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

Abstract

A search for compressed supersymmetry in the stau-neutralino coannihilation region with a soft tau lepton and a high transverse momentum jet from initial state radiation (ISR) is presented. The search targets final states with exactly one hadronically-decaying tau lepton and large missing transverse momentum due to the natural kinematic boost from the ISR jet. The data sample corresponds to an integrated luminosity of 77.4 fb−1 of proton-proton collisions at 13 TeV collected with CMS detector at the CERN LHC in 2016 and 2017. The distribution of the transverse mass between the tau and the missing transverse energy is found to be consistent with the Standard Model predictions. Upper limits are set on the cross section for chargino and neutralino production with an ISR jet. For a compressed mass spectrum scenario in which the mass difference between the lightest neutralino and the chargino is 50 GeV, an upper limit of 290 GeV is set on the mass of the chargino, which exceeds the sensitivity obtained by other stau searches to date.