Open charm production in heavy ion collisions and the Color Glass Condensate

TL;DR

This paper analyzes open charm production in heavy-ion collisions within the Color Glass Condensate framework, focusing on how the saturation scale $Q_s$ relative to the charm mass $m$ reshapes production patterns. Using $k_T$-factorization with a modeled unintegrated gluon distribution, it demonstrates that charm yields scale with $N_ ext{coll}$ at RHIC midrapidity ($Q_s oughly m$) and transition toward $N_ ext{part}$ (or $ ext{sqrt}(N_ ext{part}^A)$ in $p(d)A$) at forward rapidities where $Q_s o ext{larger than } m$, while predicting harder charm spectra than collinear predictions. The work connects initial-state saturation to measurable observables such as the total transverse momentum of the charm pair and provides predictions for quenching in hot and cold media, finding a slower $p_T$-dependence of the heavy-quark quenching factor due to the intrinsic hardness induced by saturation. Overall, the study highlights distinctive saturation-driven centrality and rapidity dependencies in open charm that can serve as probes of CGC dynamics and $Q_s$ at RHIC and the LHC.

Abstract

We consider the production of open charm in heavy ion collisions in the framework of the Color Glass Condensate. In the central rapidity region at RHIC, for the charm quark yield we expect N(coll) (number of collisions) scaling in the absence of final-state effects. At higher energies, or forward rapidities at RHIC, the saturation scale exceeds the charm quark mass; we find that this results in the approximate N(part) (number of participants) scaling of charm production in AA collisions and N(part)^A scaling in p(d)A collisions, similarly to the production of high pT gluons discussed earlier. We also show that the saturation phenomenon makes spectra harder as compared to the naive parton model approach. We then discuss the energy loss of charm quarks in hot and cold media and argue that the hardness of the spectrum implies very slow dependence of the quenching factor on pT.

Figures (4)

• Figure 1: Production of $q\bar{q}$ pair in heavy-ion collisions in $k_T$-factorization approach.
• Figure 2: Dependence of the charmed meson yield on centrality at midrapidity and pseudorapidity $\eta=2$ for dAu and Au-Au collisions.
• Figure 3: The charmed meson spectrum in heavy-ion collisions at various energies.
• Figure 4: Quenching factors for hot and cold media $\hat{q} = 0.2,\, 0.05,\, 0.01,\, 0.0025$ GeV$^3$. $L=5$ fm.