Status of the experiment for the search of a dark photon at VEPP–3

The status of the experiment to search for a new gauge boson, A′, in e + e − annihilation by means of a positron beam incident on a gas hydrogen target internal to the bypass at the VEPP-3 storage ringis reported. The search method is based on a missing mass spectra in reaction e + e − → γ A′. It allows observation of the A′ signal independently of its decay modes and life time. The projected result of this experiment corresponds to an upper limit on the square of coupling constant e 2 = (0.2 ÷ 1.0) · 10 −7 with a signal-to-noise ratio of two to one at A′ mass of 5–20 MeV.