaluated by the yield of electron • Represent the normalization factor to the acceptance used in simulation • 0.71  0.08 • Centrality dependence:eembed • Evaluated by the embedding method • Minimum Bias0.71  0.08 • 00-20 %0.65  0.07 • 20-40% 0.76  0.08 • 40%-92%0.86  0.09 • EMCal timing cut:eemct • Evaluated by the analysis of real data • 0.94  0.06 • Formula for calculation Converter run East arm electron yield per event West arm has permanent dead area run number

  10. Final Results • B dN/dy is measured as a function of number of participants • 00-20 % • (3.9  1.6  1.0) x 10-4 • 20-40 % • (2.5  1.2  0.7) x 10-4 • 40-92 % • (6.9  3.7  1.9) x 10-5 • B dN/dy per binary collisions is calculated. • 00-20 % (Nbinary 791) • (4.9  2.0  1.3) x 10-7 • 20-40 % (Nbinary 297) • (8.5  4.0  2.2) x 10-7 • 40-92 % (Nbinary 45) • (1.5  0.8  0.6) x 10-6 • comparison • Binary scaling using p-p data • NA50 data • Normal absorption 6.4mb, 7.1mb

  11. Analysis to be done • Reduce systematic errors • Results shown here are preliminary form. • more statistics • Run2 : Dataset collected by J/ytrigger • Software trigger that calculate the invariant mass of electron candidate • Trigger bias study is on going • statistics will be 2 times larger than current results • Future run • p-p, d-A run will give the baseline nuclear effect

  12. Summary • PHENIX experiment successfully collect 25M minimum bias events during the Run2 period. They are used in the preliminary analysis shown here • We have measured J/yyields (B dN/dy at y=0) in 3 centrality bin. • B dN/dy per binary collision at y=0 have seems to decrease in most central collision • To discuss physics , we need to analyze more data

  13. J/y in 3 centrality bins NJ/y =4.5  2.1  0.5 NJ/y =3.5  1.9  0.5 NJ/y =5.9  2.4  0.7

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