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[tilde above]) in supersymmetric models that exhibit coannihilation between the τ[tilde above] and the lightest neutralino (χ[tilde above][superscript 0 over subscript 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 (Δm) between the chargino (χ[tilde above][superscript ± over subscript 1]) or next-to-lightest neutralino (χ[tilde above][superscript 0 over subscript 2]), and the χ[tilde above][superscript 0 over subscript 1]. The mass of the τ[tilde above] is assumed to be the average of the χ[tilde above][[superscript ±] over subscript 1] and χ[over ˜][superscript 0 over subscript 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[tilde above][superscript ± over subscript 1], χ[tilde above][superscript 0 over subscript 2], and τ[tilde above] production cross sections for Δm(χ[tilde above][superscript ± over subscript 1],χ[tilde above][superscript 0 over subscript 1])=50 GeV, resulting in a lower limit of 290 GeV on the mass of the χ[tilde above][superscript ± over subscript 1], which is the most stringent to date and surpasses the bounds from the LEP experiments.