Comparative overview of differential measurements at ATLAS and CMS

TL;DR

This paper compares the methods and results of differential top quark measurements at ATLAS and CMS, highlighting their workflows, techniques, and recent findings to test QCD and search for new physics.

Contribution

It provides a comparative overview of the analysis techniques and recent differential cross section results from ATLAS and CMS experiments.

Findings

Consistent differential cross section measurements across experiments.

Techniques for event selection, background estimation, and unfolding are similar.

Recent results constrain new physics and improve QCD models.

Abstract

The study of the top quark has a central role for both the ATLAS and CMS experiments. The measurement of the $t\bar{t}$ production differential cross section, in particular, is sensitive to existence of new resonances, it is a stringent test of perturbative QCD calculations and it is used to improve the modelling of $t\bar{t}$ production. ATLAS and CMS provided a large number of results during the last years at $\sqrt{s}$=7, 8, 13 TeV, in different regions of the phase space, considering different channels and topology and measuring the cross section as a function of the kinematic variables of the $t\bar{t}$ system, the top quarks and/or their decay products. Even if the individual steps are dependent on the specific analysis all the differential cross section measurements proceed through the same workflow: the event selection, the background determination, the reconstruction of the $t\bar{t}$ system, the definition of the fiducial phase space, the unfolding applied to remove the effect of limited acceptance and resolution of the detector and the evaluation of the systematic uncertainties. In the following I will focus on the techniques used by ATLAS and CMS to perform some of these steps while presenting a selection of recent results by the two experiments.