Description
Final states with three well isolated leptons and large ETmiss are well motivated in the
search for supersymmetry. Compressed supersymmetric spectra, where the mass difference
between the chargino or second lightest neutralino and the lightest supersymmetric particle
is relatively small (10-50 GeV), is an ongoing objective at the Large Hadron Collider (LHC).
Compressed scenarios are explored by selecting 3-lepton events with an additional relatively
hard initial-state radiation (ISR) jet and sizeable missing transverse energy. This permits the
use of softer leptons in the analysis, which is experimentally challenging both for triggering
and the particle reconstruction. The 3-lepton and ISR selection is explored here using Run-1
data delivered by the Large Hadron Collider and recorded with the ATLAS detector. No
significant excess were found above the Standard Model expectations. The new search was
interpreted in terms of 95% confidence-level exclusion limits on the masses of the charginos
and neutralinos. Results are summarised in arXiv:1509.07152.
