Sivers effect and the spin asymmetry in meson production ∗ H. Mahdizadeh Saffar a , A. Mirjalili a , M.M. Yazdanpanah b , S.Atashbar Tehrani c a Physics Department, Yazd University, 89195-741, Yazd, Iran b Faculty of Physics, Shahid Bahonar University of Kerman, Kerman, Iran c Researcher independent, P.O. Box 1149-8834413, Tehran, Iran Abstract The transverse polarization of nucleon and the transverse momentum of its unpolarized constituent partons are cor- related with each other. This can be fairly described by the Sivers effect. In recent years this effect is cynosure and produces privilege aspects from both theoretical and experimental views. To extend our knowledge from nucleon structure, this effect has an outstanding role. One way to obtain the Sivers function which is essentially depends on transverse momentum of partons, is to employ the Semi inclusive DIS (SIDIS) process. In this article a new parametrization for the concerned piece of Sivers function is used which is different with respect to what has been done in [1]. The required collinear PDF is getting from HERAPDF parametrization group. The unknown parameters which exist in Sivers function can be extracted, fitting the available experimental data for single spin asymmetry (SSA) in π + , π − production. The final analytical results for SSA are in good agreement with the HERMES experimental data. Keywords: SIDIS process; Sivers function; Single spin assymetry 1. Introduction To access the transverse momentum distribution (TMD) of partons we need to resort the SIDIS process. In this case a high energy lepton collides on a target nu- cleon and interact with it via the exchange of a photon. The target breaks up and several hadrons are produced. One of the produced hadrons is detected in addition to the scattered lepton. In this process, we need to use the unpolarized frag- mentation function which describes the fragmentation of an unpolarized quark into an unpolarized hadron. The unpolarized fragmentation function is a chiral-odd which together with the Sivers distribution function [2, 3] generates a measurable chiral-even process. The ∗ Talk given at 19th International Conference in Quantum Chromo- dynamics (QCD 16, 31th anniversary), 4 july - 8 july 2016, Montpel- lier - FR Email addresses: h.m.saffar@stu.yazd.ac.ir (H. Mahdizadeh Saffar), a.mirjalili@yazd.ac.ir (A. Mirjalili), myazdan@mail.uk.ac.ir (M.M. Yazdanpanah), atashbar@ipm.ir (S.Atashbar Tehrani) Sivers function is a T-odd one which describes distribu- tion of the unpolarized quarks (unknown spin state) in a transversely polarized nucleon and implies that unpo- larized quarks can have an asymmetric distribution in a transversely polarized nucleon. The full SIDIS cross section can be written with re- spect to some different structure functions which in- cludes different polarizations for incoming and outgoing particles. In order to calculate these structure functions, it is needed to define the asymmetries. They could be given by the ratio of convolution of spin dependent to spin independent distribution and fragmentation func- tions [4]. We intend here to calculate the single spin asymme- try using the Sives function. The Sivers function can be written in terms of TMD and the parton distribution functions (PDFs). We use the HERAPDF parametriza- tion model for the required PDFs. Other required pa- rameterized function in Sivers function is changed with respect to [1]. The unknown parameters can be obtained by fitting the available data for spin asymmetries in me- Available online at www.sciencedirect.com Nuclear and Particle Physics Proceedings 282–284 (2017) 48–52 2405-6014/© 2016 Elsevier B.V. All rights reserved. www.elsevier.com/locate/nppp http://dx.doi.org/10.1016/j.nuclphysbps.2016.12.010