A search for slow, lightly ionizing particles in cosmic rays

A surface search was made using a small-area four-layer scintillator detector. Slow lightly ionizing particles created in cosmic ray interactions in the atmosphere which arrived within 13 ms of the shower front were searched for. In a live time of 2.55 x 10⁵ s 394,608 showers of two or more muons and 21,038 showers of four or more muons were recorded. No multiple muon events were recorded in which a trailing particle was identified above the expected random background, with a velocity between 7.4 x 10⁻⁵c and 6.7 x 10⁻³c. The detector operated without a trigger and used interplanar timing information to identify potential events, and operated above a threshold of 1/400 of that of a minimum ionizing muon.