Theory input for $t\bar{t}j$ experimental analyses at the LHC

TL;DR

This paper analyzes how different theoretical inputs affect the calculation of $t\bar{t}j$ differential cross sections at the LHC, aiming to improve the precision of top quark mass measurements by reducing uncertainties.

Contribution

It introduces a study of the impact of various theoretical parameters and scale choices on $t\bar{t}j$ cross sections, proposing dynamical scales to enhance perturbative stability.

Findings

Dynamical scales reduce scale uncertainties in high-energy tails.

Jet reconstruction parameter variations have negligible impact on uncertainties.

Using dynamical scales improves NLO/LO ratio behavior.

Abstract

The precise measurement of the top quark mass, which is a fundamental SM parameter, constitutes one of the main goals of the LHC top physics program. One approach to measure this quantity uses the $\rho_\mathrm{s}$ distribution, an observable depending on the invariant mass of the $t\bar{t}j$ system. To fully exploit the experimental accuracy achievable in measuring top quark production cross sections at the LHC, the theory uncertainties associated to these measurements need to be well under control. To this end we present a study of the effect of varying the theoretical input parameters in the calculation of differential cross sections of the $t\bar{t}j$ process. Thereby we studied the influence of the jet reconstruction procedure, as well as the effect of various renormalization and factorization scale definitions and different PDF sets. The variation of the $R$ parameter in the jet reconstruction algorithm was found to have negligible influence on the scale variation uncertainty. A strong reduction of scale uncertainties and a better behaviour of the NLO/LO ratios using selected dynamical scales instead of a static one in the high energy tails of differential distributions was observed. This is particularly interesting in the context of the top quark mass measurements through the $\rho_\mathrm{s}$ distribution, in which the perturbative stability can be improved by applying the proposed dynamical scale definition.