Speaker
Description
In the high-energy $p + p$ collisions, the transverse single spin asymmetry for very forward neutron production was measured by the PHENIX experiment at three different collision energies, 62, 200, and 500 GeV. It has been explained by an interference between $\pi$ (spin-flip) and $a_1$ (spin non-flip) exchange with a non-zero phase shift. In June 2017, the RHICf experiment has measured the very forward neutron asymmetry at $\sqrt{s} = 510$ GeV by installing a new sampling calorimeter at the zero-degree area of the STAR experiment. In this talk, we present the result for the single spin asymmetry for very forward neutron production as functions of longitudinal momentum fraction and transverse momentum covering up to the highest transverse momentum ever measured, about 1 GeV/$c$. Recently, the asymmetry measured by the PHENIX experiment at 200 GeV was unfolded and shown to increase in magnitude with the transverse momentum without a clear longitudinal momentum fraction dependence. The neutron asymmetry measured by RHICf at 510 GeV and that by PHENIX at 200 GeV can be compared ant the validity of the $\pi$ and $a_1$ exchange model can also be tested in a wider transverse momentum coverage.
| Submitted on behalf of a Collaboration? | Yes |
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