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Abstract

A measurement of the B0 meson lifetime using B0 → J/ψ K∗0 decays in data from 13 TeV proton–proton collisions with an integrated luminosity of 140 fb−1 recorded by the ATLAS detector at the LHC is presented. The measured effective lifetime is τ = 1.5053 ± 0.0012 (stat.) ± 0.0035 (syst.) ps. The average decay width extracted from the effective lifetime, using parameters from external sources, is d = 0.6639 ± 0.0005 (stat.) ± 0.0016 (syst.) ±0.0038 (ext.) ps−1, where the uncertainties are statistical, systematic and from external sources. The earlier ATLAS measurement of s in the B0 s → J/ψφ decay was used to derive a value for the ratio of the average decay widths d and s for B0 and B0 s mesons respectively, of d s = 0.9905±0.0022 (stat.)±0.0036 (syst.)±0.0057 (ext.). The measured lifetime, average decay width and decay width ratio are in agreement with theoretical predictions and with measurements by other experiments. This measurement provides the most precise result of the effective lifetime of the B0 meson to date.