Search for the pair production of long-lived supersymmetric partners of the tau lepton in proton-proton collisions at $\sqrt{s}$ = 13 TeV

TL;DR

This paper reports a search for long-lived supersymmetric tau partners (staus) decaying within the CMS detector, using advanced graph neural network techniques to identify displaced tau leptons, and sets new exclusion limits on their masses and decay lengths.

Contribution

First search employing a graph neural network for identifying displaced tau leptons from long-lived staus at the LHC, extending previous exclusion limits.

Findings

Excluded stau masses between 126-260 GeV for certain decay lengths.

Set new limits on stau proper decay lengths up to 333 mm.

Improved sensitivity over previous supersymmetry searches.

Abstract

Gauge-mediated supersymmetry-breaking models provide a strong motivation to search for a supersymmetric partner of the tau lepton (stau) with a macroscopic lifetime. Long-lived stau decays produce tau leptons that are displaced from the primary proton-proton interaction vertex, leading to an unconventional signature. This paper presents a search for the direct production of long-lived staus decaying within the CMS tracker volume in proton-proton collisions at $\sqrt{s}$ = 13 TeV, performed for the first time with an identification algorithm based on a graph neural network dedicated to displaced tau leptons. The data sample, corresponding to an integrated luminosity of 138 fb$^{-1}$, was recorded with the CMS experiment at the CERN LHC between 2016 and 2018. This search excludes, at 95% confidence level, stau masses, $m_\tilde{\tau}$, in the 126$-$260 (906$-$425) GeV range for a proper decay length of 50 mm in the maximally mixed (mass-degenerate) scenario, while for $m_\tilde{\tau} $ = 200 GeV, stau proper decay lengths are excluded in the range 21$-$94 (6$-$333) mm. These results improve the exclusion limits compared to previous searches, and extend the parameter space explored in the context of supersymmetry.