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TMD and Transverse Spin Measurements at COMPASS: status and perspectives

TMD and Transverse Spin Measurements at COMPASS: status and perspectives. Franco Bradamante Trieste University and INFN on behalf of the COMPASS Collaboration. Transverse momentum, spin, and position distributions of partons in hadrons. ECT* June 11, 2007. Outlook. COMPASS

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TMD and Transverse Spin Measurements at COMPASS: status and perspectives

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  1. TMD and Transverse Spin Measurementsat COMPASS:status and perspectives Franco BradamanteTrieste University and INFNon behalf of the COMPASS Collaboration Transverse momentum, spin, and position distributions of partons in hadrons ECT* June 11, 2007 F. Bradamante

  2. Outlook • COMPASS • Results on asymmetries • Transversity Distribution Function • Sivers Distribution Function • Other TMD Distribution Function • Conclusions and future programs F. Bradamante

  3. COMPASS • beam: 160 GeV/c polarisation - 76% (2002-03) - 80% (2004) • intensity 2·108 µ+/spill (4.8s/16.2s) • high energy beam • large angular acceptance • broad kinematical range two stages spectrometer Large Angle Spectrometer (SM1), Small Angle Spectrometer (SM2) tracking, calorimetry, PID NEW TECHNOLOGIES MuonWall SM2 E/HCAL E/HCAL SM1 MuonWall Polarised Target SciFi Silicon Micromegas GEMs Straws SDC MWPC W45 RICH mbeam F. Bradamante

  4. 3He – 4He Dilution refrigerator (T~50mK) superconductive Solenoid (2.5 T) Dipole (0.5 T) the COMPASS target system (2002-2004) solid state target operated in frozen spin mode • 2002-2004: 6LiD • dilution factor f = 0.38 polarization PT = 50%~20% of the timetransversely polarised • during data taking with • transverse polarization • dipole field always  • polarization reversal in the 2 cells after ~ 5 days • 2006: • PTM replaced with • the large acceptance • COMPASS magnet • 2 3 cells two 60 cm long cells with opposite polarisation (systematics) dN/dz 4000 2000 0 -1000 0 1000 zvtx (mm) F. Bradamante

  5. SIDIS events (106) 11 days (19) 9 days (14) 14 days (24) data taking with transversely polarised target 2002-2004: 6LiD F. Bradamante

  6. SIDIS kinematics F. Bradamante

  7. SIDIS kinematics F. Bradamante

  8. Outlook • COMPASS • Results on asymmetries • Transversity Distribution Function • Sivers Distribution Function • Other TMD Distribution Function • Conclusions and future programs F. Bradamante

  9. Transversity Distribution Function three quark distribution functions (DF) are necessary to describe the structure of the nucleon at LO unpolarised DF DF of a quark with momentum xP in a nucleon well known – unpolarised DIS q(x) f1q (x) helicity DF difference of DF of quarks with spin parallel or anti parallele to the nucleon spinin a longitudinally polarised nucleon known – polarised DIS Dq(x) g1q(x) transversity DF difference of DF of quarks with spin parallel or anti parallele to the nucleon spinin a transversely polarised nucleon DTq(x) = q↑↑(x) - q↑↓(x) h1q(x), dq(x), dTq(x) largely unknown ALL 3 OF EQUAL IMPORTANCE F. Bradamante

  10. Transversity Distribution Function DTq(x),h1q(x),dq(x), dTq(x) , q=uv, dv, qsea • properties: • probes the relativistic nature of quark dynamics • no contribution from the gluons  simple Q2 evolution • positivity (Soffer) bound • first moments: tensor charge • sum rule for transverse spinin Parton Model framework • it is related to GPD’s • ischiral-odd: decouples from inclusive DIS Bakker, Leader, Trueman, PRD 70 (04) F. Bradamante

  11. Transversity DF: how to measure it the Transversity DF is chiral-odd: observable effects are given only by the product ofTq (x)and an other chiral-odd function can be measured in SIDIS on a transversely polarised target via “quark polarimetry” all measured in COMPASS F. Bradamante

  12. the fragmentation function of a transversely polarised quark has aspin dependent part “Collins” FF: Collins asymmetry the “quark polarimetry” relies on the Collins effect a quark moving “horizontally” and polarized “upwards” would emit the leading meson preferentially on the “left” side of the jet in SIDIS the “Collins angle” is • C = h-s’ = h+S - p h,s’,Sazimuthal angles of the hadron momentum, of the spin of the fragmenting quark and of the nucleon in the GNS F. Bradamante

  13. Collins asymmetry distribution of the hadrons: ± refer to the opposite orientation of the transverse spin of the nucleon PT (f·PT) is the target polarisation; DNNis the transverse spin transfer coefficient initial  struck quark in each angular bin one measures the quantities - reduces acceptance variation effects - at first order, spin independent effects cancel out and fitting them the “Collins Asymmetry” is extracted F. Bradamante

  14. Collins Fragmentation Function measurable in e+e– annihilation • first attempts to measured it from the correlation between the azimuthal angles of p’s from e+e– annihilation using LEP data most recent data, shown at SPIN2006 UL and UC double ratios last year: great news from BELLE the Collins FF has been measured in e+e– annihilation, and it is different from zero! measurement of the correlation between the azimuthal angles of p‘s in the near jet and in the far jet from e+e– annihilation F. Bradamante

  15. Collins asymmetry transversely polarised deuteron target charged hadrons(mostly pions) • 2004: first results from2002 dataPRL94 (2005) 202002 confirmed by • 2006: final results from2002-2004 data NPB765 (2007)31 asymmetries compatible with zero within the statistical errors (syst. errors much smaller) the same with leading h F. Bradamante

  16. preliminary 2002-2004 Collins asymmetry naïve interpretation of the data (parton model, valence region) • proton data  unfavored Collins FF ~ – favored Collins FF at variance with unpol case u quark dominance (d quark DF ~ unconstrained) • deuteron data some (small) effect expected even if  cancellation between Tu (x) and Td (x) access to Td (x) F. Bradamante

  17. Efremov et al, PRD 73, 094025 (2006) chiral quark-soliton model Vogelsang Yuan, PRD 72, 054028(2005) Soffer bound Anselmino et al, BNL UM 2006 Soffer bound & Tq = q Collins asymmetry 2005-2006: theoretical work mainly fitting HERMES data comparing with BELLE and COMPASS 2002 data • favored Collins FF ~ – unfavored Collins FF • u-dominance • agreement with the first Belleand COMPASS 2002 data • marginal agreement with the new deuterium data using the new Belle, the HERMES and the COMPASS 2002-2004 data first extraction from transverity from a global analys A. Efremov, A. Prokudin, P. Schweitzer F. Bradamante

  18. results on deuteron for p+andp– , K+and K– from 2003-2004 data C4F10 threshold: p~2 GeV/c K ~ 10 GeV/c Collins asymmetry for pions and kaons together with measurements on different targets, relevant for flavour decomposition F. Bradamante

  19. Collins asymmetry for pions and kaons preliminary 2002-2004 data proton (2002-05  DIS07) preliminary 2003-2004 data deuteron COMPASS sign convention F. Bradamante

  20. Transversity DF: how to measure it the Transversity DF is chiral-odd: observable effects are given only by the product ofTq (x)and an other chiral-odd function can be measured in SIDIS on a transversely polarised target via “quark polarimetry” alternative way to access transversity not sensible to transverse momenta F. Bradamante

  21. two-hadron asymmetries in inclusive production of hadron pairs, one can define the angle f Rand measure an azimuthal asymmetry from the modulation of the number of events in RS=fR - fs’ presently unknown being measured in e+e- (BELLE) expected to depend on the hadron pair invariant mass F. Bradamante

  22. 2002-2004 data all +/- pairs 2002-2004 data all +/- pairs preliminary x deuteron COMPASS kin two-hadron asymmetries deuteron target as expected from the measured values of the Collins asymmetry, also the two hadron asymmetry ~ 0 (whatever the size of the Interference Fragmentation Function) similar results ordering in pTh, z A. Bacchetta, M. Radici PRD74(2006)114007 model for DiFF F. Bradamante

  23. two-hadron asymmetries identified hadrons on the deuteron target F. Bradamante

  24. p+p– K+p– p+K– K+K– two-hadron asymmetries identified hadrons on the deuteron target F. Bradamante

  25. two-hadron asymmetries identified hadrons on the deuteron target p+p– K+p– p+K– K+K– F. Bradamante

  26. F. Bradamante

  27. Transversity DF: how to measure it the Transversity DF is chiral-odd: observable effects are given only by the product ofTq (x)and an other chiral-odd function can be measured in SIDIS on a transversely polarised target via “quark polarimetry” alternative way to access transversity independent on Transverse Momentum … the favorite in some models (statistics) F. Bradamante

  28. L polarimetry S x 10 all Q2 F. Bradamante

  29. L polarimetry systematic errors not larger than statistical errors RICH ID not used yet; some other improvement in selection still foreseen F. Bradamante

  30. Outlook • COMPASS • Results on asymmetries • Transversity Distribution Function • Sivers Distribution Function • Other TMD Distribution Function • Conclusions and future programs F. Bradamante

  31. Measurement of the Sivers DF in SIDIS • requires final/initial-state interactions quark rescattering via soft gluon exchange • should change sign from SIDIS to DY (important test !!) • it is related to the parton orbital angular momentum in a transversely polarized nucleon it is the most famous of the TMD parton distribution functions it is related to an intrinsic asymmetry in the parton transverse momentum distribution induced by the nucleon spin F. Bradamante

  32. S Sivers asymmetry appears in SIDIS as a modulation in the “Sivers angle” S • S = h- S hazimuthal angle of hadron momentum Sazimuthal angle of the spin of the nucleon the “Sivers angle” Sand the “Collins angle” C are independent the Collins and Sivers asymmetries can be disentangled and extracted from the same data in SIDIS on a transversely polarised target F. Bradamante

  33. Sivers asymmetry the Collins and Sivers asymmetries can be disentangled and extracted from the same data in SIDIS on a transversely polarised target 2002-2004 data NPB765(2007)31 to extract the Collins and Sivers asymmetries the measured quantities are fitted separately with the functions check: fit of with (“2D fit”) 8 parameter fit B. Parsamyan F. Bradamante

  34. Sivers asymmetry deuteron targettransversely polarised charged hadrons(mostly pions) • 2004: results from2002 dataPRL94(2005)202002 confirmed by • 2006: results from2002-2004 data NPB765(2007)31 asymmetries compatible with zero within the statistical errors (systematic errors much smaller) F. Bradamante

  35. Sivers asymmetry for pions and kaons preliminary 2002-2004 data proton (2002-05  DIS07) preliminary 2003-2004 data deuteron F. Bradamante

  36. proton data asymmetry for p+ > 0, asymmetry for p-≈ 0 Sivers DF for d-quark ≈ - 2 Sivers DF for u-quark • deuteron data preliminary 2002-2004 2 Sivers asymmetry naïve interpretation of the data(parton model, valence region) preliminary 2002-2004 the measured asymmetriescompatible with zero suggest F. Bradamante

  37. Sivers asymmetry 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 F. Bradamante

  38. Outlook • COMPASS • Results on asymmetries • Transversity Distribution Function • Sivers Distribution Function • Other TMD Distribution Function • Conclusions and future programs F. Bradamante

  39. semi-inclusive cross-section18 structure functions 4 A Bacchetta, M Diehl, K Goeke, A Metz, P Mulders, M Schlegel (06) 1 2 2 6 3 F. Bradamante

  40. semi-inclusive cross-section18 structure functions Cahn A Bacchetta, M Diehl, K Goeke, A Metz, P Mulders, M Schlegel (06) EMC E665ZEUS CLASHERMES Boer- Mulders F. Bradamante

  41. semi-inclusive cross-section8 tgt transverse spin dependent asymmetries, 4 LO Sivers transversity ……. 5 3 by now allmeasured by COMPASSon deuteron talk by B. Parsamyan F. Bradamante

  42. target transverse spin dependent asymmetries (LO) g1Tis the only parton DF which is chiral-even, T-even, leading twist function in addition to the unpolarised DF and to the helicity DF again cancellation between the u and d quarks in the deuteron ? F. Bradamante

  43. Outlook • COMPASS • Results on asymmetries • Transversity Distribution Function • Sivers Distribution Function • Other TMD Distribution Function • Conclusions and future programs F. Bradamante

  44. Conclusions both Collins effect and Sivers effect have been shown to be there NEW PROPERTIES of MATTER TRANSVERSITY CAN BE MEASURED First global analysis being done ! THE WORK STARTS NOW ! Many TMD PDF and FF to be measured PRECISION NEEDED F. Bradamante

  45. Parton Model F2p(x,Q2) = ½ ei2 [qi (x,Q2) + qi (x,Q2)] unpolarised PDF Unpolarized DIS Structure Function(x,Q2) still big uncertainty for G(x) at large x ! F. Bradamante

  46. Parton Model  g1p = ½ ei2 [qi (x,Q2) + qi (x,Q2)] helicity PDF Asymmetry Analysis Collaboration, M. Hirai, S. Kumano and N. Saito, PRD (2004) F. Bradamante

  47. F. Bradamante

  48. Anselmino et al Anselmino et al Collins et al Vogelsang, Yuan Sivers asymmetry 2005-2006: theoretical work on the interpretation of the data use of the new HERMES results to exctract the Sivers DF Vogelsang Yuan (2005), Anselmino et al (2005), Collins et al (2006) • good fits to the new proton from HERMES • comparison (or fit) with the deuteron COMPASS 2002 data ok with ranging from to Anselmino et al., hep-ph/0511017 F. Bradamante

  49. “Global” fits work on global fits ongoing also in Trieste see talk of A. Martin in Freiburg, March 2007 “International Workshop on Hadron Structure and Spectroscopy” interesting problems: Correlation between Cfav and Cunf in BELLE measurement Error bands in DF’s and FF’s F. Bradamante

  50. Outlook • COMPASS • Results on asymmetries • Transversity Distribution Function • Sivers Distribution Function • Other TMD Distribution Function • Conclusions and future programs F. Bradamante

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