Speaker
Description
In recent decades, there have been numerous efforts to understand the origin of the unexpectedly large transverse single spin asymmetry ($A_{N}$) of inclusive hadron productions at forward rapidities observed in $p^{\uparrow}$+$p$ collisions at different center-of-mass energies ($\sqrt{s}$). Several theories have been proposed to explain this phenomenon, including the twist-3 contributions in the collinear factorization framework, the transverse-momentum-dependent contributions from the initial-state quark and gluon (Sivers functions), and/or final-state Collins fragmentation functions. However, there are indications that diffractive processes might also contribute to the large $A_{N}$, based on the previous analyses of $A_{N}$ for forward $\pi^{0}$ and electromagnetic jets (EM-jets) in $p^{\uparrow}$+$p$ collisions at STAR [1]. A direct measurement of the $A_{N}$ of diffractive processes could shed more light on the origin of the large $A_{N}$.
The STAR experiment provides an ideal opportunity to measure the $A_{N}$ for the diffractive processes at the forward rapidities with the data collected from Forward Meson Spectrometer and Roman Pot detectors. This talk will present the analysis updates and preliminary results on $A_{N}$ for inclusive and diffractive EM-jets at forward rapidity ($2.6 < \eta < 4.2$) using $p^{\uparrow}$+$p$ collisions at $\sqrt{s} =$ 200 GeV and 510 GeV at STAR. The $A_{N}$ for photon multiplicity-dependent EM-jets in the inclusive and diffractive processes will be explored, and the contribution of $A_{N}$ from diffractive processes to the inclusive processes will be discussed.
[1] (STAR) J. Adam et al., Phys. Rev. D 103, 092009 (2021)
