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Probing the Gluon Polarization with A LL of J/  at RHIC. Ming X. Liu Los Alamos National Lab (PHENIX Collaboration). Spin Crisis and Gluon Polarization. Proton Spin Puzzle: Asymptotic limit. PCAC. Gluons may play a significant role !. lepton beam. g *.  or . heavy flavor. gluon.

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Probing the Gluon Polarization with A LL of J/  at RHIC


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    1. Probing the Gluon Polarization with ALL of J/ at RHIC Ming X. Liu Los Alamos National Lab (PHENIX Collaboration) PANIC05 M. Liu

    2. Spin Crisis and Gluon Polarization • Proton Spin Puzzle: • Asymptotic limit • PCAC Gluons may play a significant role ! PANIC05 M. Liu

    3. lepton beam g*  or  heavy flavor gluon  or  nucleon target Gluon Polarization Measurements: (SI)DIS • Semi-inclusive DIS • HERMES @ DESY • high-pT hadron pairs • SMC @ CERN • high-pT hadron pairs • COMPASS @ CERN • high-pT hadron pairs • open charm PANIC05 M. Liu

    4. proton beam  or  gluon photon  or  proton beam proton beam  or  gluon heavy flavor gluon  or  proton beam @RHIC-SPIN • Polarized hadron collisions • double longitudinal spin asymmetry • leading-order gluon interactions • direct-photon production • heavy-flavor production PANIC05 M. Liu

    5. The PHENIX Detectors • Central Arms • |h| < 0.35, Df ~ p • g, p0, e, p+-, ... – Identified • Momentum, Energy • Muon Arms • 1.2 < |h| < 2.4 • Momentum (MuTr) • Open charm, J/ etc PANIC05 M. Liu

    6. cceX bbeX J/ x A New Probe: Heavy Quarks • Sensitive to gluon polarization: Dg(x) • Gluon-gluon interaction dominates at LO PHYTHA estimate: Double spin asymmetry: Karliner & Robinett, Phys.Lett.B324 (1994) aLL Decay modes: e+e-, +-, e, eX, X 1.5 2 5 PANIC05 M. Liu

    7. J/ production mechanism • LO NRQCD: mix of various processes hep-ph/0509335 G. Nayak et al. PANIC05 M. Liu

    8. Partonic asymmetry for ggJ/ X J/ production mechanism (cont.) Teryaev and Tkabladze PRD56(97)7331 • NLO RNQCD: “final state” mixture ratios: fixed from other data PANIC05 M. Liu

    9. PHENIX, PRL 92, 051802 (2004) NLO NRQCD and PHENIX data Theoretical predictions of J/Ψ production at RHIC are in good agreement with the PHENIX data: COM process dominant • PRD 68 (2003) 034003 G. Nayak, M. Liu, F. Cooper • PRL 93 (2004) 171801 F. Cooper, M. Liu, G. Nayak PANIC05 M. Liu

    10. ALL Measurement with J/+- • Experimental approach • Polarization=47% (average) • R is from Beam-Beam-Counter scalers • N_Jpsi Yield PANIC05 M. Liu

    11. + - +(-) +(-) J/ Yield Measurements • Fill by fill: (N+- - N++,--) • Detector efficiency variation canceled out • Have Open charm, DY and other background (<10%) • Gaussian+Exponential background • Used to estimate the background under J/Psi peak Dimuon mass distributions PANIC05 M. Liu

    12. Raw Asymmetries Fill by Fill: NJ/ > 10 per fill 2 sigma cut: 2.78 < Mass < 3.42 <RL> = 1.0089(3) PANIC05 M. Liu

    13. Statistical Test • Beam polarization shuffling • random beam polarization values • repeat 10,000 times PANIC05 M. Liu

    14. Background Estimation Background Raw Asymmetry: Left of the peak: 2.0 < Mass < 2.5 ALL(raw)= 0.0107  0.0220 Under the peak: ALL(raw)= -0.0351  0.0318 N = 988  31 +- ++, -- Dimuon mass distributions PANIC05 M. Liu

    15. Log(x) ALL vs pT First spin physics result from J/ - J/y: produced via almost pure gluon fusion - sensitive to gluon polarization PANIC05 M. Liu

    16. Summary and Outlook • First measurement of double spin asymmetry with J/Psi from longitudinally polarized p-p collisions • Almost pure gluon fusion • 10k J/psi, statistically limited • Expect x100 more statistics in the future • Work in progress • J/Psi polarization measurement • Open charm - much larger statistics from run5 and will tell us more about gluon polarization • Need more theoretical work • J/ production mechanism • Polarized gluon PDFs • Excellent QCD test ground with polarization • Where does the nucleon get its spin? • Still don’t know … but RHIC-SPIN will help us to find the answer • and we will learn a lot more about the nature of strong interactions PANIC05 M. Liu

    17. + J/ * - More on J/ Production Mechanism- J/Psi polarization - a key probe?- Spin dynamics in pQCD α= +1: transversely polarized α= -1: longitudinally polarized α= 0: no polarization hep-ph/0106120 M. Kramer PANIC05 M. Liu

    18. + J/ * - GRSV λ=1 λ=0 NRQCD Calculations of ALL • NRQCD LO Helicity dependent double-spin asymmetry hep-ph/0509335 G. Nayak et al. PANIC05 M. Liu