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The Importance of Higher Twist Corrections in Polarized DIS

11th International Workshop on Deep Inelastic Scattering St. Petersburg, April 23 - 27, 2003. The Importance of Higher Twist Corrections in Polarized DIS. E. L eader, A. S idorov , D. S tamenov,. LSS. OUTLINE. Peculiarity of the polarized DIS.

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The Importance of Higher Twist Corrections in Polarized DIS

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  1. 11th International Workshop on Deep Inelastic Scattering St. Petersburg, April 23 - 27, 2003 The Importance of Higher TwistCorrections in Polarized DIS E. Leader, A. Sidorov, D. Stamenov, LSS

  2. OUTLINE Peculiarity of the polarizedDIS Phys. Rev. D67 (2003) 0740xx [hep-ph/0212085]

  3. An important difference between the kinematic regionsof theunpolarized and polarized data sets While in the determination of the PD in the unpolarized case wecan cut the low Q2 and W2 data in order to eliminate theless known non-perturbative HT effects, it is impossible toperform such a procedure for the present data on thespin-dependent structure functions without loosing too muchinformation. HT corrections should beimportant !

  4. DATA CERN EMC - SMC - 185 exp.p. DESY HERMES - SLAC E142, E154 - E143, E155 - The data on are really the experimentalvalues of thequantity very well approximated with even wheng(h) cannot been neglected

  5. Theory In QCD target masscorrections which are exactly calculable J. Blumlein, A.Tkabladze In pQCD Nf - a number of flavours (=3 in ouranalysis)

  6. Factorization scheme dependence Beyond the LO approximation the PD are scheme depended! In the unpolarized case In the polarized case because of the gluonanomaly n=1 The larger DG the bigger thedifference

  7. On theoretical grounds we prefer to use the JETscheme (allhard effects are absorbed in the Wilson coefficient functions). Carlitz, Collins, Mueller (1988) Efremov, Teryaev (1989); Muller, Teryaev (1997) Anselmino, Efremov, Leader (1995) In the JET scheme (as well as in AB scheme) it is meaningfulto directly interpret DS as the contribution of thequark spins to the nucleon spin and to compare its value obtainedfrom DIS region with the predictions of the different(constituent, chiral, etc.) quark models at low .

  8. Connection between Theory andExperiment E.Leader, A.Sidorov, D.Stamenov [hep-ph/0212085] Eur. Phys. J. C23, 479 (2002) GRSV,LSS

  9. SMC;Blumlein, Bottcher (GRSV)

  10. METHOD of ANALYSIS R1998 (SLAC) NMC Input parton densities 8-2(SR) = 6 par. associated with PD

  11. SR for the firstmoments of the polarized PD coming from the hyperon semi-leptonic decays are conventionally used in addition to fix two of the free parameters. isospin SU(2) symmetry F and D the SU(3) parameters SU(3)flavour symmetry treatment of the hyperon b-decays From KTeV exper. SU(3) breaking is at most of order 20%

  12. RESULTS OF ANALYSIS Kinematic region - 185 exp. p. Quality of the fits

  13. Higher twist effects

  14. NLO polarized PD NLO(JET)

  15. n=1 moments of PD, JET scheme, Q2=1GeV2 the correlations between the parametersare takeninto account N.B.DS in JET scheme does NOT depend on Q2.

  16. JLAB preliminary hep-ex/0302020 significantimprovement of the precision of the data • LSS 2001 (Q2 = 5 GeV2) • [21] Leader,Sidorov,Stamenov, Euro Phys. J. C23, 479 (2002)

  17. Very recent (unpublished) results from the fit to the world data including the JLAB and HERMES/ddata ia very good description of the HERMES/d data c2=11.0 for 18 points iPD( g1NLO+ HT) practically do NOT change !! Ch. Weiskopf 02-043 Thesis (2002)

  18. HT corrections to g1 are better determined now, especially for the neutron target HT/n changes essentialy at region

  19. CONCLUSIONS The fit to the present data on g1is essentiallyimproved, especially in the LO case, when the higher twist terms are included in the analysis. The size of HT corrections have been extracted from the data in model independent way well consistent with

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