Speaker
Description
There have been numerous attempts, both theoretical and experimental, to understand the origin of the unexpectedly large transverse single spin asymmetry ($A_{N}$) for the inclusive hadron production at forward rapidities observed in $p^{\uparrow}$+p collisions at various center-of-mass energies. The twist-3 contributions in the collinear factorization framework and the transverse-momentum-dependent contributions from the initial-state quark and gluon Sivers functions and/or final-state Collins fragmentation functions are potential explanations to this puzzle. Previous analyses of $A_{N}$ for forward $\pi^{0}$ and electromagnetic jets in $p^{\uparrow}$+p collisions at STAR indicated that there might be non-trivial contributions to the large $A_{N}$ from diffractive processes [1]. The STAR Forward Meson Spectrometer (FMS) and Endcap ElectroMagnetic Calorimeter (EEMC) can detect photons, neutral pions, and eta mesons in the forward direction, with pseudo-rapidity coverages of $2.6 < \eta < 4.2$ and $1.0 < \eta < 2.0$, respectively. In this talk, we will present the latest preliminary results and analysis updates on $A_{N}$ for inclusive and diffractive electromagnetic jets in the FMS and EEMC using $p^{\uparrow}$+p data at $\sqrt{s} =$ 200 GeV and 510 GeV collected at STAR.
[1] (STAR) J. Adam et al., Phys. Rev. D 103, 092009 (2021)
| Submitted on behalf of a Collaboration? | Yes |
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