J/Psi Production at RHIC

1. J/Psi Production at RHIC Ming X. Liu P-25, LANL • Physics Motivation • Study QCD dynamics (HI) • Nucleon Structure (Spin) • RHIC/PHENIX

2. J/Psi production @ high energy • J/Psi production & pQCD • Factorization model • cc pair production (initial state effects) • cc pair hadronization (final state effects) • Color Singlet Model • Color Octet Model • Color Evaporation Model

3. Physics with J/Psi @RHIC • J/Psi as a probe of QGP formation • Final state effects • Nucleon structure function • Initial state effects • Quark and Gluon distributions • QCD dynamics • Spin in QCD • hadronization

4. J/Ymm decays measured / expected CERN SPS results (NA50, NA38, NA51) Prediction by Matsui and Satz (Phys. Lett. B178, 416 (1986)) that Debye color screening will lead to suppression of charmonium production in heavy ion collisions, if a quark-gluon plasma is formed. Expected J/Y yields are corrected for "ordinary" nuclear absorption assuming 6.4 mb absorption cross section Many arguments about whether this is strong evidence of QGP at SPS energies, but it is clearly VERY interesting!

5. Normal Nuclear Absorption of J/Y Nucleus A Survival probability = PA . PB zA,B PA,B =  exp(-rsJ/Y-N z) dz zprod where r = local nucleon density sJ/Y-N = J/Y-on-nucleon s sJ/Y-N = 7.1 + 0.9 mb from a fit to CERN A . B data zA J/Y zB Nucleus B

6. Nuclear Effect : p-A data Dimuon pair absorption vs. target mass. The results are consistent with an absorption cross section of zero for Drell-Yan and different non-zero absorption cross sections for the onia.

7. J/Psi production and QGP @RHIC • More recent predictions of increased J/Psi production at RHIC from recombination. • The best test is to measure charmonium yields in pp, pA, and AA • PHENIX can measure charmonium decay yields to e-e and mu-mu for pp, pA and AA collisions with colliding beams of 100A GeV/c. • First results from PHENIX for J/Psi production at sqrt(s) = 200A GeV in pp and AuAu collisions will be presented in this talk.

8. + Proton Structure Parton Model g u d x x

9. J/Psi physics @RHIC-SPIN • Proton Spin Puzzle and G • Asymptotic limit Experimentally - Naïve expectation  = 1 - Relativistic Estimation  ~ 0.6 HERMES’99 Gluons may play a significant role !

10. J/Psi and Gluon polarization • Spin physics in longitudinally polarized p+p collisions • Double-longitudinal spin asymmetry (ALL) of the J/ production  polarized gluon density

11. J/Psi physics @RHIC-SPIN • Test of QCD with spin degree of freedom • J/Psi polarization and production mechanism • CDF/E866 results • Color Octet Model • Good total cross-section • Failed to explain J/Psi polarization

12. RHIC @ BNL • RHIC parameters • p+p, Au+Au, d-Au • Sqrt(s) = 50 ~500 GeV • polarization • Runs • Run-1 1999-2000 • Low luminosity • Sqrt(s)=130GeV, Au+Au • Run-2 2001-2002 • Sqrt(s)=200GeV • Au+Au • p+p, pol ~20% • Run-3 2002-2003 • Sqrt(s)=200 • d+Au • p+p, pol~40%

13. PHENIX Experiment

14. PHENIX Experiment in Run 2 Electrons ( |h| < 0.35) Charged tracks (Beam-Beam, Drift Chamber, Pad Chambers) + RICH rings + EM Calorimeter clusters Muons (1.2 < h < 2.2) Muon Identifier roads + Muon Tracker tracks

15. 1000 nb-1 800 600 400 200 PHENIX 0 0 18 36 Days RHIC Integrated p+p luminosity RHIC delivered 700nb-1 to PHENIX After an online vertex cut, PHENIX recorded 150 nb-1 Presentpreliminary analysis used data from: 81 nb-1(1.7 x 109)+- 48 nb-1(1.0 x 109) e+e- 1/1/02

16. The PHENIX Muon Arm • Detect muons with ptot>2 GeV/c, 1.2< <2.2 (South Arm) • Pre-hadron-rejection with Central Magnet steel (int~5) • Muon Tracking Chamber (MuTr) • Measure momentum of muons with cathode-readout strip chambers at 3 stations inside Muon Magnet • Muon Identifier (MuID) • /µ separation with 5-layer sandwich of chambers (Iarocci tubes) and steel • Trigger muons • Successfully operated first time during Run-2 MuID Muon Magnet MuTr

17. Event Display

18. Muon LVL-1 Trigger • Coincidence of fired MuID planes of each “quadrant” • One quadrant for “single-muon trigger” and more than one quadrant for “dimuon trigger” used for this analysis • Inefficiencies from hardware dead time is 1~2% MuID µ ‘Quadrant’ trigger Quadrant

19. J/+- signal 3.16+-0.26 GeV • Significant enhancement of unlike-sign pair in the J/ mass region • Peak (3156  74 MeV/c2) is consistent with J/ mass • Mass width (257  75 MeV/c2) is consistent with expectation further improvement is expected • NJ/ = 36 in 2.5<mass<3.7GeV/c assuming same count of unlike and like-sign pairs from background (confirmed with simulation) • Systematic error on the count ~10 % by changing mass cut

20. d/dy|y=1.7 result • NJ/ = 36  7 (stat.)  4 (syst.) • Accreco= 0.0163  0.031 • BBCJ/L = 0.60  0.12 nb-1 • y: rapidity coverage = 1.0 Br (J/+-)dJ//dy|y=1.7. = 37  7 (stat.) 11 (syst.) nb PHENIX Preliminary

21. J/pT distribution and <pT> • pT shape is consistent with the PYTHIA (color-singlet model) prediction 1.2<y<2.2 PHENIX Preliminary <pT>y=1.7 = 1.66  0.18 (stat.)  0.09 (syst.) GeV/c (pT<5 GeV/c) High pT contribution is expected to be small (~3%) assuming pT function shape consistent with Tevatron data

22. Electron Measurement with the Central Arms • Charged tracks are identified with Drift Chambers (DC) and Pad Chambers (PC1/2/3) • Ring Imaging CHerenkov detector (RICH) and Electro-Magnetic Calorimeter (EMCal, i.e. PbSc/PbGl) are used to identify electrons • EMCal is also used for electron/photon Trigger || < 0.35 Beam pipe  =  Cross section of the PHENIX Central Arms

23. Electron Identification

24. Electron LVL-1 Trigger and its Efficiency • At least one energy sum of EMCal 2x2 towers exceeds the threshold (0.8GeV)  single electron/photon trigger • Trigger efficiency for J/e+e- is estimated to be0.90 + 0.06 - 0.07 • Use Monte-Carlo tuned to describe single-photon efficiencies with real data well Energy sum EMCal 11cm 1 PMT (Tower) e+-

25. NJ/ = 24  6 (stat.)  4 (syst.) J/ e+e- signal

26. d/dy|y = 0 result NJ/y = 24  6(stat.)  4(syst.) Accreco= 0.0163  0.0020 run-run= 0.87  0.09  additional Run-by-Run correction factor trig= 0.90 + 0.06 – 0.07 BBCJ/ = 0.75  0.11 L = 48  10 nb-1 y = 1.0  Br (J/e+e-)d/dy|y = 0 = 52  13 (stat.)  18 (syst.) nb PHENIX Preliminary

27. J/Y Rapidity Distribution Gaussian and PYTHIA shape fits give essentially the same integral. The quoted result is the average of the two fits. s (pp->J/Y) = 3.8 + 0.6 (stat) + 1.3 (sys) mb

28. Cross Section vs Color Evaporation Model* * See J.F. Amundson et al., Phys. Lett. B 390 (1997) 323.

29. 80 mb-1 40 0 60 88 4 32 0 28 Days RHIC Integrated AuAu Luminosity Only 50% of RHIC beam vertex distribution satisfied PHENIX online vertex cuts After online vertex cuts (+45 cm) and 60% PHENIX uptime, we recorded 24 mb-1. Present preliminary analysis uses minbias data only from 4 mb-1(26 x 106)for ee

30. Au-Au ee Invariant Mass Spectra

31. Color-Singlet Model prediction PYTHIA p+p s=200GeV GRV94LO Gluon fusion only • Other contributions will be small (’, b-quark) • Disagrees with our result by factor ~6

32. Color-Octet Model prediction • Work in progress (P-25/T8 collaboration) • Large uncertainties from extraction of color-octet matrix elements, charm-quark mass, PDF, and so on. • Needs more help from theorists to better understand the production mechanism: • pT distribution • Rapidity distribution • Total cross section • Polarization

33. Summary and Outlook • Inclusive J/ production cross section was measured. • both e+e- decay channel (|y|<0.35) and +- decay channel (1.2<y<2.2) in Run-2 p+p collisions at s = 200 GeV. • Br(J/+-) dJ//dy|y=1.7 = 37  7(stat.)  11(syst.) nb • Br(J/e+e-) dJ//dy|y=0 = 52  13(stat.)  18(syst.) nb • Rapidity fit including both results gives • J/ = 3.8  0.6(stat.)  1.3(syst.) µb agrees with the Color-Evaporation model prediction. • J/Psi analysis with Au+Au data is in progress • With expected much improved statistics, many of the physics discussed above will be addressed in coming years.