Polarized Semi-Inclusive DIS in Current and Target Fragmentation - PowerPoint PPT Presentation

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Polarized Semi-Inclusive DIS in Current and Target Fragmentation

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  1. Polarized Semi-Inclusive DIS in Current and Target Fragmentation • Introduction • The flavor separation of the quark helicity distributions • The spin and azimuthal asymmetries in the current and target fragmentation regions • Polarization of Λs produced in SIDIS of polarized leptons on unpolarized target • Conclusions Aram Kotzinian Torino University & INFN On leave in absence from YerPhI, Armeniaand JINR, Russia AramKotzinian

  2. Lepton-Nucleon EM Interactions • Study of Confinement in QCD • Structure of nucleon & hadronization dynamics • Elastic – Form-factors • Exclusive – GPDs • DIS – DFs • SIDIS: • CFR: DFs & Fragmentation Functions • TFR: Fracture Functions • More general: Hadronization Functions Spin phenomena play crucial role in all channels AramKotzinian

  3. DIS AramKotzinian

  4. Nucleon Spin from polarized DIS Quark Spin Nucleon spin Orbital Angular Momentum Gluon Spin Spin Sum Rule COMPASS 2005 LSS 2005 AramKotzinian

  5. SIDIS in LO QCD: CFR h q q N p Well classified correlations in TMD distr. and fragm. functions Sivers distribution Mulders distribution Boer distribution Helicity distribution Collins effect in quark fragmentation AramKotzinian

  6. SIDIS in LO QCD: TFR q N h 1994: Trentadue & Veneziano; Graudenz; … Fracture functions: conditional probability of finding a parton q with momentum fraction x and a hadron h with the CMS energy fraction z More correlations for TMD dependent FracFuncs AramKotzinian

  7. Ed. Berger criterion (separation of CFR &TFR) The typical hadronic correlation length in rapidity is Illustrations from P. Mulders: AramKotzinian

  8. LUND String Fragmentation q h Rank from diquark Rank from quark Soft Strong Interaction qq Parton DF, hard X-section & Hadronizationare factorized Implemented in LEPTO + JETSET (hadronization) AramKotzinian

  9. Flavor separation using SIDIS HERMES analysis Leader & Stamenov, 2003: Non-negative strange quark polarization is almost impossible AramKotzinian

  10. Purity method for flavor separation h q q N Purities are calculated using LEPTO AramKotzinian

  11. LO SIDIS in LEPTO - Before - After Target remnant quark • Example: valence • struck quark Natural question:does Lund hadronization exactly correspond to independent quark fragmentation in the CFR with z>0.2? (A.K.2004) The important property of FFs is universality: • Independence of Bjorken variable x • Target type independence • Process type independence AramKotzinian

  12. Bjorken variable dependence of “FFs” in LEPTO The dependence of “FFs” on x cannot be attributed to Q2 evolution AramKotzinian

  13. Target type dependence of “FFs” in LEPTO Example of target remnant: removed valence u-quark: There is dependence of “FFs” on the target type at 10% level AramKotzinian

  14. LUND string fragmentation The primary hadrons produced in string fragmentation come from the string as a whole, rather than from an individual parton. AramKotzinian

  15. Hadronization Functions (HF) Even for meson production in the CFR the hadronization in LEPTO is more complicated than SIDIS description with independent FFs We are dealing with LUND Hadronization Functions: More general framework -- Fracture Functions (Teryaev, T-odd, SSA…) LEPTO is a model for Fracture Functions: Violation of naïve x-z factorization and isotopic invariance of FF The dependence on target flavor is due to dependence on target remnant flavor quantum numbers.What about spin quantum numbers? AramKotzinian

  16. Dependence on target remnant spin state (unpolarized LEPTO) Example: valence u-quark is removed from proton. Default LEPTO: the remnant (ud) diquark is in 75%(25%) of cases scalar(vector) Even in unpolarized LEPTO there is a dependence on target remnant spin state (ud)0: first rank Λ is possible (ud)1: first rank Λ is impossible AramKotzinian

  17. Target remnant in Polarized SIDIS JETSET is based on SU(6) quark-diquark model 90% scalar 100% vector Probabilities of different string spin configurations depend on quark and target polarizations, target type and process type AramKotzinian

  18. Polarized SIDIS & HF and -- spin dependentcross section and HFs These Eqs. coincide with those proposed by Gluk&Reya (polarized FFs). In contrast with FFs, HFs in addition to zdepend on x and target type double spin effect, as in DFs. AramKotzinian

  19. Asymmetry The standard expression for SIDIS asymmetry is obtained when For validity of purity method most important is the second relation AramKotzinian

  20. Toy model (A.K.2003) In JETSET there is a pointer indicating whether produced hadron is coming from quark or diquark end of the string. Symmetric LUND fragmentation: each string breaking starting with equal probabilities from q or qq end. AramKotzinian

  21. PEPSI MC Model A: default PEPSI Model B: neglect contribution of events to asymmetries with hadrons originated from diquark AramKotzinian

  22. Beam Energy Dependence • Situation is different • for higher energies: • dependencies of “FFs” • extracted from MC • on x, target type • and target remnant • quantum numbers • are weaker AramKotzinian

  23. Conclusions 1 • LUND MC is proved to be capable to describe data in a wide range of kinematics. • The new concept of (polarized) hadronization is introduced and studied using LEPTO event generator • The hadronization in LEPTO is more general than simple LO x-z factorized picture with independent fragmentation, for example, it describes well TFR. • It necessary to modify PEPSI MC event generator by including polarization in hadronization. • The purity method have to be modified to include polarized HFs. • Within this new approach one can include all hadrons (CFR+TFR) for flavor separation analysis. • More studies on the accuracy of different methods of the polarized quark DF extraction using SIDIS asymmetries are needed. • Alternative measurements are highly desirable • SIDIS at different beam energies: COMPASS, JLab, EIC • W production in polarized p+p collisions • (Anti)neutrino DIS on polarized targets (Neutrino Factory) AramKotzinian

  24. Λ-polarization in TFR • Melnitchouk & Thomas:Meson Cloud Model • 100 % anticorrelated with target polarization • contradiction with neutrino data for unpolarized target • Longitudinal polarization of Λ in the TFR AramKotzinian

  25. Karliner, Kharzeev , Sapozhnikov, Alberg, Ellis & A.K. Nucleon wave function contains an admixture with component: π,K masses are small at the typical hadronic mass scale: a strong attraction in the − channel. pairs from vacuum in state Intrinsic Strangeness Model Polarized proton: Spin crisis: AramKotzinian

  26. J.Ellis, A.K. & D.Naumov (2002) AramKotzinian

  27. Rank from diquark Rank from quark qq q  NOMAD (43.8 GeV) COMPASS (160 GeV) Λ parent No clean separation of the quark and diquark fragmentation AramKotzinian

  28. Λ polarization in quark & diquark fragmentation Λ polarization from the quark fragmentation Λ polarization from the diquark fragmentation AramKotzinian

  29. Spin Transfer • We use Lund string fragmentation model incorporated in LEPTO6.5.1 and JETSET7.4. • We consider two extreme cases when polarization transfer is nonzero: • model A: • the hyperon contains the stuck quark: Rq = 1 • the hyperon contains the remnant diquark: Rqq = 1 • model B: • the hyperon originates from the stuck quark: Rq ≥ 1 • the hyperon originates from the remnant diquark: Rqq ≥ 1 AramKotzinian

  30. Fixing free parameters • We vary two correlation coefficients ( and ) in order to fit our models A and B to the NOMAD Λ polarization data. • We fit to the following 4 NOMAD points to find our free parameters: AramKotzinian

  31. Results Predictions for JLab 5.75 GeV AramKotzinian

  32. Predictions for CLAS Predictions for xF-dependence at JLab 12 GeV Red squares with error bars – projected statistical accuracy for 1000h data taking (H.Avagyan). AramKotzinian

  33. Predictions for EIC 5 GeV/c electron + 50 GeV/c proton, Good separation of the quark and diquark fragmentation allows to distinguish between different spin transfer mechanisms from quark and diquark AramKotzinian

  34. Conclusions 2 • Predictions for Λ polarization are very sensitive to production mechanism • A phenomenological polarized intrinsic strangeness + SU(6) model is able to describe all available data on longitudinal polarization of Λ in full kinematic range • New measurements at different energies will serve as a test for proposed models AramKotzinian

  35. Unpolarized SIDIS & Cahn effect M.Anselmino, M.Boglione, U.D’Alesio, A.K., F.Murgia and A.Prokudin:PRD 71, 074006 (2005) A.K.:arXiv:hep-ph/0504081 x & z are light cone variables defined with respect z & axes No exact factorization ! AramKotzinian

  36. Unpolarized SIDIS & Cahn effect Ji et al: QCD factorization holds for approximation Quadratic in Linear in and proportional to AramKotzinian

  37. Comparison with data Non Gaussian tail; x, z and flavor dependence of intrinsic and fragmentation transv. momentum AramKotzinian

  38. 2 + In standard approach the effective treatment of the Sivers effect is adopted as correlation in quark distribution in transversely polarized nucleon Brodsky, Hwang & Schmidt, 2002: FSI Collins, 2002; Belitski, Ji &Yuan, 2003: Wilson gauge link Boer, Mulders & Teryaev, 1997: twist three gluonic pole AramKotzinian

  39. Parameterization for Sivers effect AramKotzinian

  40. Data AramKotzinian

  41. New HERMES data AramKotzinian

  42. Quark intrinsic transverse momentum in LEPTO - Generate virtual photon – quark scattering in collinear configuration: - Before - After hard scattering - Generate intrinsic transverse momentum of quark (Gaussian kT) - Rotate in l-l’ plane - Generate uniform azimuthal distribution of quark (flat by default) - Rotate around virtual photon AramKotzinian

  43. Implementing Cahn and Sivers effects in LEPTO The common feature of Cahn and Sivers effects Unpolarized initial and final quarks Fragmenting quark-target remnant system is similar to that in default LEPTO but the direction of is now modulated Cahn: Sivers: Generate the final quark azimuth according to above distributions AramKotzinian

  44. Results: Cahn Imbalance of measured in TFR and CFR: neutrals? AramKotzinian

  45. Results: Sivers Predictions for xF-dependence at JLab 12 GeV Red triangles with error bars – projected statistical accuracy for 1000h data taking (H.Avagyan). z and xBj-dependences AramKotzinian

  46. Results: Sivers JLab 12 GeV AramKotzinian

  47. SSA in PP-interactions h ST P P E704. Curves: by Anselmino et al, STAR (hep-ex/0505024) Both the active quark and the polarized proton remnant are flying in forward direction. Which final hadrons provide transverse momentum balance? AramKotzinian

  48. Both Cahn and Sivers effects are implemented in LEPTO. Possible effects of polarized hadronization were neglected. Existing data in CFR are well described by modified LEPTO The measured Cahn effect in the TFR is not well described Is there an universal mechanism describing SSA in SIDIS and PP interactions? It will be interesting to implement Cahn and Sivers effects in PHYTIA It is important to perform new measurements of both effects in the TFR (JLab, HERMES, Electron Ion Colliders) This will help better understand hadronization mechanism Do the neutral hadrons compensate Cahn effect in CFR? Multihadron final states distributions can enhance effects Is there a similarity with PP-reaction? Fracture Function “Global” analysis Classification of spin and TMD dependent correlations in Fracture Functions Conclusions 3 AramKotzinian

  49. Conclusions • Spin phenomena in SIDIS can play very important role for modeling and understanding the QCD dynamics • Access to TFR opens a new field both for theoretical and experimental investigations • JLab@12 GeV is ideally placed to make important breakthroughs over a wide spectrum of discovery in nucleon structure and hadronization dynamics Thanks for hospitality @ JLab AramKotzinian

  50. Support Slides AramKotzinian