Observation of single top quark production in association with a Z boson in proton-proton collisions at $\sqrt{s} =$ 13 TeV

Understand

The observation of single top quark production in association with a Z boson and a quark (tZq) is reported.

• Events from proton-proton collisions at a center-of-mass energy of 13 TeV containing three charged leptons (either electrons or muons) and at least two jets are analyzed.
• The data were collected with the CMS detector in 2016 and 2017, and correspond to an integrated luminosity of 77.4 fb$^{-1}$.
• The increased integrated luminosity, a multivariate lepton identification, and a redesigned analysis strategy improve significantly the sensitivity of the analysis compared to previous searches for tZq production.