Precision measurement of the B0 meson lifetime using B0→J/ψK∗0 decays with the ATLAS detector

A measurement of the B0 meson lifetime using B0→J/ψK∗0 decays in data from 13 TeV proton–proton collisions with an integrated luminosity of 140fb-1 recorded by the ATLAS detector at the LHC is presented. The measured effective lifetime is (Formula presented.) The average decay width extracted from the effective lifetime, using parameters from external sources, is (Formula presented.) where the uncertainties are statistical, systematic and from external sources. The earlier ATLAS measurement of Γs in the Bs0→J/ψϕ decay was used to derive a value for the ratio of the average decay widths Γd and Γs for B0 and Bs0 mesons respectively, of (Formula presented.) 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.