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

Fritz-Herbert Heinsius DIS 2004 The COMPASS Collaboration Broad Physics Program  G/G semi inclusive DIS –flavor dependent quark helicity density distributions  q –transverse quark spin distribution function h 1 (x) –polarised  fragmentation –vector mesons hadron spectroscopy with hadron beams 230 physicists from 12 countries 28 institutes

Fritz-Herbert Heinsius DIS 2004 Spin of the Nucleon = ½ ħ GG QCD analysis of g 1 (x,Q 2 ) Photon gluon fusion open charm high-p T ½  DIS:  ≈0.3 (CERN, SLAC, DESY) LGLG Measure generalized parton distributions LqLq

Fritz-Herbert Heinsius DIS 2004  G from QCD Analysis of g 1 polarised gluon distribution from QCD fits: Blümlein & Böttcher: fit to polarised data of EMC, E142, E143, E155, SMC, Hermes Nucl. Phys. B636 (02) 225 Hermes (2000)

Fritz-Herbert Heinsius DIS 2004 Spin of the Nucleon = ½ ħ GG QCD analysis of g 1 (x,Q 2 ) Photon gluon fusion open charm high-p T ½  DIS:  ≈0.3 (CERN, SLAC, DESY) LGLG Measure generalized parton distributions LqLq

Fritz-Herbert Heinsius DIS 2004 N  G/G at COMPASS Photon gluon fusion COMPASS SPS LHC Beam: µ + / spill (4.8s / 16.2s) Luminosity: ~ cm -2 s -1 Beam polarization: -76% Beam momentum: 160 GeV/c

Fritz-Herbert Heinsius DIS 2004  G/G at COMPASS N Polarised 6 LiD Target P target : 50% Dilution: 40% Two 60 cm long target cells with opposite polarisation Superconducting Solenoid (2.5 T ) 3 He – 4 He dilution refrigerator (T~50mK) Dipol (0.5 T) Reconstructed interaction vertices

Fritz-Herbert Heinsius DIS 2004  G/G at COMPASS 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 p T → experiment easy → theory difficult Photon gluon fusion N

Fritz-Herbert Heinsius DIS 2004 COMPASS Spectrometer 2003/04 

Fritz-Herbert Heinsius DIS 2004 New Technologies for Tracking and Particle ID Scintillating fiber trackers GEM MicroMegas Readout electronics Large area drift detectors TDC RICH CsI & MWPC readout Radiator: C 4 F 10

Fritz-Herbert Heinsius DIS 2004 and hadron calorimeters hadrons  Particle Identification  (mrad) p(GeV/c) p   With RICH Essential for reconstruction of D-Mesons

Fritz-Herbert Heinsius DIS 2004  G/G: Open Charm  PGF at NLO: Bojak, Stratmann NPB 540 (1999) 345; Contogouris et al. N D Photon-Gluon Fusion

Fritz-Herbert Heinsius DIS 2004 Cuts: z D > 0.2 |cos  * | < 0.85 (Background) 10 < p K < 35 GeV/c (RICH PID) M K  s -M K  -m  [MeV/c 2 ] M K  -m D 0 [MeV/c 2 ] D* tagging: D*→D 0  Cut on D 0 M K  s -M K  -m  [MeV/c 2 ]

Fritz-Herbert Heinsius DIS 2004 M K  -m D 0 [MeV/c 2 ] D* tagging : D*→D 0  D 0 →K  M K  s -M K  -m  [MeV/c 2 ] M K  -m D 0 [MeV/c 2 ] 317 D 0 80% 2002 data Cut on D*

Fritz-Herbert Heinsius DIS 2004  G/G: Prospects from Open Charm 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  G/G from data: 0.24

Fritz-Herbert Heinsius DIS 2004  G/G: Pairs of High p T Hadrons Current fragmentation –x F > 0.1 –z > high p T hadrons –p T > 0.7 GeV/c –p T1 2 + p T2 2 > 2.5 (GeV/c) 2 –m(h 1 h 2 ) > 1.5 GeV/c 2 Photon Gluon Fusion h1h1 h2h2 N

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

Fritz-Herbert Heinsius DIS 2004 How to get ΔG/G Photon Gluon Fusion QCD-Compton Leading Order fractions of cross section determined by Monte Carlo

Fritz-Herbert Heinsius DIS 2004 Additional Background Resolved Photon VMD - Pomeron Relevant for Q 2 <1 (GeV/c) 2

Fritz-Herbert Heinsius DIS 2004 Next Steps in high- p T Analysis Monte Carlo studies are in progress: PYTHIA –simulates all processes –PYTHIA used in HERMES analysis (Q 2 unmeasured) LEPTO –simulates PGF, QCD-Compton and LO DIS –LEPTO used in SMC analysis (Q 2 >1 (GeV/c) 2 selected) Projected error on  G/G for data (assuming fraction of PGF events is ¼ ): 0.05 [0.16 for Q 2 >1 (GeV/c) 2 ]

Fritz-Herbert Heinsius DIS 2004 Expected error on ΔG/G More COMPASS physics Inclusive and semi- inclusive asymmetries M. Leberig Transverse asymmetry A UT for charged pions H. Fischer COMPASS Summary First glance at open charm PGF with polarised target and beam Good perspectives for ΔG from high-p T hadron pairs proposal

Fritz-Herbert Heinsius DIS 2004 End of Talk

Fritz-Herbert Heinsius DIS 2004  G/G at COMPASS Open charm First reconstruction of charmed mesons with polarised target and beam: High p T hadron pairs Measured asymmetry from 2002 data: M K  -m D 0 [MeV/c 2 ] 317 D 0 80% 2002 data

Fritz-Herbert Heinsius DIS 2004 High p T cuts

Fritz-Herbert Heinsius DIS 2004 COMPASS Acceptance

Fritz-Herbert Heinsius DIS 2004 detection of VUV photons ( nm) Ring Imaging CHerenkov Counter (RICH) 116 VUV mirrors, surface area: 21 m 2 Photon detection 5.3 m 2 MWPCs 16 CsI Photocathodes 84,000 analog readout channels 5 m 6 m 3 m photondetectors: CsI MWPC mirrorwall vessel radiator: C 4 F 10 Single event single photon:  1.2 mrad ring:  0.4 mrad photons/ringn ~14 3  /K sep.up to 40 GeV/c