Spin of the proton and its transverse spin structure at RHIC

Spin of the protonand its transverse spin structureat RHICHERMES seminar at Tokyo TechNovember 9, 2005Yuji Goto (RIKEN)

Yuji Goto (RIKEN)

RHIC QCD collider

Yuji Goto (RIKEN)

RHIC polarized-proton collisionLuminosity 11031 cm-2sec-1 at s = 200 GeV achieved81031 cm-2sec-1 at 200 GeV and 21032 cm-2sec-1 at 500 GeV in the futurePolarization 50% achieved 70% in the future

Yuji Goto (RIKEN)

STAR and PHENIX 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

Yuji Goto (RIKEN)

RHIC/PHENIX polarized-proton runs2005 First long longitudinal-spin polarized-proton runFigure of merit (LP4) more than 40 times larger thanthat of previous runs

Yuji Goto (RIKEN)

Where is the proton spin ?Origin of the nucleon spin 1/2polarized DIS experiments showed the quark contribution is only 10-30%gluon contribution ?Scaling violation in polarized DIS

Semi-inclusive DIShigh-pT hadron pairsopen charm productionB. Adeva et al., PRD 58, 112002 (1998).P.L. Anthony et al., PLB 493, 19 (2000).

Yuji Goto (RIKEN)

Gluon contribution ?Polarized hadron collisionleading-order gluon measurement

ALL of 0direct photon productionheavy-flavor productiongg + qg dominantsensitive to the gluon reaction

Yuji Goto (RIKEN)

PHENIX ALL of 0* at input scale Q2 = 0.4 GeV- Run5 conclusively excludes GRSV maximal scenarios.- Data consistent with GRSV standard and GRSV G = 0.GRSV-max: g = 1.84

GRSV-std: g = 0.42at Q2=1(GeV/c)2best fit to DIS data

Theory modelC.L. (%)GRSV-std17.1-21.7*GRSV-max (Dg=g)0.0-0.0*GRSV Dg=016.7-18.4*GRSV Dg=g0.0-0.7

Yuji Goto (RIKEN)

Single transverse-spin asymmetryLeft-right asymmetry

Forward-rapidityFermilab-E704fixed-target experiment at s = 19.4 GeV

Yuji Goto (RIKEN)

STAR forward pionRun2 resultsIn agreement with several models including different dynamics:Sivers: spin and k correlation in initial state (related to orbital angular momentum?)Collins: Transversity distribution function & spin-dependent fragmentation function suppressed? (hep-ph/0408356) Qiu and Sterman (initial-state) / Koike (final-state) twist-3 pQCD calculations

Yuji Goto (RIKEN)

STAR forward pionRun3 resultsPositive AN at large positive xF has been confirmedLarger significance to be non-zero & positive than published dataThe first measurement of negative xF AN has been done, and is consistent with zeroSensitive to twist-3 gluon-gluon correlationStatistical error only for =4.1

Yuji Goto (RIKEN)

STAR outlookDisentangling the dynamics of AN viaHigher precision AN measurement vs xF and pT AN with mid rapidity correlationForward jetProposal for forward calorimeter upgradeHeavy mesons and direct photons Low x gluons in nuclei Mid rapidity jetsDi-jet kT balance gluon Sivers functionInside jet particle correlation Collins function * Transversity

Yuji Goto (RIKEN)

Mid-rapidity at PHENIXDifferent kinematic regionforward-rapidity at STAR (xF > 0.3)quark-gluon reaction dominantlarge contribution from x ~ 0.6 quark polarization/transversitymid-rapidity at PHENIX (xF ~ 0)contribution from both gluon-gluon and quark-gluon reactionsx = 0.03 0.1small quark polarization/transversityno gluon transversity in leading twistnegligible transversity & Collins effect contribution

Yuji Goto (RIKEN)

Mid-rapidity at PHENIXRun2 resultsAN for both 0 and charged hadrons consistent with zero at mid-rapidity~5 times smaller asymmetry than STAR forward-rapidity data (~10%)comparable data with Fermilab-E704 for 0 and charged hadrons

Yuji Goto (RIKEN)

Forward neutron asymmetryPHENIX local polarimeter R&D at IP12

Yuji Goto (RIKEN)

Forward neutron asymmetryHadron CalEM CalAN = 0.1260.0080.041AN = 0.1160.0180.020preliminarypreliminarypreliminaryvery forward neutronAN ~ -12%xF > 0.2pT < 0.3 GeV/c

Yuji Goto (RIKEN)

Local polarimeter at PHENIXLongitudinal component of the proton polarization at PHENIX410 GeV run in 2005analyzing power of local polarimeter roughly the same despite doubling of energy2005 run

Yuji Goto (RIKEN)

Back-to-back jet at PHENIXBoer and Vogelsang find that this parton asymmetry will lead to an asymmetry in the distribution of back-to-back jetsShould also be able to see this effect with fragments of jets, and not just with fully reconstructed jetsBoer and Vogelsang, Phys.Rev.D69:094025,2004

Yuji Goto (RIKEN)

Back-to-back jet at PHENIXMeasurement of the gluon Sivers function via AN for di-hadron angular correlationsSivers distribution is a transverse parton momentum distribution correlated with the nucleons spin axis, which could arise from orbital angular momentumError bars: Expected sensitivity with P=60% and 7 pb-1

Yuji Goto (RIKEN)

Back-to-back jet at STAR

Yuji Goto (RIKEN)

Spin dependence of kT of jetsPossible helicity effectWe may observe net effect (after averaging over impact factor)kT largerkT smallerSame helicityOpposite helicity

Yuji Goto (RIKEN)

Spin dependence of kT of jetsRun3 result: hint of helicity dependence ?not yet sureRun5 data should yield a definite answer.

Yuji Goto (RIKEN)

SummaryRHIC data began to provide restriction to the gluon-spin contribution to the proton spinWe need to know contribution of the orbital angular momentum as the final pieceRHIC has potential measurements of the orbital angular momentum and/or transverse spin structure of the protonsingle transverse-spin asymmetriesSivers effect/function measurementsWe will have some transverse-spin run in 2006

Yuji Goto (RIKEN)

Backup slides

Yuji Goto (RIKEN)

Naohitos analysis

Yuji Goto (RIKEN)

Vertical vs radial run in 2006Boer and Vogelsang, PRD69:094025,2004STST1 = 01 = /21 = 0 :1 = /2 :private communication, Boer and Vogelsang

Yuji Goto (RIKEN)

Spin dependence of kT of jetsBack-to-back nature of jets is broken by initial/final state transverse momentum kT e.g., intrinsic kT, soft gluon radiation

Orbital angular momentum: kT r introduces intrinsic kT in the initial state measurement of jet kT gives an access to parton orbital angular momentum

Yuji Goto (RIKEN)

Transversity at PHENIXTransversity throught +- interference FFnon-vanishing support only in the mass region,

Yuji Goto (RIKEN)

Transversity throught +- interference FFProjected asymmetrySmall aymmetry below5% but good rate! For 32pb-1 (1 week of running)5.2 Million events in 32 pb-115% with pair after cuts

Yuji Goto (RIKEN)