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Measurement of Charmonia at Mid-Rapidity at RHIC-PHENIX

This paper discusses the measurement of charmonia, specifically J/ψ, in p+p collisions at RHIC-PHENIX. The study aims to understand the production of quarkonia and the importance of feed-down from cc into J/ψ. The methodology involves measuring J/ψ→e+e- and cc→J/ψg→e+e-g and correcting for acceptance, background, and normalization regions.

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Measurement of Charmonia at Mid-Rapidity at RHIC-PHENIX

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  1. 1 Measurement of charmonia at mid-rapidity at RHIC-PHENIXccJ/yge+e-g in p+p collisions at √s=200GeV Susumu Oda CNS, University of Tokyo For the PHENIX collaboration 2007/09/24 62nd annual JPS meeting Hokkaido University

  2. 2 0 mb 3 mb Red : Au+Au |y|<0.35 Magenta : Cu+Cu |y|<0.35 Blue : Au+Au 1.2<|y|<2.2 Aqua : Cu+Cu 1.2<|y|<2.2 peripheral central Motivation A paper about J/y production in Cu+Cu collisions will be submitted in few weeks. • Quarkonia are good probes of QGP. • J/y is the most studied quarkonium in heavy ion collisions. • Feed down from cc into J/y is important. Direct J/y ccJ/yX y’J/yX BJ/yX

  3. 3 DDbar threshold y(2S) hc(2S) cc2(1P) hc(1P) cc1(1P) cc0(1P) g g J/y(1S) g hc(1S) e+e- BR=5.94% 0-+ 1-- 0++ 1++ 1+- 2++ JPC Charmonium system

  4. 4 E672/E706 E369 WA11 HERA-B CDF E705 E610 Precise measurements only Error of Rcc<=0.1 RHIC energy Fraction of J/y from cc decay Measurement of cc at RHIC is required.

  5. 5 Color Singlet Model NRQCD CSM+Comover Color Evaporation Model Theoretical model predictions Measurement of cc at RHIC is required to understand quarkonia production.

  6. 6 How to measure Rcc • Find J/ye+e- (2.9<Mee<3.3GeV). • Find ccJ/yg (DM=Meeg-Mee~0.44GeV). • Correct acceptance event by event. • Subtract background by event mixing of J/y and g. • Normalization regions : 0.1-0.3GeV and 0.6-0.8GeV • Run-5 (2005, 3.8 pb-1) and Run-6 (2006, 10.7 pb-1) p+p200GeV data is used. cc conditional efficiency if J/y is detected J/y acceptance Average over J/y cc acceptance

  7. 7 e- g p p e+ PHENIX detector • Beam beam counter • Collision vertex • Drift chamber, pad chamber • Charged particle tracking • Ring imaging Cherenkov counter • Electron identification • Electromagnetic calorimeter • Photon identification and energy measurement • Electron identification p+p  cc+X  J/yg+X  e+e-g+X

  8. 8 mainly p02g Cut parameters and peaks Event cut • |Zvertex|<30 cm Electron cut • RICH nPMT>=2 • pT>0.2 GeV • 0.5<Energy/momentum<2 Pair cut • 2.9<mass(e+e-)<3.3GeV EMCal energy resolution s(E)=58MeV (PbSc) s(E)=42MeV (PbGl) @ E=500MeV Photon cut • Energy cut (Eg >0.3 GeV) • Electromagnetic shower profile • Fiducial cut (noisy EMC towers are removed) • Charged particle veto (35cm x 35cm) PYTHIA simulation (cc1, |yg|<0.5) NJ/y=3679 Red : N+-=4040 Blue : N+++N--=218 J/ye+e- Run-5+6 p+p Run-6 p+p 0.6<pT<0.65GeV/c Eg>0.2GeV p02g

  9. 9 J/y acceptance and cc conditional efficiency if J/y is detected from GEANT (PISA) simulation ccJ/yge+e-g ~10% J/ye+e- ~2% for |yJ/y|<0.5 pT,J/y (GeV/c) pT,cc (GeV/c) cc acceptance~2%*10%=0.2%1/30,000 of produced cc is detected by PHENIX central arm

  10. 10 Feasibility study using PYTHIA and GEANT simulation Input Rcc=0.32 N(direct J/y):N(cc1J/yg):N(cc2J/yg)=68%:16%:16% NJ/y=3744 Black : Foreground Blue : Background Red: Foreground-background Green : Normalization regions (0.1<DM<0.3GeV and 0.6<DM<0.8GeV)

  11. 11 Black : Foreground Blue : Background Red: Foreground-background Green : Normalization regions Feasibility study using simulation (continued) Input Rcc=0 Input Rcc=0.68 Input Rcc=0.32 Input Rcc=1

  12. 12 Real data (Run-5 and Run-6 p+p 200GeV) Black : Foreground Blue : Background Red: Foreground-background Green : Normalization regions The fraction of J/y from cc feed down (Rcc) seems to be small.

  13. 13 RHIC energy Summary and outlook • The contribution of cc is important to understand the J/y data in heavy ion collisions. • Search for the cc meson via J/yg decay in p+p collisions is ongoing. • The fraction of J/y from cc feed down (Rcc) seems to be small. • The Rcc value will be obtained soon. • More and more statistics are needed (Run-8, 9, …) for detail study.

  14. Backups

  15. Acceptance of p0

  16. Ratio of cross sections Limited knowledge Green : pA Blue : pA Aqua : ppbar For simplicity, I assumed And I used mean of masses in simulation. (3510.66MeV+3556.20MeV)/2 Expected width of the convoluted peak (Gaussian sigma) is ~50MeV. I neglect cc0 contribution.

  17. PHENIX Run 5 200GeV p+p (c - J/) Mass (GeV/c2) (c - J/) Mass (GeV/c2) Previous result, Run-5 p+p 200GeVNJ/y=960

  18. Questions from audience

  19. Question 1 • Is it better to use muon pairs? The statistics of muon pairs are 5 times larger than electron pairs. • No. • The fraction of decays with J/y going to muon arm and gamma going to central arm is small. • So, the statistics of J/y+g in muon+central arms and the statistics in central arm are almost equivalent. • But, the energy of gamma in muon+central arm configuration is low, E~0.1(0.2)GeV. • This is worse situation than the central arm case with E~0.4GeV. • Does the fact mean that the cc measurement is not possible at RHIC-PHENIX? • No. • It can be possible in p+p collisions as I showed, while the larger statistics is needed. • But, it is very hard in heavy ion collisions. • (The measurement with NCC+FVTX+muon trigger is interesting even in heavy ion collisions, but the statistics are still necessary.)

  20. Question 2 • Is it better to use the isolation cut (p0 veto)? • No. • The acceptance of low-pT p0 is small, ~3% at p0 pT=0.6GeV/c (slide 15). • So, the p0 veto will not be effective for the cc measurement and it will introduce larger systematic error only.

  21. Question 3 • You did not take into account the cc0 contribution in your PYTHIA+GEANT simulation. Why? • Because the branching ratio of cc0J/yg decay is small, only 1.3% (slide 3). • If the production cross section of cc0 is much larger than ones of cc1 and cc2, we cannot neglect it. • But, we know the cc0 fraction is not large in the fixed target experiment and Tevatron. • So, the cc0 contribution can be negligible.

  22. Question 4 • In the PYTHIA+GEANT simulation, the net (foreground-background) distribution is lower than zero at the lower side of the cc peak. Why? • There is correlation between J/y and g in the foreground and most of g come from p02g decays. The correlation leads high mass of J/yg pairs. In the background, however, there is no correlation between J/y and g, and the J/yg pair mass is smaller. Therefore, the net distribution is lower than zero in simulation in the lower side. But, actually, this fact is not observed in the real data. Though, the J/y statistics is the same in the simulation and real data. • Why don’t you include such effect in your background subtraction? • I don’t believe the prediction capability of PYTHIA at such level.

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