Inclusive production of $J/\psi$ meson in proton-proton collisions at BNL RHIC

TL;DR

This paper calculates inclusive $J/$ production cross sections in proton-proton collisions at RHIC using the $k_t$-factorization approach, identifying dominant mechanisms and comparing results with experimental data to constrain gluon distributions.

Contribution

It introduces a comprehensive $k_t$-factorization calculation of $J/$ production, highlighting the importance of radiative $$ decays and direct color-singlet mechanisms, and compares different unintegrated gluon distributions with data.

Findings

Radiative $$ decays and direct color-singlet are dominant mechanisms.

Some unintegrated gluon distribution functions are inconsistent with RHIC data.

Kwieci
44ski UGDFs best describe the experimental results.

Abstract

Inclusive cross sections for $J/\psi$ production in proton-proton collisions were calculated in the $k_t$-factorization approach for the RHIC energy. Several mechanisms were considered, including direct color-singlet mechanism, radiative decays of $\chi_c$ mesons, decays of $\psi'$, open-charm associated production of $J/\psi$ as well as weak decays of B mesons. Different unintegrated gluon distributions from the literature were used. We find that radiative $\chi_c$ decays and direct color-singlet contributions constitute the dominant mechanism of $J/\psi$ production. These process cannot be consistently treated within collinear-factorization approach. The results are compared with recent RHIC data. The new precise data at small transverse momenta impose stringent constraints on UGDFs. Some UGDFs are inconsistent with the new data. The Kwieci\'nski UGDFs give the best description of the data. In order to verify the mechanism suggested here we propose $J/\psi$ -- jet correlation measurement and an independent measurement of $\chi_c$ meson production in $\pi^+ \pi^-$ and/or $K^+ K^-$ decay channels. Finally, we address the issue of \J spin alignment.