Investigating charm quark energy loss in medium with the nuclear modification factor of D⁰-tagged jets

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 D⁰→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^chjet' 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 2 σ in 20 'p_T^chjet' 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.