Speaker
Description
Through the 21st and 22nd International Workshop on Deep Inelastic Scattering, a possibility of the non-perturbative contribution for the non-zero transverse single spin asymmetry of $\pi^0$ ($2 < \eta < 4$) was brought up. Bigger asymmetry was observed in more isolated final state which was connected with the non-perturbative event topology. Since the non-perturbative contribution has been studied by only the forward $\pi^0$ production where the perturbative process was expected to be the major interaction rather than non-perturbative one, the RHICf experiment measured the very forward ($\eta > 6$) $\pi^0$ to study the role of the non-perturbative interaction in more detail. We installed a new electromagnetic calorimeter at the zero-degree area of the STAR experiment at the Relativistic Heavy Ion Collider and measured the $\pi^0$ over the kinematic range of $x_F > 0.25$ and $0 < p_T < 1 $ GeV/$c$ in June, 2017. A clear non-zero asymmetry was observed even in low $p_T < 1$ showing a similar $x_F$ dependence with the forward $\pi^0$ one as the $p_T$ approached to 1 GeV/$c$. The non-perturbative interaction may induce its own non-zero asymmetry and there may be also a non-negligible contribution from it in the forward $\pi^0$ asymmetry. We present the first measurement of the very forward $\pi^0$ asymmetry and its result. A future aspect to more precisely study both of the perturbative and non-perturbative contribution will be also discussed.
