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CIPANP 2009

CIPANP 2009. Tenth Conference on the Intersections of Particle and Nuclear Physics. Transverse Spin Effects In Semi-Inclusive DIS at COMPASS Rainer Joosten University of Bonn on behalf of the COMPASS Collaboration. ( E',k '). ( E,k ). g * q=( n ,q ). Semi-inclusive DIS.

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CIPANP 2009

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  1. CIPANP 2009 Tenth Conference on the Intersections of Particle and Nuclear Physics Transverse Spin Effects In Semi-Inclusive DIS at COMPASS Rainer JoostenUniversity of Bonn on behalf of the COMPASS Collaboration

  2. (E',k') (E,k) g*q=(n,q ) Semi-inclusive DIS I will focus (mostly) on SIDIS 1-hadron production: using different targets (p, d, n) and identifying the final hadron one can perform flavour separation unique feature of SIDIS < lepton nucleon

  3. q(x) = q+(x) + q-(x) Transverse Spin Physics Integrated over kT: three quark distribution functions contribute in leading order f1(x) g1(x) Dq(x) = q+(x) – q-(x) Helicity h1(x) DTq(x) decouples from inclusive DIS because helicityof quark must flip DTq(x) = qT(x) – qT(x) Transversity Þ SIDIS

  4. h q q h Collins-Effect The CollinsFFcorrelatesthe transversespin of thefragmentingquarkand the transversemomentumPh of producedhadron h The measured asymmetry AColl gives access to the transversity distribution times the Collins fragmentation function:

  5. Sivers Collins Full SIDIS cross-section in NLO A Bacchetta, M Diehl, K Goeke, A Metz, P Mulders, M Schlegel (06) 18 structure functions 8 modulations (4 LO) transverselypolarizedtarget

  6. Sivers Effect Distribution of unpolarized quarks with transverse momentum kT in a transversely polarized nucleon The presence of spin can distort the distribution of quarks (needs orbital angular momentum of quarks) The Sivers asymmetry: A distortion in the distribution of quarks in transverse space can give rise to a nonzero Sivers function

  7. COMPASS • high energy beam • large angular acceptance • broad kinematical range Polarized Target: 2002-2004:6LiD (PT≈ 50%) 2007: NH3 (PT≈ 85%) solid target cells Polarization reversal: once a week • two stage spectrometer • Large Angle Spectrometer (SM1), • Small Angle Spectrometer (SM2) • PID • RICH in LAS MuonWall SM2 E/HCAL E/HCAL SM1 MuonWall Polarised Target RICH • beam: • 160 GeV/c • longitudinal polarisation -76% • intensity 2·108 µ+/spill (4.8s/16.2s) mbeam

  8. Deuteron Results: Sivers Effect Physics Letters B 673 (2009) 127–135 Deuteron Target 2002-2004 Data arecompatiblewith 0 ! Strongindication of cancelation of u and d quarkSiversFunctions in deuterontarget Constrains d quarkcontribution in global fit only statistical errors shown Systematic error below 30% of the statistical one final results from 2002-2004 data

  9. Extracting the SiversFunction usual unpolarised fragmentation function new results using latest HERMES (p) and COMPASS (d) pion and kaon data

  10. Deuteron Results: Collins Effect Physics Letters B 673 (2009) 127–135 Deuteron target 2002-2004 only statistical errors shown Asymmetriescompatiblewith 0 ! Againindication of cancelation of u and d Quark contributionfor a deuterontarget Access to d quarkcontribution in global fit Systematic error below 30% of the statistical one final results from 2002-2004 data

  11. ExtractingTransversity A. Prokudin: Transversity 08, Ferrara new results using latest HERMES (p) COMPASS (d) pion data, and BELLE data

  12. Event Selection DIS cuts: • Q2>1 (GeV/c)2 • 0.1<y<0.9 • W>5 GeV/c2 • All hadrons • Energy Deposit in HCALs>Thr. ( 4 GeV HCal1 and 5 GeV Hcal2 ) • pT>0.1 GeV/c • z>0.2

  13. Asymmetry Extraction Splitting middle cell into two parts • two couples of cells with opposite polarization • two independent values for the asymmetries per period • 2D Binned Maximum Log-Likelihood Fit: • eight by eight grid in fh and fS; • in each bin of the matrix one expects Nj counts :

  14. Asymmetry Extraction - II Separation of acceptance and spin dependent modulations: Coupling of two cells (u,d) with opposite polarization () and two periods (p1,p2) with opposite target polarization: Reasonable assumption: 4 · 64 = 256 nonlinear equations 1 + 8 + 3 · 64 = 201 fit parameter Systematic error: For this analysis: overall systematic error is 30% and 50% of the statistical error for Collins and Sivers respectively

  15. Sivers asymmetry– proton data systematic errors ~ 0.5 sstat the measured symmetries are small, compatible with zero

  16. Sivers asymmetry– proton data comparison with the most recent predictions from M. Anselmino et al. arXiv:0805.2677

  17. Sivers asymmetry– proton data comparison with predictions from S.Arnold, A.V.Efremov, K.Goeke, M.Schlegel and P.Schweitzer, arXiv:0805.2137

  18. Collins over the full 2007 sample Analysis of the data collected in the first part of the 2007 run • Reproduction of the data with improved quality • Improve quality checks • New unbinned Likelihood asymmetry extraction resulting in an increase of usable statistics for the Collins asymmetries by ~ a factor 3

  19. Collins asymmetry systematic errors ~ 0.5 sstat at small x, the asymmetries are compatible with zero in the valence region the asymmetries are different from zero, of opposite sign for positive and negative hadrons, and have the same strength and sign as HERMES

  20. Compass proton data comparison with M. Anselmino et al. predictions

  21. Compass proton data comparison with HERMES data

  22. Transversity in 2-Hadron Production • R defined by: • R = (z1p2 – z2p1)/(z1+z2) • (X. Artru, hep-ph/0207309) R

  23. Transversity in 2-Hadron Production The measured asymmetry ARS is a convolution of Transversity and the „Interference Fragmentation Function“

  24. Data selection in 2-Hadron Production • DIS cuts as in the 1-Hadron analysis • Hadron cuts:

  25. Transversity in 2-Hadron Production

  26. CONCLUSIONS • Transversity, Collins Function and Sivers Function • Great progress in determining transversity, Sivers and Collins function based on pion and kaon data by HERMES, Belle and COMPASS • COMPASS Collins Asymmetry on Proton Target: • different from zero, comparable to HERMES • agreement with predictions of Anselmino et al. • COMPASS Sivers Asymmetry on Proton Target: • small and compatible with zero within the statistical errors Extraction of the Sivers asymmetry on the full 2007 run difficult • Hadron Pair-Production: • Asymmetry significantly different from zero • - in agreement with predictions • Two hadron Interference FF different from zero

  27. Outlook ThankYou !! • We have abundant and good data on tape! • Now we willanalyze all data and learn as much as possible from it! • There is more to come from COMPASS a proposal has been worked out and submitted to Cern’s SPSC: A long transverse spin run is planned for the year 2010

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