SIDIS measurements of transverse and longitudinal spin azimuthal

SIDIS measurements of transverse and longitudinal spin azimuthal asymmetries related to higher twist PDFs Harut Avakian (JLab) Transversity 2011, Aug 29, 2011 H. Avakian, Transversity 2011 1

Outline • Higher twists in SIDIS • quark-gluon correlations • experimental results • model calculations and lattice simulations • Future measurements • measuring higher twist distributions in di-hadron production • extraction of HT functions from azimuthal asymmetries • Physics background to leading observables • Summary Quark-gluon correlations (like k. T-effects ) lead to azimuthal modulations in hadron production in hard scattering processes. H. Avakian, Transversity 2011 2

SIDIS kinematical plane k. T p┴ PT = p┴ +z k. T H. Avakian, INT, Nov 9

Azimuthal distributions in SIDIS T h. t. EMC (1987) Large cosf modulations observed by EMC were reproduced in electroproduction of hadrons in SIDIS with unpolarized targets at COMPASS and HERMES

Measurements of SS azimuthal asymmetries in SIDIS HERMES (2000) CLAS preliminary p+ pp 0 COMPASS 0. 18<x<0. 24 Large sinf modulations have been observed in electroproduction of hadrons in SIDIS with longitudinally polarized targets H. Avakian, Transversity 2011 5

Beam SSA: ALU Jlab/HERMES/COMPASS HERMES CLAS W. Gohn(DIS 2011) CLAS C. Schill(DIS 2011) HT SSAs are comparable at JLab, HERMES and COMPASS H. Avakian, Transversity 2011 6

SSA at large x. F CLAS COMPASS 0 moves to lower x. F with energy? ANL s=4. 9 Ge. V BNL s=6. 6 Ge. V FNAL s=19. 4 Ge. V H. Avakian, Transversity 2011 RHIC s=62. 4 Ge. V 7

More polarized target HT SSAs Longitudinally polarized Transversely polarized How transversely polarized quarks were generated? Sivers type H. Avakian, Transversity 2011 Collins type 8

Collins Effect: azimuthal modulation of the fragmentation function FUT∞h 1 H 1┴ y hadronizing quark pol. PT f C s. T fh f. S’ x s. T(q×PT)↔ H 1┴ f. C D(z, PT)=D 1(z, PT)+H 1┴(z, PT) sin(fh- f. S’) Contributions in large sinusoidal modulations observed in experiments from Collins fragmentation PT fh y f. S=p x What makes them transversely polarized in the lepton plane? H. Avakian, Transversity 2011 9

Transverse force on the polarized quarks Quark polarized in the x-direction with k. T in the y-direction Force on the active quark right after scattering (t=0) Interpreting HT (quark-gluon-quark correlations) as force on the quarks (Burkardt hep-ph: 0810. 3589) H. Avakian, Transversity 2011 10

Beam SSA: ALU from CLAS @ JLab Photon Sivers Effect Afanasev & Carlson, Metz & Schlegel, Gamberg et al. Beam SSA from initial distribution (Boer-Mulders TMD) F. Yuan using h 1┴ from MIT bag model 0. 5<z<0. 8 Beam SSA from hadronization (Collins effect) by Schweitzer et al. H. Avakian, Transversity 2011 11

Model predictions for higher twists “interaction dependent” H. A. , A. Efremov, P. Schweitzer, F. Yuan ar. Xiv: 1001. 5467 Models agree on a large HT distributions H. Avakian, Transversity 2011 12

Lattice calculations of HT distributions (PDFs in terms of Lorenz invariant amplitudes Musch et al, ar. Xiv: 1011. 1213) Lattice provides important complementary information on FT for all HT distributions H. Avakian, Transversity 2011 13

Lattice calculations of HT distributions Lattice provides important cross check with data and models for all HT TMDs (Musch et al, ar. Xiv: 1011. 1213) Lattice results for u-d can be directly compared to models and data. H. Avakian, Transversity 2011 14

Current Fragmentation h Twist-2 Twist-3 A. Bacchetta et al. hep-ph/0611265 • Several unknown distribution and fragmentation functions involved, making extraction model dependent • Factorization of higher twists in k. T-dependent SIDIS not proved H. Avakian, Transversity 2011 15

BGMP: extraction of k. T-dependent PDFs Need: project x-section onto Fourier mods in b. T-space to avoid convolution Boer, Gamberg, Musch &Prokudin ar. Xiv: 1107. 5294 generated acceptance 0. 3<x<0. 36 0. 5<z<0. 6 Bessel weighting • provides a model independent way to study kinematical dependences of TMD requires wide range in hadron PT 16 H. Avakian, Transversity 2011

Dihadron Fragmentation h 1 - fractions of energy carried by a hadrons h 2 • Factorization proven • Evolution known • Extracted at BELLE for pp pairs, planned for p. K pairs Dihadron productions offers exciting possibility to access HT effects H. Avakian, Transversity 2011

Dihadron Fragmentation • Significant Di. FF published by BELLE • Evolution effects small for Di. FF/D 1 • Di. FF represent the easiest way to measure the polarization of a fragmenting quark • Di. FF contain information on interferences between different channels H. Avakian, Transversity 2011 18

Dihadron Fragmentation Dihadron production cross section in case of one photon exchange +. . H. Avakian, Transversity 2011 19

SSA in Dihadron production Difference of asymmetries measured with unpolarized and longitudinally polarized targets depends only on the Di. FF and HT functions H. Avakian, Transversity 2011 20

Dihadron beam SSA with CLAS 6 CLAS-e 1 dvcs CLAS-e 1 f p +p p 0 p+ preliminary Significant dihadron asymmetries measured at 6 Ge. V by CLAS H. Avakian, Transversity 2011 21

Dihadron production with CLAS 12 Use the clas. DIS (LUND based) generator + FASTMC to study pp and p. K pairs x. F - momentum in the CM frame p p p K CFR-CFR TFR p p Dihadron sample defined by SIDIS cuts+x. F>0 (CFR) for both hadrons H. Avakian, Transversity 2011 22

Dihadron production with CLAS 12 c. QSM JLab PR 12 -11 -109: 54 days of unpolarized proton and deuteron running will allow precision measurement of HT distribution e spectator model bag model H. Avakian, Transversity 2011 23

HT effects as background: Boer-Mulders distribution Pasquini&Yuan(2010) Background contributions : Higher twist azimuthal moments kinematical HT (Cahn) dynamical HT (Berger-Brodsky) Radiative correction Acceptance Gamberg et al (2008) Sun et al (2008) “flavor blind” Wide range in Q 2 and PT accessible with CLAS 12 are important for cos 2 f studies (all background contributions are HT) H. Avakian, Transversity 2011 24

Azimuthal moments of A 1 and flavor decomposition EIC Acceptance in f (and PT) may affect the A 1 and flavor decomposition ( in particular Ds extractions) in SIDIS? H. Avakian, Transversity 2011 25

Summary q. Latest experimental data indicate that quark-gluon/quark correlations leading to spin and azimuthal asymmetries may be very significant q. Measurements of HT are consistent in sign and magnitude for SIDIS experiments at very different energies q. Higher Twist distributions are accessible in single and double spin azimuthal asymmetries, can be calculated in models and lattice q. Di-hadron production provide exciting possibility to measure HT functions in model independent way within collinear factorization q. Higher twists are indispensable part of SIDIS analysis and their understanding is crucial for interpretation of SIDIS leading twist observables H. Avakian, Transversity 2011 26

Support slides…. H. Avakian, Transversity 2011 27

FAST-MC for CLAS 12 SIDIS MC in 8 D (x, y, z, f, f. S, p. T, l, p) Simple model with 10% difference between f 1 (0. 2 Ge. V 2) and g 1 widths with a fixed width for D 1 (0. 14 Ge. V 2) p┴ PT = p┴ +z k. T CLAS 12 acceptance & resolutions Events in CLAS 12 Lund-MC Reasonable agreement of kinematic distributions with realistic LUND H. Avakian, Transversity 2011 28

Hadronization in current and target regions h 1 h 2 Anselmino/Barone/Kotzinian ar. Xiv: 1107. 2292 (2011) Fracture Function: h 1 h 2 conditional probabilities to find a quark with certain polarization and longitudinal momentum fraction x. B and transverse momentum k. T inside a nucleon fragmenting into a hadron carrying a fraction z of the nucleon longitudinal momentum and a transverse momentum PT H. Avakian, Transversity 2011 29

HT effects with transverse target H. Avakian, Transversity 2011 30

Higher Twist SSAs Target sinf SSA (Bacchetta et al. 0405154) Discussed as main sources of SSA due to the Collins fragmentation In jet SIDIS only contributions ~ D 1 survive The same unknown fragmentation function Beam sinf SSA With H 1┴ (p 0)≈0 (or measured) Target and Beam SSA can be a valuable source of info on HT T-odd distribution functions H. Avakian, Transversity 2011 31

Dihadron simulations with LUND-MC @6 Ge. V H. Avakian, Transversity 2011 32

Azimuthal moments with unpolarized target quark polarization H. Avakian, JLab, Transversity Nov 25 2011 33

Azimuthal moments with unpolarized target quark polarization H. Avakian, JLab, Transversity Nov 25 2011 34

SSA with unpolarized target quark polarization H. Avakian, JLab, Transversity Nov 25 2011 35

Measurements of SS azimuthal asymmetries in SIDIS Large cosf and sinf modulations have been observed in electroproduction of hadrons in SIDIS with polarized and unpolarized targets HERMES (2000) CLAS (2003) EMC (1987) Related to spin-orbit correlations in fragmentation? H. Avakian, Transversity 2011 36

SSA with unpolarized target quark polarization H. Avakian, JLab, Transversity Nov 25 2011 37

SSA with long. polarized target quark polarization H. Avakian, Transversity 2011 38

SSA with long. polarized target quark polarization H. Avakian, Transversity 2011 39

SSA with unpolarized target quark polarization H. Avakian, Transversity 2011 40

SSA with unpolarized target quark polarization H. Avakian, Transversity 2011 41

SSA with transversely polarized target quark polarization H. Avakian, Transversity 2011 42

Twist-3 PDFs : “new testament” H. Avakian, Transversity 2011 43

H. Avakian, Transversity 2011 44

Studies of Dihadron Electroproduction in DIS with Unpolarized and Longitudinally Polarized Hydrogen and Deuterium Targets Harut Avakian (JLab) JLab PAC 38, Aug 24, 2011 Proposal PR 12 -11 -109 • Measure hadron pairs in current and target fragmentation regions • Study higher-twist distribution functions and interference effects in hadronization Spokespersons: S. Anefalos-Pereira (LNF-INFN) , H. Avakian (JLab), A. Courtoy (U. Pavia) K. Griffioen (W&M), L. Pappalardo (INFN-Ferrara) H. Avakian, Transversity 2011 45

Model predictions: polarized target • Models agree on a large target SSA for pp pair production • Deuteron target measurements provide complementary information on flavor dependence H. Avakian, Transversity 2011 46

The azimuthal terms at low Pt σSIDIS=σDIS·∑ei 2[qi(x, Q 2)Di(z)]·be-bp. T 2{1+Acos(φ)+Bcos(2φ)} A and B are the weights of the azimuthal terms (σ ( LT and σTT) Solid lines are Cahan theoretical predictions • A ~ (Pt/Q)·ξ • B ~ (Pt 2/Q 2)·ξ 2 Where ξ= z 2/(1+z 2) At <Pt> ~0. 05 Ge. V A ~ B ~ 0 for SIDIS A and B are much larger in exclusive pion production (open symbols) • No significant difference between the results for π- or π+ , or H and D. • At low Pt the azimuthal dependence is consistent with zero. H. Avakian, Transversity 2011 47