Examination of Jet Substructure Evolution Using Temporal Reclustering in ALICE √s = 5.02 TeV pp Collisions*

The Quark-Gluon Plasma (QGP), created in collisions of ultra-relativistic heavy ions, enables unique experimental studies of QCD processes. In particular, collisions often generate high-momentum, collimated sprays of particles called jets, which can carry information from the initial hard scatterings of partons to hadronization and detection. Thus, in uncovering a jet’s history, we may access the temporal progression of the QGP medium. Previous work studied jet histories with the Cambridge/Aachen (C/A) jet reclustering algorithm, which assumes angular ordering of partonic splittings. While this property holds in the vacuum conditions of proton-proton (pp) collisions, the QGP allows for medium-induced emissions that are not necessarily angularly ordered.

This work presents the first experimental investigations of the evolution of various jet substructure variables using a time-ordered reclustering scheme called the τ algorithm (so named to reference the time for an emission to act as an independent radiation source). We apply the τ algorithm in the minimal-background conditions of ALICE √s = 5.02 TeV pp collisions and compare jet substructure results to those found using the C/A algorithm, especially in their access to the “formation time”. Finally, we present our outlook for extending this analysis to jets in LHC Run 3 Pb+Pb collisions.