Search for single production of a vector-like B' quark decaying to a top quark and a W boson in the single-lepton final state in proton-proton collisions at $\sqrt{s}$ = 13 TeV

Abstract

A search is presented for the single production of a narrow-width vector-like B' quark that decays to a t quark and a W boson, with one of the decay products yielding an electron or muon. The data were collected from 2016 to 2018 by the CMS experiment at the LHC in proton-proton collisions at $\sqrt{s}$ = 13 TeV, corresponding to an integrated luminosity of 138 fb$^{-2}$. The search is performed in a single-lepton final state, where the B' quark candidate is reconstructed from an electron or muon, missing transverse momentum, one large-radius jet, and one small-radius jet if the t quark decays leptonically. The originating particles of large-radius jets are identified using a neural-network-based tagger, and the dominant background contributions are modeled from data using a neural autoregressive flow network. This search is the most sensitive to date to the single production of narrow-width B' quarks, excluding singlet B' quarks with $Γ/m_\mathrm{B'}$ = 5% for masses between 0.8 and 1.23 TeV. Limits are also placed on the production cross section of single B' quarks produced in association with t quarks, and on the coupling factor of the B' quark to electroweak bosons.