Probing jet-medium interactions via jet substructure observables in relativistic heavy-ion collisions

We present a comprehensive study of jet substructure observables in $pp$ and PbPb collisions at √sNN = 5.02~TeV using a multi-phase transport model. To suppress background contamination, the constituent subtraction method is employed for both PbPb and smeared $pp$ events. The jet splitting momentum fraction (zg) and the groomed jet mass to the ungroomed jet transverse momentum (Mg / pT,jet) are reconstructed using the Soft Drop algorithm with two grooming parameter settings. With zcut = 0.1 and $β= 0.0$, a slight modification in the zg distribution is observed in central PbPb collisions, whereas a pronounced enhancement in the high Mg / pT,jet region is found, particularly at low pT,jet and in more central events. A detailed analysis of the dynamical evolution stages reveals that this enhancement primarily originates from jet-medium interactions, whereas the contributions from hadronization and hadronic rescatterings are largely mitigated by the grooming procedure. In contrast, under a stronger grooming condition (zcut = 0.5, $β= 1.5$), no significant changes in Mg / pT,jet are observed, indicating that the medium-induced modifications are predominantly associated with large-angle scattering.