Search for High-Energy Muons from Cygnus X-3

A total of 1.9×${10}^6$ good-quality high-energy muon events were analyzed from the data of the underground Kamioka nucleon-decay experiment. No definite sign of excess flux was observed in the direction of Cygnus X-3 and in its phase interval of 0.7 to 0.8. The 90%-C.L. (confidence level) upper limit for the excess flux is 2.2×${10}^{-12\mathrm{}}$ ${\mathrm{cm}}^{-2\mathrm{}}$ ${\sec }^{-1\mathrm{}}$ for rock overburden greater than 2400 m of water equivalent.