Abstract
This paper presents a search for direct electroweak gaugino or gluino pair production with
a chargino nearly mass-degenerate with a stable neutralino. It is based on an integrated luminosity
of 36.1 fb−1 of pp collisions at √s = 13 TeV collected by the ATLAS experiment
at the LHC. The final state of interest is a disappearing track accompanied by at least one jet
with high transverse momentum from initial-state radiation or by four jets from the gluino decay
chain. The use of short track segments reconstructed from the innermost tracking layers
significantly improves the sensitivity to short chargino lifetimes. The results are found to be
consistent with Standard Model predictions. Exclusion limits are set at 95% confidence level on the
mass of charginos and gluinos for different chargino lifetimes. For a pure wino with a lifetime of
about 0.2 ns, chargino masses up to 460 GeV are excluded. For the strong production channel, gluino
masses up to 1.65 TeV are excluded assuming a chargino mass of
460 GeV and lifetime of 0.2 ns.