A Toolkit of the Stop Search via the Chargino Decay

TL;DR

This paper develops a set of kinematic variables, including new compatible-masses variables, to improve the detection of top squark decays in compressed spectra at the LHC, enhancing signal-background discrimination.

Contribution

It introduces novel compatible-masses variables and demonstrates their effectiveness in distinguishing stop signals from top backgrounds in di-leptonic decay channels.

Findings

Different variable combinations optimize detection for various spectra.

New variables improve signal significance in challenging compressed scenarios.

Method applicable to other new physics searches with top backgrounds.

Abstract

The top squark (stop) may dominantly decay to a bottom quark and a chargino if the mass difference between the stop and the lightest neutralino is comparable or less than the top quark mass. Such a moderately compressed spectrum is a challenging scenario for the stop search at the Large Hadron Collider, because it is difficult to separate the signals from the top and anti-top background. In this paper we focus on the di-leptonic decay channel, and consider many kinematic variables as possible discriminators. These include several MT2 variables and new "compatible-masses" variables which fully utilize all kinematic information of the background. We use several sample spectra with different characteristics to study the efficiencies of these variables in distinguishing the signal from the background. The finding is that different combinations of variables or strategies should be used for different spectra to maximally enhance the signal significance and expand the reach of the stop search in this scenario. The new variables that we proposed in this paper are also useful for other new physics searches with di-leptonic top and anti-top events as the dominant background.