A measurement of soft-drop jet observables in $pp$ collisions with the ATLAS detector at $\sqrt{s} = 13$ TeV

TL;DR

This paper presents measurements of jet substructure observables using the soft-drop grooming technique in proton-proton collisions at 13 TeV, comparing results with QCD predictions and simulations to enhance understanding of jet physics.

Contribution

First detailed measurement of soft-drop jet observables in $pp$ collisions at 13 TeV, including comparisons with QCD calculations and Monte Carlo models.

Findings

Jet mass and opening angle are well described by high-order QCD calculations.

Momentum sharing is nearly independent of $oldsymbol{ ext{α}_S}$ and well modeled.

Data agree with theoretical predictions across different pseudorapidity regions.

Abstract

Jet substructure quantities are measured using jets groomed with the soft-drop grooming procedure in dijet events from 32.9 fb$^{-1}$ of $pp$ collisions collected with the ATLAS detector at $\sqrt{s} = 13$ TeV. These observables are sensitive to a wide range of QCD phenomena. Some observables, such as the jet mass and opening angle between the two subjets which pass the soft-drop condition, can be described by a high-order (resummed) series in the strong coupling constant $\alpha_S$. Other observables, such as the momentum sharing between the two subjets, are nearly independent of $\alpha_S$. These observables can be constructed using all interacting particles or using only charged particles reconstructed in the inner tracking detectors. Track-based versions of these observables are not collinear safe, but are measured more precisely, and universal non-perturbative functions can absorb the collinear singularities. The unfolded data are directly compared with QCD calculations and hadron-level Monte Carlo simulations. The measurements are performed in different pseudorapidity regions, which are then used to extract quark and gluon jet shapes using the predicted quark and gluon fractions in each region. All of the parton shower and analytical calculations provide an excellent description of the data in most regions of phase space.