A new technique for the observation of EeV and ZeV cosmic rays

Abstract

We describe a new technique tor the detection of EeV (10 18 eV) and ZeV (10 21 eV) cosmic rays in the atmosphere. The technique uses the fact that the Čerenkov light emitted by atmospheric extensive showers generated by primaries in this energy range is brighter than the fluctuations in the ambient light of the night sky, even with a full moon present. The Cerenkov light is also brighter than fluctuations in the twilight sky, and can even be of similar size as fluctuations in direct sunlight. For the highest energy cosmic rays ( E > 1 ZeV), this may allow optical detection with on-time efficiency limited only by the weather. The energy, angular, and X max resolution of the technique is examined as a function of the background day and night sky conditions. Using a “shadowing” method for determining the direction of the original cosmic ray primary, angular resolution between 0.3° to − 3 ° is possible, depending upon the zenith angle and energy of the primary, and the amount of background light. This resolution is equal to or better than the expected angular resolution obtained through the usual timing techniques. The technique gives an energy resolution 3% < ΔE/E < 40%, and X max resolution 18 g cm −2 < δ X max < 70 g cm −2, dependent upon primary energy, zenith angle, and sky conditions.