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RESULTS ON Δ G FROM EXPERIMENT @ CERN Jan Paweł Nassalski

RESULTS ON Δ G FROM EXPERIMENT @ CERN Jan Paweł Nassalski Sołtan Institute for Nuclear Studies, Warsaw On befalf of COMPASS Collaboration. Δ G from QCD fits to g 1 is badly determined. AAC2004: M. Hirai, S. Kumano and N. Saito, P hys. R ev. D (2004). NLO fits:.

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RESULTS ON Δ G FROM EXPERIMENT @ CERN Jan Paweł Nassalski

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  1. RESULTS ONΔGFROM EXPERIMENT @ CERN Jan Paweł Nassalski Sołtan Institute for Nuclear Studies, Warsaw On befalf of COMPASS Collaboration J.P. Nassalski

  2. ΔG from QCD fits to g1 is badly determined AAC2004: M. Hirai, S. Kumano and N. Saito, Phys.Rev.D (2004) NLO fits: Glück, Reya, Stratmann, Vogelsang Blümlein, Böttcher Leader,Sidorov, Stamenov Hirai, Kumano, Saito: ΔG = 0.449 ± 1.266 Large uncertainty Use processes where ΔG is probed directly J.P. Nassalski

  3. ΔG from Photon-Gluon Fusion (PGF) Enhance the contribution to the final state from: Hard scale set by pt Large pt hadrons 1) • Large statistics, but ... • Large background from other processes • Theoretical uncertainties Hard scale set by mcharm 2) also • Clean theory, but ... • Difficult experimentaly USE ANY Q2 J.P. Nassalski

  4. Beam momentum 160 GeV intensity 2.108 µ+/spill (4.8s/16.2s) luminosity ~5 . 1032 cm-2 s-1 longitudinal polarization ~ -76% LHC SPS μ+ N Target 6LiD longitudinal polarization +53%, -50% J.P. Nassalski

  5. COMMON MUON and PROTON APPARATUSfor STRUCTUREand SPECTROSCOPY THE COMPASS COLLABORATION Czech Republic, Finland, France, Germany, India, Israel, Italy, Japan, Poland, Portugal, Russia, Switzerland Bielefeld, Bochum, Bonn, Burdwan, Calcutta, CERN, Dubna, Erlangen, Freiburg, Heidelberg, Helsinki, Lisbon, Mainz, Miyazaky, Moscow, Munich, Nagoya, Prague, Protvino, Saclay, Tel Aviv, Torino, Trieste, Warsaw 31 Institutes, more than 270 physicists and students J.P. Nassalski

  6. Data collected More detectors Improved reconstruction 2005: no data taking 2006: taking data with an improved setup J.P. Nassalski

  7. Asymmetry determination TARGET cell u cell d Before reversal After reversal • Opposite polarizations, Pt≈ ± 50% • Polarization reversed • - by field rotation every ~8 h • - by microvawes 2-3 times/year • Dilution factor <f>≈ 0.4 BEAM <Pμ>≈ -76% DEPOLARIZATON F. <D>≈ 0.6 We use event-by-event weighting to optimize determination of ΔG. J.P. Nassalski

  8. Δg(x) from charmed mesons: J.P. Nassalski

  9. Open charm (D0) signal • about 30cm thick 6LiD target cell  No charm decay vertex reconstruction • K/π identification in RICH important • use D* tagging;  Cut on mD0 with D* tagging mD0 without D* tagging J.P. Nassalski

  10. Δg from D* and D0 Dominant contribution: PGF Use event weighting to calculate : where we determined using the MC (Aroma) parametrisation and took into account correlation between and J.P. Nassalski

  11. Δg from D* and D0 Δg/g COMPASS preliminary J.P. Nassalski

  12. Δg(x) from large pt hadrons • Two hadrons at large pt: pt,1(2) > 0.7GeV, (pt,1)2 + (pt,2)2 > 2.5GeV2 • Exclude resonance region: M1,2 > 1.5GeV • Supress contribution from the target fragmentation region: xF, z > 0.1 • Consistent LO analysis: • - PDF, • - aLL, • - parton showers OFF in JETSET. J.P. Nassalski

  13. Contributions to the asymmetry at large pt LO + QCD Compton + PGF + Resolved photon processes small at small x small at large Q2 Q2 >1GeV2 , x<0.05: ONLY PGF CONTRIBUTING TO THE ASYMMETRY Q2 < 1GeV2: ALL PROCESSES CONTRIBUTING TO THE ASYMMETRY J.P. Nassalski

  14. Q2bigger then1 GeV2 J.P. Nassalski

  15. Δg from large pt: Q2 > 1 GeV2 Monte Carlo (LEPTO) tuned to reproduce the data 10% of data Use event weighting to calculate : COMPASS preliminary Only PGF contributing to the asymmetry: -0.75±0.15 0.34±0.07  From MC COMPASS preliminary J.P. Nassalski

  16. Q2smaller then1 GeV2 J.P. Nassalski

  17. Δg from large pt: Q2 < 1 GeV2 90% of data hard soft: resolved photon soft: small-pt R – fraction: • (Δf’/f)N : use parametrisations • GRSV2000/GRV2000, • (Δf’/f)γ: assume minimal and • maximal scenarios; • Gluck, Reya, Sieg, EPJ C20(2001)271 QCD-C LP • PYTHIA tuned to describe • the data, J.P. Nassalski

  18. Δg from large pt: Q2 < 1 GeV2 COMPASS preliminary assuming PYTHIA J.P. Nassalski

  19. Results on Δg COMPASS 2-h, Q2>1GeV2 COMPASS 2-h, Q2<1GeV2 COMPASS open charm J.P. Nassalski

  20. Conclusions • Three independent results from COMPASS indicate that Δg (in LO) • is small at ηg≈ 0.1 • Open charm result has the smallest theoretical uncertainty but requires more • data to be statisticaly significant. • High pt, small Q2 result has the smallest error, • assuming correct simulation of small Q2 physics by PYTHIA. J.P. Nassalski

  21. Outlook • Reduction of statistical errors on Δg/g • after including 2004 data: • - from open charm: 0.73  0.57, • - from large pt, Q2 >1GeV2: 0.31  0.22, • - from large pt, Q2 <1GeV2: 0.089  0.065. • Further improvements in the analysis: • - use Neural Networks to increase RPGF, • - NLO analysis. • Resuming data taking in 2006 with improved experimental setup: • - RICH upgrade, • - larger acceptance of polarized target solenoid, • - ..... J.P. Nassalski

  22. The spectrometer Hodoscopes E/HCAL2 E/HCAL1 SM2 RICH1 Muon Wall 2, MWPC SM1 Polarised Target MWPC, Gems, Scifi,W45 Muon Wall 1 Straws, Gems m beam Micromegas, SDC, Scifi J.P. Nassalski

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