Measurement of the relative width difference of the B⁰-B⁰ system with the ATLAS detector

This paper presents the measurement of the relative width difference ΔΓd/Γd of the B⁰-B⁰ system using the data collected by the ATLAS experiment at the LHC in pp collisions at √s=7 TeV and √s=8 TeV and corresponding to an integrated luminosity of 25.2 fb⁻¹. The value of ΔΓd/Γd is obtained by comparing the decay-time distributions of B⁰→J/ψKS and B⁰→J/ψK*⁰(892) decays. The result is ΔΓd/Γd =(−0.1±1.1 (stat.)±0.9 (syst.))×10⁻². Currently, this is the most precise single measurement of ΔΓd/Γd. It agrees with the Standard Model prediction and the measurements by other experiments.