Measurement of hadronic event shapes in high-$p_{\textrm{T}}$ multijet final states at $\sqrt{s} = 13$ TeV with the ATLAS detector

TL;DR

This paper presents measurements of event-shape variables in high-energy proton-proton collisions at 13 TeV using the ATLAS detector, comparing data with Monte Carlo simulations to test QCD predictions at various jet multiplicities.

Contribution

It provides the first detailed measurement of hadronic event shapes in multijet final states at 13 TeV, highlighting discrepancies with theoretical models.

Findings

Discrepancies at low jet multiplicities between data and simulations.

Better shape agreement at high jet multiplicities but normalization issues.

Measurements extend to scales beyond 2 TeV.

Abstract

A measurement of event-shape variables in proton-proton collisions at large momentum transfer is presented using data collected at $\sqrt{s} = 13$ TeV with the ATLAS detector at the Large Hadron Collider. Six event-shape variables calculated using hadronic jets are studied in inclusive multijet events using data corresponding to an integrated luminosity of 139 fb$^{-1}$. Measurements are performed in bins of jet multiplicity and in different ranges of the scalar sum of the transverse momenta of the two leading jets, reaching scales beyond 2 TeV. These measurements are compared with predictions from Monte Carlo event generators containing leading-order or next-to-leading order matrix elements matched to parton showers simulated to leading-logarithm accuracy. At low jet multiplicities, shape discrepancies between the measurements and the Monte Carlo predictions are observed. At high jet multiplicities, the shapes are better described but discrepancies in the normalisation are observed.