On the Strange Spin Asymmetry at RHIC

Abstract

A peculiar effect in p-p and p-N (N for nucleus) was observed at Relativistic Heavy Ion Collider (RHIC). In p-p scattering with polarized incoming proton, there is asymmetry in the sense that the protons with vertical polarization with respect to scattering plane give rise to more neutrons slightly deflected to right than to left (see the figure of the article). In p-N scattering of vertically polarized protons, the effect is also observed for neutrons but is stronger and has opposite sign for heavier nuclei! The effect came as a total surprise and is not understood. It seems, however, that the effects for proton and nuclear targets must have different origin since otherwise it is difficult to understand the change of the sign.