Search for direct top squark pair production in final states with two leptons in root s=13 TeV pp collisions with the ATLAS detector

Abstract

The results of a search for direct pair production of top squarks in events with two opposite-charge leptons (electrons or muons) are reported, using

36.1

fb

- 1

of integrated luminosity from proton-proton collisions at

s

= 13

TeV collected by the ATLAS detector at the Large Hadron Collider. To cover a range of mass differences between the top squark

t ~

and lighter supersymmetric particles, four possible decay modes of the top squark are targeted with dedicated selections: the decay

t ~

→ b

χ ~

1

±

into a b-quark and the lightest chargino with

χ ~

1

±

→ W

χ ~

1

0

, the decay

t ~

→ t

χ ~

1

0

into an on-shell top quark and the lightest neutralino, the three-body decay

t ~

→ b W

χ ~

1

0

and the four-body decay

t ~

→ b ℓ ν

χ ~

1

0

. No significant excess of events is observed above the Standard Model background for any selection, and limits on top squarks are set as a function of the

t ~

and

χ ~

1

0

masses. The results exclude at 95% confidence level

t ~

masses up to about 720 GeV, extending the exclusion region of supersymmetric parameter space covered by previous searches.