Production and decay of a pair of bottom mesons, one charged and one neutral, have been observed in a 200-TeV cosmic-ray helium interaction in an emulsion chamber. Analysis of the event indicates that the charged meson decays most probably via a $b\to \mu$ quark transition, which would imply a nonzero $V_{\mu b}$ element in the Kobayashi-Maskawa matrix. The simplest decay scheme consistent with the data is $B^{-}\to D_s^{-}\eta \eta$. The neutral decay is interpreted as $B^0\to D^{-}{e}^{+}\nu$.

• Received 18 December 1989

DOI:https://doi.org/10.1103/PhysRevD.41.3336