ATLAS collaboration (2855 authors)Aguilar-Saavedra, Juan AntonioAmor Dos Santos, Susana PatriciaAnjos, NunoAraque, Juan PedroCantrill, RobertCarvalho, JoãoCastro, Nuno FilipeConde Muiño, PatriciaDa Cunha Sargedas De Sousa, Mario JoseFiolhais, MiguelGalhardo, BrunoGomes, AgostinhoGonçalo, RicardoJorge, PedroLopes, LourencoMachado Miguens, JoanaMaio, AméliaManeira, JoséOleiro Seabra, Luis FilipeOnofre, AntónioPalma, AlbertoPedro, RuteSantos, HelenaSaraiva, JoãoSilva, JoséTavares Delgado, AdemarVeloso, FilipeWolters, Helmut2019-02-042019-02-042016-06-14http://dx.doi.org/10.1007/JHEP06(2016)081http://hdl.handle.net/10400.26/27093This paper presents the measurement of the relative width difference ΔΓ$_{d}$ /Γ$_{d}$ of the $ {B}^0\hbox{-} {\overline{B}}^0 $ system using the data collected by the ATLAS experiment at the LHC in pp collisions at $ \sqrt{s}=7 $ TeV and $ \sqrt{s}=8 $ TeV and corresponding to an integrated luminosity of 25.2 fb$^{−1}$. The value of ΔΓ$_{d}$ /Γ$_{d}$ is obtained by comparing the decay-time distributions of B$^{0}$ → J/ψK$_{S}$ and B$^{0}$ → J/ψK$^{*0}$(892) decays. The result is ΔΓ$_{d}$ /Γ$_{d}$ = (−0.1±1.1 (stat.)± 0.9 (syst.)) × 10$^{−2}$. Currently, this is the most precise single measurement of ΔΓ$_{d}$ /Γ$_{d}$ . It agrees with the Standard Model prediction and the measurements by other experiments.engjournal article2019-02-04