Target Fragmentation studies at JLab

1. CLAS Collaboration Target Fragmentation studies at JLab M.Osipenko in collaboration with L. Trentadue and F. Ceccopieri, May 20,SIR2005, JLab, Newport News, VA

2. Plan of Study Semi-inclusive reactions Light mesons () Baryons (p, n, ) momentum sum rule separation separation current fragmentation target fragmentation current fragmentation target fragmentation fragmentation functions fracture functions Low Q2? Diffraction double moments in pQCD Pomeron structure function M. Osipenko

3. SI Structure functions • Unpolarized cross section is described by four functions: separation requires a measurement of 5-dimensional cross section • Beam longitudinal polarization asymmetry produces one more structure function: longitudinal polarization of CEBAF beam achieves 85% M. Osipenko

4. SIDIS In the Bjorken limit: Target fragmentation Current fragmentation This mixture is presently studied at JLab factorization proved factorization is not necessary M. Osipenko

5. Longitudinal Momentum • CEBAF beam energy in combination with CLAS acceptance allow to explore current fragmentation for light mesons and target fragmentation for baryons. • In DIS Feynman permits to disentangle two regions, however, at small invariant masses W separation is ambiguous. 6 GeV beam energy + p  target target current current current target M. Osipenko

6. Rapidity gap at CLAS p Separation of the current and target fragments: Berger criterion DIS only! current Exclusive Boundary MX~Mn No kinematical cuts! We have to study entire set of mechanisms. + Useful kinematics W>2 GeV current Q2=2 GeV2 M. Osipenko

7. New CLAS data • Unpolarized Semi-inclusive electroproduction of + has been recently measured with CLAS. • For the first time complete 5-dimensional cross sections were extracted. • Direct separation of different SI structure functions. CLAS Preliminary x=0.28-0.32 z=0.16-0.19 pT=0.41-0.53 GeV Q2=2.23-2.66 GeV2 M. Osipenko

8. + production results • CLAS preliminary results suggest dominance of the current fragmentation mechanism in H2 down to rather low Q2 and z values, • No significant target fragmentation contribution is found. Q2=3 GeV2 CLAS • The same pT behavior for all structure functions => trivial kinematical factors for azimuthal asymmetries <cos> and <cos2> • H3 contribution is negative • H4 is mostly positive • Suggest only internal transverse motion of quarks (Cahn)? current • LO QCD prediction given by a product of GRV PDFs and Kretzer FFs saturates experimental data leaving no room for large positive target fragmentation contribution. Preliminary Preliminary CLAS Q2=2.4 GeV2, x=0.26, z=0.23 M. Osipenko

9. Nucleon Semi-Inclusive Possible reactions on the proton: epe′p′X andepe′nX HERA JLab LT approximation only! current fragmentation target fragmentation GeV2 • Below pp-threshold there is no need for kinematical cuts! Direct access to the fracture functions M(x,z,Q2) and their properties. M. Osipenko

10. Diffraction CLAS sees diffraction! In the Regge limit and Regge trajectory intercept, 1.1 for Pomeron structure function of the Regge trajectory epe′p′X epe′nX Need p-n difference to select of pure gluonic content of exchanged object. HERA CLAS M. Osipenko

11. Fracture Functions • Separation of different fracture functions: MT,ML, MLT etc. related to different structure functions H1, H2, H3 etc. H1 and H2 Rosenbluth separation • Test of diffractive factorization of the fracture functions where • Extraction of various moments and comparison to pQCD • Contribution of the target fragmentation in the pion electroproduction M. Osipenko

12. Summary • Measured +semi-inclusive electro-production in the JLab region does not show a large target fragmentation contribution suggesting therefore naïve pQCD picture, • We are extracting polarized and unpolarized proton and neutron semi-inclusive electroproduction cross sections at highest JLab beam energy 6 GeV: epe′p′X and epe′nX TO DO: • Comparison of pT dependences to theory (Cahn, Berger, pQCD), • Separation different fracture functions MT, ML, MLT etc., • Test of diffractive factorization hypothesis, • Extraction of the fracture function moments and a comparison to pQCD predictions, • Contribution of the target fragmentation in pion SIDIS at JLab. M. Osipenko

13. Background u-channel nucleon production: ~F2(x,Q2) Higher Twist contribution M. Osipenko

14. Fracture functions • DGLAP evolution equation with standard splitting functions • Momentum sum rule • Process independent definition Hadron-hadron collisions N1+N2hX + In assumption of the factorization M. Osipenko

15. Previous data Semi-inclusive nucleon electroproduction was measured at SLAC, Cornell, DESY, HERA and CERN. Only unpolarized data and most of variables are integrated over. HERA CERN • Below pp-production threshold only target fragmentation can contribute GeV2 Cornell • Large t-range from 0.1 up to 4-5 GeV2 • Good particle identification: possibility to make p-n difference • Polarization observables: new information on the fracture functions M. Osipenko

16. Outline • Semi-inclusive reactions • Structure functions • SIDIS • Separation of different fragmentation regions • Nucleon semi-inclusive electroproduction • Diffraction • Previous measurements • Expected results • Summary M. Osipenko

17. Semi-inclusive Reactions epe′hX 5 independent variables • Need to detect the scattered electron in a coincidence with the hadron h, • Require a good particle identification, • To extract the cross section in all five variables the complete 4 acceptance is necessary. • => CLAS is the best place to do this! M. Osipenko

18. Kinematical Separation (for ) Current fragmentation Hadron rapidity Target fragmentation Current Pion electroproduction Target x=0.3, Q2=3 GeV2 Separation is possible by means of a cut on the energy flow from the virtual photon to the measured hadron. M. Osipenko

19. Kinematical coverage • Complete measurement of fracture functions: • Almost whole z-range • Possibility to access 5-dimensional cross section • Allows to extract pT dependence • Entire -range covered GeV2 E1-6 DATA E1-6 DATA GeV2 E1-6 DATA E1-6 DATA GeV2 M. Osipenko

20. Mulders Rapidity Gap M. Osipenko

21. Regge Approach • Structure functions of Regge trajectories CLAS-Note-01-006 neutron efficiency in EC Need p-n difference to select of pure gluonic content of exchanged object. neutron efficiency in SC • Test of Veneziano duality Two component duality: equivalence of Pomeron and the background M. Osipenko

22. Λ Polarization e e’ 1 Λ p 2 π (H. Avakian) L– unique tool for polarization study due to it’s self-analyzing parity violating weak decay. • (ud)-diquark is a spin and isospin singlet => s-quark carries entire spin of , K+ q=-s  q q=1/2 `q=1/2 =1 •  polarization in TFR provides information on contribution of strange sea to proton spin. Polarized beam gives unique possibility to perform an “acceptance independent” measurement of  polarization in electroproduction. 6 W.Melnitchouk and A.W.Thomas ‘96 J.Ellis, D.Kharzeev, A. Kotzinian ‘96 M. Osipenko

23. pT dependence Distribution of Gaussian width of measured pT slopes for different structure functions. H2+H1 H3 H4 M. Osipenko