Single transverse-spin asymmetry of very forward neutron production in polarized p + p collisions at PHENIX

Abstract

The cross section and xF dependence of AN of very forward neutron production in polarized p + p collisions at = 200 GeV were measured in the PHENIX experiment at RHIC. The measured cross sections were consistent with the xF scaling claimed by the ISR experiment which measured neutron production in p + p collisions at from 30.6 to 62.7 GeV. These cross sections for large xF neutron production, as well as those in e + p collisions at HERA, are mainly described by one-pion exchange. At PHENIX, significant negative AN was observed in the forward region, and no significant backward AN was observed. We also measured and pT dependence of AN of very forward neutron production at from 62.4 to 500 GeV. The observed large asymmetry of neutron production is considered to come from the interference between the spin-flip amplitude of the pion exchange and spin-non-flip amplitude of all Reggeon exchange. Therefore, the neutron asymmetry has a sensitivity to other Reggeon exchange amplitude even if it is a small amplitude.