# Exploration of jet substructure using iterative declustering in pp and Pb-Pb collisions at LHC energies

## TL;DR

This paper presents novel measurements of jet substructure in proton-proton and lead-lead collisions at LHC energies, using iterative declustering and grooming techniques to explore medium effects on jet evolution.

## Contribution

It introduces the first measurement of the distribution of the number of hard splittings in jets and compares these to Monte Carlo predictions to study jet-medium interactions.

## Key findings

- Suppression of symmetric splittings at large angles in Pb-Pb collisions.
- Enhancement of small-angle splittings in Pb-Pb collisions.
- No significant change in the total number of splittings between systems.

## Abstract

The ALICE collaboration at the CERN LHC reports novel measurements of jet substructure in pp collisions at $\sqrt{s}$= 7 TeV and central Pb-Pb collisions at $\sqrt{s_{\rm{NN}}}$ = 2.76 TeV. Jet substructure of track-based jets is explored via iterative declustering and grooming techniques. We present the measurement of the momentum sharing of two-prong substructure exposed via grooming, the $z_{\rm{g}}$, and its dependence on the opening angle, in both pp and Pb-Pb collisions. We also present the first measurement of the distribution of the number of branches obtained in the iterative declustering of the jet, which is interpreted as the number of its hard splittings. In Pb-Pb collisions, we observe a suppression of symmetric splittings at large opening angles and an enhancement of splittings at small opening angles relative to pp collisions, with no significant modification of the number of splittings. The results are compared to predictions from various Monte Carlo event generators to test the role of important concepts in the evolution of the jet in the medium such as color coherence.