Studies of the transverse structure of the nucleon at JLab

1. Studies of the transversestructure of the nucleon at JLab Marco Mirazita INFN – LaboratoriNazionali di Frascati INPC2013 – Firenze, 2-7 June 2013

2. From PDFs to TMDs • Parton Distributions Functions (PDFs) • parton model in collinear approximation xP P • Transverse Momentum Dependent distributions (TMDs) • parton model with gluons and sea quarks • partons have transverse momentum  angular momentum • full decomposition of the nucleon spin xP+kT P

3. FF DF TMDs in SIDIS • Many terms already at leading order • higher order suppressed by M/Q • Structure Function Fragmentation Function qh • Azimuthal modulation • Beam and/or target polarizations • Cross section difference • Spin Asymmetries

4. TMD measurements at JLab • Very high luminosity • Transversely polarized He target Hall B • High luminosity • large acceptance • Very high luminosity • precision measurements

5. Transverse target SSA on neutron Hall A Collins effect Sivers effect • Small Collins • Larger Sivers for p+ than for p- HERMES proton data • Different results from the proton • non-zero Collins signal for p+ • opposite behaviourfor Sivers

6. Double spin asymmetry R=1 • small differences among pions • fairly flat distributions R=0.6 R=0.4 Comparison with gaussian model New CLAS data under analysis 2D (x,pT) extraction PRELIMINARY

7. Extracting TMD from data Phenomenological fits of asymmetries - gauss PT dependence Bessel-weighting method allows the model-independent extraction of TMDs Monte Carlo implementation of gauss model f1 Double Spin Asymmetry Distorsions due to phace space limits D1 Fourier-transform of TMDs in bT space - no convolution integrals - directly comparable with lattice

8. Di-hadron way to TMDs Single hadron production • Double hadron production • struck quark fragmenting in a hadron pair Unpolarized cross section e+e-→(pp) (pp) X • Advantages • - no convolution • Disadvantages • - more complicated kinematics • - unknown but measurable DiFF

9. CHL-2 JLab at 12 GeV target DC3 q DC1 DC2 Hall A - SBS Solid Hall C – HMS/SHMS beam pipe CLAS12 RICH RICH Hall B – CLAS12

10. SIDIS measurements at JLab12 PROTON CLAS12 p/K Hall C p/K CLAS12 p/K CLAS12 p/K Solid p • proton and neutron targets, unpolarized as well as longitudinally and transversely polarized • complementary detectors • ID of final hadrons D2 CLAS12 p/K Hall C p/K CLAS12 p/K 3He flavor separation of TMDs Solid p Hall A p/K Solid p

11. Sivers Asymmetry in CLAS12 for p

12. Transversity at JLab12 with DiHadrons Measurements with polarized protons Measurements with polarized neutrons CLAS12 SoLID

13. Conclusions • Correlation of spin and transverse momentum of partons is crucial to understand the nucleon structure in terms of quark and gluon degrees of freedom • Measurements of azimuthal dependencies of single and double spin asymmetries indicate that these correlations may be significant • JLab with the 6 GeV electron beam has played a major role in these studies • Studies of the spin-structure of the nucleon is one of the main driving forces behind the upgrade of Jefferson Lab

15. Boer-Mulders effect unpolarized hydrogen target z=0.11 z=0.17 pT2=0.004 pT2=0.06 z=0.23 z=0.30 pT2=0.12 pT2=0.21 z=0.37 z=0.49 pT2=0.34 pT2=0.50 amplitudes are positive in low-z and high pT2regions and show a strong kinematic dependence predicted amplitudes are very small and agree with data only in high-z and low pT2regions

16. Cahn effect z=0.11 z=0.17 pT2=0.06 pT2=0.004 z=0.23 z=0.30 pT2=0.12 pT2=0.21 z=0.37 z=0.49 pT2=0.34 pT2=0.50 amplitudes are significantly non-zero and show a sign change (positive to negative) towards high pT2 predicted amplitudes have similar trends but are systematically larger

17. PT dependence of the cross section Unpolarized SIDIS pion production transverse momentum dependence of f1 Hall C up+ dp- Siversasimmetry Simplified analysis assuming only valence quarks and two FF u and d quarks have different transverse momentum widths

18. Accessing HT terms at JLab Beam spin asymmetry in pion SIDIS Higher Twist TMD table - suppressed ~M/Q • polarized quarks in unpolarized nucleon HT analog of Sivers HT correction to D1 and Collins qgq correlation forces acting on the quarks • same asymmetry for charged and neutral pions null Collins contribution? • non-zero contribution from g

19. Sivers and Collins withkaons SIVERS COLLINS • Significantly positive K+moments • K- moments consistent with zero • K+ amplitude>p+amplitude • Unexpected from u-quark dominance • K+ and + asymmetries consistent within error bars • K- and - asymmetries may have opposite sign

20. Transversity PDF model-independentextraction in collinearapproximation proton • DiFFfrom BELLE data • SIDIS DiHadron data • red: Hermes • blue: COMPASS • Curvesfrom Torino parametrization (gauss) deuteron A. Courtoy, DIS2012

21. The Multi-Hall SIDIS program at JLab M. Aghasyan, K. Allada, H. Avakian, F. Benmokhtar, E. Cisbani, J-P. Chen, M. Contalbrigo, D. Dutta, R. Ent, D. Gaskell, H. Gao, K. Griffioen, K. Hafidi, J. Huang, X. Jiang, K. Joo, N. Kalantarians, Z-E. Meziani, M. Mirazita, H. Mkrtchyan, L.L. Pappalardo, A. Prokudin, A. Puckett, P. Rossi, X. Qian, Y. Qiang, B. Wojtsekhowski for the Jlab SIDIS working group • The complete mapping of the multi-dimensional SIDIS phase space will allow a comprehensive study of the TMDs and the transition to the perturbative regime. • Flavor separation will be possible by the use of different target nucleons and the detection of final state hadrons. • Measurements with pions and kaons in the final state will also provide important information on the hadronization mechanism in general and on the role of spin-orbit correlations in the fragmentation in particular. • Higher-twist effects will be present in both TMDs and fragmentation processes due to the still relatively low Q2 range accessible at JLab, and can apart from contributing to leading-twist observables also lead to observable asymmetries vanishing at leading twist. These are worth studying in themselves and provide important information on quark-gluon correlations.

22. Bessel analysis of BSA Boer,Gamber,Musch,Prokudin - arXiv:1107.5294 Bessel-weighted cross section asymmetry Test of the extraction of Fourier-transformed TMDs with MonteCarlo data