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Gluon and Spin

Gluon and Spin. Introduction Δ G from scaling violations Δ G/G from hadron production Open charm Hadron pairs Single hadrons Δ G in pp RHIC. G. Mallot CERN/COMPASS. How it all began. All started 1987 with the discovery by the EMC. Ellis-Jaffe sum rule violated

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Gluon and Spin

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  1. Gluon and Spin • Introduction • ΔG from scaling violations • ΔG/G from hadron production • Open charm • Hadron pairs • Single hadrons • ΔG in pp RHIC G. Mallot CERN/COMPASS Freiburg March 2007

  2. How it all began All started 1987 with the discovery by the EMC • Ellis-Jaffe sum rule violated • Quark spin contribute little to nucleon spin • Where is the nucleon spin? Freiburg March 2007

  3. Theory Input 1988 PRL 60 (1988) 1471 PLB 206 (1988) 309 ZPC 41 (1988) 239 PLB 212 (1988) 391 Freiburg March 2007

  4. Considered Options • Small-x extrapolation? (CR) • Skyrmions: ΔG = 0 possibly ( BEK) • Bjorken sum rule broken? (only proton data at that time)Measurement wrong? (LA) • Large ΔG ~ 2-3 at EMC Q2 could mask quark spin via axial anomaly (ET, AR)requires fine tuning of cancelation of ΔG and orbital angular momentum Freiburg March 2007

  5. How to measure ΔG/G First step: Is ΔG indeed in the order 2-3 ? • Scaling violations in g1, however no polarised ep collider! • Longitudinal double-spinasymmetries in hadron production via photon-gluon fusion (Hendlmeier) • LDSA in pp collisions at RHIC ( Aidala ) Freiburg March 2007

  6. F2(x,Q2) g1(x,Q2) Freiburg March 2007

  7. NLO QCD fits • Several groups performing World Data fits • Example AAC, new fit 2006 • Still large uncertainty in G, even sign not determined • Extra difficulties in polarized case • No positivity condition • No momentum sum rule Freiburg March 2007

  8. New COMPASS A1d data PLB647 (2007) 8 Freiburg March 2007

  9. COMPASS NLO QCD fit • New g1d data + world data •  G > 0 and  G < 0 • | G|' 0.2–0.3 • a0 = 0.33§0.03§0.05 • s = -0.08§0.01§0.02 cf.: New Hermes Fit: a0 = 0.330 ± 0.011 ± 0.025 ± 0.028 (evol) s = -0.085 ± 0.013 ± 0.08 ± 0.09  G > 0  G < 0 Freiburg March 2007

  10. COMPASS QCD fit • Not yet included in fits: final Hermes g1d • Uncertainty due to parametrisation not included Freiburg March 2007

  11. ΔG = - 0.309 ΔG = 0.336 ΔG as Function ofΔG • Two distinct solutions • ΔG > 0 preferred • ΔG < 0 preferred by small-x points Freiburg March 2007

  12. QCD fit Q2 = 3 GeV2 Freiburg March 2007

  13. Photon–gluon fusion (PGF) • Gluon polarisation is measurable in PGF • measure • calculate and • using Monte Carlo Freiburg March 2007

  14. Hadron production • LO analysis of hadron-pair asymmetries: • open charm: single D meson AROMA, RAPGAP cleanest process wrt physics background • high-pThadron pairs with Q2 > 1 GeV2 LEPTO • high-pThadron pairs with Q2 < 1 GeV2 PYTHIA • NLO (photo production) • open charm Bojak, Stratmann • single incl. high-pT hadronJaeger. Stratmann, Vogelsang • hadron pairs: LO done, Hendlmeier, Stratmann, Schäfer • NLO underway • All analyses up to now in LO (plus parton showers) Freiburg March 2007

  15. Open Charm: D’s from D*’s D* → D πs→K ππs slow pion required 2002–2004 D0 → K ππ0 D0 → K π Freiburg March 2007

  16. Open charm: MC • analysis uses event aLL weighting, • aLL estimated with NN from event kinematics • indispensable due to large variation of aLL • good correlation of 0.82 between generated and reconstructed aLL aLL generated aLL reconstructed (NN) Freiburg March 2007

  17. Light hadron production Resolved photons Ratios for processes for Q2 < 1 Freiburg March 2007

  18. Example: kT tuning nucleon photon • systematic error: • determined using 15 independent MC simulations • exploring the parameter space • in kT of nucleon and photon • fragmentation functions • parton shower on/off, • renormalisation scale Freiburg March 2007

  19. Resolved photons • More than 50%, however assuming a min and maxscenario, shows little difference. • Probing photon at large x, where photon PDF rather well determined u/u Glück, Reya, Sieg Freiburg March 2007

  20. Data versus MC • excellent to good agreement for all kinematics variables pT Freiburg March 2007

  21. Gluon polarisation high-pT pairs; Q2>1GeV2 : 2002–2003 high-pT pairs; Q2< 1GeV2 : 2002–2004 Open charm: Freiburg March 2007

  22. G/G from high-pT pairs • GRSV-max strongy disfavoured New HERMES point Freiburg March 2007

  23. COMPASS QCD fit • Note NLO fits, LO data Freiburg March 2007

  24. New Hermes analysis Single inclusive hadrons P. Liebing at spin 2006 Freiburg March 2007

  25. Can we learn more about x? here Lepto and Q2>1 All processes PGF events (MC) Freiburg March 2007

  26. Splitting in xg bins? Compass • Splitting of high-pT, Q2<1 data in 3 xg bins under study • Optimizing correlation of rec. and `true’ xg (NN) • More significant with 2006 data Freiburg March 2007

  27. RHIC: polarised pp • pp at RHIC Freiburg March 2007

  28. pp: NLO Calculations In much better shape: Jäger,Schäfer, Stratmann, Vogelsang; de Florian Jäger,Stratmann,Vogelsang; Signer et al. Gordon,Vogelsang; Contogouris et al.; Gordon, Coriano Bojak, Stratmann Summary by Stratmann, DIS2006 Freiburg March 2007

  29. π0production at RHIC • Phenix Freiburg March 2007

  30. Direct photons • good agreement ofcalc. and data at collider energies Freiburg March 2007

  31. Towards a global analysis 1st moment at input W.Vogelsang, M. Stratmann (DIS2006, work in progress) Freiburg March 2007

  32. 1st moment Dg 0.31  0.32 (DIS+p0) 0.47  1.08 (DIS only) Significant reduction of the Dg uncertainty Sign problem gg process dominates Ds [Dg(x)] 2 Positive or negative Dg? c2p0: 11.18(Dg>0) vs. 11.05 (Dg<0) (8 data points) Dg from p0 production (RUN05) Slide from Hirai DIS2006 • Consistent results • 1st moment (0.1<xBj<1) • Dg>0: 0.30  0.30 • Dg<0: 0.32  0.42 • Large-x is positive Freiburg March 2007

  33. Inclusive jets at STAR from Kiryluk, DIS2006 Freiburg March 2007

  34. Summary • all results indicate G small compared to anomaly inspired hypotheses • sign still undefined • G still could carry most of the nucleon’s spin • need data on xg-dependence to pin down the shape • need to include COMPASS and HERMES high-pT data in starting global analyses (NLO calculations) • looking forward to 500 GeV/c at RHIC Freiburg March 2007

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