On the exclusion limits in $t\bar{t}+$DM searches at the LHC

TL;DR

This paper emphasizes the significance of higher-order corrections and off-shell effects in accurately determining exclusion limits in top-antitop plus dark matter searches at the LHC, using advanced NLO QCD predictions.

Contribution

It provides the first detailed comparison of NLO QCD predictions with off-shell effects against simpler models for $t\bar{t}+$DM searches, improving the accuracy of exclusion limits.

Findings

NLO QCD with off-shell effects significantly alters exclusion limits.

Simpler models like narrow-width approximation can underestimate or overestimate limits.

Full off-shell calculations provide more reliable constraints on the mediator model.

Abstract

In these proceedings we discuss the importance of higher-order corrections and off-shell effects for the calculation of signal strength exclusion limits in $t\bar{t}+$DM searches at the Large Hadron Collider. We present limits for the spin-0 s-channel mediator model using state-of-the-art NLO QCD predictions with full off-shell effects for the relevant $t\bar{t}$ and $t\bar{t}Z$ background processes. These are then compared to less sophisticated predictions using either the narrow-width approximation or LO calculations in order to asses the respective effects.