Probing the Stau-Neutralino Coannihilation Region at the LHC with a soft tau lepton and an ISR jet

TL;DR

This study proposes a new LHC search strategy for dark matter in compressed supersymmetric spectra using a soft tau lepton and an ISR jet, enhancing sensitivity to previously inaccessible regions.

Contribution

It introduces a novel methodology combining a soft tau lepton with an ISR jet to probe compressed mass spectra in supersymmetry, improving detection prospects at the LHC.

Findings

Expected significances > 3σ for certain mass ranges with 30 fb⁻¹ data.

Method effectively reduces Standard Model backgrounds.

Compressed regions not excluded by current experiments can be probed.

Abstract

We present a feasibility study, to search for dark matter at the LHC, in events with one soft hadronically decaying tau lepton and missing transverse energy recoiling against a hard $p_{T}$ jet from initial state radiation. This methodology allows the search for Supersymmetry in compressed mass spectra regions, where the mass difference between the lightest neutralino, $\tilde\chi_1^0$, and the stau (the tau superpartner), $\tilde{\tau}$, is small. Several theoretical models predict a direct connection between thermal Bino dark matter and staus within this scenario. We show that compressed regions, not excluded by ATLAS nor CMS experiments, are opened up with the increase in experimental sensitivity reached with the proposed methodology. The requirement of a hard jet from initial state radiation combined with a soft tau lepton is effective in reducing Standard Model backgrounds, providing expected significances greater than 3$\sigma$ for $\tilde{\chi}_{1}^{\pm}$ masses up to 300 GeV and $\tilde{\tau}$-$\tilde{\chi}_{1}^{0}$ mass gaps below 25 GeV with only 30 fb$^{-1}$ of 13 TeV data from the LHC.