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Transverse Spin Phenomena in Lepton Scattering - Recent Progress and New Results

This presentation discusses the recent progress and new results in the field of transverse spin phenomena in lepton scattering. Topics covered include polarized deep inelastic scattering, transversity distribution function, Sivers distribution function, other TMD distribution functions, and conclusions. The talk highlights the experiments at HERMES, COMPASS, and CLAS, along with the measurements of Collins asymmetry and the Collins fragmentation function.

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Transverse Spin Phenomena in Lepton Scattering - Recent Progress and New Results

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  1. Transverse Spin Phenomena in Lepton ScatteringAnna MartinTrieste University and INFN Trieste October 4, 2006

  2. in this fieldFANTASTIC PROGRESS SINCE SPIN2004 EXPERIMENTS: Collins mechanism has been firmly established and there is a first check of universality  transversity can be measured in SIDIS Sivers mechanism is real THEORY: important developments on connection between Sivers effect and Orbital Angular Momentum assessing universality (lN vs pp) ... and many new ideas ... VERY ACTIVE FIELD: many interesting theoretical & experimental talks at a lot of material: I will not be able to show all the results

  3. Content of this talk • Polarised DIS and Experiments • Transversity Distribution Function new results • Sivers Distribution Function new results • Other TMD Distribution Function new results • Conclusions HERMES COMPASS CLAS

  4. P inclusive hadrons Deep Inelastic Scattering key role in investigating the partonic structure of the necleons only the final lepton is detected inclusive DIS Q2 >> M2, W2>> M2 in addition, detection of final hadrons semi-inclusive DIS (SIDIS)

  5. Polarised SIDIS Experiments transverse spin effects are an important part of the program of the present experiments JLAB experiments electron beam, energy 6 GeV to be upgraded to 12 GeV (long pol target, till now) HERMES at DESY electron beam, energy 27.5 GeV internal H↑ gas target (2002-2005) COMPASS at CERN long pol m beam, energy 160 GeV solid state target (2002-2004 with 6LiD↑)

  6. 0.02 < x < 0.6 CLAS 0.15 < x x 0 50 100 Q2 [GeV/c]2 0.004 < x < 0.4 10 -3 10 -2 10 -1 1 x

  7. Content: • Polarised DIS and Experiments • Transversity Distribution Function new results • Sivers Distribution Function new results • Other TMD Distribution Function new results • Conclusions

  8. Spin Structure of the Nucleons three quark distribution functions (DF) are necessary to describe the structure of the nucleon at LO q(x) f1q (x) unpolarised DF quark with momentum xP in a nucleon well known – unpolarised DIS helicity DF quark with spin parallel to the nucleon spinin a longitudinally polarised nucleon known – polarised DIS Dq(x) g1q(x) DTq(x) = q↑↑(x) - q↑↓(x) h1q(x), dq(x), dTq(x) transversity DF quark with spin parallel to the nucleon spinin a transversely polarised nucleon still unkown ALL 3 OF EQUAL IMPORTANCE

  9. Transversity Distribution Function DTq(x), h1q(x),dq(x), dTq(x) , q=uv, vv, qsea contribution of the quarks to the transverse spin of the nucleon • Properties: • is chiral-odd: decouples from incl DISbecause helicity of quark must flip • probes the relativistic nature of quark dinamics • no contribution from the gluons simple Q2 evolution • positivity (Soffer) bound • first moments:tensor charge • sum rule for transverse spin Bakker, Leader, Trueman, PRD 70 (04)

  10. 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 otherchiral-odd function can be measured in SIDIS on a transversely polarised target via “quark polarimetry”

  11. Measurement of the Transversity DF in SIDIS “Collins asymmetry” in the chiral-odd partner is the Collins Fragmentation Function the “quark polarimetry” relies on the Collins effect(J. Collins, 93) a quark moving “horizontally” and polarized “upwards” would emit the leading meson preferentially on the “left” side of the jet the fragmentation function has aspin dependent part “Collins” FF: unknown …

  12. C Collins effect in SIDIS distribution of the hadrons: ± refer to the opposite orientation of the transverse spin of the nucleon PT is the target polarisation; DNNis the transverse spin transfer coefficient initial  struck quark the “Collins angle” is • C = h-s’ =h+S - p • C = h+S(Trento) h,s’,Sazimuthal angles of hadron momentum, of the spin of the fragmenting quark and of the nucleon from the azimuthal distribution of the hadrons one measures the “Collins Asymmetry” using different targets (p, d, n) and identifying the final hadron one can performflavour separation unique feature of SIDIS

  13. e- j2-p Q j1 e+ What have we learnt over the past 2 years ?Collins Effect great news from BELLE measurement of the correlation between the azimuthal angles of p‘s in the near jet and in the far jet from e+e– annihilation ( … no results yet at ) A0 Final results A12 significant non-zero asymmetries, rising behavior with z z1 Collins effect is a real phenomenon spin dependent FF can be measured in e+e– annihilation z2

  14. What have we learnt over the past 2 years ? Collins Asymmetry - p+ and p- asymmetries from HERMES proton target 2002-2005 NEW RESULTS (DIS2005) 2002-2003 data • unexpected large p- • positive p+and negative p- asymmetries confirmed with larger statistics: the Collins FF is ≠ 0, transverity is ≠ 0

  15. What have we learnt over the past 2 years ?Collins Asymmetry - h+ and h- asymmetries from COMPASS deuteron target PRL 94, 202002 (2005) 2002-2004 hadrons: mostly pions 2002 data cancellationbetween p and n ? NEW RESULTS 2002- 2004 data (DIS2006) asymmetries compatible with zero within the smaller statistical errors preliminary 2002-2004 preliminary 2002-2004

  16. What have we learnt over the past 2 years ?Collins Asymmetry naïve interpretation of the data (parton model, valence region) • new proton data preliminary 2002-2004 asymmetry for p+~ opposite to asymmetry for p- unfavored Collins FF ~ opposite favored Collins FF at variance with unpolarised case  u quark dominance • new deuteron data preliminary 2002-2004 some (small) effect expected even if  cancellation between Tu (x) and Td (x) handle on Td (x)

  17. What have we learnt over the past 2 years ? Anselmino et al, BNL UM 2006 Soffer bound & Tq = q preliminary COMPASS 2002-2004 preliminary COMPASS 2002-2004 Vogelsang Yuan, PRD 72, 054028 (2005) Soffer bound Vogelsang and Yuan Efremov et al Efremov et al, PRD 73, 094025 (2006) chiral quark-soliton model preliminary COMPASS 2002-2004 preliminary COMPASS 2002-2004 Anselmino et al, SB Anselmino et al, Tq = q recent theoretical work favored Collins FF ~ – unfavored Collins FF u-dominance agreement with Belle comparison with the new COMPASS 2002-2004 prelim data

  18. Aerogel n=1.03 C4F10 n=1.0014 Also new: Collins asymmetry for K± together with different targets, relevant for flavour decomposition there are very recent results for the Collins asymmetry • on proton for K+ and K–(HERMES, DIS2006) • on deuteron for p+ and p– , K+ and K– (COMPASS, GPD06) C4F10

  19. Collins Asymmetry for Pions and Kaons very recent results; comparison with phenomenological calculations already available (M. Anselmino et al) HERMES preliminary 2002-2004 data proton COMPASS sign convention COMPASSpreliminary 2003-2004 data deuteron

  20. Measurement of the Transversity DF in SIDIS hadron-pair asymmetries alternative way to access transversity measurement from HERMES using longitudinally polarised target data NEW RESULTS: measurements from HERMES and COMPASS on transversely polarised proton and deuteron targets more on Friday Session 2B R. Joosten, M. Contalbrigo, M. Radici

  21. Two Hadron Asymmetries in inclusive production of hadron pairs, one can define the angle f R┴ and measure an azimuthal asymmetry from the modulation of the number of events infRS=fR┴- fs’orfRS=fR┴+fS presently unknown can be measured in e+e- (BELLE) expected to depend on the hadron pair invariant mass

  22. What have we learnt over the past 2 years ?Two Hadron Asymmetries 2002-2004 data all +/- pairs 2002-2004 data all +/- pairs preliminary x proton HERMES kin deuteron COMPASS kin 1/10 0.004<x<0.4 AND deuteron target NEW RESULTS deuteron target NEW RESULTS proton target A. Bacchetta, M. Radicihep-ph/0608037 model for DiFF (expected to be overestimated) • positive moments for all invariant mass bins • first evidence for non-zero FF  small errors (order of ~%)  small asymmetries! cancellation? similar results ordering in pTh, z inspired to the string fragm. model also these data can be described by models

  23. Measurement of the Transversity DF in SIDIS polarimetry alternative way to access transversity no results NEW RESULTS from COMPASS presented here for the first time more on Friday Session 2A A. Ferrero

  24. L polarimetry S x 10 all Q2

  25. NEW L polarimetry systematic errors not larger than statistical errors RICH ID not used yet

  26. Content: • Polarised DIS and Experiments • Transversity Distribution Function new results • Sivers Distribution Function new results • Other TMD Distribution Function new results • Conclusions

  27. Measurement of the Sivers DF in SIDIS • presently, the most studied in SIDIS together with the Transversity DF • it is one of the TMD parton distribution functions • is related to an intrinsic asymmetry in the parton transverse momentum distribution induced by the nucleon spin • requires final/initial-state interactionsquark rescattering via soft gluon exchange • should change sign from SIDIS to DY • it is related to the parton orbital angular momentum in a transversely polarized nucleon on its properties and the relation with angular momentum  talks by Budkart, Vogelsan, .... and several others in the next days

  28. 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” Care independent  the Collins and Sivers asymmetries can be disentangled and extracted from the same data in SIDIS

  29. What have we learnt over the past 2 years ?Sivers Asymmetry NEW RESULTS 2002-2004 data proton target 2002-2005 2002-2003 data  significant positive asymmetry for positive pions with a factor ~4 in statistics p+ asymmetry > 0p– asymmetry compatible with 0 the Sivers effect is a real effect

  30. preliminary COMPASS 2002-2004 What have we learnt over the past 2 years ?Sivers Asymmetry deuteron target2002-2004 2002 data PRL 94, 202002 (2005) hadrons: mostly pions cancellationbetween p and n ? NEW RESULTS 2002- 2004 data factor ~7 in statistics: asymmetries still compatible with zero

  31. 2 What have we learnt over the past 2 years ?Sivers Asymmetry naïve interpretation of the data (valence region) • new proton data preliminary 2002-2004 asymmetry for p+ > 0, asymmetry for p-≈ 0 Sivers DF for d-quark ≈ - 2 Sivers DF for u-quark • new deuteron data preliminary 2002-2004 the measured asymmetriescompatible with zero suggest

  32. What have we learnt over the past 2 years ?Sivers Asymmetry  F. Bradamante talk, yesterday also, 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, S. Gardner SLAC-PUB-12062, Aug 2006. Subm. Phys.Lett.B, hep-ph/0608219

  33. Anselmino et al Anselmino et al Collins et al Vogelsang, Yuan What have we learnt over the past 2 years ?Sivers Asymmetry recent 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 Anselmino et al., hep-ph/0511017 first qualitative picture of the Sivers functions to progress more data from the experiments are vital

  34. Also new: Sivers Asymmetry for K± very recent results; phenomenological calculations already available (M. Anselmino et al) HERMES preliminary 2002-2004 K+ and K– on proton (DIS06) COMPASSpreliminary 2003-2004 p+ and p– , K+ and K– on deuteron (GPD06)

  35. Content: • Polarised DIS and Experiments • Transversity Distribution Function new results • Sivers Distribution Function new results • Other TMD Distribution Function new results • Conclusions

  36. other Azimuthal Asymmetries in SIDIS related to TMD PDF and/or FF (LO) inclusive DIS Boer-Mulders, 98 long. polarized target transv. polarized target polarized beam and target inclusive DIS

  37. TMD Asymmetries in SIDIS (LO) • AColl ~ sin(fh + fS) Collins asymmetry already seen • ASiv ~ sin(fh - fS) Sivers asymmetry • ~ sin(3fh - fS) inverstigatedat HERMES and COMPASS • ~ cos(fh - fS) g1T and FFinverstigatedat COMPASS • ~ cos2fh “Boer-Mullders” DF and Collins FF results from CLAS also for and other higher order TMD Asymmetries no preliminary results yet

  38. (Boer – Mulders DF) correlation between the transverse momentum and transverse spin of quarks in an unpolarised nucleon times Collins FF can be measured inHERMES, COMPASS, CLAS, H1, ZEUS

  39. (Boer – Mulders DF) difficult to measure • background higher twist terms (f. i. Cahn) • radiative correction, acceptance + … M.Osipenko CLAS 5.7 GeV (preliminary)

  40. Content: • Polarised DIS and Experiments • Transversity Distribution Function new results • Sivers Distribution Function new results • Other TMD Distribution Function new results • Conclusions

  41. Future measurements in SIDIS “SHORT” TERM • Collins and Sivers asymmetries more statistics from HERMES (2005 data) p0 asymmetries (HERMES) weighted asymmetries (HERMES and COMPASS) • Boer-Mulders, and other hadron asymmetriesfrom HERMES, COMPASS, JLAB • Proton data from COMPASS (2007) • Neutron (p, d) data from JLAB (upgrade at 12 GeV) “LONGER” TERM the present experiments can not precisely map all transverse spin effects in SIDIS • COMPASS program after 2010 • polarized ep collider

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