A Toolkit of the Stop Search via the Chargino Decay
Yang Bai, Hsin-Chia Cheng, Jason Gallicchio, Jiayin Gu

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…
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