  Two analyses searching for the production of supersymmetric particles through
the electroweak interaction are presented: the chargino search, targeting the
pair production of charginos decaying into W bosons and neutralinos, and the
displaced track search, looking for charged tracks arising from the decays of
higgsinos into pions. These searches target compressed phase spaces, where the
mass difference between the next-to-lightest and lightest supersymmetric
particle is relatively small. The searches use proton-proton collision data
collected at a centre-of-mass energy of 13 TeV with the ATLAS detector at the
LHC. In the chargino search, the targeted mass difference between charginos and
neutralinos is close to the mass of the W boson. In such phase space, the
chargino pair production is kinematically similar to the WW background, making
the chargino signal experimentally challenging to be discriminated from the WW
background. Machine learning techniques are adopted to separate the
supersymmetric signal from the backgrounds. The results exclude chargino masses
up to about 140 GeV for mass splittings down to about 100 GeV, superseding the
previous results in particularly interesting regions where the chargino pair
production could have hidden behind the looking-alike WW background. In the
displaced track search, the mass difference between the produced sparticles and
the lightest neutralinos goes down to 0.3 GeV. The experimental signature has a
low momentum charged track with an origin displaced from the collision point.
The results show that the analysis has the sensitivity to exclude different
hypotheses for higgsino masses up to 175 GeV if no excess is observed in data.
For lower masses, the larger signal cross-section allows to achieve higher
significance for different mass splitting scenarios. All these signal
hypotheses have not been probed by any existing analysis of LHC data.
