13.—A Search for the Quark in Extensive Air Showers, using a Counter-controlled Cloud Chamber

SynopsisA search is reported for the relativistic e/3 quark among the cores of Extensive Air Showers initiated by primaries with energies greater than 1014 eV. The detector is a high-pressure cloud chamber filled with helium at 28 atmospheres, and is counter controlled. The experimental conditions avoid the criticisms levelled at the McCusker experiment and are such that the tracks of e/3 quarks cannot be simulated by singly charged shower particles either through statistical variations in primary ionisation or otherwise. The primary ionisation density, measured using a gap-counting technique on post-expansion electron and muon tracks, is compared with predictions from the theory of Budini et al. (1960). The agreement achieved shows that the theory is a reliable foundation for methods of identifying quark candidates, and measuring charges. The experiment has been running for 5000 hours. No quark candidates have been found. With an acceptance angle of 0·3 sr and an area of 140 cm2, this sets the upper limit of flux of e/3 quarks at 4 × 10−9 cm−2 sec−1 sr−1 with 95 per cent, confidence. The experiment is being continued.