Measurement of the Z boson invisible width at TeV with the ATLAS detector

A measurement of the invisible width of the Z boson using events with jets and missing transverse momentum is presented using 37 ${\text{fb}}^{-1}$ of 13 TeV proton–proton data collected by the ATLAS detector in 2015 and 2016. The ratio of $Z\to \text{inv}$ to $Z\to \ell \ell $ events, where inv refers to non-detected particles and ℓ is either an electron or a muon, is measured and corrected for detector effects. Events with at least one energetic central jet with ${p}_{\text{T}}\ge 110$ GeV are selected for both the $Z\to \text{inv}$ and $Z\to \ell \ell $ final states to obtain a similar phase space in the ratio. The invisible width is measured to be $506±2\phantom{\rule{0.25em}{0ex}}\text{(stat.)}±12\phantom{\rule{0.25em}{0ex}}\text{(syst.)}$ MeV and is the single most precise recoil-based measurement. The result is in agreement with the most precise determination from LEP and the Standard Model prediction based on three neutrino generations.