Frank Ellinghaus University of Mainz / University of Colorado (for the PHENIX Collaboration)

1. arXiv:1009.6224 Cross section and double helicity asymmetry for eta mesons and their comparison to neutral pion production at PHENIX Frank Ellinghaus University of Mainz / University of Colorado (for the PHENIX Collaboration) Spin2010 October 1st, FZ Jülich, Germany

2. PDFs fitted using F2 at Q2=4 U=u+cu, D=d+sd Parton Distribution Functions (PDFs) • From fits to F2 measurements, unpolarized PDFs • can be inferred • q=u,d (s,c) • The total fraction of nucleon momentum carried by quarks: • Gluons carry the other half! U=u+cu, D=d+sd Frank Ellinghaus, University of Colorado

3. Polarized PDFs extracted from fits to g1(proton, deuteron) Results from Inclusive Polarized DIS • Analogous to unpolarized (F2) case, g1 can be used to fit polarized PDFs: • Result: Quarks carry only about 30 % of the nucleon spin (0.3) • Gluon contribution G not well constrained due to small range in xB,Q2 (no polarized ep collider) …but polarized pp Collider !!! -> Frank Ellinghaus, University of Colorado

4. pC Polarimeters STAR RHIC @ BNL Polarimeter (H jet) Spin Rotators Siberian Snakes Relativistic Heavy Ion Collider also provides longitudinally and transversely polarized proton beams at s = 62.4 GeV, 200 GeV, 500 GeV Frank Ellinghaus, University of Colorado

5. PHENIX Detector Frank Ellinghaus, University of Colorado

6. The PHENIX Detector for Spin Physics Central Detector: • g/p0/h : • Electromagnetic Calorimeter: PbSc + PbGl, h < |0.35|, f = 2 x 90 • Drift Chamber Global Detectors: • Relative Luminosity • Beam-Beam Counter (BBC) • Zero-Degree Calorimeter (ZDC) • Local Polarimetry -ZDC Frank Ellinghaus, University of Colorado

7. PHENIX longitudinally polarized pp Runs Frank Ellinghaus, University of Colorado

8. 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 Frank Ellinghaus, University of Colorado

9. h reconstruction via gg decay • EPbSC > 0.2 GeV, EPbGl > 0.2 GeV • Cut on Shower shape of cluster • Charge veto: track in • PC3 is considered • Time-of-flight cut • Energy asymmetry cut: E1-E2 / E1+E2 < 0.7 • pT > 2 GeV • |zvertex| < 30 cm • Peak extractionmethods: • Gauss+Pol2 • Gauss+Pol1 • Varioussidebands ( peakandwidth • from MC) Frank Ellinghaus, University of Colorado

10. 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 Frank Ellinghaus, University of Colorado

11. 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) Frank Ellinghaus, University of Colorado

12. h cross section PHENIX, arXiv:1009.6224 • Run 6 h cross section • 7 orders of magnitude • Large range in pT • Extraction of FFs from e+e- data • and this (large range in pT) pp • result ( gluon FFs). • Extraction uses method/code • from DSS (de Florian, Sassot, • Stratmann, PRD75, 2007) -> Frank Ellinghaus, University of Colorado

13. h FFs – Data C. Aidala et al., arXiv:1009.6145 PHENIX run 6 largest data set. Frank Ellinghaus, University of Colorado

14. Impact of PHENIX data on FF extraction Truncated second moment: C. Aidala et al., arXiv:1009.6145 PHENIX Run 6 data constrains light quark FFs better than e+e-. Large range in pT is the key(other pp -> eta-> gg from 2.5 to 12 GeV in pT) Frank Ellinghaus, University of Colorado

15. Sensitivity to DG: eta versus pion • Sensitivity to polarized gluon via gg and qg scattering • very similar for pt < 10 GeV. • Different sensitivity above 10 GeV likely within uncertainties, (which are difficult to quantify) Frank Ellinghaus, University of Colorado

16. 2 < pT < 3 GeV/c 3 < pT < 4 GeV/c 4 < pT < 5 GeV/c 5 < pT < 6 GeV/c Mgg (MeV) Mgg (MeV) Mgg (MeV) Mgg (MeV) Inclusive h Asymmetries in pp -> h X Relative luminosity R using beam-beam counters Frank Ellinghaus, University of Colorado

17. Measure Access to DG: Add the pieces… Access to polarized gluon distribution function via double helicity asymmetry in inclusive polarized pp scattering: subprocess asym+frac (FFs) from DIS Frank Ellinghaus, University of Colorado

18. Adding Run 9 data (preliminary) Run 5+6: 11 pb-1 Adding Run 9: 14 pb-1 Frank Ellinghaus, University of Colorado

19. Strong impact of Star jets and Phenix p0 in measured range. • Eta can now be included in next global fit • Shape of DG(x) cannot be extracted -> All “missing” spin can be at low x…. • Lower x can be probed in 500 GeV running (first run was in 2009) • Photons from eta start to merge later than the ones from pizero. First pol. PDF extraction using pp data DSSV, PRL 101, 2008 First “global” (DIS+SIDIS+pp) analysis! DG small in measured range (0.05 < x< 0.2). Contribution at small or large x? Frank Ellinghaus

20. : sensitivity to Ds? • DIS analyses (HERMES, COMPASS, NLO fits) -> Ds small and negative • SIDIS HERMES/COMPASS -> Ds zero or small and positive for x > 0.01 • DSSV uses latest FFs from DSS, both fits include the HERMES SIDIS Data • -> node at about 0.02 • DNS also included (HERMES) SIDIS, but has less flexible func. form and • uses (quite different) FFs from KKP and Kretzer Frank Ellinghaus, University of Colorado

21. Eta / pizero cross section ratio Ratio from single pass over data  minimizing systematic uncertainties • 9.7% luminosityuncertaintycanclescompletely. • Manyotheruncertaintiescancelcompletelyorto a • large degree • global energyscale • non-linear energyscale • triggerefficiencies • Photon ID efficiencies • … Fit to constant above 2 GeV or 3 Gev yields: Frank Ellinghaus, University of Colorado

22. Ratio compared to NLO pQCD • Ratio has much reduced experimental uncertainties (see last slide) • Theoretical scale uncertainty should largely cancel. Including ratio in global fits should reduce uncertainties on eta and pi0. Frank Ellinghaus, University of Colorado

23. Summary • Eta cross section measured over large range in pT • Important input for extraction of eta FF • “Precise” Eta / pizero cross section ratio measured • Ratio should further constrain eta FF when included in fit • h double helicity asymmetry measured • data ready to be included in global QCD fits in order to further constrain polarized PDFs Frank Ellinghaus, University of Colorado

24. BACKUP Frank Ellinghaus, University of Colorado

25. h reconstruction via gg decay • Energy asymmetry cut: E1-E2 / E1+E2 < 0.7 • pT > 2 GeV • |zvertex| < 30 cm • Fit:Gauss+Pol3 2<pT<3 GeV Frank Ellinghaus, University of Colorado