Review of DG in DIS and pp a lot has happened since Kyoto Frank EllinghausUniversity of Mainz / University of Colorado

October 2008SPIN08, Charlottesville, USA

In the beginning.

Electron polarization transfers to virtual photonsCompare DIS cross sections with aligned and antialigned ep spins~g1 (proton) > 0-> Larger cross section for anti-aligned ep Spins -> Higher probability for aligned quark-proton SpinsPolarize electrons and nucleons (started in mid 1970s at SLAC)G. Baum et al, PRL 51, 1983

Results from Inclusive Polarized DISAnalogous to unpolarized (F2) case, g1 can be used to fit polarized PDFs:Result: Quarks carry only 30% of the nucleon spin (0.3) HERMES: PRD 75:012007 (2007) COMPASS: PLB 647:8 (2007)

Gluon contribution G not well constrained due to small range in xB,Q2 (no polarized ep collider)try DIRECT measurements ->

DG via direct measurement in DISPhoton-Gluon Fusion: g* g -> qqbar ccbar production, detect D-mesons, hard scale provided by charm mass, clean channel (low BG), statistically limited detect hadrons (or hadron pairs) with Q2>1 GeV2(hard scattering) More BG sources with difficult to determine or/and model-dependent fractions and asymmetries. Larger sample detect hadrons (or hadron pairs) using all Q2 Even more BG sources with difficult to determine or/and model-dependent fractions and asymmetries. Largest sample

Fixed Target DISBeam: 27.6 GeV e+/e-; 50-55% polarization

Target: H, D 80-85% polarization

The golden channel2002-2004 analysis: hep-ex/0802.2160F. KunneTuesday2002-2006 preliminary analysis: tagged D0

COMPASS: Hadron Pairs, Q2 > 1 (GeV/c)2LEPTO with JETSET tuned to data pT>0.7 GeV/c for both hadrons increases PGF contr. Q2 > 1 (GeV/c)2 provides hard scale At least two add. subprocesses to be considered500k eventsK. KurekTuesday

COMPASS: Hadron Pairs, Q2 < 1 (GeV/c)2PYTHIAAdd. Sensitivity to DG, but polarized PDFs of photon unmeasured pT>0.7 GeV/c for both hadrons increases PGF contr. S pT2 > 2.5 (GeV/c)2 provides hard scale Add. contr. (about 50%) from resolved-photon processes PGFQCDCLOPLB 633 (2005) 25preliminary

HERMES, hadrons, all Q2 PYTHIA (tuned to data)

Summary Direct DIS measurementsg/g=0 is likely small with unknown sign!

RHIC @ BNLRelativistic Heavy Ion Collider also provides longitudinally and transverselypolarized proton beams at s = 200 GeV, 62.4 GeV, (500 GeV, 2009+)Polarimeter (H jet)Spin RotatorsSiberian Snakes

PHENIX and STARLarge acceptanceAzimuthal symmetryHigh rate capabilityLimited acceptance

PHENIX longitudinally polarized pp Runs(Similar numbers for STAR. Experiments can separately choose longitudinal or transverse polarization.)

DG via direct measurement in ppAccess to polarized gluon distribution function via double helicity asymmetry in inclusive polarized pp scattering, e.g.,

from DISpQCD, fragmentation fcts.

First: Check unpolarized case!Using a set of unpolarized PDFs ( + fragmentation functions in case of hadron (p0) production) the cross section agrees with NLO pQCD calculations.

STAR -- jetsRun 6 preliminaryRun 5 (2005): PRL 100, 23 (2008) DG = G(x), -G(x) excluded; GRSV-std excluded with 99% CLRun 6 preliminaryM. SarsourFriday No inconsistency with DIS data due to generally large uncertainties on Dg(x). Small or negative gluon contribution to nucleon spin favored in this model. Data also consistent with GS-C ->

Model dependence of DG Measurement averages over certain x range Shape of DG(x) cannot be extracted -> Value for first moment model dependent

PHENIX -- p0 at 200 GeVRun 5: Phys.Rev.D76:051106,2007Run 6: arXiv:0810.0694GRSV: Glueck et al., PRD 63 (2001) DG = G(x), -G(x) excluded; GRSV-std slightly disfavoredK. NakanoTuesdayRun 5 + Run 6

STAR p0, PHENIX h, PHENIX J/PsiPHENIX h excludes DG = G(x), -G(x)J. Seeletoday

p+, p , p0 and the sign of DGEspecially in the region where qg scattering is dominant (pT > 5 GeV),the increasing contribution of d quarks (Dd

Charged hadrons at STARA. Kocoloskitoday

Direct Photons at s=200 GeVRun-5At the end of the day all these (and the DIS, SIDIS) asymmetry data need to go into a global QCD fit in order to extract DG! ->

-> small unc. from FFs-> better access to sign of DG (Dq times DG)Theoretically clean Golden Channel is luminosity hungryDominated by qg Compton:R. Bennetttoday

First pol. PDF extraction using pp dataDSSV, arXiv: 0804.0422First global (DIS+SIDIS+pp) analysis!DG small in measured range (0.05 < x< 0.2).Contribution at small or large x?M. StrattmannTuesday

At fixed xT = 2pT/sqrt(s) cross-section is 2 orders of magnitude higher at 62.4GeV than at 200GeVSignificant result at high xT from small data set at 62.4 GeV (0.04 pb-1) when compared to 200 GeV data (1.8pb-1)pQCD applicable for pT > 2 GeV/c

Accessing different x-rangesPHENIX: p0 ALL at s=62.4 GeV Increased sensitivity to larger x K. NakanoTuesdayarXiv: 0810.0701

Summary & OutlookPHENIX and STAR data provided a significant constraint on the polarized gluon PDF in a global QCD fit to all DIS, SIDIS and pp data -> DG(x) small in measured range (0.05 < x < 0.2)Direct measurements by HERMES+COMPASS support this finding with somewhat larger uncertainties.No sensitivity to shape of DG(x) -> all the missing spin can still be at smaller x.

HERMES: final word (long paper) soonCOMPASS: Open Charm: Add 2007 data (small improvement) High-pT hadrons, Q2>1 (GeV/c)2: Add 2006+2007 data (significant improvement)PHENIX+STAR: Different beam energies (500 GeV, 2009+) and rapidities will give access to an order of magnitude smaller x Correlation measurements will provide sensitivity to shape of DG(x)