Abstract

A search for electroweak production of supersymmetric particles in scenarios with compressed mass spectra in final states with two low-momentum leptons and missing transverse momentum is presented. This search uses proton-proton collision data recorded by the ATLAS detector at the Large Hadron Collider in 2015-2016, corresponding to 36.1 fb$^{-1}$ of integrated luminosity at $\sqrt{s}=13$ TeV. Events with same-flavor pairs of electrons or muons with opposite electric charge are selected. The data are found to be consistent with the Standard Model prediction. Results are interpreted using simplified models of R-parity-conserving supersymmetry in which there is a small mass difference between the masses of the produced supersymmetric particles and the lightest neutralino. Exclusion limits at 95% confidence level are set on next-to-lightest neutralino masses of up to 145 GeV for Higgsino production and 175 GeV for wino production, and slepton masses of up to 190 GeV for pair production of sleptons. In the compressed mass regime, the exclusion limits extend down to mass splittings of 2.5 GeV for Higgsino production, 2 GeV for wino production, and 1 GeV for slepton production. The results are also interpreted in the context of a radiatively-driven natural supersymmetry model with non-universal Higgs boson masses.

Highlights

  • Supersymmetry (SUSY) [1,2,3,4,5,6] predicts new states that differ by half a unit of spin from their partner StandardModel (SM) particles, and it offers elegant solutions to several problems in particle physics

  • Events of interest are selected using a two-level trigger system [51], consisting of a first-level trigger implemented in hardware, which is followed by a software-based high-level trigger

  • MG5_aMC@next-to-leading order (NLO) v2.2.2 with PYTHIA versions 6.428 or 8.186 and the ATLAS A14 tune was used to simulate production of a Higgs boson in association with a W or Z boson, as well as events containing tt and one or more electroweak bosons. These processes were generated at NLO in the matrix element except for tt þ WW=tt, t þ tt, and t þ Z, which were generated at LO

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Summary

INTRODUCTION

Supersymmetry (SUSY) [1,2,3,4,5,6] predicts new states that differ by half a unit of spin from their partner Standard. The third scenario is favored by such dark matter arguments, but involves the pair production of the scalar partners of SM charged leptons (sleptons l ) In this scenario, the sleptons have masses near the weak scale and just above the mass of a pure bino LSP. A search for electroweak production of supersymmetric particles in compressed mass spectra scenarios with final states containing two soft same-flavor opposite-charge leptons (electrons or muons) and a large magnitude (EmT iss) of missing transverse momentum, pmT iss, is presented in this paper.

ATLAS DETECTOR
COLLISION DATA AND SIMULATED
EVENT RECONSTRUCTION
SIGNAL REGION SELECTION
BACKGROUND
Irreducible background
Reducible background
SYSTEMATIC UNCERTAINTIES
VIII. RESULTS AND INTERPRETATION
Findings
CONCLUSION
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