Jet Shape Resummation Using Soft-Collinear Effective Theory

TL;DR

This paper develops a theoretical framework using soft-collinear effective theory to resum large logarithms in jet shape calculations, enabling precise comparisons with LHC data and insights into parton shower dynamics.

Contribution

It introduces a factorized form for the jet shape that incorporates resummation at next-to-leading logarithmic order within SCET, advancing the precision of jet substructure predictions.

Findings

Resummation improves agreement with LHC measurements.

Collinear parton shower dominates jet shape features.

Power corrections and non-perturbative effects are significant in certain regimes.

Abstract

The jet shape is a classic jet substructure observable that probes the average transverse energy profile inside a reconstructed jet. The studies of jet shapes in proton-proton collisions have served as precision tests of perturbative Quantum Chromodynamics (QCD). They have also recently become the baseline for studying the in-medium modification of parton showers in ultra-relativistic nucleus-nucleus collisions. The jet shape is a function of two angular parameters $R$ and $r$, which can be at hierarchical scales. Its calculation suffers from large logarithms of the ratio between the two scales, and these phase space logarithms can conveniently be resummed in the framework of soft-collinear effective theory (SCET). We find that, up to power corrections, the integral jet shape can be expressed in a factorized form which involves only the ratio between two jet energy functions. Resummation is performed at next-to-leading logarithmic order using renormalization-group evolution techniques. Comparisons to jet shape measurements at the LHC are presented to verify the dominant role of the collinear parton shower and to identify the kinematic region in which power-suppressed soft modes and non-perturbative effects may play a role.