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

<jats:title>Abstract</jats:title><jats:p>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 centre-of-mass energy of <jats:inline-formula><jats:alternatives><jats:tex-math>$$\sqrt{s}$$</jats:tex-math><mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML">
<mml:msqrt>
<mml:mi>s</mml:mi>
</mml:msqrt>
</mml:math></jats:alternatives></jats:inline-formula> = 13 T<jats:inline-formula><jats:alternatives><jats:tex-math>$$\text {eV}$$</jats:tex-math><mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML">
<mml:mtext>eV</mml:mtext>
</mml:math></jats:alternatives></jats:inline-formula> between 2015 and 2018 with the ATLAS detector at the LHC, corresponding to an integrated luminosity of 136 fb<jats:inline-formula><jats:alternatives><jats:tex-math>$$^{-1}$$</jats:tex-math><mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML">
<mml:msup>
<mml:mrow/>
<mml:mrow>
<mml:mo>-</mml:mo>
<mml:mn>1</mml:mn>
</mml:mrow>
</mml:msup>
</mml:math></jats:alternatives></jats:inline-formula>. Long-lived charginos are characterised by a distinct signature of a short and then disappearing track, and are reconstructed using at least four measurements in the ATLAS pixel detector, with no subsequent measurements in the silicon-microstrip tracking volume nor any associated energy deposits in the calorimeter. The final state is complemented by a large missing transverse-momentum requirement for triggering purposes and at least one high-transverse-momentum jet. No excess above the expected backgrounds is observed. Exclusion limits are set at 95% confidence level on the masses of the chargino and gluino for different chargino lifetimes. Chargino masses up to 660 (210) G<jats:inline-formula><jats:alternatives><jats:tex-math>$$\text {eV}$$</jats:tex-math><mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML">
<mml:mtext>eV</mml:mtext>
</mml:math></jats:alternatives></jats:inline-formula> 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 below 2.1 T<jats:inline-formula><jats:alternatives><jats:tex-math>$$\text {eV}$$</jats:tex-math><mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML">
<mml:mtext>eV</mml:mtext>
</mml:math></jats:alternatives></jats:inline-formula> are excluded for a chargino mass of 300 G<jats:inline-formula><jats:alternatives><jats:tex-math>$$\text {eV}$$</jats:tex-math><mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML">
<mml:mtext>eV</mml:mtext>
</mml:math></jats:alternatives></jats:inline-formula> and a lifetime of 0.2 ns.</jats:p>