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Gluon polarization measurements at

Gluon polarization measurements at. F.-H. Heinsius (Universität Freiburg) on behalf of the COMPASS collaboration. DIS 2004, Š trbsk é Pleso, 14.4.2004. The COMPASS Collaboration. 230 physicists from 12 countries 28 institutes. Broad Physics Program D G/G semi inclusive DIS

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Gluon polarization measurements at

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  1. Gluon polarization measurements at F.-H.Heinsius (Universität Freiburg) on behalf of the COMPASS collaboration DIS 2004, Štrbské Pleso, 14.4.2004

  2. The COMPASS Collaboration 230 physicists from 12 countries 28 institutes Broad Physics Program • DG/G • semi inclusive DIS • flavor dependent quark helicity density distributions Dq • transverse quark spin distribution function h1(x) • polarised Lfragmentation • vectormesons • hadron spectroscopy with hadron beams

  3. Spin of the Nucleon = ½ ħ QCD analysis of g1(x,Q2) DIS: DS≈0.3 (CERN, SLAC, DESY) ½ DS DG Photon gluon fusion Lq LG open charm high-pT Measure generalized parton distributions

  4. DG from QCD Analysis of g1 polarised gluon distribution from QCD fits: Hermes (2000) Blümlein & Böttcher: fit to polarised data of EMC, E142, E143, E155, SMC, Hermes Nucl. Phys. B636 (02) 225

  5. Spin of the Nucleon = ½ ħ QCD analysis of g1(x,Q2) DIS: DS≈0.3 (CERN, SLAC, DESY) ½ DS DG Photon gluon fusion Lq LG open charm high-pT Measure generalized parton distributions

  6. DG/G at COMPASS 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 Photon gluon fusion N

  7. DG/G at COMPASS Polarised 6LiDTarget Ptarget: 50% Dilution: 40% 3He – 4He dilution refrigerator (T~50mK) Superconducting Solenoid (2.5 T) Dipol (0.5 T) Two 60 cm long target cells with opposite polarisation Reconstructed interaction vertices N

  8. DG/G at COMPASS Photon gluon fusion q = c cross section difference in charmed meson production → theory well understood → experiment challenging q = u,d,s cross section difference in 2+1 jet production. In COMPASS: Events with 2 hadrons with high pT → experiment easy → theory difficult N

  9. COMPASS Spectrometer 2003/04 m+

  10. New Technologies for Tracking and Particle ID TDC GEM Large area drift detectors MicroMegas Scintillating fiber trackers RICH CsI & MWPC readout Radiator: C4F10 Readout electronics

  11. Particle Identification p, m K p q(mrad) p(GeV/c) hadrons m With RICH and hadron calorimeters Essential for reconstruction of D-Mesons

  12. DG/G: Open Charm DsPGF at NLO:Bojak, Stratmann NPB 540 (1999) 345; Contogouris et al. Photon-Gluon Fusion D N

  13. D* tagging: D*→D0p Cut on D0 MKpps-MKp -mp [MeV/c2] Cuts: zD > 0.2 |cos q*| < 0.85 (Background) 10 < pK < 35 GeV/c (RICH PID) MKpps-MKp -mp [MeV/c2] MKp -mD0 [MeV/c2]

  14. D* tagging : D*→D0p, D0→K p 80% 2002 data Cut on D* 317 D0 MKp -mD0 [MeV/c2] MKpps-MKp -mp [MeV/c2] MKp -mD0 [MeV/c2]

  15. First reconstruction of charmed mesons with polarised target and beam Very challenging because vertex reconstruction inside massive target event rate small compared to background Improvements gains in 2003 and 2004 spectrometer performance double beam time in 2004 better beam reconstruction several improvements in reconstruction algorithms and analysis methods Projected error on DG/G from 2002-2004 data: 0.24 DG/G: Prospects from Open Charm

  16. Current fragmentation xF>0.1 z>0.1 2 high pT hadrons pT > 0.7 GeV/c pT12+ pT22>2.5 (GeV/c)2 m(h1h2) > 1.5 GeV/c2 DG/G: Pairs of High pT Hadrons Photon Gluon Fusion h1 h2 N

  17. Improvements: 2003 and expected 2004 data will give a factor of 4 more data better reconstruction algorithm COMPASS Result two target cells, opposite polarisation, polarisation flipped every 8 hours Asymmetry in production of hadron pairs with high pT: 2002 data up to now systematic error contains only studies on false asymmetries due to target or spectrometer effects

  18. How to get ΔG/G fractions of cross section determined by Monte Carlo Leading Order QCD-Compton Photon Gluon Fusion

  19. Additional Background Resolved Photon Relevant for Q2<1 (GeV/c)2 VMD - Pomeron

  20. Next Steps in high-pT Analysis Monte Carlo studies are in progress: • PYTHIA • simulates all processes • PYTHIA used in HERMES analysis (Q2 unmeasured) • LEPTO • simulates PGF, QCD-Compton and LO DIS • LEPTO used in SMC analysis (Q2>1 (GeV/c)2 selected) • Projected error on DG/G for 2002-2004 data (assuming fraction of PGF events is ¼ ): 0.05[0.16 for Q2>1 (GeV/c)2]

  21. More COMPASS physics Inclusive and semi-inclusive asymmetries M. Leberig Transverse asymmetry AUT for charged pions H. Fischer Expected error on ΔG/G COMPASS Summary First glance at open charm PGF with polarised target and beam Good perspectives for ΔG from high-pThadron pairs proposal

  22. End of Talk

  23. DG/G at COMPASS Open charm First reconstruction of charmed mesons with polarised target and beam: 80% 2002 data 317 D0 High pT hadron pairs Measured asymmetry from 2002 data: MKp -mD0 [MeV/c2]

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