Measurement of the Mass Difference m(B0) - m(B+)

Abstract

Using 230 × 10 6 B ¯¯¯ B events recorded with the BABAR detector at the e + e − storage rings PEP-II, we reconstruct approximately 4100 B 0 → J / ψ K + π − and 9930 B + → J / ψ K + decays with J / ψ → μ + μ − 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 ± 0.05 ± 0.03 ) MeV / c 2 .