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COMPASS experiment Status and reacent results

COMPASS experiment Status and reacent results. Ewa Rondio, Institute for Nuclear Studies, Warsaw, Poland Brookhaven , 3 May 200 5. The COMPASS Collaboration (230 Physicists from 12 Countries).

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COMPASS experiment Status and reacent results

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  1. COMPASS experimentStatus and reacent results Ewa Rondio, Institute for Nuclear Studies, Warsaw, Poland Brookhaven, 3 May 2005

  2. The COMPASS Collaboration(230 Physicists from 12 Countries) Bielefeld, Bochum, Bonn (ISKP & PI), Erlangen, Freiburg, Heidelberg, Mainz, München (LMU & TU) Dubna (LPP and LNP), Moscow (INR, LPI, State University), Protvino CERN Warsaw (SINS), Warsaw (TU), Warsaw (UW) Helsinki Prag Nagoya Saclay Lisboa Torino(University,INFN) Trieste(University,INFN) Burdwan, Calcutta Tel Aviv

  3. COMPASS: THE new fixed target facility at CERN !COmmon Muonand Proton Apparatus for Structureand Spectroscopy. - HISTORY • 1996 COMPASS proposal • 1997 conditional approval • 1998 MoU • 1999 – 2001 construction & installation • 2001 technical run • 2002, 2003, 2004 data taking • 2005 breakat Cern (LHC) • Restart in 2006 • at least until 2010 26. June 1998 Now 2004 8. April 1999

  4. nucleon spin structure • Gluon Polarization G/G • transverse spin structure function h1(x) • Flavor dependent polarized quark helicity densities q(x) • spin dependent fragmentation functions D • Exclusive VM-Production q Physics Goals Contribute to the understanding of the non-perturbative physics of the nucleon nucleon spectroscopy • Primakoff-Reactions • polarizability of  and K • glue balls and hybrids • charmed mesons and baryons • semi-leptonic decays • double-charmed baryons

  5. LHC COMPASS SPS

  6. The COMPASS Experiment Beam:2 . 108 µ+/ spill (4.8s / 16.2s) Beam momentum: 160 GeV/c Luminosity:~5 . 1032 cm-2 s-1Beam polarization:-76%

  7. COMPASS spectrometer Muon filter 2 MWPCs Beam:160 GeV µ+ 2.8. 108 µ/spill (4.8s/16.2s) ECal2 & Hcal2 SM2 ~50m Muon filter 1 ECal1 & Hcal1 RICH GEM & MWPCs SciFi SM1 GEM & MWPCs Silicon SciFi Scintillating fibers Polarization: • Beam: -76% • Target: max. 57% GEM & Straws Micromegas &Drift chambers Polarized target

  8. New detector technologies MicroMegas Trigger-System Straws Scintillating fiber trackers calorimeter readout GEM Readout electronics

  9. 3 m 6 m Single event vessel mirror wall photon detectors: CsI MWPC 5 m radiator: C4F10 Ring Imaging CHerenkov Counter (RICH) 116 VUV mirrors, surface area: 21m2 single photon: s >1.2 mrad ring: s >0.4 mrad photons/ring n ~14 /K sep. up to 40 GeV/c Photon detection 5.3 m2 MWPCs 16 CsI Photocathodes 84,000 analog readout channels detection of VUV photons (165-200 nm)

  10. K p hadrons e,μ hadron identification K p By RICH …and hadron calorimeters p(GeV/c) q(mrad) 

  11. COMPASS – two programs  with muon beam • Muons: data taking from 2002 -> 2004 will continue in 2006  with hadron beam • Hadrons: pilot run in 2004 Main goal

  12. Electric & Magnetic polarizability The Primakoff reaction ’, p1’ , p1  + Z  ’ + Z +  s1 = ( p1’ - k’ )2  *, k first data taken in 2004 expected ~30k events , k’ Z, p2’ Z, p2 t= ( p2’ – p2 )2

  13. Muon program : data 2002-2004 ongoing analysis • A1d and influence on QCD fit • Do and Do* for ΔG/G from open charm • DG/G from„high pT” sample: perturbative region (Q2>1GeV2) and photoproduction region (Q2<1GeV2) • Transversity studies (Collins and Sivers asymmetries) for single and two hadrons • Land Lhyperon production • Vector mesons • Search for pentaquarks In this talk – results with longitudinal target polarization

  14. Kinematic range covered Excellent for non-perturbative & perturbativephysics • small xBj • very small Q2  Q2 > 100 (GeV/c)2

  15. 3He – 4He Dilution refrigerator (T~50mK) superconductive Solenoid (2.5 T) Dipole (0.5 T) 1 2 two 60 cm long Target-Containers with opposite polarization 3 4 polarized 6LiD target 4 possible spin combinations: reversed every 8 hours or: reversed once a week Polarization: ~50%

  16. Asymmetry A1

  17. measurement of A1dalso test of the detector and of systematic effects controle PLB 612, 154 (2005) False asymmetries (combining configurations with the same spin orientation) Asymmetry for configuration With opposite spins - Spin effects expected Weighting with fDPt was used to optimize statistical accuracy Asymmetry can be calculated for combinations without expected effect (false asymmetry) or where spin effect is expected (A1)

  18. DOUBLE SPIN ASYMMETRY A1d COMPASS: 2002+2003 data 34 Million DIS events Q2 > 1 (GeV/c)2 0.1 < y < 0.9 more to come ftom 2004 Data displayed at experimental <Q2> of every xBj bin

  19. QCD fit with all DIS spin data, effect of Compass A1D

  20. NLO evolution, calculations on grid (x,Q2) scheme, χ2 minimization using Minuit 10 parameters fitted NDF : 173-10 Χ2 probability 14%

  21. Compass g1dand it’s influence on the QCD fit scheme with Compass new deuterium g1 data without

  22. Semi-inclusive asymmetries – also avalaiable Improvement at low x, consistent with SMC

  23. N DG/G at COMPASS Photon Gluon Fusion q = c cross section differencein charmed mesonproduction → theory well understood → experiment challenging q= u,d,s cross section difference in 2+1 jet productionin COMPASS: events with2 hadrons with high pT → experimentaly easier → theory difficult

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

  25. 80% 2002 data 317 D0 Cut on D* MKpps-MKp -mp[MeV/c2] MKp -mD0 [MeV/c2] D* tagging: D*→D0p Cuts: zD > 0.2 |cos *| < 0.85 (Background) 10 < pK < 35 GeV (RICH PID) MKpps-MKp -mp[MeV/c2] MKp -mD0[MeV/c2]

  26. Asymmetry for events with charm production (D0 and D*) D* is cleaner, but low statistics From here to ΔG/G • partonic asymmetrirs aLLPGF are needed

  27. Partonic asymmetries are calculated from parametrization obtained for MC simulated events good description of data with MC is required what MC parameters are best Result on ΔG/G can be expected soon from 2002-2004: s(DG/G) = 0.24 from open charm

  28. Hadron pairs with z „large” pT Idea proposed by • R.D.Carlitz, J.C.Collins and A.H.Mueller,Phys.Lett.B 214, 229 (1988). • A.Bravar,D.von Harrach and A.Kotzinian, Phys.Lett.B 421, 349 (1998) . Used in the analysis : • HERMES, A.Airapetian et al., Phys.Rev.Lett.84, 2584 (2000). • SMC, B.Adeva et al., Phys.Rev.D 70, 0102002 (2004)

  29. where:AlNlhhXmeasuredasymmetry, Δq/q approximated using A1 asymmetry N, aLL partonic asymmetry, R fraction of contributing processes

  30. h1 h2 N DG/G: pairs of high pT hadrons Photon Gluon Fusion • Current fragmentation • xF>0.1 • z>0.1 • 2 high pT hadrons • pT > 0.7 GeV/c • pT12+ pT22>2.5 GeV2 • m(h1h2) > 1.5 GeV

  31. Analysis done with LEPTO generator Initial and final state parton showers used Fragmentation function parameters modified kT statndard value (0.44) DG/G: pairs of high pT hadrons with Q2 >1 GeV2, 0.4 < y < 0.9 Asymmetry in production of hadron pairs with high pT: result for 2002+2003 data from this using RPGF obtained from MC with Uses only ~10% of data

  32. For Q2<1GeV2 much more datadifficulties with additional processes contributing (Pythia)

  33. Low Q2 scattering – Pythia simulation Contributing processes - sample after „high pT” selections signal background Contribution from the structure of the photon Contribution from the structure of the nucleon

  34. Systematic errors : • Quark polarization in the photon for VMD – minimum and maximum scenarios

  35. MC uncertainties • Missing NLO: scale dependence, parton shower on/off • tuning of parameters and data/MC parton fragmentation partons kT in nucleon and photon biggest uncertainty from kT in photon

  36. Data/MC

  37. From 2002 and 2003 data Obtained by averaging results for min. and max scenario in VDM

  38. Single hadons, low Q2

  39. Expected precission on the asymmetryteoretical calculations byB. Jaeger, A. Schaefer and M. Stratmann in NLO

  40. SUMMARY AND OUTLOOK • CERN is again contributing to the NUCLEON SPIN PUZZLE • Compass running in 2002-2004 brought interesting PHYSICS RESULTS, some already published MANY MORE IN PREPARATION data taking restarts in 2006 Approved program untill ~2010 with muon beams on polarized targets and hadron beams After  study of GPDS with DVCS and exclusive mezon production on hydrogen target (+recoil detector)

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