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Spin of the proton and its transverse spin structure at RHIC. HERMES seminar at Tokyo Tech November 9, 2005 Yuji Goto (RIKEN). RHIC – QCD collider. RHIC pC Polarimeters. Absolute Polarimeter (H  jet). BRAHMS & PP2PP. PHOBOS. Siberian Snakes. Siberian Snakes. PHENIX. STAR.

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Spin of the proton and its transverse spin structure at RHIC


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    1. Spin of the protonand its transverse spin structureat RHIC HERMES seminar at Tokyo Tech November 9, 2005 Yuji Goto (RIKEN)

    2. RHIC – QCD collider Yuji Goto (RIKEN)

    3. RHIC pC Polarimeters Absolute Polarimeter (H jet) BRAHMS & PP2PP PHOBOS Siberian Snakes Siberian Snakes PHENIX STAR Spin Rotators (longitudinal polarization) Spin flipper Spin Rotators (longitudinal polarization) Solenoid Partial Siberian Snake Pol. H- Source LINAC BOOSTER Helical Partial Siberian Snake AGS 200 MeV Polarimeter AGS Internal Polarimeter Rf Dipole AGS pC Polarimeters Strong AGS Snake installed and commissioned during in 2004 run installed in 2005 and to be commissioned to be commissioned RHIC polarized-proton collision • Luminosity 11031 cm-2sec-1 at s = 200 GeV achieved • 81031 cm-2sec-1 at 200 GeV and 21032 cm-2sec-1 at 500 GeV in the future • Polarization 50% achieved – 70% in the future Yuji Goto (RIKEN)

    4. STAR and PHENIX • STAR detector • 2 coverage for jet measurement • barrel TPC and EMC • endcap EMC • PHENIX detector • limited acceptance • high resolution central EMCal • high-rate trigger and DAQ • forward muon detectors Yuji Goto (RIKEN)

    5. s = 200 GeV P recorded L recorded LP4 data volume 2001-2002 transverse-spin run 15% 0.15 pb-1 20 TB first polarized proton collisions 2003 longitudinal-spin run 27% 0.35 pb-1 1.5 nb-1 35 TB spin rotators commissioned, AGS p-C CNI polarimeter 2004 commissioning run (longitudinal spin) 40% 0.12 pb-1 3.3 nb-1 35 TB AGS warm snake commissioned, gas-jet absolute polarimeter 2005 longitudinal-spin run 49.5/44.5% 3.8 pb-1 205 nb-1 262 TB AGS cold snake installed RHIC/PHENIX polarized-proton runs 2005 – First long longitudinal-spin polarized-proton run Figure of merit (LP4) more than 40 times larger than that of previous runs Yuji Goto (RIKEN)

    6. lepton beam g*  or  heavy flavor gluon  or  nucleon target Where is the proton spin ? • Origin of the nucleon spin 1/2 • polarized DIS experiments showed the quark contribution is only 10-30% • gluon contribution ? • Scaling violation in polarized DIS • Semi-inclusive DIS • high-pT hadron pairs • open charm production B. Adeva et al., PRD 58, 112002 (1998). P.L. Anthony et al., PLB 493, 19 (2000). Yuji Goto (RIKEN)

    7. proton beam  or  gluon photon  or  proton beam proton beam  or  gluon heavy flavor gluon  or  proton beam Gluon contribution ? • Polarized hadron collision • leading-order gluon measurement • ALL of 0 direct photon production heavy-flavor production gg + qg dominant sensitive to the gluon reaction Yuji Goto (RIKEN)

    8. PHENIX ALL of 0 GRSV-max: g = 1.84 GRSV-std: g = 0.42 at Q2=1(GeV/c)2 best fit to DIS data * at input scaleQ2 = 0.4 GeV - Run5 conclusively excludes GRSV maximal scenarios. - Data consistent with GRSV standard and GRSV G = 0. Yuji Goto (RIKEN)

    9. left right Single transverse-spin asymmetry • Left-right asymmetry • Forward-rapidity • Fermilab-E704 • fixed-target experiment at s = 19.4 GeV Yuji Goto (RIKEN)

    10. STAR collaboration, hep-ex/0310058, Phys. Rev. Lett. 92 (2004) 171801 STAR STAR forward pion • Run2 results • In agreement with several models including different dynamics: • Sivers: spin and k correlation in initial state (related to orbital angular momentum?) • Collins: Transversity distribution function & spin-dependent fragmentation function  suppressed? (hep-ph/0408356) • Qiu and Sterman (initial-state) / Koike (final-state) twist-3 pQCD calculations Yuji Goto (RIKEN)

    11. STAR forward pion • Run3 results • Positive AN at large positive xF has been confirmed • Larger significance to be non-zero & positive than published data • The first measurement of negative xF AN has been done, and is consistent with zero • Sensitive to twist-3 gluon-gluon correlation Statistical error only for <h>=4.1 Yuji Goto (RIKEN)

    12. Current FPD h=4.2 h=3.2 ~2.4m square ~1500 cells h=2.5 STAR outlook • Disentangling the dynamics of AN via • Higher precision AN measurement vs xF and pT • AN with mid rapidity correlation • Forward jet • Proposal for forward calorimeter upgrade • Heavy mesons and direct photons • Low x gluons in nuclei • Mid rapidity jets • Di-jet kT balance  gluon Sivers function • Inside jet particle correlation  Collins function * Transversity Yuji Goto (RIKEN)

    13. Mid-rapidity at PHENIX • Different kinematic region • forward-rapidity at STAR (xF> 0.3) • quark-gluon reaction dominant • large contribution from x ~ 0.6 quark polarization/transversity • mid-rapidity at PHENIX (xF~ 0) • contribution from both gluon-gluon and quark-gluon reactions • x = 0.03 – 0.1 • small quark polarization/transversity • no gluon transversity in leading twist • negligible transversity & Collins effect contribution Yuji Goto (RIKEN)

    14. Fermilab-E704 Mid-rapidity at PHENIX • Run2 results • AN for both 0 and charged hadrons consistent with zero at mid-rapidity • ~5 times smaller asymmetry than STAR forward-rapidity data (~10%) • comparable data with Fermilab-E704 for 0 and charged hadrons Yuji Goto (RIKEN)

    15. Neutron Veto EM Cal Base Charge Veto PbWO4 Hadron Cal Base Scintillator Post-shower Pb W+Fiber Cal Forward neutron asymmetry • PHENIX local polarimeter R&D at IP12 Yuji Goto (RIKEN)

    16. Forward neutron asymmetry Hadron Cal EM Cal AN = 0.1160.0180.020 AN = 0.1260.0080.041 preliminary preliminary preliminary very forward neutron AN ~ -12% xF > 0.2 pT < 0.3 GeV/c Yuji Goto (RIKEN)

    17. Longitudinal component of the proton polarization at PHENIX 410 GeV run in 2005 analyzing power of local polarimeter roughly the same despite doubling of energy Local polarimeter at PHENIX 2005 run Yuji Goto (RIKEN)

    18. Ng = Nd (E704) 2 0  j1 h ST j2 Back-to-back jet at PHENIX • Boer and Vogelsang find that this parton asymmetry will lead to an asymmetry in the  distribution of back-to-back jets • Should also be able to see this effect with fragments of jets, and not just with fully reconstructed jets Boer and Vogelsang, Phys.Rev.D69:094025,2004 Yuji Goto (RIKEN)

    19. Back-to-back jet at PHENIX • Measurement of the gluon Sivers function via AN for di-hadron angular correlations • Sivers distribution is a transverse parton momentumdistribution correlated with the nucleon’s spin axis, which could arise from orbital angular momentum • Error bars: Expected sensitivitywith P=60% and 7 pb-1 Yuji Goto (RIKEN)

    20. Back-to-back jet at STAR Yuji Goto (RIKEN)

    21. Spin dependence of kT of jets • Possible helicity effect • We may observe net effect (after averaging over impact factor) kT larger kT smaller Same helicity Opposite helicity Yuji Goto (RIKEN)

    22. Spin dependence of kT of jets • Run3 result: hint of helicity dependence ? • not yet sure • Run5 data should yield a definite answer. Yuji Goto (RIKEN)

    23. Summary • RHIC data began to provide restriction to the gluon-spin contribution to the proton spin • We need to know contribution of the orbital angular momentum as the final piece • RHIC has potential measurements of the orbital angular momentum and/or transverse spin structure of the proton • single transverse-spin asymmetries • Sivers effect/function measurements • … • We will have some transverse-spin run in 2006 Yuji Goto (RIKEN)

    24. Backup slides

    25. Naohito’s analysis Yuji Goto (RIKEN)

    26. Vertical vs radial run in 2006 Boer and Vogelsang, PRD69:094025,2004 private communication, Boer and Vogelsang 1 = /2 1 = 0 ST ST 1 = /2 : 1 = 0 : Yuji Goto (RIKEN)

    27. Spin dependence of kT of jets • Back-to-back nature of jets is broken by initial/final state transverse momentum kT(e.g., intrinsic kT, soft gluon radiation) • Orbital angular momentum: kT× rintroduces intrinsic kT in the initial state  measurement of jet kT gives an access to parton orbital angular momentum Yuji Goto (RIKEN)

    28. Maximum Asymmetry Interference Fragmentation 200 GeV Jet Proton Structure 500 GeV Hard Scattering Process Jet Transversity at PHENIX • Transversity throught +- interference FF • non-vanishing “support”only in the mass region , Yuji Goto (RIKEN)

    29. Transversity throught +- interference FF • Projected asymmetry For 32pb-1 (1 week of running) 5.2 Million events in 32 pb-1 15% with pair after cuts Small aymmetry below 5% but good rate! Yuji Goto (RIKEN)