Measurement of the Z boson invisible width at $\sqrt{s}=13$ TeV with the ATLAS detector

Abstract

A measurement of the invisible width of the $Z$ boson using events with jets and missing transverse momentum is presented using 37 $\mbox{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 $\ell$ 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 $Z\to \ell \ell$ 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.

41 pages in total, author list starting page 24, 7 figures, 1 table, published in Phys. Lett. B 854 (2024) 138705. All figures including auxiliary figures are available at https://atlas.web.cern.ch/Atlas/GROUPS/PHYSICS/PAPERS/STDM-2019-01