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New measurement of  G/G at COMPASS

New measurement of  G/G at COMPASS. Sébastien Procureur (CEA - Saclay) on behalf of the COMPASS collaboration. New measurement of G/G at COMPASS 41 st Rencontres de Moriond S.Procureur. The nucleon spin. ½= ½ΔΣ + ΔG + L q + L g. quark spin. gluon spin. orbital momenta.

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New measurement of  G/G at COMPASS

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  1. New measurement of G/G at COMPASS Sébastien Procureur (CEA - Saclay) on behalf of the COMPASS collaboration New measurement of G/G at COMPASS 41st Rencontres de Moriond S.Procureur

  2. The nucleon spin ½= ½ΔΣ+ ΔG+Lq+Lg quark spin gluon spin orbital momenta Prediction 1: ΔΣ ~ 0.75 (Naive quark model) Prediction 2: ΔΣ ~ 0.6 (QCD & s=0) Experiment: a0 = ΔΣ – (3S/2)ΔG~ 0.2! (EMC,…)  A large G =G(xg) is expected! New measurement of G/G at COMPASS 41st Rencontres de Moriond S.Procureur

  3. Beam:2 . 108 µ+/ spill (4.8s / 16.2s) Luminosity: ~5 . 1032 cm-2 s-1 Beam polarization: -76% Beam momentum: 160 GeV/c LHC COMPASS SPS COMPASS experiment New measurement of G/G at COMPASS 41st Rencontres de Moriond S.Procureur

  4. How to access to (G/G)(xg)? Spin asymmetries ALL of the main diagrams in DIS: Photon gluon fusion (PGF) LO Compton ALL= ALL  *  Only PGF is sensitive to (G/G)(xg) (but S suppressed) New measurement of G/G at COMPASS 41st Rencontres de Moriond S.Procureur

  5.  : no physical background  : low statistics Selections of PGF Open charm channel c scale: mc c q = c, then c D0 or D* K, New measurement of G/G at COMPASS 41st Rencontres de Moriond S.Procureur

  6. (ΔG/G)(xg) with open charm ALL/D = D* D0+   K+  +  • 2002-03: (G/G)(xg)= -1.08  0.73(stat) • 2002-04: [(G/G)(xg)] = 0.43 (analysis in progress) New measurement of G/G at COMPASS 41st Rencontres de Moriond S.Procureur

  7.  : no physical background : large statistics  : low statistics : physical background Selections of PGF Open charm channel High pT hadrons channel c scale: mc scale: pT , Q² c q = c, then c D or D* K, (q,q) (h1,h2) with high transverse momentum wrt * direction New measurement of G/G at COMPASS 41st Rencontres de Moriond S.Procureur

  8. ALL/D = RpgfG/GaLLpgf + Rqcdcq/qaLLqcdc + Rqqq/qaLLgq (G/G) + RqgG/GaLLqg (q/q) + … (G/G)(xg) with high pT hadrons Resolved photons! (low Q²)  Need a Monte Carlo simulation  What about polarisations of partons in virtual photon? New measurement of G/G at COMPASS 41st Rencontres de Moriond S.Procureur

  9. Monte Carlo simulation Event generator PYTHIA is used for low Q² analysis (+ GEANT for spectrometer simulation) Q² pT Data & MC Q² pT Data/MC  Good description of the data by the simulation! New measurement of G/G at COMPASS 41st Rencontres de Moriond S.Procureur

  10. Results of simulation RPGF  30% RRes.Phot  50% Relevant parameters were then varied to estimate the uncertainties due to MC New measurement of G/G at COMPASS 41st Rencontres de Moriond S.Procureur

  11. Resolved photon asymmetry • Problem: polarized PDFs of virtual photons not measured! q,pert(xp,²) calculable • Solution: -q,npert(xp,0²) < q,npert(xp,0²) < q,npert(xp,0²) measured! • Allows us to obtain a range for (q/q)and (G/G) !  Adds a limited uncertainty to the estimation of (G/G)(xg) 1st estimation of the resolved photon asymmetry! New measurement of G/G at COMPASS 41st Rencontres de Moriond S.Procureur

  12. Results (1) Values used for extraction of (G/G)(xg) [PLB 633 (2006) 25-32] New measurement of G/G at COMPASS 41st Rencontres de Moriond S.Procureur

  13. Results (1) • Equiv. stat. * ~2.4 with 2004 data! • Asymmetries compatible with 2002-03 Values used for extraction of (G/G)(xg) [PLB 633 (2006) 25-32] NEW New measurement of G/G at COMPASS 41st Rencontres de Moriond S.Procureur

  14. Results (2)  Favours small values of G New measurement of G/G at COMPASS 41st Rencontres de Moriond S.Procureur

  15. Outlook • More results soon available with 2004 data: • Q² > 1 (GeV/c)² high pT events: • Open charm selection  No resolved photons!  No physical background! For the future: • Optimization of event selection with a neural network • Bins in xg (requires improvement of xg reconstruction) • 2006 data with new COMPASS magnet(larger xg) already in progress! New measurement of G/G at COMPASS 41st Rencontres de Moriond S.Procureur

  16. Conclusion • 2004 data confirms results from 02-03 (FOM *2.4) • G is small (or G(xg) has a node around 0.1) • still the most precise determination of (G/G)(xg)  G not large  ΔΣ small ( predictions) ½= ½ΔΣ+ ΔG+Lq+Lg ½0.2 + 0.4+0.0 + 0.0 possible scenarios: ½0.2 + 0.0+0.4 New measurement of G/G at COMPASS 41st Rencontres de Moriond S.Procureur

  17. Spares New measurement of G/G at COMPASS 41st Rencontres de Moriond S.Procureur

  18. A1 at COMPASS (2002-2003) • Agreement with previous experiments • Improve stat at small x New measurement of G/G at COMPASS 41st Rencontres de Moriond S.Procureur

  19. g1 at COMPASS PLB 612(2005),154  = 0.202 + 0.042 – 0.077 (without COMPASS)  = 0.237 + 0.024 – 0 029 (with COMPASS) New measurement of G/G at COMPASS 41st Rencontres de Moriond S.Procureur

  20. Transversity at COMPASS Collins Sivers PRL 94(2005),202002 • Asymetries compatible with 0 ( HERMES)  p/n compensation? New measurement of G/G at COMPASS 41st Rencontres de Moriond S.Procureur

  21. Results of PHENIX (PANIC05) ¨ GRSV: M. Gluck, E. Reya, M. Stratmann, and W. Vogelsang, Phys. Rev. D 53 (1996) 4775. * At input scale: Q2 = .4 GeV

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