Measurement of the associated production of a single top quark and a Z boson in pp collisions at $\sqrt{s} =$ 13 TeV

TL;DR

This paper reports the first measurement of the production cross section of a single top quark in association with a Z boson at 13 TeV, using CMS data, with a significance of 3.7 standard deviations.

Contribution

It provides the first measurement of the tZq production cross section at 13 TeV using final states with three leptons, improving understanding of top quark and electroweak boson interactions.

Findings

Measured cross section: 123^{+33}_{-31} fb

Observed significance: 3.7 standard deviations

Expected significance: 3.1 standard deviations

Abstract

A measurement is presented of the associated production of a single top quark and a Z boson. The study uses data from proton-proton collisions at $\sqrt{s} =$ 13 TeV recorded by the CMS experiment, corresponding to an integrated luminosity of 35.9 fb$^{-1}$. Using final states with three leptons (electrons or muons), the tZq production cross section is measured to be $\sigma$(pp$\to$tZq$\to$Wb$\ell^+\ell^-$q) = $123 ^{+33}_{-31}$ (stat) $^{+29}_{-23}$ (syst) fb, where $\ell$ stands for electrons, muons, or $\tau$ leptons, with observed and expected significances of 3.7 and 3.1 standard deviations, respectively.