Search for Supersymmetry with a Compressed Mass Spectrum in Events with a Soft τ Lepton, a Highly Energetic Jet, and Large Missing Transverse Momentum in Proton-Proton Collisions at √s = 13  TeV

Abstract

The first search for supersymmetry in events with an experimental signature of one soft, hadronically decaying τ lepton, one energetic jet from initial-state radiation, and large transverse momentum imbalance is presented. These event signatures are consistent with direct or indirect production of scalar τ leptons (τ) in supersymmetric models that exhibit coannihilation between the τ and the lightest neutralino (χ⁰₁), and that could generate the observed relic density of dark matter. The data correspond to an integrated luminosity of 77.2  fb⁻¹ of proton-proton collisions at √s=13  TeV collected with the CMS detector at the LHC in 2016 and 2017. The results are interpreted in a supersymmetric scenario with a small mass difference (Δm) between the chargino (χ±₁) or next-to-lightest neutralino (χ⁰₂), and the χ⁰₁. The mass of the τ is assumed to be the average of the χ±₁ and χ⁰₁ masses. The data are consistent with standard model background predictions. Upper limits at 95% confidence level are set on the sum of the χ±₁, χ⁰₂, and τ production cross sections for Δm(χ±₁,χ⁰₁)=50  GeV, resulting in a lower limit of 290 GeV on the mass of the χ±₁, which is the most stringent to date and surpasses the bounds from the LEP experiments