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RHIC-Spin: Results and Outlook

RHIC-Spin: Results and Outlook. KEK Workshop on High-Energy Hadron Physics with Hadron Beams January 7, 2010 Yuji Goto (RIKEN/RBRC). Outline. Longitudinal-spin asymmetry measurement Collinear (spin) structure of the nucleon gluon-spin contribution to the nucleon spin

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RHIC-Spin: Results and Outlook

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  1. RHIC-Spin:Results and Outlook KEK Workshop on High-Energy Hadron Physics with Hadron Beams January 7, 2010 Yuji Goto (RIKEN/RBRC)

  2. Outline • Longitudinal-spin asymmetry measurement • Collinear (spin) structure of the nucleon • gluon-spin contribution to the nucleon spin • sea-quark contribution (with weak boson measurement) • Transverse-spin asymmetry measurement • Multi-dimensional (spin) structure • orbital angular momentum inside the nucleon

  3. RHIC

  4. RHIC polarized proton-proton collider BRAHMS & PP2PP PHOBOS Absolute Polarimeter (H jet) RHIC pC Polarimeters PHENIX Full Helical Siberian Snakes STAR Spin Rotators Spin Rotators Pol. H- Source LINAC BOOSTER Partial Solenoidal Snake rf Dipole AGS Warm Partial Helical Siberian Snake 200 MeV Polarimeter AGS Internal Polarimeter AGS pC Polarimeters Cold Partial Helical Siberian Snake

  5. RHIC runs(PHENIX data sets) • Longitudinal-polarization runs • Transverse-polarization runs

  6. RHIC performance (from slides shown by Thomas Roser at RHIC Retreat 2009)

  7. RHIC runs • 200-GeV program • gluon polarization measurement (almost) achieved in 2006 • 1st stage program to be done in 2009 (+ another run) by more statistics and more variety of data for gluon polarization • 500-GeV program • started in 2009 for sea-quark polarization measurement with weak boson • Production run will start in 2011 • 3/4 longitudinal-spin & 1/4 transverse-spin

  8. PHENIX and STAR • STAR detector • 2 coverage for jet measurement • barrel TPC and EMC • endcap EMC • PHENIX detector • limited acceptance • high resolution central EMCal • high-rate trigger and DAQ • forward muon detectors

  9. Longitudinal-spin asymmetries • Gluon-spin contribution to the nucleon spin • Sea-quark spin contribution • with weak boson measurement

  10. Double-helicity asymmetries • Comparison with GRSV model with different gluon polarization Midrapidity jet at STAR Midrapidity 0 at STAR GRSV: NLO pQCD calculation by Gluck, Reya, Stratmann and Vogelsang, PRD 63, 094005 (2001).

  11. Double-helicity asymmetries Comparison with GRSV model with different gluon polarization 0 Midrapidity 0 at s = 200 GeV PRL103, 012003 (2009). Midrapidity 0 at s = 62.4 GeV PRD79, 012003 (2009).

  12. Gluon spin contribution - results • GRSV-std [g = 0.4 at Q2 = 1 (GeV/c)2] rejected on more than 3-sigma level • Strong constraints for gluon-spin contribution to explain remaining part of the nucleon spin Midrapidity jet at STAR Midrapidity 0 at PHENIX

  13. Global analysis result de Florian, Sassot, Stratmann and Vogelsang, PRL 101, 072001 (2008). • New analysis by DSSV • PHENIX + STAR + SIDIS + DIS • Smaller g than GRSV-std [g = 0.4 at Q2 = 1 (GeV/c)2] • Strong constraint on the size of g(x) for 0.05 < x < 0.2 by the RHIC data

  14. Gluon spin contribution - plan • 2009 run (+ another run?) • Correlation channel: jet-jet at STAR • better constraint on parton scattering kinematics East Barrel + Endcap West Barrel + Endcap East + East & West + West East Barrel + West Barrel

  15. Gluon spin contribution - plan PHENIX upgrades VTX silicon vertex tracker inclusive jet open charm correlation channels better constraint on parton scattering kinematics jet + jet / jet + photon barrel VTX to be installed in 2010

  16. Sea-quark polarization - introduction • Large uncertainty in anti-quark polarization • Weak boson measurement • Parity-violating asymmetry at forward rapidity at backward rapidity

  17. Sea-quark polarization - introduction • Uncertainty and yield of lepton • W- l- at backward rapidity • sensitive to anti-u quark polarization • W+  l+at midrapidity • sensitive to anti-d quark polarization

  18. 2009 RHIC Run • s = 500 GeV run started • Sea-quark polarization measurement started • midrapidity W+ e+measurement midrapidity positron yield at PHENIX midrapidity e+/e- yieldat STAR

  19. RPC2 RPC1(a,b) RPC2 RPC3 RPC3 Sea-quark polarization - plan Muon tracker FEE • PHENIX plan • Muon-trigger upgrade • muon tracker FEE • RPC Central arm W+ e+measurement from 2009 run Muon arm measurement with muon-trigger upgrade from 2011 70 & 300 pb-1 300 & 1300 pb-1 • anti-d quark pol • anti-d quark pol • anti-u quark pol

  20. Sea-quark polarization – plan • STAR plan • FGT upgrade • Forward GEM Tracker • e+/e- separation Barrel EMC W+ e+measurement from 2009 run Endcap measurement with FGT upgrade from 2011 300 pb-1 300 pb-1

  21. Transverse-spin - introduction Multi-dimensional structure of the nucleon Orbital angular momentum inside the nucleon Shape of the nucleon quark distribution with parallel spin to the nucleon quark distribution with anti-parallel spin to the nucleon direction of nucleon spin NSAC Long Range Plan arXiv:0809.3137 G. A. Miller, PRC68, 022201(R) (2003)

  22. Transverse-spin - results Forward rapidity 0 at STAR at s = 200 GeV Forward identified particles at BRAHMS +  Forward rapidity 0 at PHENIX at s = 62.4 GeV K p

  23. Transverse-spin - results • Results at forward rapidity • Explained as a mixture of Sivers effect, Collins effect, and higher-twist effect • Why similar asymmetry on K+ (valence+sea) and K- (sea+sea)? • Why large asymmetry on anti-proton? • How to distinguish Sivers effect? • Back-to-back jet • How to separate initial-state and final-state interaction with remnant partons? • Forward photon + jet • Drell-Yan process

  24. 2 0  h Transverse-spin - results • Back-to-back jet at STAR • Sensitive to the Sivers effect, but no asymmetry measured even in kinematic region sensitive to the polarized-quark scattering • Initial-state and final-state interaction with remnant partons • Different sign • attractive or repulsive • Cancellation of both effect • (Cancellation of u and d quarks, too)

  25. Forward photon + jet • Sivers effect only with initial-state interaction (repulsive only) • Higher yield can be obtained • STAR forward photon measurement with FMS (Forward Meson Spectrometer) and Endcap EMC • PHENIX forward photon measurement with MPC(Muon Piston Calorimeter) and possible forward calorimeter upgrade (FOCAL) • no process • dependence A. Bacchetta et al., • PRL 99, 212002 (2007). • AN in photon+jet production forward photon η > 2 • jet -1 < η < 0 • NSAC milestone for transverse spin (HP13, 2015) • correct process • dependence

  26. Summary • Polarized proton-proton collision • Complementary to the polarized DIS • Longitudinal-spin asymmetry measurement at RHIC • g measured in RHIC 200-GeV program • small to explain remaining part of the nucleon spin • correlation channel for better constraint on parton scattering kinematics • Sea-quark polarization with weak-boson measurement in RHIC 500-GeV program started from 2009 • detector upgrades underway for production runs from 2011 • for better precision of  and g • Transverse-spin asymmetry measurement at RHIC • Multi-dimensional structure of the nucleon • related to the orbital angular momentum inside the nucleon & shape of the nucleon • Important role of initial-state and final-state interaction with remnant partons inside the nucleon • forward photon+jet and Drell-Yan process

  27. Backup Slides

  28. Introduction Origin of the nucleon spin 1/2 ? Polarized DIS experiments Virtual-photon - quark scattering EMC experiment at CERN total quark spin constitutes a small fraction of the nucleon spin integration in x = 0 ~ 1 makes uncertainty more data to cover wider x region with more precise data necessary SLAC/CERN/DESY/JLAB experiments Polarized proton-proton collision quark-quark + quark-gluon + gluon-gluon scatterings sensitive to the gluon RHIC polarized proton-proton collider experiments perturbative QCD applicable sea-quark with weak boson measurement “proton spin crisis”

  29. FNAL-E704 • Longitudinal-spin asymmetry measurement • Double-helicity asymmetry • For g: gluon-spin contribution • s = 19.4 GeV • low statistics • applicability of perturbative QCD questionable to extract the gluon-spin contribution from the asymmetry data ALL(0): PLB 261 (1991) 197. ALL(multi-): PLB 336 (1994) 269.

  30. FNAL-E704 • Transverse-spin asymmetry measurement • Left-right asymmetry • Large asymmetries discovered at forward rapidity • no large asymmetry expected at this “high energy” • AN mq / s • development of many models based on perturbative QCD

  31. 2009 RHIC Run (Run-9) s = 500 GeV run started Lpeak = 9.6×1031 cm-2s-1 Lave = 10 pb-1 / week (as of April 2) Sea-quark polarization central arm W+ e+measurement at PHENIX from Run9 Gluon polarization lower x coverage x < 0.02 70 & 300 pb-1 • anti-d quark pol

  32. Cross sectionmeasurements • Applicability of NLO perturbative QCD • Used for polarized measurement Midrapidity 0 at PHENIX Midrapidity jet at STAR

  33. Cross section measurements Forward rapidity 0 at STAR for transverse-spin asymmetry measurement Midrapidity direct-photon at PHENIX for gluon polarization measurement in the future

  34. lepton beam g*  or  heavy flavor gluon  or  nucleon target Gluon spin contribution - introduction • Scaling violation in polarized DIS • spanning a limited range of Q2 • Semi-inclusive DIS • high-pT hadron pairs • open charm production B. Adeba et al., PRD 58, 112002 (1998). P.L. Anthony et al., PLB 493, 19 (2000).

  35. proton beam  or  gluon photon  or  proton beam proton beam  or  gluon heavy flavor gluon  or  proton beam Gluon spin contribution - introduction • Polarized proton collision • Double-helicity asymmetries of 0 and jet direct photon production heavy-flavor production gg + qg dominant sensitive to the gluon reaction

  36. Gluon spin contribution - results G constraint strong constraint of G as found by DSSV from s = 200 GeV 0 ALL results (0.02 < x < 0.3) constraint at 3 of -0.7 < G[0.02,0.3] < 0.5 is nearly shape independent other probes also will constrain G, and be used in future global fits Midrapidity 0 at s = 200 GeV PRL103, 012003 (2009).

  37. Transverse-spin - introduction Extension of distribution functions GPD (Generalized Parton Distribution) and TMD (Transverse-Momentum Dependent) distribution M. Diehl, Trento workshop, June 2007

  38. TMD functions (and transversity) u-quark u-quark d-quark d-quark Sivers function: correlation between nucleon transverse spin and parton transverse momentum (kT) Transversity: correlation between nucleon transverse spin and parton transverse spin Boer-Mulders function: correlation between parton transverse spin and parton transverse momentum (kT)

  39. Transverse-spin - results • Results at forward rapidity • Explained as a mixture of Sivers effect, Collins effect, and higher-twist effect • Why similar asymmetry on K+ (valence+sea) and K- (sea+sea)? • Why large asymmetry on anti-proton? • PHENIX 0 at midrapidity • Constraints on gluon Sivers distribution M. Anselmino, et al., PRD 74, 094001 (2006)

  40. Sivers function measurement Sign of Sivers function determined by single transverse-spin (SSA) measurement of DIS and Drell-Yan processes Should be opposite each other Initial-state interaction or final-state interaction with remnant partons Test of TMD factorization Explanation by Vogelsang and Yuan… From “Transverse-Spin Drell-Yan Physics at RHIC,” Les Bland, et al., May 1, 2007 DIS Drell-Yan “toy” QED attractive repulsive QCD

  41. Sivers function measurement < 1% level multi-points measurements have already been done for SSA of DIS process comparable level measurement needs to be done for SSA of Drell-Yan process for comparison

  42. Drell-Yan at RHIC Statistically limited due to the small yield of the Drell-Yan process Large background from b-quark b-quark Drell-Yan • “Transverse-Spin Drell-Yan Physics at RHIC,” Les Bland, et al., May 1, 2007

  43. Summary • Polarized proton-proton collision • Complementary to the polarized DIS • Longitudinal-spin asymmetry measurement at RHIC • g measured in RHIC 200-GeV program • small to explain remaining part of the nucleon spin • Sea-quark polarization with weak-boson measurement in RHIC 500-GeV program started from 2009 • for better precision of  and g • Transverse-spin asymmetry measurement at RHIC • Multi-dimensional structure of the nucleon • related to the orbital angular momentum inside the nucleon & shape of the nucleon • Important role of initial-state and final-state interaction with remnant partons inside the nucleon

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