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

Abstract: We present a comprehensive study of jet substructure observables in $pp$ and PbPb collisions at $\sqrt{s_{NN}} = 5.02$~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 ($z_g$) and the groomed jet mass to the ungroomed jet transverse momentum ($M_g / p_{T,\text{jet}}$) are reconstructed using the Soft Drop algorithm with two grooming parameter settings. With $z_\text{cut} = 0.1$ and $\beta = 0.0$, a slight modification in the $z_g$ distribution is observed in central PbPb collisions, whereas a pronounced enhancement in the high $M_g / p_{T,\text{jet}}$ region is found, particularly at low $p_{T,\text{jet}}$ 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 ($z_\text{cut} = 0.5$, $\beta = 1.5$), no significant changes in $M_g / p_{T,\text{jet}}$ are observed, indicating that the medium-induced modifications are predominantly associated with large-angle scattering.