Search for particles with charge 2/3e in cosmic rays

Abstract
The flux of particles with charge equal to of the electron charge which reach sea level from the vertical with relativistic velocities was found to be less than 2.7 × 10−10 cm−2 sr−1 s−1 at 90% confidence level. The particles were identified through their characteristic energy loss in a 48-counter hodoscope. The result seems inconsistent with a model of hadrons as being a composite of quarks.