Search for highly charged particles in cosmic rays

The recently obtained results on e⁺e^? → hadrons and multigamma production in pp collisions provide some support for a previously made argument that heavy, highly charged subnucleons may exist, and a search for such particles in cosmic rays has been made. In 620 hours no candidates were detected, and an upper limit for the unaccompanied particle flux of 7 · 10^?10 cm^?2 sec^?1 sr^?1 at sea level under 600 g/cm² concrete is obtained with 90% confidence.