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Hard scattering processes: Experiment

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## Hard scattering processes: Experiment

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**Hard scattering processes: Experiment**N.C.R. Makins *) University of Illinois at Urbana-Champaign SIR Workshop – Jefferson Lab, May 17-20, 2005 • Introduction • Semi-inclusive spin and azimuthal asymmetries and TMD distributions • Hard exclusive processes and GPDs • Conclusions *) in collaboration with H. Avakian**Physics Motivation**Orbital Angular Momentum (OAM) in the focus. Transverse momentum of quarks is a key to OAM. Parton Distribution Functions generalized to contain information not only on longitudinal, but also on the transverse distribution of partons: Complementary sets of non-perturbative functions sensitive to different aspects of transverse distributions • Generalized Parton Distributions (GPD) H, E ... • Transverse-momentum dependent (TMD) parton distributions**Probability to find a quark u in a nucleon P with a certain**polarization in a position r and momentum k Wpu(x,k,r) “Parent” Wigner distributions d3r d2kT (FT) GPD TMD ~ ~ TMD PDFs:fpu(x,kT),g1,f┴1T, h1,h┴1L GPDs: Hpu(x,x,t), Epu(x,x,t), H,E,… 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 x=0,t=0 dx d2kT PDFs fpu(x,kT),g1, h1 FFs F1pu(t),F2pu(t).. Some PDFs same in exclusive and semi-inclusive analysis Analysis of SIDIS and DVMP are complementary**Favored / disfavoredfragmentation functions:**Quark Polarization from Semi-Inclusive DIS (SIDIS) In SIDIS, a hadron h is detected in coincidence with the scattered lepton: Flavor Tagging: Flavor content of observed hadron h is related to flavor of struck quarkq via the fragmentation functions D(z) scaling variable**First 5-flavor fit to Δq(x)**Final Δq Measurement from HERMES using all polarized data taken from 1996 - 2000 No evidence of anti-quark polarization, or flavor-asymmetry, Ds≈0 Sensitive to factorization more in talks by Zhu, Christova**CLAS 5.7 GeV**A1p-kinematic dependence for p+/-/0 A1p HERMES CLAS PRELIMINARY • No significant z-dependence of A1 in the range 0.3<z<0.7 • x dependence of CLAS A1p(A┴=0) consistent with HERMES data at 3 times higher Q2 and with LUND-MC (lines).**SIDIS: factorization studies**A1p++p- GRVS • A1 inclusive, from p+p- sum and p0 are consistent (in range 0.4<z<0.7 ) • A1pdependence can serve an important check of HT effects and applicability of simple partonic description. • There is an indication that A1p of p+ +p-is lower than inclusive at large z. more in talk by P.Bosted**p0 in Semi-inclusive DIS as a test?**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**Collins**AUT ~ Collins Effect Evidence of non 0 Collins effect First info on PT distribution undefined r contribution more details in talk by G. Schnell**Sivers**AUT ~ Sivers effect Evidence of non 0 Sivers effect For p+ consistent with increase with x,z,PT undefined r contribution**Collins and Sivers Effects at COMPASS**Collins AUT Sivers AUT No sizeable effect. Possible cancellations in isoscalar target (6LiD) undefined r contribution more details in talk by A.Bressan**‘SSA from HERMES/COMPASS‘**• check for consistency ‘‘Sivers function‘‘: hep-ph/0501196 consistent HERMES COMPASS more in A. Kotzinian’s talk**sUL ~**KM Collins Effect and Kotzinian-Mulders Asymmetry Real part of interfe-rence of wave functions with L=0 and L=1 Efremov,Schweitzer (cQSM ) undefined r contribution Independent study the Collins fragmentation with longitudinally polarized target. Measure the twist-2 Mulders TMD (transversely pol. quarks in a longitudinally pol. proton) more in P.Bosted’s talk**Beam SSA: ALU**ssinfLU’~ 1/Q (Twist-3) “Sivers” effect by F.Yuan using h1┴ “Collins” effect by Schweitzer et al. using e(x) “Sivers ” effect Afanasev & Carlson, Metz & Schlegel more details in E.Avetisyan’s talk**j2-p**e- Q j1 e+ 2-h inclusive transverse momentum dependent Xsection: Collins Function In SIDIS Collins function always coupled with some(unknown) distribution function In e+e- only the Collins FF appears!**Collins Function**First direct measurement of the non 0 Collins function Rising behaviour vs. z more details in talk by A.Ogawa**Transversity in double pion production**h1 RT quark h2 The angular distribution of two hadrons is sensitive to the spin of the quark “Collinear” dihadron fragmentation described by two functions at leading twist: D1(z,cosqR,Mpp),H1R(z,cosqR,Mpp) The relative transverse momentum of the two hadrons replaces the PT in single-pion production No transverse momentum of the pair center of mass!**2p transvers spin SSA**• Positive asymmetry observed for all invariant mass bins for proton • No evidence for a sign flip at the r-mass (Jaffe et al.) more details in talk by Kobayashi**2p transvers spin SSA**• Asymmetry vs Minv, x, z consistent with 0. • Runs using p-target (NH3)**Is the Sivers function “friend” of transversity?**b - Impact parameter transversely polarized target quark flavor polarization lead to SSA shift defined by anomalous magnetic moment of proton (M.Burkardt) Or the “relative” of GPD E T In the polarized proton u quarks are shifted (~ 0.4 fmdefined by anomalous magnetic moment of proton) down and d quark up, giving rise to left-right asymmetries**Sivers effect in the target fragmentation**xF>0 (current fragmentation) xF<0 (target fragmentation) xF- momentum in the CM frame Wide kinematic coverage required for studies of hadronization in the target fragmentation region more details in A.Kotzinian’s talk**Deeply Virtual Compton Scattering ep->e’p’g**Polarized beam, unpolarized target: ~ DsLU~ sinfIm{F1H+ x(F1+F2)H+kF2E} Kinematically suppressed Unpolarized beam, longitudinal target: ~ DVCS DsUL~ sinfIm{F1H+x(F1+F2)(H+.. } BH Kinematically suppressed Unpolarized beam, transverse target: DsUT~ sinfIm{k(F2H – F1E) + …..} x = xB/(2-xB ),k = t/4M2 Kinematically suppressed GPD combinations accessible as azimuthal moments of the total cross section.**CLAS at 4.3 GeV**HERMES 27 GeV A(f) = asinf + bsin2f Pioneering DVCSExperiments SSA flips the sign from e+ to e-**DVCS SSA: CLAS 5.7 GeV**VGG 0.15<x<0.4 1.50 <Q2< 4.5 GeV2 -t<0.5 • Higher energy increases kinematics range. • Higher statistics allows binning of ALU in Q2, t, xB • More data available from ongoing experiments more details in talk by M.Garcon**DVCS measurements at HERMES**Beam Charge Asymmetry Longitudinal Target Spin Asymmetry ~ DsC ~cosfReH Ds~sinfIm{F1H+x(F1+F2)H...} With increased statistic asymmetries may constrain GPD models More in talk by F. Ellinghause**Exclusive meson production**GPD Different final state mesons filter out different combinations of unpolarized (H,E) and polarized (H,E) GPDs. ~ ~ Asymmetry depends linearly on the GPDE, which enters Ji’s sum rule. r0 production on transverse target Provide access to different combinations of GPD E and orbital momentum contributions Ju,Jd r0 -> 2Eu + Ed r+ -> Eu - Ed K. Goeke, M.V. Polyakov, M. Vanderhaeghen, 2001 Studies needed to define on how far is the asymptotic regime and guide theory in describing HT.**Conclusions**• The new data are just the first trickle of a great wealth of upcoming information on 3D PDFs h1 h1 • Measurement of 3D PDFs requireglobal analysis of SSAs for exclusive and semi-inclusive final states measured in a wide range of kinematics at different facilities.**Questions to address in SIDIS**• How do we test the factorization and quantify its breakdown • Do we need the global analysis of exclusive and semi-inclusive processes? • How small the HT should be, to be interesting to measure? • What is the contribution to pion SIDIS observables from exclusive vector mesons • What we learn from PT-dependence of observables • What we learn from target fragmentation (xF<0) studies**r+**pion SSA from r(p+p-/p+p0) (CLAS @5.7GeV) PYTHIA at 5.7 GeV r0 Larger fraction of p+ from r at low x and large z p+ SSA at large z may also have a significant (~20%) contribution from r Exclusiver (higher twist for SIDIS) crucial for pX and ppX studies**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 Better understanding of 2 pion asymmetries will help to understand transvers spin SSA mesurements**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).**SSA: PT-dependence of sinf moment**ssinfLU(UL) ~FLU(UL)~ 1/Q (Twist-3) CLAS @5.7 GeV CLAS @4.3 GeV Beam and target SSA for p+ (not sensitive to MX-cut) are consistent with increase with PT**SIDIS: target and current fragmentation**xF>0 (current fragmentation) xF- momentum in the CM frame xF<0 (target fragmentation, TFR) • – probability of finding a parton qwith momentum fraction xand a hadron hwith energy fraction z in the proton (Trentadue & Veneziano). Wide kinematic coverage of CLAS allows studies of hadronization in the target fragmentation region**SSA in exclusive pion production**Beam SSA ALU at 6GeV Target SSA at 27.5 GeV HERMES W2>4GeV2, Q2>1.5GeV2 CLAS PRELIMINARY - Beam SSA and Longitudinally pol. Target SSA provide information on HT ( 0 at leading order)**Exclusive r measurements**CLAS at 4.3 GeV W>1.75GeV HERMES at 27.5 GeV W>2GeV Regge GPDs(VGG) Decent description in pQCD framework already at moderate Q2**e- p e-nr+**π+π0 Exclusive r+ production Exclusive r+n separated by invariant and missing masses. CLAS 5.7 GeV n r+ Provide access to different combinations of orbital momentum contributions Ju,Jd r0 -> 2Ju + Jd r+ -> Ju - Jd w -> 2Ju - Jd • Significant transverse target SSA predicted for exclusive r0, r+ • (Goeke et al hep-ph/0106012)**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