Measurement of the mass differencem(B0)−m(B+)

Abstract

Using $230\times {10}^6$ $B\overline{B}$ events recorded with the BABAR detector at the $e^{+}{e}^{-}$ storage rings PEP-II, we reconstruct approximately 4100 $B^0\to J/\psi K^{+}{\pi }^{-}$ and 9930 $B^{+}\to J/\psi K^{+}$ decays with $J/\psi \to {\mu }^{+}{\mu }^{-}$ and $e^{+}{e}^{-}$. From the measured $B$-momentum distributions in the $e^{+}{e}^{-}$ rest frame, we determine the mass difference $m(B^0)-m(B^{+})=(+0.33\pm 0.05\pm 0.03)\mathrm{MeV}/c^2$.