Collins Effect in Single Spin Asymmetries of the puparrow}p to pi X Process.pdfVIP

EPJ manuscript No. (will be inserted by the editor) ↑ Collins Effect in Single Spin Asymmetries of the p p → πX Process 5 0 1 2 3a 0 Bo-Qiang Ma , Ivan Schmidt , and Jian-Jun Yang 2 r 1 p Department of Physics, Peking University, Beijing 100871, China A Di.S.T.A., Universit`a del Piemonte Orientale “A. Avogadro” and INFN, Gruppo Collegato di Alessandria, 15100 Alessandria, 9 Italy 5 v 2 Departamento de F´ısica, Universidad T´ecnica Federico Santa Mar´ıa, Casilla 110-V, Valpara´ıso, Chile 2 1 3 Department of Physics, Nanjing Normal University, Nanjing 210097, China 0 9 0 Departamento de F´ısica, Universidad T´ecnica Federico Santa Mar´ıa, Casilla 110-V, Valpara´ıso, Chile 4 0 Institut f¨ur Theoretische Physik, Universit¨at Regensburg, D-93040 Regensburg, Germany / h p - Received: date / Revised version: date p e h ↑ : Abstract. We investigate the Collins effect in single spin asymmetries (SSAs) of the p p →πX process, by v i taking into account the transverse momentum dependence of the microscopic sub-process cross sections, X r with the transverse momentum in the Collins function integrated over. We find that the asymmetries due a to the Collins effect can only explain the available data at best qualitatively, by using our choices of quark distributions in the quark-diquark model and a pQCD-based analysis, together with several options of the Collins function. Our results indicate the necessity to take into account contributions from other effects such as the Sivers effect or twist-3 contributions.