Exploring medium properties using jet substructure measurements in pp and Pb–Pb collisions with ALICE

Abstract

Various studies of jet substructure in heavy-ion collisions offer a consistent picture of QCD medium interactions and a diverse path towards further differentiating energy loss mechanisms. Some results, however, remain disjoint: the jet mass and jet angularities, including girth and thrust, are stronglycorrelated observables which have given seemingly conflicting answers on the angular quenching of jets traversing the quark–gluon plasma (QGP). ALICE has carried out new systematic measurements of these and other perturbativelycalculable angularities using consistent definitions, resolving the girth-mass problem, and revealing quenching effects at broad angles. Concurrently, applying Soft Drop grooming isolates the narrowing in the core of quenched jets. Grooming can also be employed to resolve medium scattering centers, with varying methods used to focus on regions of the splitting phase space. We present the first application of dynamical grooming in heavy-ion collisions to search for excess kT,g emissions as a signature of point-like scatters, providing new constraints on searches for in-medium Molière scattering. We also present a novel shift from studying jet-medium opacity from the angular perspective to a time-like one. By employing a new time reclustering strategy, we potentially enable a time-dependent study of jet substructure observables. We compare all results to assorted jet quenching models, providing new critical information on medium evolution as a function of angular, momentum, and time structure.