A measurement of the invisible partial decay width of the $Z$ boson is presented which constitutes a precision test of the electroweak structure of the Standard Model of particle physics. The $Z$ boson decay width into invisible particles is measured with the ATLAS detector at the Large Hadron Collider using 37 $\textrm{fb}^{-1}$ recorded proton-proton collisions at a centre-of-mass energy of 13 TeV.
Events with missing transverse momentum and at least one highly energetic jets are compared to events with $Z$ boson decays into pairs of electrons or muons associated with jets. The corresponding ratios are corrected for detector effects and combined to form a ratio of branching fractions $\hat{R}^{\textrm{miss}}$. Combining this ratio with the leptonic $Z$ boson width measured at the Large Electron-Positron Collider yields $\Gamma(Z\rightarrow\textrm{inv})$ = $506\pm2 ~(\text{stat.}) \pm12 ~(\text{syst.}) \,\text{MeV}$. This result is in excellent agreement with the Standard Model prediction as well as previous measurements, and represents the single most precise recoil-based measurement of the invisible partial width of the $Z$ boson.