Why stop at two tops? Search for exotic production of top quarks in final states with same-sign leptons and $b$-jets at 13 TeV

TL;DR

This paper searches for rare events with same-sign leptons and b-jets at 13 TeV, testing models like vector-like quarks and four top quark production, setting limits on new physics scenarios.

Contribution

It introduces a search strategy for exotic top quark production in same-sign lepton final states at 13 TeV, focusing on models with four top quarks and setting new limits.

Findings

No significant excess observed over Standard Model background.

95% confidence level limits set on vector-like quark and four top quark production.

Constraints placed on models predicting enhanced same-sign lepton events.

Abstract

An analysis is presented of events containing jets including at least one $b$-tagged jet, sizable missing transverse momentum, and at least two charged leptons including a pair of the same electric charge, with the scalar sum of the jet and lepton transverse momenta being large. Standard Model processes rarely produce these final states, but several models of physics beyond the Standard Model predict an enhanced production rate of such events. Specific models with this feature are considered here: vector-like $T$, $B$, and $T_{5/3}$ quark pair production, and four top quark production under three scenarios (Standard Model, contact interaction, and extra-dimensions). A data sample of 3.2 fb$^{-1}$ of $pp$ collisions at a center-of-mass energy of $\sqrt{s}$=13 TeV recorded by the ATLAS detector at the Large Hadron Collider is used in this analysis. Several signal regions are defined, in which the consistency between the data yield and the background-only hypothesis is checked, and 95% confidence level limits are set on various signal models. The focus here is on models yielding signatures with four top quarks.