Search for quarks in cosmic rays at sea level

A search has been made for fractionally charged particles in cosmic rays by using a telescope composed of 5 scintillation counters and 16 wire spark chambers. The geometric factor for acceptance of particles is 5 200 cm2 sr. Wire chambers are used to ensure that one and only one charged particle has passed through the counters. During about 800 hours of observation no event has been found which could be accepted as due to the passage of quarks. The upper limit of their intensity in cosmic rays is placed at 3.1 × 10−10 cm−2 sr−1 s−1.