Probing Saturation Effect in Heavy Meson Pair Correlation in Forward $pA$ Collisions

Abstract

Forward two-particle correlations in $pA$ collisions have long been recognized as a particularly sensitive observable for exploring gluon saturation effects. In the back-to-back regime, two-particle correlations receive substantial contributions from both soft-gluon radiation and saturation effects. In this work, we study heavy meson pair correlations in forward proton-nucleus collisions by incorporating a unified Sudakov resummation for heavy meson pair correlations in the Color Glass Condensate effective theory. Our results are in good agreement with the LHCb $\Delta \varphi$ measurements for $D^0{\bar{D}}^0$ pairs in forward $pp$ and $pA$ collisions, as well as with the measurements of $J/\psi$ pairs from $b\bar{b}$ decays in forward $pp$ collisions. We further present predictions for the $\Delta \varphi$ distribution and azimuthal anisotropies of $D\bar{D}$ and $B\bar{B}$ correlations in the forward rapidity region at the Large Hadron Collider. A pronounced mass hierarchy is found in both the nuclear modification factor $R_{pA}$ and the azimuthal anisotropy ratio $⟨\cos 2{\varphi }_{qP}{⟩}_{pA}/⟨\cos 2{\varphi }_{qP}{⟩}_{pp}$, with stronger suppression for bottom meson pairs than for charm meson pairs. As the rapidity increases, the suppression becomes more pronounced while the mass hierarchy remains robust. This study will help us to search for the saturation signal via heavy-meson pair correlations in forward $pA$ collisions.

16 pages, 15 figures; includes newly added subsections; version accepted for publication in EPJC