Search for Fractionally Charged Particles in Showers of Low Density

A search was made for relativistic quarks of charge e/3 in cosmic-ray showers at sea level. A hodoscope of wire proportional counters was used, which was capable of measuring location and specific ionization of several particles arriving simultaneously. An upper limit for the flux of quarks observed singly in the apparatus was established, with 90% confidence, at 1.9 ×{} 10^-9 sec^-1 cm^-2 sr^-1. Corresponding limits were set for quarks with one and two accompanying particles at, respectively, 6.5 ×{} 10^-10 sec^-1 cm^-2 sr^-1 and 2.2 ×{} 10^-9 sec^-1 cm^-2 sr^-1.