Inclusive production ofJ/ψmeson in proton-proton collisions at BNL RHIC

Abstract

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