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 ( ˜ χ 0 1 ), 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 ( Δ m ) between the chargino ( ˜ χ ± 1 ) or next-to-lightest neutralino ( ˜ χ 0 2 ), and the ˜ χ 0 1 . The mass of the ˜ τ is assumed to be the average of the ˜ χ ± 1 and ˜ χ 0 1 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 , ˜ χ 0 2 , and ˜ τ production cross sections for Δ m ( ˜ χ ± 1 , ˜ χ 0 1 ) = 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.