# Transverse Single Spin Asymmetry in $p+p^\uparrow \rightarrow J/\psi +X$

## TL;DR

This paper estimates the transverse single spin asymmetry in J/psi production in polarized proton collisions using a generalized parton model, comparing results with experimental data and exploring TMD evolution effects.

## Contribution

It provides the first estimates of TSSA in J/psi production within the GPM framework using the gluon Sivers function fitted from PHENIX data, including TMD evolution effects.

## Key findings

- Results agree with PHENIX data at 200 GeV
- Predictions made for 115 GeV and 500 GeV energies
- TMD evolution impacts the asymmetry estimates

## Abstract

We present estimates of transverse single spin asymmetry (TSSA) in $p+p^\uparrow \rightarrow J/\psi+X$ within the colour evaporation model of charmonium production in a generalized parton model (GPM) framework, using the recently obtained best fit parameters for the gluon Sivers function (GSF) extracted from PHENIX data on TSSA in $p+p^\uparrow \to \pi^0+X$ at midrapidity. We calculate asymmetry at $\sqrt{s} = 200$ GeV, and compare the results with PHENIX data on TSSA in the process $p + p^\uparrow \to J/\psi+X$. We also present estimates for asymmetry at $\sqrt{s} = 115 $ GeV corresponding to the proposed fixed target experiment AFTER@LHC and at $\sqrt{s} = 500$ GeV corresponding to the higher RHIC energy. Finally, we investigate the effect of the transverse momentum dependent (TMD) evolution of the densities involved, on the asymmetry.