Measurement of the relative width difference of the $B^0$-${\bar{B}}^0$ system with the ATLAS detector

Abstract

This paper presents the measurement of the relative width difference $\Delta {\Gamma }_d/{\Gamma }_d$ of the $B^0$-${\bar{B}}^0$ 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 $\Delta {\Gamma }_d/{\Gamma }_d$ is obtained by comparing the decay-time distributions of $B^0\to J/\psi K_S$ and $B^0\to J/\psi K^{\ast 0}(892)$ decays. The result is $ΔΓ_d / Γ_d = (-0.1 \pm 1.1~\mbox{(stat.)} \pm 0.9~\mbox{(syst.)}) \times 10^{-2}$. Currently, this is the most precise single measurement of $\Delta {\Gamma }_d/{\Gamma }_d$. It agrees with the Standard Model prediction and the measurements by other experiments.

20 pages plus author list + cover page (38 pages total), 5 figures, 2 tables, submitted to Journal of High Energy Physics, All figures including auxiliary figures are available at http://atlas.web.cern.ch/Atlas/GROUPS/PHYSICS/PAPERS/BPHY-2015-01/