Global fitting of single spin asymmetry: an attempt

Abstract

We present an attempt of global analysis of Semi-Inclusive Deep Inelastic Scattering (SIDIS) $\ell p^{\uparrow }\to {\ell }^{\prime }\pi X$ data on single spin asymmetries and data on left-right asymmetry $A_N$ in $p^{\uparrow }p\to \pi X$ in order to simultaneously extract information on Sivers function and twist-three quark-gluon Efremov-Teryaev-Qiu-Sterman (ETQS) function. We explore different possibilities such as node of Sivers function in $x$ or $k_{\perp }$ in order to explain "sign mismatch" between these functions. We show that ${\pi }^{\pm }$ SIDIS data and ${\pi }^0$ STAR data can be well described in a combined TMD and twist-3 fit, however ${\pi }^{\pm }$ BRAHMS data are not described in a satisfactory way. This leaves open a question to the solution of the "sign mismatch". Possible explanations are then discussed.

Comments: 11 pages, 7 figures