Search for a Leptophobic B-Boson via $\eta$ Decay at Jlab

A leptophobic $B$-boson couples predominantly to quarks and arises from a new $U(1)_B$ baryon number gauge symmetry. Its leading decay is $B\rightarrow \pi^0\gamma$ for the mass range of 140--620 MeV~\cite{Tulin1204}. This offers a great experimental opportunity to search for such weakly-coupled gauge bosons in the sub-GeV mass range through the doubly-radiative decay $\eta\rightarrow B\gamma\rightarrow\pi^0\gamma\gamma$. The Jlab Eta Factory (JEF) experiment has been recently developed to search for $B$ through this decay channel, with sensitivity to the baryonic fine structure constant as low as $10^{-7}$. This sensitivity indirectly constrains the existence of anomaly cancelling fermions at the TeV-scale. The proposed search for $B$ in the three-photon final state ($B\rightarrow\pi^0\gamma\rightarrow 3\gamma$) is complementary to a world-wide effort searching for a dark heavy photon $A^{\prime}$ at the high-intensity frontier