Measurement of the mass of theBs0meson

We measure the mass of the ${\mathit{B}}_{\mathit{s}}^0$ meson by reconstructing the decay chain ${\mathit{B}}_{\mathit{s}}^0$→J/ψφ, J/ψ→${\mathrm{\mu }}^{+}$ ${\mathrm{\mu }}^{\mathrm{-}}$, and φ→${\mathit{K}}^{+}$ ${\mathit{K}}^{\mathrm{-}}$. The data are obtained from 19.3 ${\mathrm{pb}}^{\mathrm{-}1}$ of integrated luminosity of p¯p collisions at √s=1.8 TeV using the Collider Detector at Fermilab. A sample of 80 000 inclusive J/ψ→${\mathrm{\mu }}^{+}$ ${\mathrm{\mu }}^{\mathrm{-}}$ events is used to study systematic biases in track reconstruction and to calibrate the momentum scale. We reconstruct the kinematically similar decays ${\mathit{B}}^{+}$→J/ψ${\mathit{K}}^{+}$ and ${\mathit{B}}^0$→J/ψ${\mathit{K}}^{\mathrm{*}0}$ to study the mass measurement technique used for the ${\mathit{B}}_{\mathit{s}}^0$ meson. Based on the observation of 32 ± 6 candidates, the mass of the ${\mathit{B}}_{\mathit{s}}^0$ meson is measured to be 5369.9 ± 2.3 ± 1.3 MeV/${\mathit{c}}^2$ and the mass difference between ${\mathit{B}}_{\mathit{s}}^0$ and the average mass of ${\mathit{B}}^{+}$ and ${\mathit{B}}^0$ is determined to be 89.7 ± 2.7 ± 1.2 MeV/${\mathit{c}}^2$. © 1996 The American Physical Society.