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Spin and azimuthal asymmetries in SIDIS at JLAB

This paper discusses the spin and azimuthal asymmetries observed in Semi-Inclusive Deep Inelastic Scattering (SIDIS) at Jefferson Lab. It explores the kinematics and factorization of SIDIS, as well as the single spin asymmetries. The paper also presents future measurement prospects and summarizes the findings.

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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 DNP-2005 Physics Motivation Jlab kinematics and factorization Single Spin Asymmetries Future measurements Summary * In collaboration with H. Avakian, V.Burkert and L.Elouadrhiri P. Bosted, DNP 2005

  2. xF>0 (current fragmentation) Single pion production in hard scattering h xF<0 (target fragmentation) xF- momentum in the CM frame Target fragmentation Current fragmentation h h h h M PDF PDF GPD 1 -1 0 xF Fracture Functions kT-dependent PDFs Generalized PDFs Wide kinematic coverage of large acceptance detectors allows studies of hadronization both in the target and current fragmentation regions P. Bosted, DNP 2005

  3. Polarized Semi-Inclusive DIS Cross section is a function of scale variables x,y,z n = E-E’ y = n /E x = Q2 /2Mn z = Eh /n Hadron-Parton transition: by distribution function f1u(x): probability to find a u-quark with a momentum fraction x Parton-Hadron transition: by fragmentation function Dp+(p-)(z): probability for a u-quark to produce a p+(p-)with momentum fraction z z 1u P. Bosted, DNP 2005

  4. Transverse momentum of quarks • kT – led to introduction of kT dependent PDFs(TMDs) • kT – crucial for orbital momentum and spin structure studies • led to SSA in hard scattering processes • kT - important for cross section description • - PT distributions of hadrons in DIS • exclusive photon production (DVCS) • - hard exclusive vector meson cross section • - pp → p0X (E704,RHIC) cross sections Spin-Azimuthal Asymmetries: sensitive to kT To study orbital motion of quarks in semi-inclusive DIS measurements in a wide range of x,z,PT, f are required. P. Bosted, DNP 2005

  5. Unpolarized target e p Longitudinally pol. target Transversely pol. target e p SIDIS (g*p→pX) cross section at leading twist (Ji et al.) e Boer-Mulders 1998 Kotzinian-Mulders 1996 Collins-1993 structure functions = pdf × fragm × hard × soft (all universal) Off diagonal PDFs related to interference between L=0 and L=1 light-cone wave functions. To observe the transverse polarization of quarks in SIDIS spin dependent fragmentation is required! P. Bosted, DNP 2005

  6. 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, DNP 2005

  7. Z-Dependence of unpolarized cross sections Jlab E00-108, Preliminary, E=5.5 GeV Pretty good agreement with prediction using CTEQ5M PDFs and Binnewies fragmentation functions, except for z>0.7, or Mx>1.4 GeV. X=0.3, Q2=2.5 GeV2, W=2.5 GeV P. Bosted, DNP 2005

  8. CLAS Experiment Setup and Kinematics Scattering of 5.7 GeV polarized electrons off polarized NH3, ND3 • ~8M p+ in SIDIS kinematics x x P. Bosted, DNP 2005

  9. Experimental Overview • 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, probably small) • No radiative corrections applied (expected to be small) • “p+” and “p-” include some K+, K- for P>1.5 GeV • p0 events cleanly identified with two photons P. Bosted, DNP 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 if factorization works and current fragmentation dominance. Data at 6 GeV with Mx>1.4 GeV support this. P. Bosted, DNP 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, DNP 2005

  12. 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, DNP 2005

  13. SSA measurements at CLAS ep→e’pX W2>4 GeV2 CLAS PRELIMINARY p1sinf+p2sin2f Q2>1.1 GeV2 y<0.85 0.4<z<0.7 MX>1.4 GeV PT<1 GeV 0.12<x<0.48 p1= 0.059±0.010 p2=-0.041±0.010 p1=-0.042±0.015 p2=-0.052±0.016 p1=0.082±0.018 p2=0.012±0.019 • Significant SSA measured for pions with longitudinally polarized target • Complete azimuthal coverage crucial separation of sinf, sin2f moments P. Bosted, DNP 2005

  14. 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, DNP 2005

  15. 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: analysis in progress. P. Bosted, DNP 2005

  16. 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, DNP 2005

  17. Higher Twist SSAs Discussed as main sources of SSA due to the Collins fragmentation Target sinf SSA (Bacchetta et al. 0405154) In jet SIDIS only contributions ~ D1 survive Beam sinf SSA With H1┴ (p0)≈0(or measured) Target and Beam SSA can be a valuable source of info on HT T-odd distribution functions P. Bosted, DNP 2005

  18. 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, DNP 2005

  19. 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, DNP 2005

  20. 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 P. Bosted, DNP 2005

  21. CLAS12 High luminosity polarized (~80%) CW beam Wide physics acceptance (exclusive, semi-inclusive current and target fragmentation) Wide geometric acceptance 12GeV significantly increase the kinematic acceptance (x10 lumi) P. Bosted, DNP 2005

  22. 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 will greatly improve p0 data, and charged pions too. Much greater improvements for all reactions possible with 12 GeV upgrade due to much larger coverage of DIS kinematics. P. Bosted, DNP 2005

  23. support slides….. P. Bosted, DNP 2005

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

  26. p quark Collinear Fragmentation The only fragmentation function at leading twist for pions in eN→e’pX is D1(z) Ee =5.7 GeV No significant variation observed in z distributions of p+ for different x ranges (0.4<z<0.7, MX>1.5) and for A1p as a function of PT P. Bosted, DNP 2005

  27. SIDIS: factorization studies P.Bosted JLab data at 6GeV are consistent with factorization and partonic description for variety of ratio observables P. Bosted, DNP 2005

  28. y ST PT fC sT fS fh fS fS’ fS’ = p-fS sin(fh+fS) spin of quark flips wrt y-axis x FUU∞h1 ┴H1┴ ┴ sT(p×kT)↔ h1┴ (sTkT)(pSL)↔ h1L sinfC=sin(fh- fS’) y PT sT fC fh fS=fh ┴ cos(2fh) FUL∞h1L H1┴ Collins Effect: azimuthal modulation of the fragmentation function FUT∞h1H1┴ sT(q×PT)↔H1┴ y fC PT fC sT D(z,PT)=D1(z,PT)+H1┴(z,PT)sin(fh- fS’) fh fS’ x fC fS= p/2+fh x sin(2fh) fS’ = p-fS= p-fh P. Bosted, DNP 2005 fS’ = p-fS= p/2-fh sin(2fh)

  29. L Flavor decomposition of T-odd f┴ In jet SIDIS with massless quarks contributions from H1┴ vanish gauge link contribution With SSA measurements for p++p-and p0 on neutron and proton (p=p++p-) assuming Hfav=Hu→p+≈ -Hu→p-=-Hunfav With H1┴ (p0)≈0(or measured) target and beam HT SSAs can be a valuable source of info on HT T-odd distribution functions P. Bosted, DNP 2005

  30. 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, DNP 2005

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