Same-Sign Dilepton Excesses and Vector-like Quarks

TL;DR

This paper explains observed excesses in same-sign dilepton events at the LHC using a model with vector-like T-odd quarks decaying into top quarks, W bosons, and lightest T-odd particles, proposing a benchmark at 750 GeV.

Contribution

It introduces a novel explanation for LHC excesses using little Higgs theories with T parity and estimates bounds on T-odd quark masses through simplified models.

Findings

Excesses can be explained by T-odd quark decays in little Higgs models.

A benchmark T-odd b-prime quark mass is proposed at 750 GeV.

Bounds on T-odd quark masses are estimated using supersymmetry search limits.

Abstract

Multiple analyses from ATLAS and CMS collaborations, including searches for ttH production, supersymmetric particles and vector-like quarks, observed excesses in the same-sign dilepton channel containing b-jets and missing transverse energy in the LHC Run 1 data. In the context of little Higgs theories with T parity, we explain these excesses using vector-like T-odd quarks decaying into a top quark, a W boson and the lightest T-odd particle (LTP). For heavy vector-like quarks, decay topologies containing the LTP have not been searched for at the LHC. The bounds on the masses of the T-odd quarks can be estimated in a simplified model approach by adapting the search limits for top/bottom squarks in supersymmetry. Assuming a realistic decay branching fraction, a benchmark with a 750 GeV T-odd b-prime quark is proposed. We also comment on the possibility to fit excesses in different analyses in a common framework.