Transverse single-spin asymmetry for very forward neutral pion production in polarized p+p collisions at s = 510 GeV
Abstract
Transverse single-spin asymmetries of very forward neutral pions generated in polarized p + p collisions allow us to understand the production mechanism in terms of perturbative and non-perturbative strong interactions. During 2017 the RHICf Collaboration installed an electromagnetic calorimeter in the zero-degree region of the STAR detector at the Relativistic Heavy Ion Collider (RHIC) and measured neutral pions produced at pseudorapidity larger than 6 in polarized p+p collisions at s = 510 GeV. The large non-zero asymmetries increasing both in longitudinal momentum fraction xF and transverse momentum pT have been observed at low transverse momentum pT < 1 GeV/c for the first time at this collision energy. The asymmetries show an approximate xF scaling in the pT region where non-perturbative processes are expected to dominate. A non-negligible contribution from soft processes may be necessary to explain the nonzero neutral pion asymmetries.