Light U(1) Gauge Boson Coupled to Baryon Number

We discuss the phenomenology of a light U(1) gauge boson, $\gamma_B$, that couples only to baryon number. Gauging baryon number at high energies can prevent dangerous baryon-number violating operators that may be generated by Planck scale physics. However, we assume at low energies that the new U(1) gauge symmetry is spontaneously broken and that the $\gamma_B$ mass $m_B$ is smaller than $m_Z$. We show for $m_\Upsilon<m_B<m_Z$ that the $\gamma_B$ coupling $\alpha_B$ can be as large as $\sim 0.1$ without conflicting with the current experimental constraints. We argue that $\alpha_B\sim 0.1$ is large enough to produce visible collider signatures and that evidence for the $\gamma_B$ could be hidden in existing LEP data. We show that there are realistic models in which mixing between the $\gamma_B$ and the electroweak gauge bosons occurs only as a radiative effect and does not lead to conflict with precision electroweak measurements. Such mixing may nevertheless provide a leptonic signal for models of this type at an upgraded Tevatron.