Testing the process dependence of the Sivers function via hadron distributions inside a jet

Abstract

We study the process dependence of the Sivers function by considering the impact of color-gauge invariant initial and final state interactions on transverse spin asymmetries in proton-proton reactions within the framework of the transverse momentum dependent (TMD), generalized parton model. To this aim, we consider the azimuthal distribution of leading pions inside a fragmenting jet as well as single inclusive jet asymmetry in polarized proton proton collisions. In contrast to single inclusive pion production, in both cases we can isolate the Sivers contribution and thereby study its process dependence. The predictions for the Sivers asymmetry obtained with and without inclusion of color gauge factors are comparable in size but with opposite signs. We conclude that both processes represent unique opportunities to discriminate among the two approaches and test the universality properties of the Sivers function in hadronic reactions.

Figures (2)

• Figure 1: The Sivers asymmetry $A_N^{\sin\phi_{S_A}}$ for the $p^\uparrow p\to {\rm jet}\, \pi +X$ as a function of $p_{{\rm j}T}$, at fixed jet rapidity $\eta_{\rm j}=3.3$, for RHIC energy, $\sqrt{s}=500$ GeV. The solid (SIDIS 1 Anselmino:2005ea) and dotted (SIDIS 2 Anselmino:2008sga) curves are for the GPM calculation, and the dashed and dot-dashed ones for the CGI GPM calculation. The vertical dotted line corresponds to $x_F=0.3$.
• Figure 2: Sample Feynman diagrams for the initial (a) and final (b) state interactions for pion-jet production, illustrated here for the partonic channel $qg\to qg$ with the final $q$ identified with the observed jet.