26th International Symposium on Spin Physics (SPIN2025)

Transverse Single Spin Asymmetry of Electromagnetic Jets at Forward Rapidity in p↑+p Collisions at STAR

Not scheduled

3h 30m

Oral Three-dimensional structure of the nucleon: transverse momentum dependent parton distributions Parallel

Speaker

Weibin Zhang (UC Riverside)

Description

Transverse single spin asymmetries (TSSAs, denoted AN ) in transversely
polarized p↑ + p collisions provide critical insights into the proton’s spin structure, yet their unexpectedly large magnitudes at forward rapidities remain a
puzzle. Observed across experiments, including those at RHIC, these asymmetries have yet to be fully explained by theoretical models, such as those based on
twist-3 contributions in collinear factorization or transverse momentum depen-
dent (TMD) parton distributions. Recent STAR measurements suggested that
diffractive processes may contribute significantly to the observed AN , prompting
a deeper investigation into their role.
This talk presents precise measurements of AN for electromagnetic jets in in-
clusive and diffractive processes from p↑ +p collisions at √s = 200 and 510 GeV,
collected using the Forward Meson Spectrometer at STAR (2.5 < η < 4.2). By
isolating diffractive contributions, these results quantify their impact on inclu-
sive AN , providing new constraints on the underlying mechanisms, advancing
our understanding of the origins of large TSSAs at forward rapidities.