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

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May 20, 2005 M. Osipenko 2 Plan of Study Semi-inclusive reactions Light mesons ( ) Baryons (p, n, ) target fragmentation current fragmentation current fragmentation target fragmentation fracture functions fragmentation functions Diffraction double moments in pQCD Pomeron structure function separation Low Q 2 ? momentum sum rule

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May 20, 2005 M. Osipenko 3 SI Structure functions Unpolarized cross section is described by four functions: Beam longitudinal polarization asymmetry produces one more structure function: longitudinal polarization of CEBAF beam achieves 85% separation requires a measurement of 5-dimensional cross section

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May 20, 2005 M. Osipenko 4 SIDIS In the Bjorken limit: Current fragmentation Target fragmentation factorization proved factorization is not necessary This mixture is presently studied at JLab

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May 20, 2005 M. Osipenko 5 Longitudinal Momentum ++ p 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. target current 6 GeV beam energy

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May 20, 2005 M. Osipenko 6 Rapidity gap at CLAS Separation of the current and target fragments: Berger criterion ++ p Useful kinematics Exclusive Boundary M X ~M n DIS only! Q 2 =2 GeV 2 W>2 GeV current No kinematical cuts! We have to study entire set of mechanisms.

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May 20, 2005 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. x=0.28-0.32 z=0.16-0.19 p T =0.41-0.53 GeV Q 2 =2.23-2.66 GeV 2 CLAS

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May 20, 2005 M. Osipenko 8 + production results CLAS preliminary results suggest dominance of the current fragmentation mechanism in H 2 down to rather low Q 2 and z values, No significant target fragmentation contribution is found. Q 2 =3 GeV 2 CLAS Q 2 =2.4 GeV 2, x=0.26, z=0.23 CLAS The same p T behavior for all structure functions => trivial kinematical factors for azimuthal asymmetries and H 3 contribution is negative H 4 is mostly positive Suggest only internal transverse motion of quarks (Cahn)? 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. current

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May 20, 2005 M. Osipenko 9 Nucleon Semi-Inclusive Possible reactions on the proton: ep e′p′X and ep e′nX current fragmentation target fragmentation GeV 2 JLabHERA Below pp-threshold there is no need for kinematical cuts! Direct access to the fracture functions M(x,z,Q 2 ) and their properties. LT approximation only!

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May 20, 2005 M. Osipenko 10 Diffraction In the Regge limit and structure function of the Regge trajectory HERA Regge trajectory intercept, 1.1 for Pomeron ep e′p′X ep e′nX CLAS CLAS sees diffraction! Need p-n difference to select of pure gluonic content of exchanged object.

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May 20, 2005 M. Osipenko 11 Fracture Functions Separation of different fracture functions: M T,M L, M LT etc. related to different structure functions H 1, H 2, H 3 etc. Extraction of various moments and comparison to pQCD Test of diffractive factorization of the fracture functions H 1 and H 2 Rosenbluth separation Contribution of the target fragmentation in the pion electroproduction where

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May 20, 2005 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 p T dependences to theory (Cahn, Berger, pQCD), Separation different fracture functions M T, M L, M LT 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.

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May 20, 2005 M. Osipenko 13 Background u-channel nucleon production: ~F 2 (x,Q 2 ) Higher Twist contribution

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May 20, 2005 M. Osipenko 14 Fracture functions DGLAP evolution equation with standard splitting functions Momentum sum rule Process independent definition Hadron-hadron collisions N 1 +N 2 hX + In assumption of the factorization

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May 20, 2005 M. Osipenko 15 Previous data Below pp-production threshold only target fragmentation can contribute Large t-range from 0.1 up to 4-5 GeV 2 Good particle identification: possibility to make p-n difference Polarization observables: new information on the fracture functions Semi-inclusive nucleon electroproduction was measured at SLAC, Cornell, DESY, HERA and CERN. Only unpolarized data and most of variables are integrated over. GeV 2 HERA Cornell CERN

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May 20, 2005 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

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May 20, 2005 M. Osipenko 17 Semi-inclusive Reactions 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! 5 independent variables ep e′hX

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May 20, 2005 M. Osipenko 18 Kinematical Separation (for ) Separation is possible by means of a cut on the energy flow from the virtual photon to the measured hadron. Current fragmentation Target fragmentation Hadron rapidity Current Target x=0.3, Q 2 =3 GeV 2 Pion electroproduction

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May 20, 2005 M. Osipenko 19 Kinematical coverage Complete measurement of fracture functions: Almost whole z-range Possibility to access 5- dimensional cross section Allows to extract p T dependence Entire -range covered GeV 2 E1-6 DATA

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May 20, 2005 M. Osipenko 20 Mulders Rapidity Gap

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May 20, 2005 M. Osipenko 21 Regge Approach Structure functions of Regge trajectories CLAS-Note-01-006 Need p-n difference to select of pure gluonic content of exchanged object. neutron efficiency in SC neutron efficiency in EC Two component duality: equivalence of Pomeron and the background Test of Veneziano duality

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May 20, 2005 M. Osipenko 22 Λ Polarization p ee’ Λ π 1 2 6 (ud)-diquark is a spin and isospin singlet => s-quark carries entire spin of , polarization in TFR provides information on contribution of strange sea to proton spin. W.Melnitchouk and A.W.Thomas ‘96 J.Ellis, D.Kharzeev, A. Kotzinian ‘96 Polarized beam gives unique possibility to perform an “acceptance independent” measurement of polarization in electroproduction. – unique tool for polarization study due to it’s self-analyzing parity violating weak decay. q =1 q =1/2 ` q =1/2 K+K+ q =- s (H. Avakian)

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May 20, 2005 M. Osipenko 23 p T dependence H2+H1H2+H1 H3H3 H4H4 Distribution of Gaussian width of measured p T slopes for different structure functions.

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