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The h cross section and double helicity asymmetry in pp collisions

The h cross section and double helicity asymmetry in pp collisions. Frank Ellinghaus University of Colorado (for the PHENIX Collaboration) 10/03/06 Spin’06, Kyoto, Japan. Introduction. Status: A LL for h unmeasured, h fragmentation function unknown  no predictions for A LL yet

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The h cross section and double helicity asymmetry in pp collisions

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  1. The h cross section and double helicity asymmetry in pp collisions Frank Ellinghaus University of Colorado (for the PHENIX Collaboration) 10/03/06 Spin’06, Kyoto, Japan

  2. Introduction • Status: ALL for h unmeasured,h fragmentation function unknown no predictions for ALL yet • Additional channel (“global analysis”) • Naïve expectation (additional s+s in wave function): increased relative contribution of strange quarks and glue should lead to a different asymmetry (when compared to p0) • -> Observation of difference could help to disentangle the contributions from Dq (u,d,s) and Dg Access to polarized gluon distribution function via double helicity asymmetry: F. Ellinghaus, Spin’06, Kyoto, Japan

  3. PHENIX Detector • Photon detection: • Electromagnetic calorimeter: PbSc + PbGl, Acceptance: h < |0.35|, f = 2 x 90 • Photon trigger: Threshold ~ 1.4 GeV • Luminosity: • Beam-Beam Counter (BBC), 3.1 < h < 4.0 Photon identification: • EPbSC > 0.2 GeV, EPbGl > 0.2 GeV • Cut on Shower shape of cluster • (Charge veto cut: closest track in PC3 is considered, should be far away or very close (pair production originated from photon)) • (Time-of-flight cut) F. Ellinghaus, Spin’06, Kyoto, Japan

  4. h reconstruction via gg decay • Invariant two photon mass: 0.48 GeV < Mgg < 0.62 GeV • Energy asymmetry cut: E1-E2 / E1+E2 < 0.7 • pT > 2 GeV • |zvertex| < 30 cm • Fit:Gauss+Pol3 2<pT<3 GeV F. Ellinghaus, Spin’06, Kyoto, Japan

  5. Invariant cross section L = integrated Luminosity, based on Vernier scan using the BBC BR= Branching ratio: h 2 photons = 0.3943 ± 0.0026 fAcc = acceptance function from MC (includes smearing) effTrig (Minimum Bias data) = Trigger efficiency of MB trigger effTrig (high pT triggered data) = (Trigger effi. MB) x (Trigger effi. high pT trigger) effrec = Correct for h loss due to photon conversion (~6% in PBSC, ~8% in PbGl) x loss due to cut on shower shape (~4%) N = number of reconstructed h F. Ellinghaus, Spin’06, Kyoto, Japan

  6. facc from Monte Carlo Acceptance and smearing correction from MC (also accounts for dead regions in EmCal, minimum cuts on photon energies,…) data MC Up to 10% acceptance in PbSc for h at high pT pT F. Ellinghaus, Spin’06, Kyoto, Japan

  7. Photon/MB Trigger Efficiency Minimum Bias (MB) trigger efficiency about 80 % Photon trigger efficiency roughly stable from 4 GeV on (high pT photon trigger threshold is set to 1.4 GeV) F. Ellinghaus, Spin’06, Kyoto, Japan

  8. h cross section The relative contributions of quarks and gluons are maybe not too different…?  Need more statistics  Run 5 h cross section analysis in progress  Enables extraction of fragmentation functions from (e+e- and) pp ( gluon FFs) F. Ellinghaus, Spin’06, Kyoto, Japan

  9. Inclusive h Asymmetries Relative Luminosity R using beam-beam counters Asymmetries in bands around h peak are consistent with each other F. Ellinghaus, Spin’06, Kyoto, Japan

  10. Background corrected Asymmetry F. Ellinghaus, Spin’06, Kyoto, Japan

  11. Single Spin Asymmetries Parity violating asymmetries zero as expected F. Ellinghaus, Spin’06, Kyoto, Japan

  12. Comparison to p0 and Outlook Including Run 6 data will result in statistical power comparable to present Run 5 preliminary p0 data. F. Ellinghaus, Spin’06, Kyoto, Japan

  13. Summary • Inclusive h double helicity asymmetry has been extracted • Run 3 cross section for h available, Run 5 result soon  enables extraction of fragmentation functions  enables theoretical calculations in order to compare extracted asymmetry to theory F. Ellinghaus, Spin’06, Kyoto, Japan

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