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The h double helicity asymmetry and cross section

The h double helicity asymmetry and cross section. Frank Ellinghaus for the PHENIX Collaboration 09/30/06 RSC Meeting. Introduction. Status: A_LL for eta unmeasured, eta fragmentation function unknown -> no predictions for A_LL yet

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The h double helicity asymmetry and cross section

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  1. The h double helicity asymmetry and cross section Frank Ellinghaus for the PHENIX Collaboration 09/30/06 RSC Meeting

  2. Introduction • Status: A_LL for eta unmeasured, eta fragmentation function unknown -> no predictions for A_LL yet • Naïve expectation: increased relative contribution of strange quarks and glue (when compared to the pi0) should lead to a different asymmetry (when compared to pi0) • -> Observation of difference could help to disentangle the contributions from \delta q (u,d,s) and \delta g Access to polarized gluon distribution function via double helicity asymmetry

  3. PHENIX Detector • Photon detection: • Electromagnetic calorimeter: PbSc + PbGl, Acceptance eta <|0.35|, phi = 2*90 • Photon trigger: Threshold ~ 1.4 GeV • Luminosity: • Beam-Beam Counter (BBC), 3.1 < eta < 4.0 Photon identification: • E_PbSC > 0.1 GeV, E_PbGl > 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)) • (TOF cut)

  4. Eta reconstruction via 2 Photon decay • Invariant two photon mass: 0.48 GeV < M < 0.62 GeV • Energy asymmetry cut: E1-E2/ E1+E2 < 0.7 • Pt > 2 GeV • Fit with Gauss+Pol3 • |Z_vertex| < 30 cm

  5. Invariant cross section L = integrated Luminosity, based on Vernier scan using the BBC BR= Branching ratio: eta -> 2 photons = 0.3943 \pm 0.0026 f_Acc = acceptance function from MC (includes smearing) eff_Trig (MB data) = Trigger efficiency of MB trigger eff_Trig (ERT data) = (Trigger effi. MB) x (Trigger effi. ERT4x4c) eff_rec = Correct for eta loss due to photon conversion (~6% in PBSC, ~8% in PbGl) x loss due to cut on shower shape (~4%) N = N_measured

  6. f_acc from fastMC Acceptance and smearing correction from MC (also accounts for dead regions in EmCal, minimum cuts on photon energies,…) Up to 10% acceptance in PbSc for high p_T etas

  7. Photon/MB Trigger Efficiency MB trigger efficiency about 80 % Photon trigger efficiency roughly stable from 4 GeV on (single photon trigger threshold is set to 1.4 GeV)

  8. Eta cross section Maybe the relative contributions of quarks and gluons are similar after all? -> Need more Statistics -> Run 5 eta cross section analysis in progress -> Extraction of frag. functions from e+e- and pp in progress

  9. Asymmetry calculation Relative Luminosity R from counts in BBCs Asymmetry in bands around eta peak is consistent with each other

  10. Background corrected Asymmetry

  11. Single Spin Asymmetries

  12. Comparison to pi0 and Outlook Including Run 6 eta will result in comparable statistical power compared to present Run 5 preliminary pi0 data.

  13. Summary • Asymmetry of eta in Run 5 has been extracted (Step zero) • Run 3 cross section available, Run 5 result soon • Promises for FF’s have been made….

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