Search for physics beyond the standard model in final states with two or three soft leptons and missing transverse momentum in proton-proton collisions at $\sqrt{s} = 13~\text{TeV}$

TL;DR

This paper reports a CMS search for supersymmetry with compressed spectra in final states with soft leptons and missing transverse momentum, setting new exclusion limits on SUSY particle masses using 13 TeV collision data.

Contribution

First CMS analysis targeting compressed SUSY spectra with soft leptons, providing new exclusion limits on electroweakinos and top squarks at 13 TeV.

Findings

No significant deviation from the Standard Model observed.

Excluded electroweakino masses up to 280 GeV for small mass differences.

Excluded top squark masses up to 530 GeV for specific decay modes.

Abstract

The most recent CMS results from a search for supersymmetry (SUSY) with a compressed mass spectrum in leptonic final states will be presented. The search is targeting signatures with missing transverse momentum and two or three low-momentum (soft) leptons. The dataset used is collected by the CMS experiment during the Run-2 p-p collisions at $\sqrt{s} = {}$13 TeV at the LHC, and corresponds to an integrated luminosity of up to 137 fb$^{-1}$. The observed data are found to be in agreement with the standard model (SM) prediction and exclusion upper limits are set on the SUSY particles production cross section. The results are interpreted in terms of electroweakino and top squark pair production. In both cases, a small mass difference between the produced SUSY particles and the lightest neutralino is considered. A wino-bino and a higgsino simplified models are used for the electroweakino interpretation. Exclusion limits at 95% confidence level are set on $\tilde{\chi}_{2}^{0}$/$\tilde{\chi}_{1}^{\pm}$ masses up to 280 GeV for a mass difference between the $\tilde{\chi}_{2}^{0}$/$\tilde{\chi}_{1}^{\pm}$ and the lightest neutralino of 10 GeV for the wino-bino production. In the higgsino interpretation $\tilde{\chi}_{2}^{0}$/$\tilde{\chi}_{1}^{\pm}$ masses are excluded up to 210(150) GeV for a mass difference of 7.5(3) GeV. The results for the higgsino production are additionally interpreted in terms of a phenomenological minimal SUSY extension of the SM, excluding the higgsino mass parameter $\mu$ up to 180 GeV for bino mass parameter $M_1 = {}$800 GeV. Upper limits at 95% confidence level are set on the top squark pair production interpretation, excluding top squark masses up to 530 GeV in the four-body top squark decay model and up to 475 GeV in the chargino-mediated decay model for a mass difference between the top squark and the lightest neutralino of 30 GeV.