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Prospects for ΔG/G in COMPASS

Prospects for ΔG/G in COMPASS. Compass Physics objectives Experiment layout 2002 data: status of analysis Prospects for ΔG/G. EMC, SMC, SLAC, HERMES :. Measure ΔG (Photon gluon fusion) (Generalized Parton Distributions). Spin structure of the nucleon.

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Prospects for ΔG/G in COMPASS

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  1. Prospects for ΔG/G in COMPASS • Compass Physics objectives • Experiment layout • 2002 data: status of analysis • Prospects for ΔG/G Claude MARCHAND - DIS03 St Petersburg

  2. EMC, SMC, SLAC, HERMES : Measure ΔG (Photon gluon fusion) (Generalized Parton Distributions) Spin structure of the nucleon • How is the rest of the nucleon spin (0.35) • shared between ΔG and orbital momentum? • Or Claude MARCHAND - DIS03 St Petersburg

  3. Physics at COMPASS Common Muon and Proton Apparatus for Structure and Spectroscopy Nucleon Spin Structure: • Gluon polarization G(ηG)/G • Polarised flavour dependent parton distributions q(x) • Λ Polarization (D q) • Transverse-spin distribution functions Tq(x) Claude MARCHAND - DIS03 St Petersburg

  4. Compass: Determination of ΔG/G E161: RHIC : e.g prompt photon + jet Photon Gluon Fusion • q=c: Open charm production • q=u,d,s: high pairs Claude MARCHAND - DIS03 St Petersburg

  5. More than 220 physicists from 30 Institutes COMPASS Collaboration Bielefeld, Bochum, Bonn (ISKP & PI), Erlangen, Freiburg, Heidelberg, Mainz, München (LMU & TU) Дубна (LPP and LNP), Москва (INR, LPI, State University), . Протвино CERN Helsinki Warsawa (SINS), Warsawa (TU) Nagoya Saclay Praha Lisboa Torino (University,INFN), Trieste (University,INFN) Burdwan, Calcutta Tel Aviv Claude MARCHAND - DIS03 St Petersburg

  6. Beam:160 GeV µ+ 2 . 108 µ/spill (4.8s/16.2s) Muon filter 2 MWPCs ECal2 & Hcal2 ~50m SM2 Muon filter 1 ECal1 & Hcal1 RICH GEM & MWPCs SciFi SM1 GEM & MWPCs Silicon SciFi Scintillating fibers • Polarization: • Beam: ~80% • Target: <50%> GEM & Straws Micromegas &Drift chambers Polarized target COMPASS spectrometer Claude MARCHAND - DIS03 St Petersburg

  7. 3He – 4He dilution refrigerator (T~50mK) Compass 6LiD Polarizedtarget Dynamic Nuclear Polarization Dilution factor: ~40% Maximum Polarization:+57% Longitudinal & transverse pol. Claude MARCHAND - DIS03 St Petersburg

  8. Trigger : (H4 * H5) * (Hcal1 U Hcal2) background μ scattered μ trigger signal H5 Hodoscopes coinc matrix (tC ~ 2ns) H4 thresh HCAL hadrons target beam Compass trigger Claude MARCHAND - DIS03 St Petersburg

  9. Trackers performance for 2002 run • Detector CoordEfficiencyResolution Timing • Scintillating fibers 21 94% 130 μm 0.45 ns • MicroMegas 12 95-98% 70 μm 8 ns • Drift Chambers 24 94-97% 170 μm • Straw tubes 18 > 90% ~ 270 μm • GEM detector 40 95-98% 50 μm 12 ns • MWPC 32 97-99% • overall tracking effiency : 80 to 95 % / p DC Claude MARCHAND - DIS03 St Petersburg

  10. RICH characteristics 5.3 m2 MWPCs with CsI-Photocathodes 84000 analog readout channels (Gassiplex) 80 m3 C4F10 ultra high cleaning 116 VUV mirrors 21 m2 Rich Event-Display Claude MARCHAND - DIS03 St Petersburg

  11. K π p π μ,e K q(mrad) p(GeV/c) RICH PID performance • 1photon= 1.4 mrad (design:0.8 mrad) mass spectrum <n photons/ring> = 14 CsI –QE ~ design zoom Claude MARCHAND - DIS03 St Petersburg

  12. 2002 Data sample Statistics: • Target polarized longitudinally: ˜ 1.2 fb-1 • Target polarized transversely: ˜ 0.3 fb-1 • ~4 109 good events, 270 Tb data Reconstruction: • Average time to process one event: 600ms/ev • 4 109 ev * 0.6s/ev ~ 200 days on 200 CPUs (with 50% overhead for tape access and farm uptime) Analysis: • Calibration of trackers (T0,RT) + alignement OK, • Calibration of RICH in progress • So far, 1st pass analysis for 16% long. and 66% transv. Claude MARCHAND - DIS03 St Petersburg

  13. pT Some reconstruction figures σ~7 MeV Claude MARCHAND - DIS03 St Petersburg

  14. ρ° , φ decay angular distributions (A. Korzenev) • Λ and Λ hyperon polarizations (V. Alexhakin) • Flavor decomposition of pPDF (SI-pDIS) • Transversity from Collins asymmetry (P. Pagano) • ΔG/G from high pT pairs • ΔG/G from open charm decay Summary of physics investigated so far Claude MARCHAND - DIS03 St Petersburg

  15. Exclusive ρ° production : angular decay distributions No acceptance corr., 1/6 of 2002 stat. Eμ’ > 20 GeV, ν > 30 GeV, ΔEmiss < 2.5 GeV T L High precision measurement of density matrix elements and double spin asymmetry Claude MARCHAND - DIS03 St Petersburg

  16. Flavour decomposition of ΔΣ • Extraction of Δq • from semi-inclusive at Q²>1 GeV2 • Combine Compass d data with SMC p and d • K identified in RICH • hyp: • COMPASS: xmin = 0.003 • HERMES: xmin = 0.02 • RHIC: xmin = 0.04 Claude MARCHAND - DIS03 St Petersburg

  17. Transversity from Collins asymmetry ~ 10 Million DIS events with transverse polarization: Q2 > 1 GeV2; 0.1 < y < 0.9 zh> 0.25 ; pTh > 0.1 GeV/c Claude MARCHAND - DIS03 St Petersburg

  18. h1 h2 Leading process h1 h2 Gluon radiation (Compton) h1 h2 Photon Gluon Fusion ΔG/G from high pT pairs Measured asymmetry Claude MARCHAND - DIS03 St Petersburg

  19. Experimental cuts: • μ, μ ’ + 2 hadrons, pT > 0.7 GeV/c • 0.4 < y < 0.9 • xF hadrons > 0.1 (current fragm.) ~ 0.1 ΔG/G from high pT pairs Expected error for 2002 data: Claude MARCHAND - DIS03 St Petersburg

  20. Experimental cuts: • μ, μ ’ + K- + π+ (Rich ID) • zD > 0.25 Photon Gluon Fusion ΔG/G from charm production All h+ h- Expected statistics for 2002 data: (according to proposal) MC π+ K- (Rich) M(h+ h-) GeV Claude MARCHAND - DIS03 St Petersburg

  21. Conclusion and outlook • 2002 run: 1.2 fb-1 long. + 0.3 fb-1 trans. • Phase 1 setup fully operational • Preliminary results for: • vector mesons, Λ polarization, transversity • Prospects for ΔG/G in 2004 (based on 2002 stat): • ->δ(ΔG/G)stat ~ 0.15 for high pT events Q2>1GeV2 • (~ 0.05 for all Q2) Claude MARCHAND - DIS03 St Petersburg

  22. MicroStrip Gaseous Chambers GEM (Munich,CERN) MicroMegas (Saclay) • 40 planes, 30cm x 30cm • two dimensional read-out • spatial resolution ~50 mm • time resolution ~ 12 ns • efficiency ~ 96 – 97% • 12 planes, 40cm x 40 cm • High flux (300 kHz/strip) • spatial resolution ~70 mm • time resolution ~ 8 ns • efficiency ~ 96 – 97% Claude MARCHAND - DIS03 St Petersburg

  23. hadrons e,μ Mu/hadron ID HCal2 HCal1 Muon Wall 2 Claude MARCHAND - DIS03 St Petersburg

  24. Λ spin structure • s-s symmetry of nucleon sea Λ polarization Secondary vertex outside target 1/6 of 2002 statistics Q2 > 1 GeV2 , 0.2 < y < 0.9 Claude MARCHAND - DIS03 St Petersburg

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