Search for the Familon via $B^{\pm}\to \pi^{\pm}X^{0}$, $B^{\pm}\to K^{\pm}X^{0}$, and $B^{0}\to K_{S}^{0} X^{0}$ Decays

We have searched for the two-body decay of the B meson to a light pseudoscalar meson $h = \pi^+, K^+, K^0_S$ and a massless neutral weakly-interacting particle $X^0$ such as the familon, the Nambu-Goldstone boson associated with a spontaneously broken global family symmetry. We find no significant signal by analyzing a data sample containing 9.7 million $B\bar{B}$ mesons collected with the CLEO detector at the Cornell Electron Storage Ring, and set a 90% C.L. upper limit of $4.9 \times 10^{-5}$ and $5.3 \times 10^{-5}$ on the branching fraction for the decays $B^+ \to h^+ X^0$ and $B^0 \to K^0_S X^0$, respectively. These upper limits correspond to a lower bound of about $10^{8}$ GeV on the family symmetry breaking scale involving the third generation of quarks.