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

January 7, 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

January 7, RHIC

January 7, RHIC polarized proton-proton collider BRAHMS & PP2PP STAR PHENIX AGS LINAC BOOSTER Pol. H - Source Spin Rotators 200 MeV Polarimeter AGS Internal Polarimeter rf Dipole RHIC pC Polarimeters Absolute Polarimeter (H  jet) AGS pC Polarimeters Cold Partial Helical Siberian Snake Warm Partial Helical Siberian Snake PHOBOS Spin Rotators Full Helical Siberian Snakes Partial Solenoidal Snake

January 7, RHIC runs (PHENIX data sets) Longitudinal-polarization runs Transverse-polarization runs

January 7, RHIC performance (from slides shown by Thomas Roser at RHIC Retreat 2009)

January 7, RHIC runs 200-GeV program –gluon polarization measurement (almost) achieved in 2006 –1 st 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 /4 longitudinal-spin & 1/4 transverse-spin

January 7, 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

January 7, Longitudinal-spin asymmetries Gluon-spin contribution to the nucleon spin Sea-quark spin contribution –with weak boson measurement

January 7, 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, (2001).

January 7, Double-helicity asymmetries Comparison with GRSV model with different gluon polarization Midrapidity  0 at  s = 200 GeV PRL103, (2009). 00 Midrapidity  0 at  s = 62.4 GeV PRD79, (2009).

January 7, Gluon spin contribution - results GRSV-std [  g = 0.4 at Q 2 = 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

January 7, Global analysis result New analysis by DSSV –PHENIX + STAR + SIDIS + DIS –Smaller  g than GRSV-std [  g = 0.4 at Q 2 = 1 (GeV/c) 2 ] –Strong constraint on the size of  g(x) for 0.05 < x < 0.2 by the RHIC data de Florian, Sassot, Stratmann and Vogelsang, PRL 101, (2008).

January 7, Gluon spin contribution - plan 2009 run (+ another run?) –Correlation channel: jet-jet at STAR better constraint on parton scattering kinematics East Barrel + Endcap East Barrel + West Barrel East + East & West + West West Barrel + Endcap

January 7, 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

January 7, Sea-quark polarization - introduction Large uncertainty in anti-quark polarization Weak boson measurement –Parity-violating asymmetry at forward rapidityat backward rapidity

January 7, 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

January 7, RHIC Run  s = 500 GeV run started Sea-quark polarization measurement started –midrapidity W +  e + measurement midrapidity positron yield at PHENIXmidrapidity e+/e- yield at STAR

January 7, Sea-quark polarization - plan 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 RPC1(a,b)RPC2 RPC3 Muon tracker FEE 70 & 300 pb -1 anti-d quark pol anti-u quark polanti-d quark pol 300 & 1300 pb -1

January 7, 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 pb -1

January 7, Transverse-spin - introduction Multi-dimensional structure of the nucleon –Orbital angular momentum inside the nucleon –Shape of the nucleon direction of nucleon spin quark distribution with parallel spin to the nucleon quark distribution with anti-parallel spin to the nucleon NSAC Long Range Plan arXiv: G. A. Miller, PRC68, (R) (2003)

January 7, Transverse-spin - results  ++ KK p Forward rapidity  0 at STAR at  s = 200 GeV Forward identified particles at BRAHMS Forward rapidity  0 at PHENIX at  s = 62.4 GeV

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 January 7,

January 7, 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) 00 22  h

January 7, 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) A. Bacchetta et al., PRL 99, (2007). A N in photon+jet production forward photon η > 2 jet -1 < η < 0  NSAC milestone for transverse spin (HP13, 2015)  no process dependence  correct process dependence

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 January 7,

Backup Slides

January 7, 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”

January 7, 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 A LL (  0 ): PLB 261 (1991) 197. A LL (multi-  ): PLB 336 (1994) 269.

January 7, FNAL-E704 Transverse-spin asymmetry measurement –Left-right asymmetry –Large asymmetries discovered at forward rapidity no large asymmetry expected at this “high energy” –A N  m q /  s development of many models based on perturbative QCD

January 7, RHIC Run (Run-9)  s = 500 GeV run started –L peak = 9.6×10 31 cm -2 s -1 –L ave = 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 < & 300 pb -1 anti-d quark pol

January 7, Cross section measurements Applicability of NLO perturbative QCD –Used for polarized measurement Midrapidity  0 at PHENIX Midrapidity jet at STAR

January 7, 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

January 7, Gluon spin contribution - introduction Scaling violation in polarized DIS –spanning a limited range of Q 2 Semi-inclusive DIS –high-p T hadron pairs –open charm production lepton beam  or  nucleon target ** gluon heavy flavor B. Adeba et al., PRD 58, (1998). P.L. Anthony et al., PLB 493, 19 (2000).

January 7, Gluon spin contribution - introduction Polarized proton collision Double-helicity asymmetries of  0 and jet proton beam  or  gluon photon proton beam  or  gluon heavy flavor direct photon productionheavy-flavor production gg + qg dominant sensitive to the gluon reaction

January 7, Gluon spin contribution - results  G constraint –strong constraint of  G as found by DSSV –from  s = 200 GeV  0 A LL 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, (2009).

January 7, Transverse-spin - introduction Extension of distribution functions –GPD (Generalized Parton Distribution) and TMD (Transverse-Momentum Dependent) distribution M. Diehl, Trento workshop, June 2007

January 7, TMD functions (and transversity) Sivers function: correlation between nucleon transverse spin and parton transverse momentum (k T ) Transversity: correlation between nucleon transverse spin and parton transverse spin Boer-Mulders function: correlation between parton transverse spin and parton transverse momentum (k T ) u-quark d-quark u-quark d-quark

January 7, 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, (2006)

January 7, DISDrell-Yan “toy” QED QCD attractiverepulsive 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

January 7, 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

January 7, Drell-Yan at RHIC b-quark Drell-Yan “Transverse-Spin Drell-Yan Physics at RHIC,” Les Bland, et al., May 1, 2007 Statistically limited due to the small yield of the Drell-Yan process –Large background from b-quark

January 7, 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