Measurements of $J/\psi$ Production and Polarization in p+p and p+Au Collisions at $\sqrt{s_{{}_{\mathrm{\text{NN}}}}}$ = 200 GeV with the STAR Experiment

摘要

We present the measurements of J / ψ production at mid-rapidity via the di-muon decay channel in p+p and p+Au collisions at s NN = 200 GeV by the STAR experiment at RHIC. In p+p collisions, the measured inclusive J / ψ cross section can be qualitatively described by model calculations. The J / ψ polarization parameters, λ 𝜃 , λ ? as well as the frame-invariant quantity λ i n v , are presented as a function of transverse momentum in both the helicity and Collins-Soper frames. No significant polarization is observed. In addition, the nuclear modification factor for inclusive J/ ψ in p+Au collisions is similar to that measured in d+Au collisions and favors an additional nuclear absorption effect on top of the nuclear PDF effect.