Title: Transverse Single-Spin Asymmetry for Electromagnetic Jets at Forward Rapidities in p+p Collisions at  √s  = 200 GeV at STAR

PAs: Latiful Kabir, Chong Kim, Ken Barish, Mriganka M Mondal, TBD 

Abstract: There have been various 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^↑+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. Jet A_N is sensitive to the initial state effect and can provide access to Sivers functions. A_N for jets of different substructures can help better understand the underlying mechanism for the observed large A_N. Transversely polarized p^↑+p collisions at RHIC are ideal to disentangle the initial and final state effects. The STAR Forward Meson Spectrometer (FMS) and Endcap Electromagnetic Calorimeter (EEMC), having pseudo-rapidity coverages of 2.6 - 4.2 and 1.1 - 2.0 respectively, can be used to detect photons, neutral pions, and eta mesons. We present preliminary results of A_N for electromagnetic jets in FMS and EEMC using p^↑+p collisions at √s = 200 GeV where we explore the dependences of A_N on photon multiplicity inside the jet, jet transverse momentum, and jet energy.

Plots in pdf: Fig1, Fig2, Fig3
Plots in png: Fig1, Fig2, Fig3
Plots in eps: zip file
All plots in a pdf: Link

Numerical table for the plots: Figure 1 (xF > 0), Figure 1 (xF < 0), Figure 2, Figure 3 (xF >0), Figure 3 (xF <0)

Presentation with analysis details: Link
Run list: FMS-stream (for FMS), Physics-stream (for EEMC)
PWG presentation on systematics: Link
PWG presentation on FMS simulation: Link
 
Figure 1: A_N for EM-jet in FMS sorted by photon multiplicity inside the jet and different pt and energy bins.

Figure 2: FMS EM-jet A_N for the cases - photon multiplicity < = 2, photon multiplicity = 3 and photon multiplicity >= 4.

Figure 3: EM-jet A_N in EEMC as a function of pt sorted by EM-jet photon multiplicity.