1 Dubna, September, 2005 Aram Kotzinian Spin effects in MC generators The spin and azimuthal asymmetries in the current and target fragmentation regions The flavor separation of the quark helicity distributions Conclusions Aram Kotzinian JINR, Dubna and Torino University & INFN On leave in absence from YerPhI, Armenia Dubna, SPIN-05

2 Dubna, September, 2005 Aram Kotzinian Sivers effect in pp l + l - + X One class of nonperturbative input: only distribution functions, no hadronization effects are present Modify PYTHIA to include Sivers effect: azimuthal correlations of the parton transverse momentum and transverse spin on nucleon in distribution functions STST

3 Dubna, September, 2005 Aram Kotzinian Sivers effect in pp l + l - + X Similar values as in Anselmino et al: hep-ph/

4 Dubna, September, 2005 Aram Kotzinian SIDIS in LO QCD: CFR Well classified correlations in TMD distr. and fragm. functions Sivers distribution Boer distribution Helicity distribution Collins effect in quark fragmentation N q q h p Mulders distribution

5 Dubna, September, 2005 Aram Kotzinian SIDIS Event Generators and LUND String Fragmentation qq q Rank from diquark Rank from quark h Parton DF, hard X-section & Hadronization are factorized Implemented in PHYTIA and LEPTO + JETSET (hadronization) Soft Strong Interaction Λ ρ0ρ0 π-π- K+K+ π+π+ quark Target remnant

6 Dubna, September, 2005 Aram Kotzinian Quark transverse momentum in MC generators - Generate virtual photon – quark scattering in collinear configuration: - Before - After hard scattering - Rotate in l-l’ plane - Generate intrinsic transverse momentum of quark (Gaussian k T ) - Generate uniform azimuthal distribution of quark (flat by default) - Rotate around virtual photon

7 Dubna, September, 2005 Aram Kotzinian 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 A.K. hep-ph/

8 Dubna, September, 2005 Aram Kotzinian Results: Cahn Imbalance of measured in TFR and CFR: neutrals?

9 Dubna, September, 2005 Aram Kotzinian Results: Sivers Predictions for x F -dependence at JLab 12 GeV Red triangles with error bars – projected statistical accuracy for 1000h data taking (H.Avagyan). z, x Bj and P T dependences

10 Dubna, September, 2005 Aram Kotzinian Results: Sivers JLab 12 GeV

11 Dubna, September, 2005 Aram Kotzinian Purity method for flavor separation Purities are calculated using LEPTO N q q h

12 Dubna, September, 2005 Aram Kotzinian Bjorken variable dependence of “FFs” in LEPTO The dependence of “FFs” on x cannot be attributed to Q 2 evolution

13 Dubna, September, 2005 Aram Kotzinian Target type dependence of “FFs” in LEPTO Example of target remnant type: removed valence u-quark: There is dependence of “FFs” on the target type at 10% level

14 Dubna, September, 2005 Aram Kotzinian 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

15 Dubna, September, 2005 Aram Kotzinian For validity of purity method most important is the second relation Asymmetry Spin dependence of hadronization: A.K. (hep-ph/ , EPJ C, 2005) The standard expression for SIDIS asymmetry is obtained when and

16 Dubna, September, 2005 Aram Kotzinian Toy model using PEPSI MC Model A: default PEPSI Model B: neglect contribution of events to asymmetries with hadrons origin pointing to diquark (A.K. PLB 552, 2003)

17 Dubna, September, 2005 Aram Kotzinian 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

18 Dubna, September, 2005 Aram Kotzinian Remarks on TMD hadronization For TMD dependent HFs the new spin-azimuth correlations depending on both transverse momentum of quark in nucleon and final hadron are possible: Unpolarized lepton, long. polarized target Unpolarized target, long. polarized lepton Unpolarized lepton, trans. polarized target

19 Dubna, September, 2005 Aram Kotzinian 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. One can try to modify PEPSI MC event generator by including polarization in hadronization. The purity method have to be modified to take into account the 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 parton 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) Conclusions (flavor separation)

20 Dubna, September, 2005 Aram Kotzinian Conclusions (azimuthal asymmetries) 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 It is important to perform new measurements of both Cahn and Sivers 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? Is there Sivers effect in TFR compensating asymmetry in CFR? Access to TFR opens a new field both for theoretical and experimental investigations

21 Dubna, September, 2005 Aram Kotzinian additional slides

22 Dubna, September, 2005 Aram Kotzinian Ed. Berger criterion (separation of CFR &TFR) The typical hadronic correlation length in rapidity is Illustrations from P. Mulders:

23 Dubna, September, 2005 Aram Kotzinian Even for meson production in the CFR the hadronization in LEPTO is more complicated than SIDIS description with independent FFs Hadronization Functions (HF) More general framework -- Fracture Functions (Teryaev, T-odd, SSA…) We are dealing with LUND Hadronization Functions: LEPTO provides a model for Fracture Functions: The dependence on target flavor is due to dependence on target remnant flavor quantum numbers. What about spin quantum numbers? Violation of naïve x-z factorization and isotopic invariance of FF

24 Dubna, September, 2005 Aram Kotzinian 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

25 Dubna, September, 2005 Aram Kotzinian Target remnant in Polarized SIDIS JETSET is based on SU(6) quark-diquark model Probabilities of different string spin configurations depend on quark and target polarizations, target type and process type 90% scalar 100% vector

26 Dubna, September, 2005 Aram Kotzinian Polarized SIDIS & HF -- spin dependent cross section and HFs These Eqs. coincide with those proposed by Gluk&Reya (polarized FFs). In contrast with FFs, HFs in addition to z depend on x and target type and double spin effect, as in DFs.

27 Dubna, September, 2005 Aram Kotzinian

28 Dubna, September, 2005 Aram Kotzinian HERMES check x F ? x F > 0.1

29 Dubna, September, 2005 Aram Kotzinian LO x-z factorization