1 / 25

Review of D G in DIS and pp … a lot has happened since Kyoto

Review of D 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. e-p Spins aligned. e-p Spins antialigned. In the beginning….

jeneil
Download Presentation

Review of D G in DIS and pp … a lot has happened since Kyoto

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

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

  2. e-p Spins aligned e-p Spins antialigned In the beginning…. • Polarize electrons and nucleons (started in mid 1970s at SLAC) • Electron polarization transfers to virtual photons • Compare 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 Spins G. Baum et al, PRL 51, 1983 Frank Ellinghaus, Spin’08, Charlottesville

  3. Polarized PDFs extracted from fits to g1(proton, deuteron) Results from Inclusive Polarized DIS • Analogous 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 -> Frank Ellinghaus, Spin’08, Charlottesville

  4. DG via direct measurement in DIS Photon-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… Frank Ellinghaus, Spin’08, Charlottesville

  5. 6/30/07 Beam: 160 GeV m; 75-80% polarization Target: 6LiD; 50% polarization Fixed Target DIS Beam: 27.6 GeV e+/e-; 50-55% polarization Target: H, D 80-85% polarization Frank Ellinghaus, Spin’08, Charlottesville

  6. D*->D0 psoft The “golden” channel “tagged D0” F. Kunne Tuesday 2002-2006 preliminary analysis: 2002-2004 analysis: hep-ex/0802.2160 Frank Ellinghaus, Spin’08, Charlottesville

  7. COMPASS: Hadron Pairs, Q2 > 1 (GeV/c)2 • 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 considered LEPTO with JETSET tuned to data… K. Kurek Tuesday 500k events Frank Ellinghaus, Spin’08, Charlottesville

  8. COMPASS: Hadron Pairs, Q2 < 1 (GeV/c)2 • 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 PYTHIA PGF QCDC Add. Sensitivity to DG, but polarized PDFs of photon unmeasured LO PLB 633 (2005) 25 preliminary Frank Ellinghaus, Spin’08, Charlottesville

  9. Good sensitivity, but model dependent g/g=0 -> contribution of quarks Results from different (proton, deuterium) data samples and different event topologies are consistent. HERMES, hadrons, all Q2 PYTHIA (tuned to data) Frank Ellinghaus, Spin’08, Charlottesville

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

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

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

  13. PHENIX longitudinally polarized pp Runs (Similar numbers for STAR. Experiments can separately choose longitudinal or transverse polarization.) Frank Ellinghaus, Spin’08, Charlottesville

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

  15. First: Check unpolarized case! PHENIX -- p0 STAR -- jets PRL 97, 252001 (2006) PRD76:051106,2007 Using a set of unpolarized PDFs ( + fragmentation functions in case of hadron (p0) production) the cross section agrees with NLO pQCD calculations. Frank Ellinghaus, Spin’08, Charlottesville

  16. STAR -- jets M. Sarsour Friday Run 6 preliminary Run 6 preliminary Run 5 (2005): PRL 100, 23 (2008) • DG = G(x), -G(x) excluded; • GRSV-std excluded with 99% CL • 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

  17. Model dependence of DG • Measurement averages over certain x range • Shape of DG(x) cannot be extracted -> Value for first moment model dependent Frank Ellinghaus, Spin’08, Charlottesville

  18. PHENIX -- p0 at 200 GeV Run 5 + Run 6 Run 5: Phys.Rev.D76:051106,2007 Run 6: arXiv:0810.0694 GRSV: Glueck et al., PRD 63 (2001) K. Nakano Tuesday DG = G(x), -G(x) excluded; GRSV-std slightly disfavored Frank Ellinghaus, Spin’08, Charlottesville

  19. A. Hoffman today X. Wang Friday STAR p0 consistent with PHENIX STAR – p0, PHENIX – h, PHENIX J/Psi J. Seele today PHENIX h excludes DG= G(x), -G(x) Frank Ellinghaus, Spin’08, Charlottesville

  20. Fraction of pion production PHENIX Preliminary s=62.4 GeV p+, p –, p0 and the sign of DG Especially in the region where qg scattering is dominant (pT > 5 GeV), the increasing contribution of d quarks (Dd<0) leads to: A. Morreale Tuesday A. Datta today “Model independent” conclusion possible once enough data is available. Frank Ellinghaus, Spin’08, Charlottesville

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

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

  23. Strong impact of Star jets and Phenix p0 in measured range. • Shape of DG(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 • Different ranges in x can be probed in: • 500 GeV (2009+, lower x) and 62 GeV running (larger x, larger scale unc.) -> • different rapidities -> First pol. PDF extraction using pp data M. Strattmann Tuesday DSSV, arXiv: 0804.0422 First “global” (DIS+SIDIS+pp) analysis! DG small in measured range (0.05 < x< 0.2). Contribution at small or large x? Frank Ellinghaus, Spin’08, Charlottesville

  24. Accessing different x-ranges S. Wissink Friday STAR: p0 ALL 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 K. Nakano Tuesday PHENIX: p0 ALL at s=62.4 GeV arXiv: 0810.0701 Increased sensitivity to larger x Frank Ellinghaus, Spin’08, Charlottesville At fixed xT = 2pT/sqrt(s) cross-section is 2 orders of magnitude higher at 62.4GeV than at 200GeV Significant 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…

  25. 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 -> 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) soon • COMPASS: • 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) Frank Ellinghaus, Spin’08, Charlottesville

More Related