Single-Spin Asymmetries in $p^\uparrow p \to \pi X$ and Chiral Symmetry

Abstract

We study a possible origin of single spin asymmetries in the large $p_T$ inclusive production of hadrons in the scattering of unpolarized protons or leptons on transversely polarized nucleons. Such asymmetry is related to the single-spin asymmetry for the process $\p^\uparrow \to q+X$ or, equivalently, to the off-diagonal matrix element of the quark density operator $\bar \psi \gamma^+ \psi$; this quantity need not be zero if transverse momentum and spin-isospin interactions are taken into account. The different signs for the large single spin asymmetries observed in $\p^\uparrow p \to \pi^+ X$ and $\p^\uparrow p \to \pi^- X$ can be explained as a consequence of chiral symmetry. Crucial tests of the model are suggested.