Collins Effect in Single Spin Asymmetries of the $p^{\uparrow}p \to πX$ Process

Abstract

We investigate the Collins effect in single spin asymmetries (SSAs) of the $p^{\uparrow}p \to πX$ process, by taking into account the transverse momentum dependence of the microscopic sub-processes cross sections, with the transverse momentum in the Collins function integrated over. We find that the asymmetries due to the Collins effect can only explain the available data at best qualitatively, by using our choices of quark distributions in the quark-diquark model and a pQCD-based analysis, together with several options of the Collins function. Our results indicate the necessity to take into account contributions from other effects such as the Sivers effect or twist-3 contributions.

Figures (2)

• Figure 1: The $z$-dependence the ratio $\frac{\Delta D (z,k_{c\perp})}{2 D (z,k_{c\perp})}$ at a given value of $k_{c\perp}=k_{c\perp}^0=M_C$ for the four options of the Collins function. The solid, dashed, dash-dotted, and dotted curves are corresponding to the results for the 4 options of Collins function respectively.
• Figure 2: The single spin asymmetries of $p^{\uparrow}p \to \pi X$ process. The calculated results in the quark-diquark model: (a), (b), and (c), in the pQCD based analysis: (d), (e), and (f), and in the quark-diquark model with more negatively polarized valence $d$-quark: (g), (h), and (i). The solid, dashed, dash-dotted, and dotted curves are corresponding to the results for the 4 options of Collins function respectively. The experimental data are given by the E704 Group E704