  High-luminosity experiments are able to search for new physics at low
energies, which could have evaded detection thus far due to very weak couplings
to the Standard Model. The DarkLight experiment at Jefferson Lab is designed to
search for a new U(1) vector boson A' in the mass range 10-100 MeV through its
decay A' -> e+ e-. In this paper, we demonstrate that DarkLight is also
sensitive to an A' decaying to invisible final states. We analyze the DarkLight
reach for invisible A' bosons assuming a nominal two month running time,
including the possibility of augmenting the DarkLight design to include photon
detection. We also propose two new analysis techniques that might prove useful
for other high-luminosity searches: a cut on missing energy to improve the
invariant mass resolution, and a cut on the sign of the missing invariant
mass-squared to mitigate pileup. We compare the DarkLight reach to existing
experimental proposals, including a complementary search using the VEPP-3
positron beam.
