Speaker
Description
In the high-energy $p+p$ collisions, the transverse single spin asymmetry for very forward neutron production has been interpreted by an interference between $\pi$ (spin flip) and $a_1$ (spin non-flip) exchange with a non-zero phase shift. The $\pi$ and $a_1$ exchange model predicted the neutron asymmetry would increase in magnitude with transverse momentum ($p_{\scriptsize{\textrm{T}}}$) in $p_{\scriptsize{\textrm{T}}} < 0.4$ GeV/$c$. In June 2017, the RHICf experiment installed an electromagnetic calorimeter at the zero-degree area of the STAR experiment at the Relativistic Heavy Ion Collider and measured the neutron asymmetry in a wide $p_{\scriptsize{\textrm{T}}}$ range of $0 < p_{\scriptsize{\textrm{T}}} < 1$ GeV/$c$ from polarized $p+p$ collisions at $\sqrt{s} = 510$ GeV. The RHICf data allows us to study the kinematic dependence of the neutron asymmetry in detail, which not only can test the $\pi$ and $a_1$ exchange model in the wider $p_{\scriptsize{\textrm{T}}}$ range but also can enrich our understanding for the spin-involved diffractive particle production mechanism. We present the final result of the neutron asymmetry measured by the RHICf experiment. A new theoretical trial to understand the RHICf result based on the Reggeon exchange will also be discussed.
| Submitted on behalf of a Collaboration? | Yes |
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