The possibility for the existence of a leptophobic $U(1)$
gauge boson associated to baryon symmetry is scrutinized in the
MeV-GeV mass range by means of
an exhaustive analysis of the corresponding golden channels
$\eta\to\pi^0\gamma\gamma$ and $\phi\to\pi^0\eta\gamma$.
Using the latest experimental data on these two processes and
taken also into account the Standard Model contributions from
scalar and vector meson exchanges,
we are able to obtain the best 95\% exclusion limits up-to-date
of the mass $m_B$ and coupling $\alpha_B$ to known particles
of this hypothetical $B$ boson.