Search for Charge-23Quarks Produced by Cosmic Rays

The flux of quarks with a charge equal to $\frac{2}{3}$ the charge of the electron which reach sea level from the vertical with relativistic velocities was measured to be less than 2.0×${10}^{-9\mathrm{}}$ ${\mathrm{cm}}^{-2\mathrm{}}$ ${\mathrm{sr}}^{-1\mathrm{}}$ ${\sec }^{-1\mathrm{}}$ at a 90% confidence level. Particles with fractional charge were identified through their characteristic energy loss in each of seven scintillation counters.