Heavy quark colorimetry of QCD matter

TL;DR

Heavy quark colorimetry investigates how heavy quarks propagate through QCD matter, focusing on radiative energy loss and its mass-dependent suppression. Framed within the BDMS quenching formalism, the work shows the dead cone effect reduces heavy-quark gluon radiation and quenching relative to light quarks, predicting a substantial enhancement of heavy-to-light hadron ratios (e.g., $D/\pi$) in heavy-ion collisions that scales with the medium's color-charge density. The paper provides analytical expressions for quenching factors: $Q_H(p_\perp)$ and $Q_L(p_\perp)$, with their ratio approximated by $\exp\left[ \frac{16 \alpha_s C_F}{9 \sqrt{3}} L \left( \frac{ \hat{q} M^2}{M^2+p_\perp^2} \right)^{1/3} \right]$, indicating the mass-dependent suppression is lifted at large $p_\perp$; numerically, a hot medium with $L \sim 5$ fm and $\hat{q} \sim 0.2$ GeV$^3$ can yield a factor of order 2 enhancement in $D/\pi$ around $p_\perp \sim 5$–10 GeV, though the absolute level is sensitive to infrared radiation and medium geometry.

Abstract

We consider propagation of heavy quarks in QCD matter. Because of large quark mass, the radiative quark energy loss appears to be qualitatively different from that of light quarks at all energies of practical importance. Finite quark mass effects lead to an in-medium enhancement of the heavy-to-light D/πratio at moderately large (5--10 GeV) transverse momenta. For hot QCD matter a large enhancement is expected, whose magnitude and shape are exponentially sensitive to the density of colour charges in the medium.