Semi-inclusive DIS at 12 GeV H.Avakian (JLab) For the semi-inclusive working group JLAB PAC January 10, 2005 Semi-inclusive processes Factorization at low energies Large-x behavior of valence PDFs and flavor asymmetries of the sea Transversity and transverse momentum dependent distributions Target fragmentation and intrinsic strangeness Summary Note mes

Semi-Inclusive Deep Inelastic Scattering (SIDIS) DIS: Major source of QCD tests and PDF studies Probes only the sum of quarks and anti-quarks Requires assumptions on sea No access to transversity effect in LO SIDIS: “Tagging” to distinguish different quark flavors. Provide access to quark distributions with fragmentation acting as a weight factor: Probes orbital motion of quarks. Main focus of SIDIS studies: orbital angular momentum of quarks parton distributions at large x H.Avakian, Jan 10, 2005

SIDIS kinematic plane and relevant variables H.Avakian, Jan 10, 2005

SIDIS at leading twist Unpolarized target Longitudinally pol. target Transversely pol. target e p Mulders et al. Boer Mulders e Sivers transversity Off-diagonal PDFs vanish if quarks only in s-state! In addition T-odd PDFs require FSI (Brodsky et al., Collins, Ji et al. 2002) Factorization of kT-dependent PDFs proven at low PT of hadrons (Ji et al) Universality of kT-dependent distribution and fragmentation functions proven (Collins,Mets…)

Analysis of SIDIS and DVMP are complementary Probability to find a quark u in a nucleon P with a certain polarization in a position r and momentum k PDFs fpu(x),… FFs F1pu(t),F2pu(t).. TMD PDFs: fpu(x,kT),.. d2kT x=0,t=0 dx Wpu(x,k,r) “Parent” Wigner distributions d3r (FT) GPDs: Hpu(x,x,t), … GPD Measure momentum transfer to quark kT distributions also important for exclusive studies Measure momentum transfer to target Exclusive meson data important in understanding of SIDIS measurements Some PDFs same in exclusive and semi-inclusive analysis Analysis of SIDIS and DVMP are complementary H.Avakian, Jan 10, 2005

ep→e’pX: kinematic coverage at 11 GeV Acceptance in Q2,Mx,PT gained with high luminosity and energy upgrade (at 6GeV Mx<2.5GeV, Q2<4.5GeV2, PT<1GeV) test factorization in a wide kinematic range study the transition between the nonperturbative and perturbative regimes of QCD measure PDFs and study higher twists H.Avakian, Jan 10, 2005

Collinear Fragmentation p quark Collinear Fragmentation The only fragmentation function at leading twist for pions in eN→e’pX is D1(z) Ee =5.7 GeV Hall-C Ee =5.5 GeV No significant variation observed in p+/p- ratio and in z distributions of p+ for different x ranges (0.4<z<0.7, MX>1.5)

A1p f-kinematic dependence for p+/-/0 CLAS 5.7 GeV No significant z-dependence of A1 in the range 0.4<z<0.7 (p+p0) x dependence of CLAS A1p (A2=0) consistent with HERMES data at x3 higher Q2 and with PEPSI (LUND)MC.

Polarized PDFs g1u=u,g1d=d…. Ee =11 GeV NH3+He3 g1u=u,g1d=d…. Jlab @11 GeV Asymmetry measurements with different hadrons (p+p-) and targets (p,n) allow flavor separation H.Avakian, Jan 10, 2005

Flavor decomposition: polarized sea Predictions: Instantons (QSM): JLab @11 GeV First data from HERMES  0 More data expected from RHIC W± production in future H.Avakian, Jan 10, 2005

Longitudinally polarized Target SSA for p+ Measurement of kT dependent twist-2 distribution provides an independent test of the Collins fragmentation. Real part of interfe-rence of wave functions with L=0 and L=1 In noncollinear single-hadron fragmentation additional FF H1(z,kT) Efremov et al. p Study the PT – dependence of AULsin2f Study the possible effect of large unfavored Collins function. kT quark

Transversely polarized target SSA transversely polarized quarks in a transversely polarized nucleon. AUT ~ Collins Interpretation requires large unfavored spin dependent fragmentation. No success so far in describing consistently Collins SSA for all 3 pions at least in cQSM! More data needed, new observables GSI, CERN H.Avakian, Jan 10, 2005

Transverse Target SSA @11 GeV CLAS @ 11GeV (NH3) AUT ~ Collins p+ p0 p- f1T┴, requires final state interactions + interference between different helicity states Simultaneous (with pion SIDIS) measurement of, exclusive r,r+,w with a transversely polarized target important to control the background. AUT ~ Sivers H.Avakian, Jan 10, 2005

Transversity in double pion production The angular distribution of two hadrons is sensitive to the spin of the quark h1 h2 quark RT “Collinear” dihadron fragmentation described by two functions at leading twist: D1(z,cosqR,Mpp),H1R(z,cosqR,Mpp) Collins et al, Ji, Jaffe et al, Radici et al. relative transverse momentum of the two hadrons replaces the PT in single-pion production (No transverse momentum of the pair center of mass involved ) Dihadron production provides an alternative, “background free” access to transversity H.Avakian, Jan 10, 2005

SIDIS: target fragmentation xF>0 (current fragmentation) xF - momentum in the CM frame xF<0 (target fragmentation, TFR) Wide kinematic coverage at 11 GeV allows studies of hadronization in the target fragmentation region H.Avakian, Jan 10, 2005

Λ in target fragmentation 1 Λ p 2 π L – unique tool for polarization study due to self-analyzing parity violating decay (ud)-diquark is a spin and isospin singlet → s-quark carries whole spin of L L polarization in TFR provides information on contribution of strange sea to proton spin 6 Polarized beam gives unique possibility to perform an “acceptance independent” measurement of L polarization in electroproduction. W.Melnitchouk and A.W.Thomas ‘96 J.Ellis, D.Kharzeev, A. Kotzinian ‘96

JLab at 12 GeV High luminosity polarised CW beam Wide physics acceptance (exclusive, semi-inclusive current and target fragmentation) Complementarity of high luminosity and wide geometric acceptance halls High luminosity polarised CW beam H.Avakian, Jan 10, 2005

Essential for understanding the structure of the nucleon ! Summary Semi-inclusive measurements at 12 GeV will provide precise information on the polarized valence distributions in the nucleon test the expected flavor asymmetry in the polarized sea distributions determine the essentially unknown transversity and Sivers functions with high precision and in a variety of channels sensitivity to orbital motion of quarks improve the understanding of the fragmentation process and give access to the poorly understood target fragmentation region Essential for understanding the structure of the nucleon ! H.Avakian, Jan 10, 2005

support slides….. H.Avakian, Jan 10, 2005

PT-dependence of beam SSA ssinfLU(UL) ~FLU(UL)~ 1/Q (Twist-3) In the perturbative limit 1/PT behavior expected Perturbative region Nonperturbative TMD Asymmetries from kT-odd and kT-even (g1) distribution functions are expected to have a very different behavior (flat A1p(PT) observed at 5.7 GeV). H.Avakian, Jan 10, 2005

Measuring the Q2 dependence of SSA ssinfLU(UL) ~FLU(UL)~ 1/Q (Twist-3) For fixed x, 1/Q behavior expected Wide kinematic coverage allows to check the higher twist nature of beam and longitudinal target SSAs H.Avakian, Jan 10, 2005

Constant in perturbative limit g1/f1: PT-dependence Constant in perturbative limit Asymmetries from kT-odd (f1┴, h1┴, gT..) and kT-even (g1) distribution functions are expected to have a very different behavior H.Avakian, Jan 10, 2005

Transversity Sub-leading pion opposite to leading (into page) Simple string fragmentation (Artru model) L=1 Leading r opposite to leading p(into page) r production may produce an opposite sign AUT r SIDIS @11 GeV: 2 pions p+p0(r+) Understanding of 2 pion asymmetries will help to understand transversity mesurements p+p-(r0) H.Avakian, Jan 10, 2005

Λs in target fragmentation 1 Λ p 2 π P and p- kinematics 6