Effects of color reconnection on $t\bar{t}$ final states at the LHC

TL;DR

This paper investigates how different models of color reconnection affect top quark mass measurements at the LHC, proposing new models and methods to better estimate and reduce the associated uncertainties.

Contribution

The authors introduce two new classes of color reconnection models, tune them to LHC data, and provide a more realistic estimate of the top mass uncertainty due to these effects.

Findings

The estimated top mass uncertainty from color reconnection is about 500 MeV.

Existing methods underestimate the uncertainty by not considering a wider range of models.

Future measurements can further constrain models and reduce uncertainties.

Abstract

The modeling of color reconnection has become one of the dominant sources of systematic uncertainty in the top mass determination at hadron colliders. The uncertainty on the top mass due to color reconnection is conventionally estimated by taking the difference in the predictions of a model with and a model without color reconnection. We show that this procedure underestimates the uncertainty when applied to the existing models in {\sc Pythia}~8. We introduce two new classes of color reconnection models, each containing several variants, which encompass a variety of scenarios that could be realized in nature and we study how they affect the reconstruction of the top mass. After tuning the new models to existing LHC data, the remaining spread of predictions is used to derive a more realistic uncertainty for the top mass, which is found to be around 500 MeV. We also propose how future LHC measurements with $t\bar{t}$ events can be used to further constrain these models and reduce the associated modeling uncertainty.