Measurement of the fluctuations in the depth of maximum of showers produced by primary particles of energy greater than 1.5×1017eV

Abstract

Measurements of the RMS fluctuation of the depth of shower maximum sigma (X_m) as a function of energy are reported from 1.5*10¹⁷ to 10¹⁹ eV. The results are based on a study of the risetimes of pulses recorded from four 34 m² water-Cerenkov detectors in 2691 showers having zenith angle less than 40 degrees . The energy dependence of sigma (X_m) is determined and found to be in reasonable agreement with what is expected for a constant mass composition and an energy-dependent nucleon-air cross section.