Investigating charm quark energy loss in medium with the nuclear modification factor of D$^0$-tagged jets

Abstract

The nuclear modification factor $R_\mathrm{AA}$ of charm jets, identified by the presence of a D$^0$ meson among the jet constituents, has been measured for the first time in Pb-Pb collisions at a centre-of-mass energy per nucleon pair $\sqrt{s_{\rm NN}} = 5.02$ TeV with the ALICE detector at the LHC. The D$^0$ mesons and their charge conjugates are reconstructed from the hadronic decay D$^0\to \mathrm K^{-}\pi^{+}$. Jets are reconstructed from D$^0$-meson candidates and charged particles using the anti-$k_\mathrm{T}$ algorithm with jet resolution parameter $R=0.3$, in the jet transverse momentum ($p_\mathrm{T}$) range $5< p_\mathrm{T}^\mathrm{ch~jet}<50$ GeV/$c$ and pseudorapidity $|\eta^\mathrm{ch~jet}| < 0.6$. A hint of reduced suppression in the charm-jet $R_\mathrm{AA}$ is observed in comparison to inclusive jets in central Pb-Pb collisions with a significance of about 2$\sigma$ in $20< p_\mathrm{T}^\mathrm{ch~jet}<50$ GeV/$c$, suggesting the in-medium energy loss to depend on both the difference between quark and gluon coupling strength (Casimir colour-charge effect) and quark mass (dead-cone effect). The data are compared with model calculations that include mass effects in the in-medium energy loss. Among these, LIDO provides the best description of the data, highlighting the role of mass effects in interpreting the results.