J/$\psi$ polarization in p+p collisions at $\sqrt{s}$ = 200 GeV in STAR

TL;DR

This paper reports measurements of J/ψ polarization in proton-proton collisions at 200 GeV, showing results consistent with theoretical models and no significant polarization observed within uncertainties.

Contribution

First measurement of J/ψ polarization at RHIC in p+p collisions at 200 GeV, providing data to test QCD production models.

Findings

J/ψ polarization is consistent with NLO+ CSM and COM predictions.

No significant polarization observed within current uncertainties.

Results help constrain charmonium production mechanisms.

Abstract

In this paper, J/$\psi$ polarization at mid-rapidity in $p+p$ collisions at $\sqrt{s}$ = 200 GeV measured in the STAR experiment at RHIC is reported. J/$\psi$ production is analyzed via the dielectron decay channel. J/$\psi$ polarization is extracted from the decay angular distribution in the helicity frame. The J/$\psi$ polarization is measured at transverse momentum range (2 - 6) GeV/c and is found to be consistent with $NLO^+$ Color Singlet Model ($NLO^+$ CSM), Color Octet Model (COM) predictions and with no polarization within current uncertainties.