Study of quark and gluon jet substructure in Z+jet and dijet events from pp collisions

TL;DR

This paper presents measurements of jet substructure in proton-proton collisions at 13 TeV, distinguishing quark- and gluon-initiated jets, and evaluates the performance of theoretical models against these data.

Contribution

It provides the first measurements of jet substructure in Z+jet events enriched in quark jets, using generalized angularities and grooming techniques to test and challenge Monte Carlo models.

Findings

Models show significant discrepancies in describing jet substructure.

Soft drop grooming affects the substructure observables.

Jet substructure varies with jet transverse momentum and radius.

Abstract

Measurements of jet substructure describing the composition of quark- and gluon-initiated jets are presented. Proton-proton (pp) collision data at $\sqrt{s}$ =13 TeV collected with the CMS detector are used, corresponding to an integrated luminosity of 35.9 fb$^{-1}$. Generalized angularities are measured that characterize the jet substructure and distinguish quark- and gluon-initiated jets. These observables are sensitive to the distributions of transverse momenta and angular distances within a jet. The analysis is performed using a data sample of dijet events enriched in gluon-initiated jets, and, for the first time, a Z+jet event sample enriched in quark-initiated jets. The observables are measured in bins of jet transverse momentum, and as a function of the jet radius parameter. Each measurement is repeated applying a "soft drop" grooming procedure that removes soft and large angle radiation from the jet. Using these measurements, the ability of various models to describe jet substructure is assessed, showing a clear need for improvements in Monte Carlo generators.