New results on SIDIS SSA from JLab  Physics Motivation  Double spin asymmetries  Single Spin Asymmetries  Future measurements  Summary H. Avakian * * In collaboration with P.Bosted, V.Burkert and L.Elouadrhiri DIS-2005 Apr 28 Jefferson Lab

Semi-Inclusive Deep Inelastic Scattering (SIDIS): Probes orbital motion of quarks through quark transverse momentum distribution Access to new PDFs not accessible in inclusive DIS. k T -dependent parton distributions Sivers transversity Mulders 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 k T -dependent PDFs proven at low P T of hadrons (Ji et al)  Universality of k T -dependent distribution and fragmentation functions proven (Collins,Mets…)

H. Avakian, DIS SIDIS kinematic plane and relevant variables

H. Avakian, DIS The CLAS Detector Scattering of 5.7 GeV polarized electrons off polarized NH 3  ~8M  + in DIS kinematics,SIDIS Q 2 >1.1GeV 2, W 2 >4GeV 2, y<0.85,  beam polarization 73%  target polarization 72% (f=0.2) x x

A 1 p -kinematic dependence for  +/-/0 CLAS 5.7 GeV A1pA1p A1pA1p No significant z-dependence of A 1 in the range 0.4<z<0.7 (     ) x dependence of CLAS A 1 p (A ┴ =0) consistent with HERMES data at 3 times higher Q 2 and with PEPSI (LUND)MC. CLAS PRELIMINARY

H. Avakian, DIS SIDIS: factorization studies A 1 inclusive, from      sum and   are consistent (in range 0.4<z<0.7 ) A 1 p dependence can serve an important check of HT effects and applicability of simple partonic description. There is an indication that  A 1 p of   +    is lower than inclusive at large z. GRVS A1+-A1+-

H. Avakian, DIS Longitudinally polarized Target SSA Measure the k T dependent twist-2 distribution and provides an independent test of the Collins fragmentation. Real part of interfe- rence of wave functions with L=0 and L=1  UL ~ KM

8 Study the Collins fragmentation mechanism with long. polarized target For  - and  0 SSA is sensitive to unfavored fragmentation SSA: x-dependence HT–SSA significant for  + and  0 (non-Collins?) A UL (  0 ) ~ H 1 favore +H 1 unfavored PRELIMINARY 5.7 GeV

For Collins fragmentation use chirally invariant Manohar-Georgi model (Bacchetta et al) Systematic error only from unknown ratio of favored and unfavored Collins functions (R= H 1 d→  /H 1 u→  ), band correspond to -2.5<R<0  - and  0 SSA will also give access to h 1L d ( If R ≈ -1 deuteron data could be crucial) CLAS-5.7GeV First glimpse of Twist-2 TMD h 1L ┴ PRELIMINARY More data required with  - &  0 Exclusive 2 pion background may be important Distribution functions from  QSM from Efremov et al

H. Avakian, DIS  0 in Semi-inclusive DIS 1)SIDIS  0 production is not contaminated by diffractive  2)HT effects and exclusive  0 suppressed 3)Simple PID by  0 -mass (no Kaon contamination) 4)Provides complementary to  +/- information on PDFs disadvantages: reconstruction efficiency (requires detection of 2  ) advantages:

H. Avakian, DIS CLAS+Inner Calorimeter (IC) IC at CLAS opens new avenue for studies of spin and azimuthal asymmetries of exclusive and semi-inclusive     CLAS CLAS+IC CLAS IC 424 PbWO4 ……..crystals Reconstruction efficiency of high energy  0 with IC increases ~ 4 times due to small angle coverage IC  E /E=0.0034/E+0.038/√E+0.022

12  UL ~ KM Longitudinally polarized target SSA using CLAS+IC Provide measurement of SSA for all 3 pions, extract the Mulders TMD and study Collins fragmentation with longitudinally polarized target Allows also measurements of 2 pion asymmetries H unf =-1.2H fav H unf =-5H fav H unf =0 50 days of CLAS+IC (5.7GeV) curves,  QSM from Efremov et al

H. Avakian, DIS Summary Spin and azimuthal asymmetries measured at 5.7 GeV with longitudinally polarized target. Double spin asymmetries of pions are consistent with factorization and partonic picture sin  and  sin2  SSA measured, providing access to the twist-2 TMD h 1L distribution and testing the Collins fragmentation Studies of spin and azimuthal asymmetries at CLAS will significantly improve the error bars for charged pions and will provide a superior measurements with neutral pions allowing precision measurement of the twist-2 k T -dependent PDF.

H. Avakian, DIS support slides…..

H. Avakian, DIS Longitudinally Pol Target: SSA for  + sin2  moment (Kotzinian-Mulders asymmetry) is a clean source of Collins SSA P 1 = ± P 2 = ± Significant sin2  term in the long.pol. x-section compared to A LU

H. Avakian, DIS Collins effect and 2 pion production Simple string fragmentation (Artru model) Sub-leading pion opposite to leading (into page) L=1  production may produce an opposite sign A UT Leading  opposite to leading  (into page) Understanding of 2 pion asymmetries will help to understand single pion mesurements ++ 00 

H. Avakian, DIS sin  SSA  + increases with PT and is consistent with HERMES measurement. A UL SSA: P T -dependence HT –SSA significant for  + and  0 CLAS PRELIMINARY

H. Avakian, DIS sin  SSA  + increases with PT and is consistent with HERMES measurement. A UL SSA: z-dependence HT –SSA significant for  + and  0 CLAS PRELIMINARY

H. Avakian, DIS Longitudinally polarized target+IC:  + Reconstruction efficiency with IC decreases ~ 40%

H. Avakian, DIS Longitudinally polarized target+IC:  - Reconstruction efficiency with IC decreases ~ 10%

H. Avakian, DIS Exclusive  + production Exclusive  +n separated by invariant and missing masses. n ++ e - p  e - n  + π+π0π+π0 Provide access to different combinations of orbital momentum contributions J u,J d   -> 2J u + J d    -> J u - J d Significant transverse target SSA predicted for exclusive   accesible with long.pol. Target with effective polarization ~20% CLAS 5.7 GeV

H. Avakian, DIS Missing mass of pions in ep→e’  X In accessible kinematics (Q 2 >1.5,W 2 >4) low M X (large z) for  0 are suppressed by current CLAS acceptance. -- 00 ++ n 00  ++

H. Avakian, DIS SIDIS: factorization studies A 1 inclusive, from      sum and   are consistent (in range 0.4<z<0.7 ) A 1 p dependence can serve an important check of HT effects and applicability of simple partonic description. There is an indication that  A 1 p of   +    is lower than inclusive at large z. A 1   +  A 1  - ___________ 1+   from-MC GRVS A1+-=A1+-=