Single-Spin Asymmetry of Neutrons in Polarized pA Collisions

Abstract

Absorptive corrections, which are known to suppress proton-neutron transitions with a large fractional momentum z -> 1 in pp collisions, become dramatically strong on a nuclear target, and they push the partial cross sections of leading neutron production to the very periphery of the nucleus. The mechanism of the pion and axial vector a1-meson interference, which successfully explains the observed single-spin asymmetry in a polarized pp -> nX, is extended to the collisions of polarized protons with nuclei. When corrected for nuclear effects, it explains the observed single-spin azimuthal asymmetry of neutrons that is produced in inelastic events, which is where the nucleus violently breaks up. This single-spin asymmetry is found to be negative and nearly A-independent.