This Letter reports a search for the production by $e^{+}$$e^{\mathrm{-}}$ annihilation of a single photon accompanied by particles that interact only weakly in matter. The search was performed at the SLAC $e^{+}$$e^{\mathrm{-}}$ storage ring PEP (√s =29 GeV) with a new detector, ASP. No unexpected signal was observed. The limit $N_{\nu }$<14 (90% C.L.) is placed on the number of light neutrino species, and the mass of scalar electrons predicted by theories of supersymmetry is constrained to $m_{ẽ}$>51 GeV/$c^2$ (90% C.L.) for $m_{\gamma ̃}$=0 and degenerate ẽ mass states.

• Received 30 October 1985

DOI:https://doi.org/10.1103/PhysRevLett.56.685