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SIDIS Cross Sections and Spin Asymmetries Predictions for Ongoing and Future Experiments

M.Elena Boglione. INFN – Sezione di Torino e Universita’ degli Studi di Torino. SIDIS Cross Sections and Spin Asymmetries Predictions for Ongoing and Future Experiments. In Collaboration with M. Anselmino, U.D’Alesio, F. Murgia, A. Prokudin, C. Turk. Outline of the talk.

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SIDIS Cross Sections and Spin Asymmetries Predictions for Ongoing and Future Experiments

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  1. M.Elena Boglione INFN – Sezione di Torino e Universita’ degli Studi di Torino SIDIS Cross Sections and Spin Asymmetries Predictions for Ongoing and Future Experiments In Collaboration with M. Anselmino, U.D’Alesio, F. Murgia, A. Prokudin, C. Turk QCD N06 - Monte Porzio Catone - 15/06/2006

  2. Outline of the talk Azimuthal and PT dependences of hadrons in unpolarized SIDIS • At small PT, (PT,<1 GeV/c) lowest order contributions + TMD distribution and fragmentation functions describe all data • At large PT, (PT,>1 GeV/c) the usual pQCD higher order collinear contributions dominate We can explain the full range of experimental data • New detailed predictions for azimuthal and PT dependences of hadrons produced at HERMES, COMPASS and JLab (6 GeV). Collins Fragmentation and Transversity Distribution Functions • New experimental data from BELLE and Hermes allow us a comprehensive fit to determine the Collins fragmentation function and to give first indications on the Transversity distribution function. • Analysis of AUTsin(fS+fh) at Hermes and COMPASS and of AU/AL at BELLE. QCD N06 - Monte Porzio Catone - 15/06/2006

  3. Azimuthal and PT dependences of hadrons in unpolarized SIDIS Lowest order term, ds0: a virtual photon with momentum q strikes a quark with transverse momentum k_|_. The final detected hadron,has transverse momentum p_|_ with respect to the direction of the fragmenting quark from wich it originates, and transverse momentum PT with respect to the photon direction. This is the main source of hadrons with small PT. QCD N06 - Monte Porzio Catone - 15/06/2006

  4. The first order term, ds1, includes the processes in which the quark emits a hard gluon and those initiated by a gluon. Here the final quark can have a large transverse momentum, even starting from a collinear configuration. This term will dominate lepto-production of hadrons with PT larger than 1 GeV/c. The second order term, ds2, will be taken into account through the K factor QCD N06 - Monte Porzio Catone - 15/06/2006

  5. EMC experimental data ZEUS experimental data QCD N06 - Monte Porzio Catone - 15/06/2006

  6. EMC experimental data E665 experimental data QCD N06 - Monte Porzio Catone - 15/06/2006

  7. ZEUS experimental data The <cosfh> modulation at small PT is a higher twist effect and decreases like1/Q for growing Q. Therefore we expect it to be smaller for ZEUS, where Q is huge, than for E665 ! We ignore the Collins and Boer-Mulders contribution: here <cos 2fh> is mainly arising from pQCD contributions. QCD N06 - Monte Porzio Catone - 15/06/2006

  8. Predictions for forthcoming measurements HERMES Experiment Hydrogen target Ee = 27.57 GeV Since PT and Q2 are very low, the perturbative effects obtained by including higher order corrections are negligible. <cosfh> and <cos2fh> are a direct consequence of the intrinsic transverse motion of partons inside the hadrons. QCD N06 - Monte Porzio Catone - 15/06/2006

  9. Predictions for Jlab Predictions for COMPASS QCD N06 - Monte Porzio Catone - 15/06/2006

  10. Spin asymmetries, Transversity and Collins fragmentation function • Recent experimental data from BELLE, HERMES and COMPASS shed some light on the Transversity distribution function and on the Collins fragmentation function. • Can we make a comprehensive analysis to extract information on both functions ? QCD N06 - Monte Porzio Catone - 15/06/2006

  11. HERMES and COMPASS have measured the weighted asymmetry AUTsin(fS+fh) as a function of xB, zh and PT. At first order in the (k_|_/Q) expansion we have: QCD N06 - Monte Porzio Catone - 15/06/2006

  12. Fit to the HERMES data QCD N06 - Monte Porzio Catone - 15/06/2006

  13. Description of COMPASS data (no fit) QCD N06 - Monte Porzio Catone - 15/06/2006

  14. Predictions for JLab QCD N06 - Monte Porzio Catone - 15/06/2006

  15. Description of BELLE data QCD N06 - Monte Porzio Catone - 15/06/2006

  16. Description of BELLE data QCD N06 - Monte Porzio Catone - 15/06/2006

  17. Description of BELLE data QCD N06 - Monte Porzio Catone - 15/06/2006

  18. Description of BELLE data We can describe BELLE data Without any fit, by using the Collins function as obtained by fitting HERMES data and fixing The transversity function to be either g1 or ½(f1+g1). BELLE data prefer h1=g1 ! QCD N06 - Monte Porzio Catone - 15/06/2006

  19. Description of BELLE data We can describe BELLE data without any fit, by using the Collins function as obtained by fitting HERMES data and fixing the transversity function to be either g1 or ½(f1+g1). BELLE data prefer h1=g1 ! QCD N06 - Monte Porzio Catone - 15/06/2006

  20. Conclusions • The Collins fragmentation function has been determined by fitting HERMES • data on AUT . The transversity function was fixed to be either g1(x) or • ½[g1(x)+f1(x)]. • With this function we obtain an excellent description of COMPASS data • on the same asymmetry. • Predictions for JLab are given. • We then reproduce the BELLE asymmetry without fitting, and find that the • Collins function as obtained from the fit to HERMES data work really well, • showing that the Collins function is universal. • BELLE data prefer h1(x)=g1(x), giving us a first indication on the size of the • transversity function QCD N06 - Monte Porzio Catone - 15/06/2006

  21. Future perspectives • We are eagerly awaiting new data from BELLE. These will allow a reliable fit to fully determine the Collins function. • Then HERMES data can be used to fix the Transversity distribution. • For a proper analysis we have to take into account all orders in the O(k_|_/Q) expansion. QCD N06 - Monte Porzio Catone - 15/06/2006

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