Speaker
Description
We study forward $\chi_{cJ}$ production in the low-$p_{\perp}$ region in proton-proton ($pp$) and proton-nucleus ($pA$) collisions at the LHC within the framework of nonrelativistic QCD (NRQCD) factorization and the Color Glass Condensate (CGC) effective field theory. Incorporating small-$x$ gluon evolution via the running-coupling Balitsky–Kovchegov equation with various initial conditions, we systematically analyze the cross-section ratio $\sigma_{\chi_{c2}}/\sigma_{\chi_{c1}}$ of $\chi_{c2}$ to $\chi_{c1}$ production and find that it depends only weakly on these initial conditions. Our predictions agree well with the LHCb measurements for $p\mathrm{Pb}$ collisions, but overshoot those for $pp$ collisions. We further investigate the feed-down fractions $F_{\chi_{c1,2}\to J/\psi}=\sigma_{\chi_{c1,2}\to J/\psi}/\sigma_{J/\psi}$. Using the measured prompt-$J/\psi$ cross section as the denominator, we find that the CGC+NRQCD predictions broadly match the data with the McLerran–Venugopalan initial condition. In contrast, calculating both prompt-$J/\psi$ and $\chi_c$ production within CGC+NRQCD yields systematic discrepancies across all tested parameter combinations. This highlights a persistent challenge in achieving a simultaneous, unified description of $\chi_c$ and prompt-$J/\psi$ production within the current framework.
