UC Berkeley

The nuclear modification factor R AA of charm jets, identified by the presence of a D0 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 s NN = 5.02 TeV with the ALICE detector at the LHC. The D0 mesons and their charge conjugates are reconstructed from the hadronic decay D 0 → K − π + . Jets are reconstructed from D0-meson candidates and charged particles using the anti-k T algorithm with jet resolution parameter R = 0.3 , in the jet transverse momentum (p T) range 5 < p T ch jet < 50 GeV/c and pseudorapidity |η ch jet| < 0.6. A hint of reduced suppression in the charm-jet R AA is observed in comparison to inclusive jets in central Pb–Pb collisions with a significance of about 2σ in 20 < p T 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. Several state-of-the-art models are consistent with the data, with the LIDO model providing the best description of the data in the common kinematic range of inclusive and D0-tagged jets, highlighting the role of mass effects in interpreting the results.