Experimental Limit on the Flux of Relic Antineutrinos from Past Supernovae

We report the result of a search in the Kamiokande II detector for the interactions of electron-type antineutrinos in the energy level 19 to 35 MeV. We measure directly a 90%-C.L. upper limit of 226 ${\mathrm{cm}}^{-2\mathrm{}}$ ${\sec }^{-1\mathrm{}}$ on the flux of electron antineutrinos with energies in that interval. An upper limit on the total flux of relic antineutrinos from past supernovae is obtained as a function of the effective equilibrium temperature of the relic antineutrino sea.