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Measurements of TMD effects at COMPASS, HERMES and RHIC

This article explores Transverse Momentum Dependent (TMD) effects through measurements at COMPASS, HERMES, and RHIC experiments, discussing azimuthal asymmetries, polarisation, quark structure, and more in nucleon structure. It highlights key findings and future implications in the study of nucleon structure.

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Measurements of TMD effects at COMPASS, HERMES and RHIC

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  1. Measurements of TMD effects at COMPASS, HERMES and RHIC Anna Martin Trieste University & INFN (Italy)

  2. Measurements of TMD effects at COMPASS, HERMES and RHIC • introduction • the HERMES and the COMPASS experiments and results for SSA in SIDIS • the RHIC experiments and results from transversely polarised pp scattering • future unpolarides azimuthal asymmetriesΛ polarisation 2h inclusive production October 18, 2010

  3. Transverse Spin and Momentum Structureof the Nucleon large international theoretical and experimental effort SIDIS on unpolarised and polarised targets:HERMES at DESY COMPASS at CERN spin experiments at JLaband eRHIC, EIC, ENC hard polarised pp scattering:spin experiments at RHIC / BNL and several (future) projects for (polarised) Drell-Yan:COMPASS FNAL, JParc, RHIC, JINR, IHEPPAX at FAIR / GSI October 18, 2010

  4. number density Sivers helicity transversity Boer Mulders The Structure of the Nucleon three distribution functions are necessary to describe the quark structure of the nucleon at LO in the collinear case taking into account the quark intrinsic transverse momentum kT , at leading order 8 PDFs are needed for a full description of the nucleon structure nucleon polarisation quarkpolarisation “TMDs” SIDIS gives access to all of them test the present description quantify the possible effects October 18, 2010

  5. DIS / SIDIS October 18, 2010

  6. DIS / SIDIS L&T pol SIDIS L pol DIS October 18, 2010

  7. HERMES and COMPASS data taking with T polarised target:2002-2005 (p) data taking with T polarised target:2002-2004 (d) 2007 (p) 2010 (p) October 18, 2010

  8. HERMES and COMPASS • polarized (<60%) e+/e- beam of 27 GeV, both helicity states • pure gas targets with T (p) and L (p,d) polarization, fast spin-flip of target • RICH PID K: 2-15 GeV • polarized (~-80%) μ+ of 160GeV • NH3 (p) and 6LiD (d) targets with T and L polarization, 2 (3) cells with opposite P,polarisation reversal every ~8h • RICH PID K: 9-50 GeV October 18, 2010

  9. Q2 (GeV2) W = 12 GeV W = 7.5 GeV W = 5 GeV W = 12 GeV Q2 (GeV2) W = 7.5 GeV 160 GeV beam 27.5 GeV beam W = 5 GeV 160 GeV W = 3.3 GeV x x HERMES and COMPASS kinematics October 18, 2010

  10. Single Spin Asymmetries in SIDIS October 18, 2010

  11. SIDIS cross-section 3 modulations with unpol target 3 modulations with L pol target 8 modulations with T pol target 18 structure functions 14 azimuthal modulations h (S) hadron (nucleon spin) azimuthal angle in GNS A Bacchetta et al., 2006 October 18, 2010

  12. SIDIS cross-section A Bacchetta et al., 2006 by now, all measured October 18, 2010

  13. azimuthal asymmetriesunpolarised target October 18, 2010

  14. unpolarised target d d d p,d p,d p,d Cahn effect Boer-Mulders + ... twist-3 Boer-Mulders Cahn effect(twist 4, 1/Q2) 3 independent azimuthal modulations October 18, 2010

  15. unpolarised target October 18, 2010

  16. DIS2004 z and PT dependencein agreement with CLASS after accounting for differences in the kinematics unpolarised target October 18, 2010

  17. COMPASS 6LiD (25% of the 2004 data) preliminary Q2 > 1 ( GeV/c )2 θγlab < 0.06 rad 0.003 < x < 0.13 0.2 < y < 0.9 W > 5 GeV/c2 0.2 < z < 0.85 0.1 < PTh < 1 GeV/c COMPASS 6LiD (25% of the 2004 data) preliminary SPIN2010 p data:COMPASS II unpolarised target deuteron October 18, 2010

  18. unpolarised target SIDIS differential cross-section deuteron JF Rajotte, Prague 2010 October 18, 2010

  19. azimuthal asymmetrieslongitudinal targetpolarisation October 18, 2010

  20. longitudinal target polarisation ... twist 3 + ... twist 3 worm-gear October 18, 2010

  21. Avakian et al., 2008 hep-ex/1007.1562 (accepted EPJC) longitudinal target polarisation small, consistent with zero within the errors COMPASS sign convention October 18, 2010

  22. longitudinal target polarisation transverse component of the target polarisation worm-gear + ... + ... pretzelosity Sivers transversity ... twist 3 twist 3 worm-gear October 18, 2010

  23. longitudinal target polarisation  was interpreted as the first signal of atransversity PDF different from zero Phys. Rev. Lett. 84 (2000) 4047 October 18, 2010

  24. π+ π0 □ d ● p π- K+ longitudinal target polarisation October 18, 2010

  25. longitudinal target polarisation proton a subleading-twist effect they can be comparable to leading-twist effects October 18, 2010

  26. (COMPASS sign convention) PLB 562(2003)182 hep-ex/1007.1562 (accepted EPJC) longitudinal target polarisation deuteron results consistent with zero also forthe other UL asymmetries next: extract the same asymmetries from the 2007 p data no evident x dependence in COMPASS October 18, 2010

  27. azimuthal asymmetriestransverse targetpolarisation October 18, 2010

  28. transverse target polarisation ... 8 modulations Sivers asymmetry Collins asymmetry October 18, 2010

  29. transversity “Collins FF” Collins asymmetry if transversity PDFs and Collins FFs different from zero modulation in the azimuthal distribution of the final state hadrons “recursive fragmentation model with quark spin”[X. Artru, arXiv:1001.1061] D. Sivers, TMD2010 data from Belle (and BaBar) October 18, 2010

  30. the COMPASS d, HERMES p, and BELLE data are well described in global fits  first extractions of the Collins FFs and the transversity PDFs, and tensor charge Collins asymmetry 2005 • first strong signals seen by HERMES on protons: MILESTONE! • no signal seen by COMPASS on deuterons interpreted as u- and d-quark cancellation M. Anselmino et al.,Ringberg Workshop on New Trends in HERA Physics 2008Nucl.Phys.Proc.Suppl.191 (2009) 98 energy dependence? October 18, 2010

  31. PLB 693 (2010) 11 Collins asymmetry - proton final HERMES results • clear signal for π+ and π-, opposite sign • K+ signal larger than π+: role of sea quarks? kT dependence of the FF? • higher twist effects?limited statistics to study Q2 dependence October 18, 2010

  32. PLB 693 (2010) 11 Collins asymmetry - proton final HEMES results • clear signal for π+ and π-, opposite sign • K+ signal larger than π+: role of sea quarks? kT dependence of the FF? • higher twist effects?limited statistics to study Q2 dependence October 18, 2010

  33. PLB 692 (2010) 240 Collins asymmetry - proton final COMPASS results from 2007 data • at small x, the asymmetries are compatible with zero • large signal in the valence region of opposite sign for positive and negative hadrons October 18, 2010

  34. SPIN2010 Collins asymmetry - proton COMPASS results from 2007 data π- π+ K- K+ October 18, 2010

  35. Collins asymmetry - proton same sign and strength: a very important, not obvious result! October 18, 2010

  36. Collins asymmetry - summary transversity is different from zero and can be measured in SIDIS thanks to the “Collins effect” the work has just started and many properties can already be extracted from the existing data more statistics is needed to map the Q2, x, z and p┴ dependencea higher precision measurement is ongoing at COMPASS October 18, 2010

  37. transverse target polarisation ... 8 modulations Sivers asymmetry Collins asymmetry October 18, 2010

  38. Sivers asymmetry 2005 • first strong signal seen by HERMES for π+ on protons • no signal seen by COMPASS for h+ andh- on deuterons interpreted as u- and d-quark cancellation  first extractions of the Sivers function from HERMES p (and COMPASS d) data good description of the existing experimental results (before the final HERMES and COMPASS p results, and the JLab E06-010 preliminary results on 3He) M. Anselmino et al., Transversity2005 October 18, 2010

  39. Sivers asymmetry - proton final HERMES results • clear signal for π+ and K+over all the measured x range • saturation for PT > 0.4 GeV/c • difference between K+ and π+: role of sea quarks? larger at lower Q2 higher twist effects in K production? no energy dependence is expected COMPASS p results October 18, 2010

  40. PLB 692 (2010) 240 h- ~ 0.5 sstat h+ ~ 0.8 sstat plusa scale (abs) uncertainty of± 0.01 systematic errors Sivers asymmetry - proton final COMPASS results from 2007 data evidence for a positive signal for h+,which extends to small x, in the region not measured before October 18, 2010

  41. SPIN2010 Sivers asymmetry - proton COMPASS results from 2007 data π- π- π+ π+ K- K- K+ K+ October 18, 2010

  42. Sivers asymmetry - proton h+ COMPASS asymmetry: same sign smaller by a factor ~ 2 October 18, 2010

  43. Sivers asymmetry - proton hints for a possible unexpectedW dependence ofthe h+ Sivers asymmetry Q2 dependence? no definite conclusion with the present accuracy: higher precision measurements needed  2010 data October 18, 2010

  44. Sivers asymmetry - summary clear evidence of a positive signal on p for positive particles several interesting points to be understood: • pT dependence • K+ asymmetries • possible Q2 / W dependence new global fits including all the most recent results October 18, 2010

  45. transverse target polarisation ... HERMES:π, K on p COMPASS: h+- on d and p Sivers Collins COMPASS: h+- on d and p all small, compatible with zero in COMPASS October 18, 2010

  46. other T SSAs October 18, 2010

  47. other T SSAs October 18, 2010

  48. transverse target polarisation ... HERMES:π, K on p COMPASS: h+- on d and p Sivers Collins HERMES: differentfrom zero COMPASS: h+- on d and p all small, compatible with zero in COMPASS October 18, 2010

  49. other T SSAs October 18, 2010

  50. azimuthal asymmetries in SIDIS - summary • many new experimental results are available • they should allow to answer at least some open questions • other measurements will come soon • 2010 COMPASS p data global fits / calculations, using • data from different experiments • all the measured SIDIS azimuthal asymmetries are needed October 18, 2010

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