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Transverse Spin Effects at the PHENIX Experiment

Transverse Spin Effects at the PHENIX Experiment. Ruizhe Yang University of Illinois. Los Alamos, April 15, 2010. Outline. Physics motivation Measurement of transverse proton spin structure Results at PHENIX Traditional transverse single spin asymmetries Alternative probes

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Transverse Spin Effects at the PHENIX Experiment

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  1. Transverse Spin Effects at the PHENIX Experiment Ruizhe Yang University of Illinois Los Alamos, April 15, 2010

  2. Outline • Physics motivation • Measurement of transverse proton spin structure • Results at PHENIX • Traditional transverse single spin asymmetries • Alternative probes • Future measurements at PHENIX Ruizhe Yang

  3. Proton as a QCD bound state Doppler free saturation spectroscopy (Polarized) DIS, pp Lamb Hydrogen atom Proton QED QCD Proton structure Lamb shift Tomonaga, Feynman, Schwinger Ruizhe Yang

  4. Nucleon spin structure: 30 years Quark Spin – Gluon Spin – Transverse Spin – GPDs – Lz SLACE80-E155 CERN EMC,SMC COMPASS FNAL E704 DESY HERMES JLAB Halls A, B, C RHIC BRAHMS, PHENIX, STAR 2000 ongoing 1995 2007 ongoing ongoing major experimental innovations semi inclusive + exclusive processes, luminosity DIS polarized proton beams, polarized proton collider polarized pp Ruizhe Yang

  5. Transversity Distribution Function Well known  Known Poorly constrained • Quark transversity (dq or h1,DTq) • First mentioned by Ralston and Soper, 1979 • QCD evolution by Mekhfi and Artru, 1990 • Positivity and Soffer bounds: • Model calculations available • Why transversity • Transversity is required to build a complete picture of proton structure • Test quark dynamics (for non-relativistic quark : ) • valence quark observable Ruizhe Yang

  6. Measurement of Transversity + Chiral Even - Chiral Odd Ruizhe Yang

  7. Measurement of transversity in pp Collins FF IFF _ _ + + _ _ + + Drell-Yan IFF Collins Martin,Schafer,Stratmann,VogelsangPRD60:117502 (1999) Jaffe, Jin, Tang, PRL 80 (1999)1166 Yuan, PRD 77, 074019 (2008)  RHIC, FAIR (need very high L, P) RHIC RHIC Ruizhe Yang

  8. Early results Left Right E704: Left-right asymmetries AN for pions: π+ π0 π- Spin structure of transversely polarized proton Define left-right asymetry Theory Expectation:Small asymmetries at high energies (Kane, Pumplin, Repko, PRL 41, 1689–1692 (1978) ) AN ~10-4 from theory Experiment: E704,Fermilab, 1991 AN ~10-1 measured Ruizhe Yang

  9. Possible origins of large AN pQCD Quark Fragmentation Proton Structure Sivers Effect: Correlation between proton spin and quark transverse momentum Collins Effect: Correlation between proton & quark spin + spin dependent fragmentation function Quark transversity Sivers distribution Collins FF D. Sivers, Phys. Rev. D 41, 83 (1990) J. C. Collins, Nucl. Phys.B396, 161 (1993) Ruizhe Yang

  10. Collins mechanism sq sq h q q h • Collins fragmentation function • spin-dependent fragmentation function • an analyzer of the quark spin J. Collins, Nucl. Phys. B396, (1993) 161 A simple model by Artru to illustrate that spin-orbital angularmomentum coupling can lead to left right asymmetriesin spin-dependent fragmentation: String breaks and a dd-pair with spin 1 is inserted. Proton spin is pointing up! L = -1 u-quark absorbs photon/gluon and flips it’s Spin. π+ picks up L=-1 to compensate for pair S=1 and is emittedto the right. Ruizhe Yang

  11. Sivers mechanism • Sivers distribution function • spin-dependent distribution function of quark transverse momentum Sivers, Phys. Rev. D 41, 83 (1990) A semi-claasical picture to explain the Sivers mechanism: Ruizhe Yang

  12. Transversity vs Sivers vs Boer-Mulders Transversity : correlation between transverse proton spin and quark spin Sivers : correlation between transverse proton spin and quark transverse momentum Boer/Mulders: correlation between transverse quark spin and quark transverse momentum Sp– Sq – coupling Sp-- Lq– coupling Sq-- Lq– coupling Ruizhe Yang

  13. Global analysis Ruizhe Yang

  14. Polarized p+p at RHIC Absolute Polarimeter (H jet) RHIC pC Polarimeters Siberian Snakes PHOBOS BRAHMS & PP2PP Siberian Snakes Spin Flipper STAR PHENIX Spin Rotators Partial Snake • 2008 Run • Large transverse data sample collected • 2009 Run • Excellent performance during first 500 GeV run at RHIC ~10 pb-1 Helical Partial Snake Strong Snake Polarized Source LINAC AGS BOOSTER 200 MeV Polarimeter Rf Dipole AGS Internal Polarimeter AGS pC Polarimeter Ruizhe Yang

  15. PHENIX Detector at RHIC Process Contribution to 0, η=0, s=200 GeV • Central Arms | η | < 0.35 • Identified charged hadrons • Neutral Pions • 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 Pion’s • Eta’s • ZDC |h| ~ 5.9 • Neutrons Ruizhe Yang

  16. Cross section measurement 0 Cross-Sections at h ~ 0 • Compare with pQCD calculation • Agreement at 200 GeV (RHIC) • Agreement at 62.4 GeV (RHIC) de Florian, Vogelsang, WagnerPRD 76,094021 (2007) Bourrely and SofferEur.Phys.J.C36:371-374 (2004) Ruizhe Yang

  17. Single spin asymmetries at mid-rapidity p0/h+/h- • First transverse measurement from data taken in 2002 • Integrated luminosity 0.15 pb-1, polarization 15% • Both were improved dramatically in recent years • Processes dominant by gg and qg • Useful to constrain gluon Sivers effect PRL 95, 202001 (2005) |h| < 0.35 Ruizhe Yang

  18. Single spin asymmetries at mid-rapidity sea Sivers(max) + valence Sivers valence Sivers only Max gluon Sivers contribution allowed by PHENIX datawhen sea + valence Sivers at 0 Max gluon Sivers contributionallowed by PHENIX datawhen sea Sivers at max gluon Sivers (theoretical max, simple positivity bound) • Use PHENIX p0 AN to constrain gluon Sivers function • Asymmetries from gluon Sivers function at percent level • More data would put stronger constraint Anselmino et al, Phys. Rev. D 74, 094011 AN Ruizhe Yang

  19. Single spin asymmetries at mid-rapidity • More data from 2008 transverse running • 20x smaller statistical uncertainty • Strong constraint on gluon Sivers function • Added eta results h+/h- pT Ruizhe Yang

  20. Asymmetries at forward rapidity p0/photon Decay photonπ0Direct photon fraction xF • Significant asymmetries observed at forward rapidity, rise as a function of xF •  valence quark effect • No asymmetries at backward rapidity •  sea quark effect • Observed clusters in forward calorimeters are p0 and photons Ruizhe Yang

  21. Asymmetries at forward rapidity • pT dependence • Theoretical expectation for the asymmetries at pT = 0 and pT = ∞ are 0 • Need more statistics at high pT • Fraction of direct photon increases at high pT Decay photonπ0Direct photon fraction pT Ruizhe Yang

  22. Asymmetries at forward rapidity h+/h- • Measured sample of h+/h- is a mixture of p and K • Roughly equal amount of p- and K- lead to 0 asymmetry in h- • Non-zero asymmetry seen in high xF bin • Covers smaller xF range and higher pT range compared to BRAHMS Ruizhe Yang

  23. Asymmetries at forward rapidity • Currently large uncertainties in pT dependence, need more statistics Ruizhe Yang

  24. Asymmetry from di-hadron production IFF _ + _ + • Measure di-hadron asymmetry with hadron pairs in central arm (0,h+) (0,h-), (h+,h-) • Asymmetry is a product of the transversity distribution and a spin-dependent di-hadron fragmentation function (Interference Fragmentation Function, or IFF) • Transversity extraction will become possible with Interference Fragmentation Function (measurement at BELLE) • Alternative approach to transversity • quark transverse momentum integrated out  no contribution from Sivers Ruizhe Yang

  25. Comparison of IFF and Collins FF h1 h2 Quark spin _   quark quark h1 h2 Collins fragmentation function h _   quark quark h (courtesy A. Bacchetta) Interference fragmentation function J. Collins, S.Heppelmann, G. Ladinsky, Nucl. Phys. B, 420 (1994) 565 Requires knowledge on quark kinematics J. Collins, Nucl. Phys. B396, (1993) 161 Ruizhe Yang

  26. Asymmetry from di-hadron production No significant asymmetries seen at mid-rapidity. Added statistics from 2008 running Ruizhe Yang

  27. Asymmetry from di-hadron production No significant asymmetries seen at mid-rapidity. Added statistics from 2008 running Ruizhe Yang

  28. Transversity from di-hadron SSA Physics asymmetry IFFmeasured in e+e- Di-hadron FF to be measured in e+e- Unpolarized quark distribution Known from DIS Hard scattering cross sectionfrom pQCD Transversity to be extracted Ruizhe Yang

  29. IFF measurement at BELLE BELLE preliminary results, A. Vossen, Dubna 2009 • Model prediction by Jaffe, Jin, Tang, Phys.Rev.Lett. 80(1998)1166 (sign change at 780 MeV), needs to be revised • Compare to model calculation (shown in red) by Bacchetta,Checcopieri, Mukherjee, Radici, Phys.Rev.D79:034029,2009 • Mass dependence : Magnitude at low masses comparable, high masses significantly larger (some contribution possibly from charm ) • z dependence : Rising behavior steeper Ruizhe Yang

  30. Sivers effect in di-jet production df Azimuthal distribution of Di-Jet production in ppBoer and Vogelsang, PRD 69, 094025 (2004) Counts Proton SpinkT Beam is in and out of pageLook at back-to-back jet opening angles df Sensitive to Sivers function only! No Collins-type effects Sivers distribution Ruizhe Yang

  31. Sivers effect in di-hadron production p0 h+/- Sivers For comparison Similar analysis possible in different combinations of rapidity • PHENIX Result from 2006 data: • Di-hadrons at central rapidities • Asymmetry consistent with zero • Analysis with large 2008 data in progress (Work in progress) Ruizhe Yang

  32. Sivers effect in heavy flavor production Measurement for m- D (m-) • D meson production dominated by gluon-gluon fusion at RHIC energy • Sensitive to gluon Sivers effect • AN measured for muons from D decay • Smear by decay kinematics Gluon Sivers=Max Gluon Sivers=0 Calculations for D mesons Anselmino et al, PRD 70, 074025 (2004) Ruizhe Yang

  33. Sivers effect in J/Y production • Exploratory measurement of AN J/Psi • J/Y production mechanism not well understood • Single spin asymmetries may shed light on production mechanism • Constraints on gluon Sivers function Yuan, PRD78:014024,2008 AN xF (Yuan) Ruizhe Yang

  34. PHENIX detector upgrades Vertex Detectors (2011-2012) |h| < 2.4 Heavy flavor tagging Separation of c/b Jet measurement Forward Calorimetery (2012-2013) 1 < |h| < 3 AN 0, Direct γ, Sivers γ-Jet Collins-type analyses Ruizhe Yang

  35. Drell-Yan and transverse spin • Double spin asymmetry ATT in Drell-Yan • Theoretically clean channel to transversity measurements • Small asymmetry suppression by sea quark transversity • Small cross section • Boer-Mulders function • Measure azimuthal distribution in Drell-Yan pair production • Possible as demonstrated by E866 • Sivers • The next milestone in RHIC Spin Plan • Important test of QCD Ruizhe Yang

  36. Sivers effect in SIDIS vs Drell Yan Attractive vs Repulsive Sivers Effects Unique Prediction of Gauge Theory Simple QED example: Drell-Yan: repulsive DIS: attractive Same inQCD: As a result: Ruizhe Yang

  37. Experiment SIDIS vs Drell Yan: A fundamental test: Sivers|DIS= − Sivers|DY HERMES Sivers Results RHIC II Drell Yan Projections 0 Sivers Amplitude M. Diefenthaler arXiv:0706.2242 (final results from HERMES just released arXiv:0906.3918) 0 0.1 0.2 0.3 x Ruizhe Yang

  38. Drell-Yan measurement at PHENIX cc bb Bland et al, Transverse Spin Drell-Yan Physics, 2007 Drell-Yan J/  ’ Isolation needed to discriminate open heavy flavor from DY, and is possible at PHENIX with forward vertex detector upgrades. Ruizhe Yang

  39. Asymmetry in photon + jet • Azimuthal asymmetry in photon + jet production at forward rapidity • Convolution of Sivers function and unpolarized PDF Bacchetta et al, PRL 99:212002 (2007 ) gluon Sivers max Boer-Mulders valence quark Sivers Sivers|DIS= − Sivers|DY Ruizhe Yang

  40. Single spin asymmetry in heavy flavor D (m) • Important probe for gluon Sivers function • Calculation for open charm available • With forward vertex detector upgrade, D meson production can be tagged on an event-by-event basis  significantly reduce systematic uncertainty of single spin measurement Anselmino et al, Phys. Rev. D 70, 074025 (2004) Ruizhe Yang

  41. Collins effect with jet measurement • Azimuthal asymmetry of hadron production inside a jet • Knowing quark kinematics  clean separation from Sivers effect F. Yuan, PRL 100:032003 (2008) Ruizhe Yang

  42. W boson measurement at PHENIX Prototype RPC MuTRG MuTRG • Ongoing detector upgrades for W measurements in the next few years • Fast online measurement of muon momenta to trigger W events • Demonstrated detector performance during 2009 running absorber W+ (m+) W- (m-) Ruizhe Yang

  43. W physics at PHENIX • Main physics goal is sea quark polarization (longitudinal) • Unpolarized ratio of W+/W- provides insight to sea quark asymmetry W+/W- l+/l- RHIC Spin Plan 2008 R. Yang, J.C. Peng, M. Grosse-Perdekamp, PLB 680 (2009) 231 Ruizhe Yang

  44. Transverse single spin asymmetry of W • Non-zero SSA predicted • Tests universality of the Sivers function: Sivers|DIS= − Sivers|DY • No contamination from Collins-like effect • Dilution from lepton decay • Sharp peak of lepton asymmetry at 40 GeV Z.B. Kang, J.W. Qiu, PRL 103:172001 (2009) Ruizhe Yang

  45. Transverse single spin asymmetry of W • Non-zero SSA predicted • Tests universality of the Sivers function: Sivers|DIS= − Sivers|DY • No contamination from Collins-like effect • Dilution from lepton decay • Sharp peak of lepton asymmetry at 40 GeV Z.B. Kang, J.W. Qiu, PRL 103:172001 (2009) Ruizhe Yang

  46. Summary and outlook Figure of merit : LP2 (pb-1) Future high luminosity transverse running at RHIC (after 2011) PHENIX upgrades FOCAL 1 < |h| < 3 (2011) FVTX |h| < 2.4 (2012) • Heavy flavor • Precise measurement of Collins effect • g-jet • Drell-Yan Ruizhe Yang

  47. Ruizhe Yang

  48. Ruizhe Yang

  49. All DFs including TMDs q(x) Unpolarized DF helicity DF Transversity DF Dq(x) dq(x) Sivers function Boer-Mulders function Ruizhe Yang

  50. Transverse Momentum Dependence in Hard Scattering: Example Inclusive Hadron Production in Deep Inelastic Scattering (SIDIS) e- current quark jet e- spectator system proton k’ k jet-axis hadron, z Spin & Transverse Momentum Energy & Momentum Ruizhe YangProton Spin Structure with Polarized p-p

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