18-22 October 2021
Matsue, Shimane Prefecture, Japan
Asia/Tokyo timezone

Transverse Single-Spin Asymmetries for $\pi^0$ and Electromagnetic Jets at Forward Rapidities in p$^\uparrow$+p Collisions at Center-of-Mass Energies of 200 GeV and 500 GeV at STAR

22 Oct 2021, 07:18
Room 601 (Kunibiki Messe)

Room 601

Kunibiki Messe

Parallel Session Presentation Transverse momentum structure (TMD) Transverse Momentum Structure (TMD)


Latiful Kabir (University of California at Riverside)


There have been numerous attempts, both experimentally and theoretically, to understand the origin of the unexpectedly large transverse single-spin asymmetries ($A_N$) for inclusive hadron production at forward rapidity in p$^\uparrow$+p collisions that persist from low to high center-of-mass energies. Two proposed potential sources are the twist-3 contributions in the collinear factorization and the transverse-momentum-dependent contributions from either the initial-state quark and gluon Sivers functions or the final-state Collins fragmentation function. To investigate the underlying physics leading to this large $A_N$, we study $\pi^0$ $A_N$ with different topologies -- isolated and non-isolated, and $A_N$ for electromagnetic jets (EM-jets) of different substructures using Forward Meson Spectrometer (FMS) detector at STAR. Jet $A_N$ is sensitive to the initial state effect and can provide access to Sivers functions. To investigate final-state effects, we measure the Collins asymmetry of $\pi^0$ inside EM-jets. We present the most recent results for these asymmetries from p$^\uparrow$+p collisions at 200 GeV and 500 GeV. We also present new preliminary results of $A_N$ for EM-jets in FMS and Endcap Electromagnetic Calorimeter (EEMC) using p$^\uparrow$+p collisions at 200 GeV where we explore the dependences of $A_N$ on photon multiplicity inside the jet, jet transverse momentum, and jet energy. These results provide rich information towards understanding the physics mechanism of large $A_N$ in hadron collisions.

Primary authors

Latiful Kabir (University of California at Riverside) zhanwen zhu

Presentation Materials