Review of  G in DIS and pp … a lot has happened since Kyoto Frank Ellinghaus University of Mainz / University of Colorado October 2008 SPIN’08, Charlottesville, USA

Frank Ellinghaus, Spin’08, Charlottesville e-p Spins antialigned In the beginning…. –Electron polarization transfers to virtual photons –Compare DIS cross sections with aligned and antialigned ep spins e-p Spins aligned  ~ g 1 (proton) > 0 -> Larger cross section for anti-aligned ep Spins -> Higher probability for aligned quark-proton Spins Polarize electrons and nucleons (started in mid 1970s at SLAC) G. Baum et al, PRL 51, 1983

Frank Ellinghaus, Spin’08, Charlottesville Results from Inclusive Polarized DIS Analogous to unpolarized (F 2 ) case, g 1 can be used to fit polarized PDFs: Polarized PDFs extracted from fits to g 1 (proton, deuteron) Result: Quarks carry only 30% of the nucleon spin (  0.3) HERMES: PRD 75: (2007) COMPASS: PLB 647:8 (2007) Gluon contribution  G not well constrained due to small range in x B,Q 2 (no polarized ep collider) …try DIRECT measurements ->

Frank Ellinghaus, Spin’08, Charlottesville  G via direct measurement in DIS Photon-Gluon Fusion:  * 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 Q 2 >1 GeV 2 (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 Q 2 Even more BG sources with difficult to determine or/and model-dependent fractions and asymmetries. Largest sample…

Frank Ellinghaus, Spin’08, Charlottesville Fixed Target DIS Beam: 27.6 GeV e+/e-; 50-55% polarization Target: H, D 80-85% polarization 6/30/07 Beam: 160 GeV  ; 75-80% polarization Target: 6 LiD; 50% polarization

Frank Ellinghaus, Spin’08, Charlottesville The “golden” channel D*->D 0  soft analysis: hep-ex/ F. Kunne Tuesday preliminary analysis: “tagged D 0 ”

Frank Ellinghaus, Spin’08, Charlottesville COMPASS: Hadron Pairs, Q 2 > 1 (GeV/c) 2 LEPTO with JETSET tuned to data… p T >0.7 GeV/c for both hadrons increases PGF contr. Q 2 > 1 (GeV/c) 2 provides hard scale At least two add. subprocesses to be considered 500k events K. Kurek Tuesday

Frank Ellinghaus, Spin’08, Charlottesville COMPASS: Hadron Pairs, Q 2 < 1 (GeV/c) 2 PYTHIA Add. Sensitivity to  G, but polarized PDFs of photon unmeasured p T >0.7 GeV/c for both hadrons increases PGF contr.  p T 2 > 2.5 (GeV/c) 2 provides hard scale Add. contr. (about 50%) from resolved-photon processes PGF QCDC LO PLB 633 (2005) 25 preliminary

Frank Ellinghaus, Spin’08, Charlottesville HERMES, hadrons, all Q 2 PYTHIA (tuned to data) Results from different (proton, deuterium) data samples and different event topologies are consistent. Good sensitivity, but model dependent  g/g=0 -> contribution of quarks

Frank Ellinghaus, Spin’08, Charlottesville Summary Direct DIS measurements  g/g=0 is likely small with unknown sign!

Frank Ellinghaus, Spin’08, Charlottesville BNL STAR Relativistic Heavy Ion Collider also provides longitudinally and transversely polarized proton beams at  s = 200 GeV, 62.4 GeV, (500 GeV, 2009+) Polarimeter (H  jet) pC Polarimeters Spin RotatorsSiberian Snakes

Frank Ellinghaus, Spin’08, Charlottesville PHENIX and STAR Large acceptance Azimuthal symmetry High rate capability Limited acceptance

Frank Ellinghaus, Spin’08, Charlottesville PHENIX longitudinally polarized pp Runs Year  s [GeV] Recorded LPol [%]FOM (P 4 L) 2003 (Run-3) pb nb (Run-4) pb nb (Run-5) pb nb (Run-6) pb nb (Run-6) pb nb -1 (Similar numbers for STAR. Experiments can separately choose longitudinal or transverse polarization.)

Frank Ellinghaus, Spin’08, Charlottesville  G via direct measurement in pp Access to polarized gluon distribution function via double helicity asymmetry in inclusive polarized pp scattering, e.g., Invariant mass spectrum of 2 photons in EMCal    (M=135MeV) Measure from DISpQCD, fragmentation fcts. Relative Luminosity R using beam-beam counters

Frank Ellinghaus, Spin’08, Charlottesville First: Check unpolarized case! Using a set of unpolarized PDFs ( + fragmentation functions in case of hadron (  0 ) production) the cross section agrees with NLO pQCD calculations. PHENIX --  0 PRD76:051106,2007 STAR -- jets PRL 97, (2006)

Frank Ellinghaus, Spin’08, Charlottesville STAR -- jets Run 6 preliminary Run 5 (2005): PRL 100, 23 (2008)  G = G(x), -G(x) excluded; GRSV-std excluded with 99% CL Run 6 preliminary M. Sarsour Friday 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 ->

Frank Ellinghaus, Spin’08, Charlottesville Model dependence of  G  g integral between GRSV - 0 GRSV - std GS-C 0<x< <x<0.3 00  0.25 00 Measurement averages over certain x range Shape of  G(x) cannot be extracted -> Value for first moment model dependent

Frank Ellinghaus, Spin’08, Charlottesville PHENIX --  0 at 200 GeV Run 5: Phys.Rev.D76:051106,2007 Run 6: arXiv: GRSV: Glueck et al., PRD 63 (2001)  G = G(x), -G(x) excluded; GRSV-std slightly disfavored K. Nakano Tuesday Run 5 + Run 6

Frank Ellinghaus, Spin’08, Charlottesville STAR –  0, PHENIX –  PHENIX J/Psi PHENIX  excludes  G  = G(x), -G(x) J. Seele today STAR  0 consistent with PHENIX X. Wang Friday A. Hoffman today

Frank Ellinghaus, Spin’08, Charlottesville  +,  –,  0 and the sign of  G Especially in the region where qg scattering is dominant (p T > 5 GeV), the increasing contribution of d quarks (  d<0) leads to: “Model independent” conclusion possible once enough data is available. Fraction of pion production  s=62.4 GeV PHENIX Preliminary A. Datta today A. Morreale Tuesday

Frank Ellinghaus, Spin’08, Charlottesville Charged hadrons at STAR A. Kocoloski today

Frank Ellinghaus, Spin’08, Charlottesville Direct Photons at  s=200 GeV Run-5 At 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  G! -> q  g q -> small unc. from FFs -> better access to sign of  G (  q times  G) Theoretically clean “Golden Channel” is luminosity hungry… Dominated by qg Compton: R. Bennett today

Frank Ellinghaus, Spin’08, Charlottesville First pol. PDF extraction using pp data DSSV, arXiv: First “global” (DIS+SIDIS+pp) analysis!  G small in measured range (0.05 < x< 0.2). Contribution at small or large x? Different ranges in x can be probed in: 500 GeV (2009+, lower x) and 62 GeV running (larger x, larger scale unc.) -> different rapidities -> Strong impact of Star jets and Phenix  0 in measured range. Shape of  G(x) cannot be extracted -> All “missing” spin can be at low x…. Next step: Mapping of x-dependence via di-jets, di-hadrons and gamma-jet M. Strattmann Tuesday

Frank Ellinghaus, Spin’08, Charlottesville At fixed x T = 2p T /sqrt(s) cross-section is 2 orders of magnitude higher at 62.4GeV than at 200GeV Significant result at high x T from small data set at 62.4 GeV (0.04 pb-1) when compared to 200 GeV data (1.8pb-1) pQCD applicable for p T > 2 GeV/c… Accessing different x-ranges PHENIX:  0 A LL at  s=62.4 GeV Increased sensitivity to larger x K. Nakano Tuesday STAR:  0 A LL at forward rapidity Increased sensitivity to smaller x Also: step towards gamma-jet correlation measurements to map out the x-dependence STAR Di-Jet measurements promising T. Sakuma Friday S. Wissink Friday arXiv:

Frank Ellinghaus, Spin’08, Charlottesville Summary & Outlook PHENIX and STAR data provided a significant constraint on the polarized gluon PDF in a global QCD fit to “all” DIS, SIDIS and pp data ->  G(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  G(x) -> all the “missing” spin can still be at smaller x. HERMES: –final word (long paper) soon COMPASS: –Open Charm: Add 2007 data (small improvement) –High-p T hadrons, Q 2 >1 (GeV/c) 2 : Add 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  G(x)