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on behalf of the COMPASS Collaboration

Gluon polarization measurement at COMPASS. O.Kouznetsov (JINR) on behalf of the COMPASS Collaboration. on behalf of the COMPASS Collaboration. ICHEP06, Moscow 26.07-02.08 2006. quarks gluons orb. mom. Nucleon s pin puzzle. Angular momentum sum rule:.

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on behalf of the COMPASS Collaboration

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  1. Gluon polarization measurement atCOMPASS O.Kouznetsov (JINR) on behalf of the COMPASS Collaboration on behalf of the COMPASS Collaboration ICHEP06, Moscow 26.07-02.08 2006 Gluon polarization measurement at COMPASS

  2. quarksgluons orb. mom. Nucleon spin puzzle Angular momentum sum rule: ½= ½ΔΣ + ΔG + Lq + Lg • Measurement of ΔG is important for two reasons: • - as an element of nucleon spin puzzle (a0(= ΔΣ) is measured to be around 0.25 instead of expected 0.6) • possible role of axial anomaly in the a0 interpretation (a0≠ ΔΣ) a0 = Gluon polarization measurement at COMPASS

  3. COmmon Muon and Proton Apparatus forStructure andSpectroscopy 160 GeV polarizedbeam, 6LiD polarized target two stage spectrometer SAS & LAS (~50 m) Hcals, Ecals, RICH for particle ID, walls LHC SPS CERN (France) N CERN (Suisse) In 2002, 2003, 2004 COMPASS has recorded 30×109 events ~ 1000 TB Gluon polarization measurement at COMPASS

  4. N Photon Gluon Fusion (PGF) Open Charm → clean channel; → but experimentally difficult; →perturbative scale fixed by the mass of the charm quarks High-pT Hadron Pairs → easy to get a statistics; → but physical background; →perturbative scale fixed by pT or Q2 cuts Gluon polarization measurement at COMPASS

  5. Asymmetry measurement two oppositely polarized 60 cm long target cells: upstream (u), downstream (d) cells polarization reversal every 8 hours counting rate asymmetry in two target cells gives the cross-section asymmetry A|| upstream downstream target polarisation PT≈ 0.50dilution factor f ≈ 0.40beam polarisation PB ≈ 0.76depolarisation factor D ≈ 0.60 Gluon polarization measurement at COMPASS

  6. Open charm golden channel, weak MC dependense small statistics, no vertex detector → no primary/secondary vertex separation Gluon polarization measurement at COMPASS

  7. Open charm • Aexpdetermined from counting rate asymmetry • no asymmetrycontribution from background • PGF/tot = S/(S+B) determined from the fit • MC is needed for aLL calculation aLL parametrised by pT, zD, y  parametrization determined with Neural Net (NN)  NN trained with AROMA  good description of data Gluon polarization measurement at COMPASS

  8. Open charm what about another channels/mesons?D0 K–+Br ~ 4 % D* tag this analysis D0 K–+ 0 Br ~ 13 % D* tag run 2006 (?) D0 K*(892)+K0- +Br ~ 6% D* tag weak signal D0 (1020)K0 K0K+K- Br ~ 0.5% --- weak signalCharged D mesons → lower production rate, no D* tag... scale ~ 13 GeV2 Gluon polarization measurement at COMPASS

  9. QCD- Compton PGF LO DIS high pT hadron pairs  considerably higher statistics but physical background, last 4 processes are important only for low Q2  qg    gq qq gg Gluon polarization measurement at COMPASS

  10. 10% of statistics PGF contribution enhancement pT > 0.7 GeV/c pT12 + pT22 > 2.5 (GeV/c)2 xF, z > 0.1 m(h1,h2) > 1.5 GeV/c2 high pT hadron pairs Q2< 1 GeV2 ← analysis →Q2> 1 GeV2 90% (500K evt) ← statistics from total → 10% 50% ← resolved photons contribution → ---- QCD-C, LO ← another background → QCD-C, LO PYTHIA ← MC generator used → LEPTO Gluon polarization measurement at COMPASS

  11. high pT hadron pairs Q2>1 GeV2 • cut on xB < 0.05 → A1d ≈ 0 → LO & QCD-C can be neglected • but they are still important for PGF event fraction estimation Gluon polarization measurement at COMPASS

  12. high pT hadron pairs Q2>1 GeV2 Results from Monte Carlo: Ratio of PGF events A||/D = -0.015 ± 0.080 (stat.)± 0.013 (syst.) scale ~ 3 GeV2 main contribution to systematic error comes from false asymmetries Gluon polarization measurement at COMPASS

  13. A||/D = RpgfG/GaLLpgf + Rqcdcq/qaLLqcdc + Rqqq/qaLLgq (G/G) + RqgG/GaLLqg (q/q) + … high pT hadron pairs Q2<1 GeV2 Results from Monte Carlo 30%(PGF) 50%(all) Resolved 7% in total, moreover the asymmetry for this kind of events is small (from A1 measurements at low Q2) : neglected Gluon polarization measurement at COMPASS

  14. MC /Real Data (bluepoints) comparison high pT hadron pairs Q2<1 GeV2 resolved photon contribution the polarized PDFs of the photon is unknown unpolarized PDFs used to constrain polarized Gluon polarization measurement at COMPASS

  15. high pT hadron pairs Q2<1 GeV2 2002-2003 published:PLB 633 (2006) 25 2002-2004 data A||/D= 0.004 ± 0.013 (stat.)± 0.003 (syst.) Syst. error: 0.052 (MC), 0.014 (false asymmetries), 0.013 (resolved photons) scale ~ 3 GeV2 Gluon polarization measurement at COMPASS

  16. QCD analysis of g1 data G>0 and G<0 solutions describe data equally well could direct measurements discriminate between them? the first moment of G is of the order 0.2-0.3 in absolute value at Q2=3 GeV2 Gluon polarization measurement at COMPASS

  17. Direct G/G measurements XG Gluon polarization measurement at COMPASS

  18. Conclusion 2002-2004 COMPASS data + 2006 (estim.) Open charm 0.28(stat.) Q2 >1 GeV2 hadron pairs 0.14(stat.) Q2 <1 GeV2 hadron pairs 0.045(stat.) Results indicate small ΔG around xg ≈ 0.1 QCD analysis of g1 shows small value of the first moment of G In contrast G ~3 is needed to solve the 1988-20?? Gluon polarization measurement at COMPASS

  19. Gluon polarization measurement at COMPASS

  20. Gluon polarization measurement at COMPASS

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