Global fitting of single spin asymmetry: An attempt

We present an attempt of global analysis of semi-inclusive deep inelastic scattering p ^→→ ^′πX data on single spin asymmetries and data on left-right asymmetry A _N in p ^→p→πX 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 in order to explain "sign mismatch" between these functions. We show that π ^± semi-inclusive deep inelastic scattering data and π0 STAR data can be well described in a combined fit based on both the transverse momentum dependent and collinear twist-three factorization formalisms; however, π ^± 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.