H. Avakian, Pavia, Sep 6 1 Harut Avakian (JLab) Study of dihadron production at JLab with the 12 GeV CLAS dectector DiFF Workshop, Pavia, Sep 6, 2011 JLab proposal PR 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, Pavia, Sep 6 2 The CLAS Collaboration

H. Avakian, Pavia, Sep 6 3 Outline Introduction Quark-gluon correlations & higher twists in SIDIS Di-hadron production Target Fragmentation Projections for 12 GeV Summary & Plans

H. Avakian, Pavia, Sep 6 44 Electroproduction of hadrons production in DIS Measurements in different kinematical regions provide complementary information on the complex nucleon structure. x F - momentum in the CM frame x F >0 (current fragmentation) x F <0 (target fragmentation) h h Target fragmentationCurrent fragmentation Fracture Functions xFxF M 0 1 h h PDF GPD k T -dependent PDFsGeneralized PDFs FF DA exclusivesemi-inclusive

EMC (1987) HERMES (2000 ) CLAS (2003 ) H. Avakian, Pavia, Sep 6 5 First measurements of azimuthal asymmetries in SIDIS Large cos  and sin  modulations have been observed in electroproduction of hadrons in SIDIS with polarized and unpolarized targets Related to spin-orbit correlations in fragmentation?

H. Avakian, Pavia, Sep 6 6 W. Gohn(DIS2011 ) CLAS 6 C.Schill(DIS2011 ) HT SSAs are comparable at JLab, HERMES and COMPASS Beam SSA: A LU from COMPASS & JLab

H. Avakian, Pavia, Sep 6 7 Collins Effect: azimuthal modulation of the fragmentation function D(z,P T )=D 1 (z,P T )+H 1 ┴(z,P T ) sin(  h  S’ ) CC y x hh PTPT sTsT  S’ CC F UT ∞h 1 H 1 ┴ s T (q×P T )↔ H 1 ┴ sin(2  h ) CC hadronizing quark pol. Contributions in large sinusoidal modulations observed in experiments from Collins fragmentation x PTPT hh S=S= y What makes them transversely polarized in the lepton plane? Collinear twist-3 PDFs

H. Avakian, Pavia, Sep 6 88 Transverse force on the polarized quarks Quark polarized in the x-direction with k T in the y-direction Boer-Mulders Force on the active quark right after scattering (t=0) Interpreting HT (quark-gluon-quark correlations) as force on the quarks (Burkardt hep-ph: ) More sum rules

H. Avakian, Pavia, Sep 6 99 Beam SSA: A LU from JLab 0.5<z<0.8 Beam SSA from hadronization (Collins effect) by Schweitzer et al. 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

H. Avakian, Pavia, Sep 6 10 Lattice calculations of HT distributions Lattice provides important complementary information on FT for all HT distributions (PDFs in terms of Lorenz invariant amplitudes Musch et al, arXiv: )

H. Avakian, Pavia, Sep 6 11 Lattice calculations of HT distributions Lattice results for u-d can be directly compared to models and data. Lattice provides important cross check with data and models for all HT TMDs (Musch et al, arXiv: )

H. Avakian, Pavia, Sep 6 12 h Current Fragmentation A. Bacchetta et al.A. Bacchetta et al. hep-ph/ Twist-2 Twist-3 Several unknown distribution and fragmentation functions involved, making extraction model dependent Factorization of higher twists in k T -dependent SIDIS not proved

FAST-MC for CLAS12 13 P T = p ┴ +z k T p┴p┴ SIDIS MC in 8D (x,y,z,  S,p T,  CLAS12 acceptance & resolutions Events in CLAS12 Reasonable agreement of kinematic distributions with realistic LUND simulation Simple model with 10% difference between f1 (0.2GeV 2 ) and g1 widths with a fixed width for D1 (0.14GeV 2 ) Lund-MC H. Avakian, Transversity 2011

14 BGMP: extraction of k T -dependent PDFs Need: project x-section onto Fourier mods in b T -space to avoid convolution 0.3<x< <z<0.6 generated Boer, Gamberg, Musch &Prokudin arXiv: acceptance H. Avakian, Pavia, Sep 6 provides a model independent way to study kinematical dependences of TMD requires wide range in hadron P T Bessel weighting

H. Avakian, Pavia, Sep 6 15 Dihadron Fragmentation h1h1 h2h2 - fractions of energy carried by a hadrons Factorization proven Evolution known Extracted at BELLE for  pairs, planned for  K pairs Dihadron productions offers exciting possibility to access HT effects

H. Avakian, Pavia, Sep 6 Dihadron Fragmentation Evolution effects small for DiFF/D 1 DiFF represent the easiest way to measure the polarization of a fragmenting quark DiFF contain information on interferences between different channels Significant DiFF published by BELLE 16

H. Avakian, Pavia, Sep 6 17 Dihadron Fragmentation Dihadron production cross section in case of one photon exchange +..

H. Avakian, Pavia, Sep 6 18 SSA in Dihadron production Difference of asymmetries measured with unpolarized and longitudinally polarized targets depends only on the DiFF and HT functions

H. Avakian, Pavia, Sep 6 19 Model predictions: unpolarized target Models agree on a large beam SSA for  pair production

H. Avakian, Pavia, Sep 6 20 Model predictions: polarized target Models agree on a large target SSA for   pair production Deuteron target measurements provide complementary information on flavor dependence

H. Avakian, Pavia, Sep 6 21 Dihadron beam SSA with CLAS6 preliminary CLAS-e1f CLAS-e1dvcs Significant dihadron asymmetries measured at 6 GeV by CLAS  

Dihadron production at JLab12  

H. Avakian, Pavia, Sep 6 23 Dihadron production with CLAS12 Use the clasDIS (LUND based) generator + FASTMC to study   and   pairs x F - momentum in the CM frame Dihadron sample defined by SIDIS cuts+x F >0 (CFR) for both hadrons    CFR-CFR   TFR

24 BELLE projections for K+  - K  pairs in CFR-CFR and TFR-CFR h1h1 h2h2 h1h1 h2h2 K  pairs will provide complementary information on quark-gluon correlations and hadronization in TFR-CFR and CFR-CFR TFR formalism based on Fracture Functions developed by Anselmino Barone & Kotzinian arXiv: (2011) TFR-CFR Hadronization in Current and Target Fragmentation Regions CFR-CFR H. Avakian, Pavia, Sep 6

25 Dihadron production with CLAS12 54 days of unpolarized proton 30 days of NH3 CLAS12 will provide precision measurements of single-beam and target asymmetries in dihadron pair production in SIDIS

H. Avakian, Pavia, Sep 6 26 Dihadron production with CLAS12 JLab PR : 54 days of unpolarized proton and deuteron running will allow precision measurement of HT distribution e bag model spectator model  QSM SU(6)

27 Azimuthal moments of A 1 and flavor decomposition Acceptance in  and P T ) may affect the A 1 and flavor decomposition ( in particular  s extractions using Kaons) in SIDIS? EIC 27

H. Avakian, Pavia, Sep 6 28 Summary Provide first measurement of higher twist distributions e and h L describing quark-gluon correlations in nucleon Study interference effects in hadronization in current and target fragmentation. Beam request: 56 days of 11 GeV and NH 3 (30days) and ND 3 (50 days) with longitudinally polarized with RICH upgrade  Latest experimental data indicate that quark-gluon correlations leading to spin and azimuthal asymmetries may be very significant  Higher twists are indispensable part of SIDIS analysis (in particular in JLab kinematics) and their understanding is crucial for interpretation of SIDIS leading twist observables Precision measurement of in   and   pairs in DIS will allow us to:

H. Avakian, Pavia, Sep 6 29 Summary-II Theory side: –importance of higher twist distributions e and h L (include in EIC program) –importance of DiFFs, relations with Collins –Models for and –Predictions for TFR, possible backgrounds –Lattice extractions, link to FSI (Boer-Mulders and Kotzinian-Mulders forces?). Experimental side: –extract from the data two pion asymmetries (         pairs) –  pairs from Belle (BaBar) –   Collins Simulations: –extract e and h L from dihadron MC –extract e and h L from single hadron MC (using BGMP) TODO list for the next PAC Prepare a dihadron proposal for the transverse target !

H. Avakian, Pavia, Sep 6 30 Support slides….

H. Avakian, Pavia, Sep 6 31 Hadronization in current and target regions h1h1 h2h2 h1h1 h2h2 Anselmino/Barone/Kotzinian arXiv: (2011) Fracture Function: conditional probabilities to find a quark with certain polarization and longitudinal momentum fraction xB 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 P T

Extraction of f 1 and g 1 TMDs Need: project x-section onto Fourier mods in bT-space to avoid convolution Bessel weighting: provides a model independent way to study kinematical dependences of TMDs requires wide range in hadron P T x=0.33 z=0.65 generated

H. Avakian, Transversity

HT effects as background: Boer-Mulders distribution Wide range in Q 2 and P T accessible with CLAS12 are important for cos2  studies (all background contributions are HT) Background contributions : Higher twist azimuthal moments kinematical HT (Cahn) dynamical HT (Berger-Brodsky) Radiative correction Acceptance “ flavor blind” Pasquini&Yuan(2010) Gamberg et al (2008) Sun et al (2008) 34 H. Avakian, Transversity 2011

35 Higher Twist SSAs Target sin  SSA (Bacchetta et al ) Beam sin  SSA In jet SIDIS only contributions ~ D 1 survive Discussed as main sources of SSA due to the Collins fragmentation With H 1 ┴ (  0 )≈0 (or measured) Target and Beam SSA can be a valuable source of info on HT T-odd distribution functions The same unknown fragmentation function H. Avakian, Pavia, Sep 6

Dihadron simulations with GeV H. Avakian, Pavia, Sep 6 36

H. Avakian, Pavia, Sep 6 37 cos  azimuthal asymmetries in SIDIS Large cos  modulations have observed by EMC were reproduced in electroproduction of hadrons in SIDIS with unpolarized targets at COMPASS and HERMES EMC (1987)

HT effects with transverse target H. Avakian, Pavia, Sep 6 38

H. Avakian, Pavia, Sep 6 39 JLab, Nov Azimuthal moments with unpolarized target quark polarization

H. Avakian, Pavia, Sep 6 40 JLab, Nov Azimuthal moments with unpolarized target quark polarization

H. Avakian, Pavia, Sep 6 41 JLab, Nov SSA with unpolarized target quark polarization

H. Avakian, Pavia, Sep 6 42 JLab, Nov SSA with unpolarized target quark polarization

H. Avakian, Pavia, Sep 6 43 SSA with long. polarized target quark polarization

H. Avakian, Pavia, Sep 6 44 SSA with long. polarized target quark polarization

H. Avakian, Pavia, Sep 6 45 SSA with unpolarized target quark polarization

H. Avakian, Pavia, Sep 6 46 SSA with unpolarized target quark polarization

H. Avakian, Pavia, Sep 6 47 SSA with transversely polarized target quark polarization

H. Avakian, Pavia, Sep 6 48 Twist-3 PDFs : “new testament”