Global fitting of single spin asymmetry: An attempt

We present an attempt of global analysis of semi-inclusive deep inelastic scattering lp up arrow -> l' pi X data on single spin asymmetries and data on left-right asymmetry A(N) in p up arrow p -> pi X in order to simultaneously extract information on the Sivers function and the twist-three quark-gluon Efremov-Teryaev-Qiu-Sterman function. We explore different possibilities such as the node of the Sivers function in x or k(perpendicular to) in order to explain sign mismatch between these functions. We show that pi(+/-) semi-inclusive deep inelastic scattering data and pi(0) STAR data can be well described in a combined fit based on both the transverse momentum dependent and collinear twist-three factorization formalisms; however, pi(+/-) BRAHMS data are not described in a satisfactory way. This leaves the question open of a solution to the sign mismatch. Possible explanations are then discussed.