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Krzysztof Kurek Andrzej Sołtan Institute for Nuclear Studies, Warsaw

G from COMPASS. on behalf of the COMPASS Collaboration. Krzysztof Kurek Andrzej Sołtan Institute for Nuclear Studies, Warsaw. DIS2006 XIV International Workshop on Deep Inelastic Scattering 20/April/2006 - 24/April/2006 Tsukuba. luminosity: ~5 . 10 32 cm -2 s -1

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Krzysztof Kurek Andrzej Sołtan Institute for Nuclear Studies, Warsaw

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  1. G from COMPASS on behalf of the COMPASS Collaboration Krzysztof Kurek Andrzej Sołtan Institute for Nuclear Studies, Warsaw DIS2006 XIV International Workshop on Deep Inelastic Scattering 20/April/2006 - 24/April/2006 Tsukuba

  2. luminosity: ~5 . 1032 cm-2 s-1 beam intensity: 2.108 µ+/spill (4.8s/16.2s) beam momentum: 160 GeV/c target polarization: ~50% • longitudinally polarised muon beam • longitudinally or transversely polarised deuteron (6LiD) target • momentum and calorimetry measurement • particle identification LHC SPS N Delta-G from COMPASS

  3. THE COMPASS SPECTROMETER Hodoscopes E/HCAL2 E/HCAL1 SM2 RICH1 Muon Wall 2, MWPC SM1 Polarised Target MWPC, Gems, Scifi, W45 (not shown) SPS 160 GeV m beam Muon Wall 1 Straws, Gems Micromegas, SDC, Scifi Scifi, Silicon Delta-G from COMPASS

  4. Content • Motivation and Nucleon spin decomposition. • Three methods of accessing in Compass. • Open charm channel method and results. • High pT hadron pairs method: - Results for events with low Q2. - Results for events with Q2 > 1 GeV2. • Conclusions. Delta-G from COMPASS

  5. Nucleon Spin decomposition ½= ½ΔΣ+ ΔG+L • A very small fraction of the proton spin is carried • by the spin of the quarks - put the naive but well- • accepted quark model into serious questioning! • (EMC (1988):a0 = = 12 ±9 ±14%while  60% expected, • confirmed by SMC, SLAC and Hermes := 20 - 30%) • The possible role of axial anomaly: measured quantity a0 = - (3 S/2) G Delta-G from COMPASS

  6. Nucleon Spin decomposition ½= ½ΔΣ+ ΔG+L • A very small fraction of the proton spin is carried • by the spin of the quarks - put the naive but well- • accepted quark model into serious questioning! • (EMC (1988):a0 = = 12 ±9 ±14%while  60% expected, • confirmed by SMC, SLAC and Hermes := 20 - 30%) • The possible role of axial anomaly: measured quantity a0 = - (3 S/2) G warning:orbital angular momentum – anomaly cancelled (X.Ji) Delta-G from COMPASS

  7. Direct measurements of G/G Photon Gluon Fusion (PGF)probes gluons LL • Open charm„golden channel” •  no background asymmetry, less MC dependent. • small statistics, NLO corrections can be important • 2 high pT hadrons (pT > 0.7, then selection on pT2) •  Large statistics •  physical background: „model” (MC) dependent, • requires very good description of data by MC. Delta-G from COMPASS

  8. Direct measurements of G/G • 2 high pT hadrons: • Low Q2 analysis (Q2<1): perturbative scale fixed by pT, • complicated physical background e.g. resolved ,low pT • High Q2 analysis (Q2>1): scale Q2,physical background • better controlled in the frame of pQCD. Physical background: resolved  (Q2<1) QCD-Compton Delta-G from COMPASS resolved  (Q2<1)

  9. Direct measurements of G/G Due to limitations of every methods - high pT hadron pairs methodsare complementaryto one another and complementary with the method using selection of open charm production! Delta-G from COMPASS resolved  (Q2<1)

  10. G/G from open charm channel Delta-G from COMPASS

  11. G/G from open charm channel D0  K+  (untagged) D*  D0+   K+ +  ~ ALL/D = Scale: <Q2>  13 GeV2 ~4* mc2 Delta-G from COMPASS

  12. G/G from open charm channel ~ ALL/D = ɑLL ɑLL– calculated with help of MC and parametrized by measured quantities (Neural Network used) ~ Delta-G from COMPASS

  13. G/G from open charm channel D0 + D* result 2002 – 2004: = -0.57 0.41(stat.) @ xg  0.15, scale 13 GeV2 The studies on the systematical uncertainty are ongoing Delta-G from COMPASS

  14. G/G from 2 high pT hadrons Delta-G from COMPASS

  15. ALL/D = RpgfG/GaLLpgf + Rqcdcq/qaLLqcdc + Rqqq/qaLLgq (G/G) + RqgG/GaLLqg (q/q) + … G/G from 2 high pT hadrons (low Q2 ) Low Q2: Q2 < 1 GeV2 30% 50% Resolved  MC event generator PYTHIA is used for low Q² analysis Delta-G from COMPASS

  16. G/G from 2 high pT hadrons (low Q2 ) Data & MC Data/MC Q² Q² pT pT Example of good description of the data by the simulation Delta-G from COMPASS

  17. G/G from 2 high pT hadrons (low Q2 ) Resolved photon asymmetry Problem: polarized PDF’s of virtual photons not measured! q,pert(xp,²) calculable -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 limiteduncertainty to the estimation of (G/G)(xg) Delta-G from COMPASS

  18. G/G from 2 high pT hadrons (low Q2 ) Values used for extraction of G/G 2002-2003 published:PLB 633 (2006) 25-32 Delta-G from COMPASS

  19. G/G from 2 high pT hadrons (Q2 >1) • Statistics smaller than in low Q2 analysis (10%) • Background better controlled – pQCD (QCD-C, LP) • LEPTO MC generator has been used for data • description (tunning similar to SMC) • pT2 > 2.5 GeV2 used. 2002-2003 data result: = 0.06 ± 0.31(stat.) ± 0.06 @ xg = 0.13 ± 0.08 Delta-G from COMPASS

  20. G/G from 2 high pT hadrons (Q2 >1) • Analysis is ongoing; 2002-2004 results expected soon • Scale is determined by Q2 and – in contrast to low Q2 • analysis – the cut pT2 > 2.5 GeV2 can be released to • smaller value to optimize „working point” • (question: higher fraction RPGF and small statistics or • lower fraction and higher statistics?) • Neural Network is tested to improve selection of PGF • subprocess and optimize „working point”. • The significant improvement is expected. Delta-G from COMPASS

  21. Results for G/G - summary Only statistical errors plotted Delta-G from COMPASS

  22. Results for G/G - summary Open charm Delta-G from COMPASS

  23. Outlook • More results soon available with 2004 data for • Q2 >1 GeV2 high pT events • For the future: • Optimization of event selection with a neural network • Bins in xg (requires improvement of xg reconstruction) • NLO in open charm analysis  No resolved photons!  No physical background! • 2006 data with new COMPASS magnet(larger xg) Delta-G from COMPASS

  24. Summary • New measurements ofG/G have been presented. • Small Gis preferred or G(xg) has a node • around 0.1. • Ellis-Jaffe sum rule seems to be violated if large G • is excluded (axial anomaly). • G  0.4 not excluded and scenario when L is small • still possible. • G  0indicatesthe important role ofangular orbital • momentumin nucleon spin decomposition described • in the frame of parton model and pQCD. Delta-G from COMPASS

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