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Collins and Sivers asymmetries on the deutron target

SPIN @ Prague 2007. Girisan Venugopal University of Bonn (on behalf of the COMPASS collaboration). Collins and Sivers asymmetries on the deutron target. COMPASS experiment @ CERN. LHC. SPS. N. fixed target experiment at the CERN SPS 240 physicists from 28 Institutes, 11 Countries.

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Collins and Sivers asymmetries on the deutron target

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  1. SPIN @ Prague 2007 Girisan Venugopal University of Bonn (on behalf of the COMPASS collaboration) Collins and Sivers asymmetries on the deutron target

  2. COMPASS experiment @ CERN LHC SPS N • fixed target experiment at the CERN SPS • 240 physicists from 28 Institutes, 11 Countries Girisan Venugopal University of Bonn

  3. COMPASS spectrometer • high energy beam • large angular acceptance • broad kinematical range • longitudinally polarised muon beam • longitudinally or transversely polarised target MuonWall SM2 E/HCAL E/HCAL Straws DC MWPC SciFi Silicon Micromegas GEMs SM1 Polarised Target Muon Wall RICH mbeam Girisan Venugopal University of Bonn

  4. The COMPASS polarized target Girisan Venugopal University of Bonn

  5. Data taking 2002-2004 transversely polarized deuteron target (6LiD) ~ 20% of the running time Reconstructed DIS events (106) Girisan Venugopal University of Bonn

  6. Event selection DIS cuts: Q2 > 1 0.1 < y < 0.9 W > 5 GeV/c Hadron selection: z > 0.2 pt > 0.1 GeV/c Q2 > 1 Statistics 2002 - 2004: 8.5 * 106 positive hadrons 7.0 * 106 negative hadrons Girisan Venugopal University of Bonn

  7. Hadron identification Cherenkov thresholds: π ~ 3 GeV/c K ~ 9 GeV/c p ~ 17 GeV/c 3 m 6 m 5 m C4F10 photon detectors 2 σπ/K separation at 43 GeV/c Girisan Venugopal University of Bonn

  8. Transverse Spin Physics At leading order, the inner structure of the nucleon can be described with three Parton Distribution Function (PDF) q(x)Momentum distribution Well known – Unpolarized DIS Δq(x)Helicity distribution known – Polarized DIS ΔTq(x)Transversity distribution Largely unknown Girisan Venugopal University of Bonn

  9. Measuring Transversity Inclusive DIS Girisan Venugopal University of Bonn

  10. Measuring Transversity Drell-Yan process SIDIS FF DTq(x) Measured in COMPASS Girisan Venugopal University of Bonn

  11. Measuring Transversity Properties of Transversity distribution fuction • is chiral-odd: decouples from inclusive DIS • Observable effects are given only by the product ofTq (x)with an otherchiral-odd function Can be measured in SIDIS on a transversely polarised target via “quark polarimetry” Girisan Venugopal University of Bonn

  12. Collins effect in SIDIS The “quark polarimetry” relies on the Collins effect The fragmentation function of a transversely polarised quark has aspin dependent part “Collins” FF: Girisan Venugopal University of Bonn

  13. Collins effect in SIDIS Fragmentation of transversely polarized quarks to unpolarized hadrons The “Collins angle” is • C = h+S - p h,,sazimuthal angles of the hadron, transverse spin of the initial quark Transversity distribution function Collins fragmentation Function (is being measured in Belle Expt) Girisan Venugopal University of Bonn

  14. Collins asymmetries π K • only statistical errors shown (~1%), systematic errors considerably smaller • small asymmetries compatible with 0 for both +π, K and -π, K (ΔTu, ΔTd cancel in deuterium ) Girisan Venugopal University of Bonn

  15. Collins: Interpretation Global fit performed by M. Anselmino et.al 2006: final results from2002-2004 data NPB765 (2007)31 Talk given by A. Prokudin (International Workshop on Structure and Spectroscopy, Freiburg) Girisan Venugopal University of Bonn

  16. Sivers effect The intrinsic transverse momentum of unpolarized quarks in a transversely polarized nucleon can introduce a different azimuthal asymmetry It is related to the parton orbital angular momentum in a transversely polarized nucleon The “Sivers angle” is • S = h- S h,,sazimuthal angles of the hadron, transverse spin of the initial quark Sivers Function Girisan Venugopal University of Bonn

  17. Sivers asymmetries π K • only statistical errors shown (~1%), systematic errors considerably smaller • small asymmetries compatible with 0 for both +π, K and -π, K Girisan Venugopal University of Bonn

  18. Sivers: Interpretation Global fit performed by M. Anselmino et.al 2006: final results from2002-2004 data NPB765 (2007)31 Talk given by A. Prokudin (International Workshop on Structure and Spectroscopy, Freiburg) Girisan Venugopal University of Bonn

  19. Sivers: Interpretation The measured asymmetry on deuteron compatible with zero has been interpreted as Evidence for the Absence of Gluon Orbital Angular Momentum in the Nucleon S.J. Brodsky and S. Gardner, PLB643 (2006) 22 Girisan Venugopal University of Bonn

  20. Summary & Outlook The measured asymmetries on a Deuteron target are very small and compatible with zero Theoretical work aimed at a first extraction of transversity and Sivers distribution function is ongoing by different groups COMPASS measures this year with proton target Girisan Venugopal University of Bonn

  21. Thank you all !!! Girisan Venugopal University of Bonn

  22. Collins : Interpretation COMPASS 2002-2004 A.V. Efremov, K. Goeke and P. Schweitzer, PRD73 (2006) 094025 (ΔTq from Chiral Quark Soliton Model ) Girisan Venugopal University of Bonn

  23. Sivers: Interpretation COMPASS 2002-2004 • M. Anselmino et al., PRD72 (2005) 094007 • 13 parameter fit to HERMES and COMPASS 2002 data to extract the Sivers functions • comparison with COMPASS 2002-2004dataok Girisan Venugopal University of Bonn

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