1. 1 CLAS-eg1 pol.-proton analysis H.Avakian (JLab) semi-SANE Collaboration Meeting April 21, 2005

2. 2 SIDIS studies require:  Factorization in SIDIS  Applicability of partonic description at JLab energies (HT <10-15%)  low W and Q^2 (direct production of resonances)  low M X in ep->e’h+X (resonances in target fragment, FSI)  Contamination from non-DIS processes  target fragmentation  exclusive production (vector mesons)

3. 3 SIDIS: Target fragmentation x F <0 ( target fragmentation, TFR ) x F >0 ( current fragmentation ) What is the fraction of target fragmentation in forward hemisphere? What is the contribution to various observables (multiplicities, asymmetries)? Rapidity (  and x F cuts are on average related to z cut

4. 4 SIDIS: Missing mass of pions in ep→e’  X Applying M X >1.4 (Q 2 >1.5,W 2 >4) we reduce the fraction of where resonances in the target fragment. -- 00 ++ n 00  ++

5. 5 A LU from CLAS 4.3 and 5.7GeV data 4.3 GeV 5.7GeV No significant dependence on beam energy No significant A LU dependence on M x beyond the neutron. DIS-cuts Q 2 >1 GeV 2 W>2 GeV y < 0.85 0.5 < z < 0.8

6. 6 SIDIS: contamination from exclusive 2  Understanding of exclusive 2 pion production at large W will help to understand single pion measurements ++ 00 Larger fraction of  + from  at low x and large z PYTHIA at 5.7 GeV Major part of exclusive 2 pions are from 

7. 7 SIDIS: analysis strategy Current: Use MC(LUND) and data comparison to define kinematic regions (in z,Mx,) where contributions from non-DIS processes and HT effect are not significant within statistical accuracy of specific measurement. Future: (also included in 12 GeV program) Perform studies of all contributing mechanisms, including 1)Higher Twist effects 2)Target fragmentation 3)Exclusive channels

8. 8 SIDIS: MC and data analysis N(i,j,k,l,m,n,h) array in a data file per run i=1,7 Q2-bins 0.453, 0.645, 0.919, 1.31, 1.87, 2.66, 3.79, 5.40 j=1,6 x-bins 0.12-0.48 k=1,8 z-bins 0.1-0.9 l=1,6 P T -bins 0.0-1.2 m=1,12  bins 0.0-360.0 n= 1-  2-  3-  h=1 helicity+ h=2 helicity- The same structure created using the PEPSI-MC with CLAS acceptance and smearing included “histo-data” files (P.Bosted) contain counts per bin, occupy small disk space and are used for data analysis. used

9. 9 PEPSI MC asymmetries GRVS set used Testing extraction procedure: Extract  u and  d using  0 Asymmetries on proton and deuteron extracted A LL for 3 pions from MC histo-data files

10. 10 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   +  A 1  - ___________- 1+  LUND-MC used to get 

11. 11 SIDIS: factorization studies A 1 inclusive and from      (HERMES published) show similar trend. Low A 1 p for   +    will lead to positive  s (require more studies) LUND-MC used to get  ep→e‘pX

12. A 1 p -for  + +  -,  0 A 1 for     +   ) can be a source of information on  s/s (Frankfurt, Strikman et al. 1989) Multiplicity of     +   ) is spin independent. (if no strangeness) and provides a unique test of partonic description HERMES

13. 13 g 1 /f 1 : P T -dependence Asymmetries from k T -odd (f 1 ┴, h 1 ┴, g T..) and k T -even (g 1 ) distribution functions are expected to have a very different behavior Constant in perturbative limit

14. 14 Precision measurements of parton distribution and fragmentation functions in hard scattering kinematics require: MC generator based on LUND-MC (PYTHIA,JETSET) tuned for JLab, including: –Semi-Inclusive DIS –Exclusive Processes –T-odd Distribution and Fragmentation –Radiative Processes After testing with CLAS this MC may provide basis for precision measurements of PDFs and FFs at JLab (SANE?)

15. 15 Summary Precision measurement of parton distribution functions will require separation of contributions from different mechanisms and global analysis of spin and azimuthal asymmetries for exclusive and semi-inclusive final states measured in a wide range of P T, ,x,Q 2

16. 16 support slides…

17. 17 Longitudinally polarized target future measurements at CLAS Sensitive to unfavored fragmentation for  - and  0 Study the Collins fragmentation mechanism with long.pol.target  0 SSA not sensitive to HT and diffractive  0 production H unf =-1.2H fav H unf =-5H fav H unf =0

18. 18 Extracting h 1L from  + A UL For Collins fragmentation use chirally invariant Manohar-Georgi model (Bacchetta et al) Distribution functions from  QSM from Efremov et al Systematic error from unknown ratio of favored and un favored Collins functions (R= H 1 d→  /H 1 u→  ), band correspond to -2.5<R<0  - and  0 SSA will give access to h 1L d ( If R ≈ -1 neutron data could be used) eg1

19. 19 Extracting h 1 and h 1L from  + A UT and A UL For Collins fragmentation use chirally invariant Manohar-Georgi model (Bacchetta et al) Distribution functions from  QSM from Efremov et al Systematic error from unknown ratio of favored and un favored Collins functions (R= H 1 d→  /H 1 u→  ), band correspond to -2.5<R<0  - and  0 SSA will give access to h 1 d /h 1L u ( If R ≈ -1 neutron data could be used)

20. 20 Measuring the Q 2 dependence of SSA  sin  LU(UL) ~F LU(UL) ~ 1/Q (Twist-3) Wide kinematic coverage allows to check the higher twist nature of beam and longitudinal target SSAs For fixed x, 1/Q behavior expected

21. 21 Polarized target: HERMES vs CLAS at 5.7GeV GRSV95 x3 difference in may account for ~15-20% in A 1 p at low x

22. 22 SIDIS: factorization studies CLAS data at 6GeV are consistent with factorization and partonic description for variety of observables with unpolarized and polarized targets. No significant variation observed in z distributions of p+ for different x ranges Double spin asymmetry for different samples consistent, indicating no significant contribution from non-DIS processes