 Solution

For the neutral strange B meson, a charged-current tree amplitude has $\bar{b}\to \bar{c}{W}^{+}$ followed by $W^{+}\to c\bar{s}$, while the initial $s$ is a spectator. The $c\bar{c}$ pair forms the J/psi meson and the $s\bar{s}$ pair forms the phi meson. Charge and quark flavour flow are conserved at each vertex except for the permitted weak flavour change. antiquark arrows point opposite their physical propagation direction.

Useful reconstruction modes are $J/\psi \to {\mu }^{+}{\mu }^{-}$ or $e^{+}{e}^{-}$, through a virtual photon, and $\varphi \to K^{+}{K}^{-}$, a strong decay. The latter is the largest individual $\varphi$ mode, with $K_L^0{K}_S^0$ also important. For the $J/\psi$, the inclusive branching fraction versus reconstruction mode distinction matters: hadronic decays dominate inclusively, principally through three gluons; each charged-lepton pair accounts for about 6%, not most decays. The charm pair lies below open-charm threshold. These distinctions are confirmed by the official particle listings.^[ref]