We have searched for a particle which combines the properties of a tachyon with those of a magnetic monopole. The tachyon monopole is assumed to exist in cosmic rays striking the earth and to be influenced by the extensive magnetic fringing field of Fermilab's 15-ft bubble chamber. By hypothesizing that the tachyon monopoles will either emit Cherenkov radiation in air or ionize Lexan plastic we set an upper limit of 5 × ${10}^{-12\mathrm{}}$ ${\mathrm{cm}}^{-2\mathrm{}}$ ${\sec }^{-1\mathrm{}}$ on their flux.

• Received 26 June 1978

DOI:https://doi.org/10.1103/PhysRevD.18.2253