# Prospects to study a long-lived charged next lightest supersymmetric particle at the LHC

## TL;DR

This paper explores the potential to study long-lived scalar tau particles at the LHC by proposing additional stopper detectors, aiming to measure decay properties and distinguish decay channels involving gravitinos and axinos.

## Contribution

It proposes a novel detector setup to study long-lived stau decays at the LHC and analyzes its sensitivity to decay parameters and different decay channels.

## Key findings

- A maximum stopper detector can be added in the CMS cavern.
- The sensitivity to stau lifetime and gravitino mass can be estimated.
- Decays involving axinos can be distinguished from gravitino decays using the proposed method.

## Abstract

If the scalar tau $\stau$ is the next lightest supersymmetric particle and decays into a gravitino ($\gravitino$) being the lightest supersymmetric particle, it will have generally a very long lifetime. In this paper, we investigate the possibility to study the decay of such a long lived scalar tau at the LHC. If we can add to the present LHC experiments additional detectors which are able to stop the stau particles and measure the produced decay products, the decay characteristics can be studied precisely at the LHC. We identify a maximum "stopper detector" that could be added in the CMS cavern, and estimate the sensitivity to the lifetime of the stau and to the mass of gravitino with this detector. The decay of the scalar tau may be significantly modified if the decay channel to the axino $\axino$ is open. We study the possibility to distinguish such decays from decays into gravitinos by measuring the process $\stau\to \axino (\gravitino) \tau \gamma$ using the stopper detector.