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Single Transverse Spin Asymmetries with

Single Transverse Spin Asymmetries with. Motivation Mid-rapidity results Forward rapidity results. APS March Meeting 2010/02/15. John Koster University of Illinois at Urbana-Champaign for the PHENIX Collaboration. Motivation. Left. Observable:

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Single Transverse Spin Asymmetries with

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  1. Single Transverse Spin Asymmetries with • Motivation • Mid-rapidity results • Forward rapidity results APS March Meeting2010/02/15 John KosterUniversity of Illinois at Urbana-Champaignfor the PHENIX Collaboration

  2. Motivation Left Observable: • Large single spin asymmetries (AN)observed over wide range of energies(4.9, 6.6, 19.4, 62.4, 200, 500) GeV Experimental results: • p p + p↓p summed cross-sections described well by pQCD • p p - p↓p difference of cross-sections not described well Present Theory: • Three proposed effectsCollins, Sivers, higher twist Up to experiment to distinguish! Current worldwide effort: • (pp) RHIC, JParc • (SIDIS) COMPASS/HERMES/JLAB • (e+e-) BELLE • xF=2 pLongitudinal / √s • Preliminary data from STARarXiv:0905.2840 [nucl-ex] • AN grows with xF • AN(η)>AN(π0) at large xF Eur.Phys.J.C36:371-374,2004

  3. Motivation (continued) • Rapidity of detected particle varies: • Production mechanism • Parton x1 , x2 0 at y=0, √s=200PLB 603,173 (2004) 0 at y=3.3, √s=200

  4. Mid-rapidity, |y|<0.38, AN p0, η Analysis Counts Similar analysis to existing PHENIX ALL • Measure AN in mass window of: • p0(Signal+Background) • η(Signal+Background) • Background • Determine background fractions (r) Asymmetries binned in pT for: • inclusive selection • with xF>0.01, xF<-0.01 Previous p0 AN measurement done with 2002 dataset. p0 η Mγγ

  5. Impact of 2002 result: Limit on Gluon Sivers Function Comparison of Exp. To Theory • Data points: p0 AN at xF=0 • Leading order model-dependant constraints on gluon Sivers function • Similar storyline to ALL • Initial data rules out maximally polarized distributions • Later data puts precise determination on distribution Anselmino et al, Phys. Rev. D 74, 094011 • Cyan: Gluon Sivers Function at positivity bound, no sea quark Sivers • Thick Red: Gluon Sivers parameterized to be 1 sigma from PHENIX 0 AN • Blue: Asymmetry from Sea quark Sivers at positivity bound • Green: Asymmetry from Gluon Sivers for case of sea quark at positivity bound

  6. Results for mid-rapidity0 AN 2002 Published Result 2008 Preliminary Result • 20x smaller error bars • Large improvement by BNL Collider/Accelerator department in both polarization and luminosity

  7. Mid-rapidity 0 andηAN • AN consistent with zero

  8. Mid-rapidity 0 AN |xF|>0.01 • AN consistent with zero

  9. Mid-rapidity η AN |xF|>0.01 • AN consistent with zero

  10. Moving to forward rapidity…

  11. Muon Piston Calorimeter AN Single Clusters Detector overview • Matching calorimeters at forward and backward rapidity 3.1<|eta|<3.9 • 2.2 x 2.2 x 18 cm3 PbWO4 scintillating crystals • 220 cm from nominal interaction point Analysis details • Photon merging effects prevent two-photon p0 analysis for E>20 GeV (pT>2 GeV/c) Analysis done with “single clusters” Yields dominated by p0’s but also get contributions from: • Electromagnetic • Direct photons • Decay photons (η, etc) • Estimated using Pythia (TuneA) • Hadronic: (p+/-,K+/-, etc.) • Estimated with GEANT. Initial estimate is <10% contamination in lowest energy bin with decreasing fraction as deposited energy increases • Qualitatively consistent with expected detector behavior Decay photon impact positions for lowand high energy p0’s

  12. Forward Single Cluster AN xF, pT binning Fraction of clusters Decay photonπ0Direct photon pT (GeV/c)

  13. Forward Single Cluster AN xF, binning GeV/c GeV/c Fraction of clusters η<3.3 η<3.3 Decay photonπ0Direct photon Eta>3.3 xF xF

  14. Single Cluster AN |xF|>0.4 pT binning Fraction of clusters Decay photonπ0Direct photon pT

  15. Summary • π0 and η asymmetries at mid-rapidity are consistent with zero • Forward single spin asymmetries are non-zero • Qualitative agreement with STAR measurements of π0 • Quantitative comparison with STAR results not performed yetNeed to evaluate effects of background on asymmetries • Extends pT reach of STAR measurement slightly

  16. Interpretation benchmark: pQCD applicability STAR: Phys.Rev.Lett.97:152302,2006. 0 Cross-Sections at y = 0Experiment vs Theory • √s=200 GeV (RHIC) Agreement • √s=19.4 GeV (FNAL/E704) Different More work needed to understand fixed target energies 0 Cross-Sections at 3<y<4High pT (low eta) agreement Eur.Phys.J.C36:371-374,2004

  17. Beam backgrounds in the MPC • Three considerations: • Charged hadrons Naturally suppressed by EMC • Background from incoming beam: Shielded by muon piston magnet:North: 387.4 cm, 220 X0, 23.1 NILSouth: 256.9 cm, 146 X0, 15.3 NILShielded by muon steel • Background from outgoing beam:Evaluated using timing cutsSmall Muon piston Muon steel MPC

  18. RHIC ∫L* and Polarization 2008 figure of merit was not a large increase over 2006 figure of meritFurther study shows PHENIX accumulated a significant and newdataset

  19. 2008 dataset highlights Polarization direction • 2006 Radial polarization • 2008 Vertical polarization • 2008 L/R asymmetry powergreatly enhanced over 2006 Measure AN at mid-rapidity 2006 2008 First polarized MPC dataset at √s=200 GeV • 2006 √s=200, MPC South installed but not fully ready until 62 GeV running • 2008 √s=200, MPC South & North eager forpp collisions Installed for 2006, but only activefor later, 62 GeV,portion Measure AN with MPC South North

  20. The tunes roots 200 proj p targ p frame cms msel 0 // turn on all prod. mechanisms manually msub 11 1 // QCD jets msub 12 1 msub 13 1 msub 28 1 msub 53 1 msub 68 1 msub 96 1 ckin 3 2.0 pytune 100 QCD_hard_p100 QCD_dgam_p100 roots 200 proj p targ p frame cms msel 0 msub 14 1 msub 18 1 msub 29 1 msub 114 1 msub 115 1 ckin 3 2.0 pytune 100 roots 200 proj p targ p frame cms msel 2 pytune 100 QCD_msel2_p100

  21. Cross-section PHENIX pi0 central arm comparison Pythia/Experiment

  22. Cross-section STAR pi0 Comparison (3.7<eta<4.15) Pythiia/Experiment

  23. Cross-section STAR pi0 Comparison (3.4<eta<4.0) Pythia/Experiment

  24. Cross-section STAR pi0 Comparison (3.05<eta<3.45) Pythia/Experiment Set QCD_hard_p100 k-factor = 1

  25. Cross-section PHENIX Direct photon comparison Pythia/Experiment Set QCD_dgam_p100 k-factor = 2

  26. PHENIX Detector at RHIC • Central Arms | η | < 0.35 • Identified charged hadrons • Neutral pions / η • Direct Photon • J/Psi • Heavy Flavor • Muon Arms 1.2 < | η | < 2.4 • J/Psi • Unidentified charged hadrons • Heavy Flavor • MPC 3.1 < | η | < 3.9 • Neutral pions / η

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