Search for Quarks in High-Energy Air Showers

Quarks of charge $\frac{1}{3}e$ and $\frac{2}{3}e$ have been searched for in air showers of energies between ${10}^{13}$ and ${10}^{15}$ eV. A hodoscope of proportional counters was placed under 15 cm of Pb. Scintillation counters on top of the lead triggered on high-multiplicity showers. No quark was detected in 2120 h. The upper limit of the quark flux in showers between ${10}^{14}$ and ${10}^{15}$ eV is, with 90% confidence, 1.0 × ${10}^{-10\mathrm{}}$ ${\mathrm{cm}}^{-2\mathrm{}}$ ${\sec }^{-1\mathrm{}}$ ${\mathrm{sr}}^{-1\mathrm{}}$ for either charge.