Search for long-lived charginos based on a disappearing-track signature using 136 fb$^{-1}$ of $pp$ collisions at $\sqrt{s}$ = 13 TeV with the ATLAS detector

A search for long-lived charginos produced either directly or in the cascade decay of heavy prompt gluino states is presented. The search is based on proton-proton collision data collected at a center-of-mass energy of $\sqrt{s}$ = 13 TeV between 2015 and 2018 with the ATLAS detector at the LHC, corresponding to an integrated luminosity of 136 fb$^{-1}$. Long-lived charginos are characterised by a distinct disappearing track signature and are reconstructed using at least four measurements in the ATLAS pixel detector, with no subsequent measurements in outermost silicon tracking volume nor any associated energy deposits in the calorimeter. The final state is complemented by at least one high transverse momentum jet and large missing transverse momentum for triggering purposes. No excess above the expected backgrounds is observed. Exclusion limits are set at 95% confidence level on the masses of the chargino and gluinos for different chargino lifetimes. Chargino masses up to 660 (210) GeV are excluded in scenarios where the chargino is a pure wino (higgsino). For charginos produced during the cascade decay of a heavy gluino, gluinos with masses up to 2.1 TeV are excluded for a chargino mass of 300 GeV and a variety of chargino lifetimes.