The soft drop momentum sharing fraction $z_g$ beyond leading-logarithmic accuracy

TL;DR

This paper develops a systematic theoretical framework to calculate the soft drop momentum sharing fraction $z_g$ beyond leading-logarithmic accuracy, revealing its sensitivity to parton charge and spin, and compares well with experimental data.

Contribution

It introduces a factorization approach for $z_g$ at NLL' accuracy, including non-global logarithms, and assesses perturbative uncertainties, advancing the understanding of jet substructure.

Findings

Excellent agreement with experimental data from ALICE, ATLAS, and STAR.

First calculation of $z_g$ beyond LL accuracy including non-global logarithms.

Demonstrates sensitivity of $z_g$ to parton charge and spin.

Abstract

Grooming techniques, such as soft drop, play a central role in reducing sensitivity of jets to e.g. underlying event and hadronization at current collider experiments. The momentum sharing fraction $z_g$, of the two branches in a jet that pass the soft drop condition, is one of the most important observables characterizing a collinear splitting inside the jet, and directly probes the QCD splitting functions. In this work, we present a factorization framework that enables a systematic calculation of the corresponding cross section beyond leading-logarithmic (LL) accuracy, showing that this measurement is not only sensitive to the QCD charge but also the spin of the parton that initiates the jet. Our results at next-to-leading logarithmic (NLL$'$) accuracy include non-global logarithms, and provide a first meaningful assessment of the perturbative uncertainty. We present a comparison to the available experimental data from ALICE, ATLAS, and STAR and find excellent agreement.