Measurement of the Z boson invisible width at $\sqrt{s}=13$ 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 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 $Z\to \mathrm{\ell }\mathrm{\ell }$ events, where inv refers to non-detected particles and $\mathrm{\ell }$ 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 $Z\to \mathrm{\ell }\mathrm{\ell }$ final states to obtain a similar phase space in the ratio. The invisible width is measured to be $506\pm 2\text{ (stat.)}\pm 12\text{ (syst.)}$ 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.