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Spin and azimuthal asymmetries in SIDIS at JLAB

Spin and azimuthal asymmetries in SIDIS at JLAB. P. Bosted *. Jefferson Lab. SIR-2005. Physics Motivation Jlab kinematics and factorization Double spin asymmetries Single Spin Asymmetries Future measurements Summary. * In collaboration with H. Avakian, V.Burkert and L.Elouadrhiri.

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Spin and azimuthal asymmetries in SIDIS at JLAB

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  1. Spin and azimuthal asymmetries in SIDIS at JLAB P. Bosted * Jefferson Lab SIR-2005 Physics Motivation Jlab kinematics and factorization Double spin asymmetries Single Spin Asymmetries Future measurements Summary * In collaboration with H. Avakian, V.Burkert and L.Elouadrhiri

  2. kT-dependentparton distributions 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. 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) Mulders, This talk transversity Sivers This talk P. Bosted, SIR-2005

  3. SIDIS kinematic plane and relevant variables P. Bosted, SIR-2005

  4. JLab Kinematics and Facorization • Traditional DIS: W>2 GeV, Q2>1.1 GeV2 • Berger criteriium for current fragmentation dominance is z>0.4 • Require z<0.7 to avoid diffractive rho meson contributions (and keep Mx>1.4 GeV) • Pt<1 GeV (approximately exponential region) • Study if factorization broken for these cuts using unpolarized data from E00-108 in Hall C P. Bosted, SIR-2005

  5. Experiment ran in August 2003 • Close-to-final data analysis • Small Q2 variation not corrected yet Hall C E00-108 data x = 0.32 PRELIMINARY No visual “bumps and valleys” in pion ratios off deuterium x = 0.32 PRELIMINARY P. Bosted, SIR-2005

  6. From E00-108 deuterium data: D-/D+ = (4 – Np+/Np-)/(4Np+/Np- - 1) z = 0.55 PRELIMINARY • D-/D+ ratio should be independent of x, and data supports this for W=2.5 GeV, Q2=2.5 GeV2, pt<0.3 GeV • but should depend on z • Find similar slope versus z as HERMES, but slightly larger values (could be due to lower average photon energy) x = 0.32 PRELIMINARY P. Bosted, SIR-2005

  7. CLAS Experiment Setup and Kinematics Scattering of 5.7 GeV polarized electrons off polarized NH3, ND3 • ~8M p+ in SIDIS kinematics x x

  8. Determination of g1/F1 (approximately A1) • Target polarization PT about 0.7 (0.3) for NH3 (ND3) • Beam polarization PB about 0.7 • Dilution factor f varies from 0.1 to 0.3: used Lund • model for n/p ratio and preliminary Hall B data • for A-dependence • Depolarization factor DLL(y) evaluated assuming R • same as for inclusive. • Assumed Aperp=0 (not measured) • No radiative corrections applied • “p+” and “p-” include some K+, K- for P>1.5 GeV • p0 events cleanly identified with two photons

  9. x-depenence of SIDIS g1/F1 • Good agreement with • HERMES p+ data at • 3x higher Q2 • x-dependence follows PEPSI • (Lund) Monte Carlo using • GRSV polarized PDFs (LO) • Magnitude also in good • agreement with simulation P. Bosted, SIR-2005

  10. SIDIS: factorization studies GRVS g1/F1 inclusive, for the sum of p+ ,p-, and for p0 are consistent with each other in the range 0.4<z<0.7, as expected in LO with factorization and current fragmentation dominance P. Bosted, SIR-2005

  11. z-depenence of SIDIS g1/F1 No significant z-dependence seen 0.3<z<0.7, as expected for factorization and current fragmentation dominance Good agreement with PEPSI predictions (including dropoff at high z for p-) CLAS 5.7 GeV PRELIMINARY P. Bosted, SIR-2005

  12. pt-depenence of SIDIS g1/F1 No pt dependence expected in LO if current fragmentation dominance and factorization Slight pt dependence seen (but results quite sensitive to pt dependence of A-dependence needed for dilution factor) Reasonable agreement with PEPSI predictions. CLAS 5.7 GeV PRELIMINARY P. Bosted, SIR-2005

  13. SIDIS g1/F1 for Deuteron CLAS 5.7 GeV PRELIMINARY Results don’t agree as well with PEPSI using GRSV, more sensitive to un-favored fragmentation function and NLO corrections than proton (although errors are about a factor of two larger) NLO QCD fits including new SIDIS CLAS data can help constrain polarized PDFs in valence region

  14. Longitudinally Polarized Target SSA • Clear fdependence seen for proton target and p+, p0 • Fit A*sin(f) + B*sin(2f) for Twist-3 and Twist-2 respectively P. Bosted, SIR-2005

  15. SSA: x-dependence Twist-2 Higher Twist Data in rough agreement with Efremov et al. predictions, except for p0 sin(f) term (evidence for terms not involving Collins fragmentation?) 5.7 GeV PRELIMINARY P. Bosted, SIR-2005

  16. First glimpse of Twist-2 TMD h1L┴ For Collins fragmentation function use HERMES data Distribution functions from cQSM from Efremov et al PRELIMINARY CLAS-5.7GeV Systematic error only from unknown ratio of favored and unfavored Collins functions (R= H1d→p+/H1u→p+), band correspond to -2.5<R<0 • More data required with p- & p0 • Exclusive 2 pion background may be important P. Bosted, SIR-2005

  17. Future: more p0 data in SIDIS advantages: • SIDIS p0 production is not contaminated by diffractive r • HT effects and exclusive p0 suppressed • Simple PID by p0-mass (no kaon contamination) • Provides complementary to p+/- information on PDFs disadvantages: reconstruction efficiency (requires detection of 2g) P. Bosted, SIR-2005

  18. 424 PbWO4 ……..crystals CLAS+Inner Calorimeter (IC) IC IC sE/E=0.0034/E+0.038/√E+0.022 CLAS+IC CLAS Reconstruction efficiency of high energy p0 with IC increases ~ 4 times due to small angle coverage CLAS IC at CLAS opens new avenue for studies of spin and azimuthal asymmetries of exclusive and semi-inclusiveg, p0,h,r+ P. Bosted, SIR-2005

  19. sUL ~ KM Longitudinally polarized target SSA using CLAS+IC 50 days of CLAS+IC curves, cQSM from Efremov et al Hunf=-5Hfav Hunf=-1.2Hfav Hunf=0 • 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

  20. 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: may be used in future NLO QCD fits. • sinf andsin2f SSA measured, providing access to the twist-2 TMD h1L distribution and testing the Collins fragmentation function • Future measurements with IC, if approved, will greatly improve p0 data. Much greater improvements for all reactions possible with 12 GeV upgrade due to much larger coverage of DIS kinematics. P. Bosted, SIR-2005

  21. support slides….. P. Bosted, SIR-2005

  22. Collins effect and 2 pion production 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 r+ Understanding of 2 pion asymmetries will help to understand single pion mesurements r0 P. Bosted, SIR-2005

  23. AULSSA: PT-dependence HT –SSA significant for p + and p 0 CLAS PRELIMINARY • sinf SSA p + increases with PT and is consistent with HERMES measurement. P. Bosted, SIR-2005

  24. AULSSA: z-dependence CLAS PRELIMINARY P. Bosted, SIR-2005

  25. Missing mass of pions in ep→e’pX p0 D++ p- p+ n D0 In accessible kinematics (Q2>1.5,W2>4) low MX(large z) for p0 are suppressed by current CLAS acceptance. P. Bosted, SIR-2005

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