Search for chargino-neutralino production using recursive jigsaw reconstruction in final states with two or three charged leptons in proton-proton collisions at $\sqrt{s}$=13 TeV with the ATLAS detector

TL;DR

This paper searches for supersymmetric chargino-neutralino pairs in proton-proton collisions at 13 TeV using recursive jigsaw reconstruction, setting mass limits up to 600 GeV and observing a 3.0 sigma excess in low mass-splitting regions.

Contribution

It introduces a novel analysis method using recursive jigsaw reconstruction to improve sensitivity in supersymmetry searches with multiple leptons.

Findings

No significant excess observed in large and intermediate mass-splitting regions.

Chargino-neutralino masses up to 600 GeV are excluded at 95% CL.

A 3.0 sigma local excess is observed in low mass-splitting regions.

Abstract

A search for electroweak production of supersymmetric particles is performed in two-lepton and three-lepton final states using recursive jigsaw reconstruction. The search uses data collected in 2015 and 2016 by the ATLAS experiment in $\sqrt{s}$ = 13 TeV proton--proton collisions at the CERN Large Hadron Collider corresponding to an integrated luminosity of 36.1 fb$^{-1}$. Chargino-neutralino pair production, with decays via W/Z bosons, is studied in final states involving leptons and jets and missing transverse momentum for scenarios with large and intermediate mass-splittings between the parent particle and lightest supersymmetric particle, as well as for the scenario where this mass splitting is close to the mass of the Z boson. The latter case is challenging since the vector bosons are produced with kinematic properties that are similar to those in Standard Model processes. Results are found to be compatible with the Standard Model expectations in the signal regions targeting large and intermediate mass-splittings, and chargino-neutralino masses up to 600 GeV are excluded at 95% confidence level for a massless lightest supersymmetric particle. Excesses of data above the expected background are found in the signal regions targeting low mass-splittings, and the largest local excess amounts to 3.0 standard deviations.