1. April 24, 2003Claude MARCHAND - DIS03 St Petersburg 1 Prospects for ΔG/G in COMPASS Compass Physics objectives Experiment layout 2002 data: status of analysis Prospects for ΔG/G

2. April 24, 2003Claude MARCHAND - DIS03 St Petersburg 2 Spin structure of the nucleon EMC, SMC, SLAC, HERMES : How is the rest of the nucleon spin (0.35) shared between ΔG and orbital momentum? Or Measure ΔG (Photon gluon fusion) (Generalized Parton Distributions)

3. April 24, 2003Claude MARCHAND - DIS03 St Petersburg 3 Physics at COMPASS Nucleon Spin Structure: Gluon polarization  G( η G )/G Polarised flavour dependent parton distributions  q(x) Λ Polarization (  D  q ) Transverse-spin distribution functions  T q(x) Common Muon and Proton Apparatus for Structure and Spectroscopy

4. April 24, 2003Claude MARCHAND - DIS03 St Petersburg 4 Determination of ΔG/G q=c: Open charm production q=u,d,s: high pairs Compass: E161: RHIC : e.g prompt photon + jet Photon Gluon Fusion

5. April 24, 2003Claude MARCHAND - DIS03 St Petersburg 5 COMPASS Collaboration Bielefeld, Bochum, Bonn (ISKP & PI), Erlangen, Freiburg, Heidelberg, Mainz, München (LMU & TU) Helsinki Saclay Tel Aviv Burdwan, Calcutta Torino (University,INFN), Trieste (University,INFN) Warsawa (SINS), Warsawa (TU) CERN Nagoya Praha Дубна (LPP and LNP), Москва (INR, LPI, State University),. Протвино Lisboa More than 220 physicists from 30 Institutes

6. April 24, 2003Claude MARCHAND - DIS03 St Petersburg 6 Polarization: Beam: ~80% Target: Beam: 160 GeV µ + 2. 10 8 µ/spill (4.8s/16.2s) Polarized target SM1 RICH ECal1 & Hcal1 Muon filter 1 SM2 MWPCs Micromegas &Drift chambers ECal2 & Hcal2 Muon filter 2 GEM & MWPCs SciFi GEM & MWPCs GEM & Straws Silicon SciFi Scintillating fibers ~50m COMPASS spectrometer

7. April 24, 2003Claude MARCHAND - DIS03 St Petersburg 7 Compass 6 LiD Polarized target Dynamic Nuclear Polarization Dilution factor: ~40% Maximum Polarization:+57% Longitudinal & transverse pol. 3 He – 4 He dilution refrigerator (T~50mK)

8. April 24, 2003Claude MARCHAND - DIS03 St Petersburg 8 COMPASS trigger scattered μbackground μ thresh Hodoscopes H5 H4 coinc matrix (t C ~ 2ns) hadrons target beam HCAL Trigger : (H4 * H5) * (Hcal1 U Hcal2) trigger signal

9. April 24, 2003Claude MARCHAND - DIS03 St Petersburg 9 Trackers performance for 2002 run Detector Coord Efficiency ResolutionTiming 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

10. April 24, 2003Claude MARCHAND - DIS03 St Petersburg 10 RICH characteristics 5.3 m 2 MWPCs with CsI-Photocathodes 84000 analog readout channels (Gassiplex) 80 m 3 C 4 F 10 ultra high cleaning 116 VUV mirrors 21 m 2 Rich Event-Display

11. April 24, 2003Claude MARCHAND - DIS03 St Petersburg 11 RICH PID performance  1photon = 1.4 mrad (design:0.8 mrad) = 14 = 14 CsI –QE ~ design  p π zoom mass spectrum  (mrad) p(GeV/c) πμ,e

12. April 24, 2003Claude MARCHAND - DIS03 St Petersburg 12 2002 Data sample Statistics: Target polarized longitudinally:˜ 1.2 fb -1 Target polarized transversely:˜ 0.3 fb -1 ~4 10 9 good events, 270 Tb data Reconstruction: Average time to process one event: 600ms/ev 4 10 9 ev * 0.6s/ev ~ 150 days on 200 CPUs Analysis: Calibration of trackers (T 0,RT) + alignement OK, Calibration of RICH in progress So far, 1st pass analysis for 16% long. and 66% transv.

13. April 24, 2003Claude MARCHAND - DIS03 St Petersburg 13 Some reconstruction figures pTpT σ~7 MeV

14. April 24, 2003Claude MARCHAND - DIS03 St Petersburg 14 Summary of physics investigated so far 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 p T pairs ΔG/G from open charm decay

15. April 24, 2003Claude 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, ΔE miss < 2.5 GeV High precision measurement of density matrix elements and double spin asymmetry TL

16. April 24, 2003Claude MARCHAND - DIS03 St Petersburg 16 Flavour decomposition of ΔΣ Extraction of Δq from semi-inclusive at Q²>1 GeV 2 Combine Compass d data with SMC p and d K identified in RICH hyp: COMPASS: x min = 0.003 HERMES: x min = 0.02 RHIC:x min = 0.04

17. April 24, 2003Claude MARCHAND - DIS03 St Petersburg 17 Transversity from Collins asymmetry ~ 10 Million DIS events with transverse polarization: Q 2 > 1 GeV 2 ; 0.1 < y < 0.9 z h > 0.25 ; p T h > 0.1 GeV/c

18. April 24, 2003Claude MARCHAND - DIS03 St Petersburg 18 ΔG/G from high p T pairs h1h1 h2h2 Leading process h1h1 h2h2 Gluon radiation (Compton) h1h1 h2h2 Photon Gluon Fusion Measured asymmetry

19. April 24, 2003Claude MARCHAND - DIS03 St Petersburg 19 ΔG/G from high p T pairs Experimental cuts: μ, μ ’ + 2 hadrons, p T > 0.7 GeV/c 0.4 < y < 0.9 xF hadrons > 0.1 (current fragm.) Expected error for 2002 data: ~ 0.1

20. April 24, 2003Claude MARCHAND - DIS03 St Petersburg 20 ΔG/G from charm production Experimental cuts: μ, μ ’ + K - + π + (Rich ID) z D > 0.25 Expected statistics for 2002 data: (according to proposal) Photon Gluon Fusion All h + h - π + K - (Rich) MC M(h + h - ) GeV

21. April 24, 2003Claude 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 p T events Q 2 >1GeV 2 (~ 0.05 for all Q 2 )

22. April 24, 2003Claude MARCHAND - DIS03 St Petersburg 22 MicroStrip Gaseous Chambers 40 planes, 30cm x 30cm two dimensional read-out spatial resolution ~50  m time resolution ~ 12 ns efficiency ~ 96 – 97% GEM (Munich,CERN)MicroMegas (Saclay) 12 planes, 40cm x 40 cm High flux (300 kHz/strip) spatial resolution ~70  m time resolution ~ 8 ns efficiency ~ 96 – 97%

23. April 24, 2003Claude MARCHAND - DIS03 St Petersburg 23 Mu/hadron ID hadrons e,μ HCal1 HCal2 Muon Wall 2

24. April 24, 2003Claude MARCHAND - DIS03 St Petersburg 24 Λ polarization Secondary vertex outside target 1/6 of 2002 statistics Q 2 > 1 GeV 2, 0.2 < y < 0.9 Λ spin structure s-s symmetry of nucleon sea