Search for single production of a vector-like T quark decaying to a top quark and a Z boson in the final state with jets and missing transverse momentum at $\sqrt{s} =$ 13 TeV

TL;DR

This paper reports a search for single production of a vector-like T quark decaying into a top quark and a Z boson, using 13 TeV proton-proton collision data from the CMS experiment, setting new limits on production cross sections.

Contribution

First search for single T quark production using the full LHC Run 2 dataset, exploring a wide mass range and decay widths, with improved sensitivity and limits.

Findings

Set upper limits on cross section times branching ratio between 15 and 836 fb.

Excluded T quark masses between 0.6 and 1.8 TeV for various decay widths.

Provided the most stringent limits to date for this decay channel.

Abstract

A search is presented for single production of a vector-like T quark with charge 2/3 $e$, in the decay channel featuring a top quark and a Z boson, with the top quark decaying hadronically and the Z boson decaying to neutrinos. The search uses data collected by the CMS experiment in proton-proton collisions at a center-of-mass energy of 13 TeV, corresponding to an integrated luminosity of 137 fb$^{-1}$ recorded at the CERN LHC in 2016-2018. The search is sensitive to a T quark mass between 0.6 and 1.8 TeV with decay widths ranging from negligibly small up to 30% of the T quark mass. Reconstruction strategies for the top quark are based on the degree of Lorentz boosting of its final state. At 95% confidence level, the upper limit on the product of the cross section and branching fraction for a T quark of small decay width varies between 15 and 602 fb, depending on its mass. For a T quark with decay widths between 10 and 30% of its mass, this upper limit ranges between 16 and 836 fb. For most of the studied range, the results provide the best limits to date. This is the first search for single T quark production based on the full Run 2 data set of the LHC.