Azimuthal asymmetry in the risetime of the surface detector signals of the Pierre Auger Observatory

Abstract

The azimuthal asymmetry in the risetime of signals in Auger surface detector stations is a source of information on shower development. The azimuthal asymmetry is due to a combination of the longitudinal evolution of the shower and geometrical effects related to the angles of incidence of the particles into the detectors. The magnitude of the effect depends upon the zenith angle and state of development of the shower and thus provides a novel observable, (sec θ)max, sensitive to the 4 mass composition of cosmic rays above 3 × 10 18 eV. By comparing measurements with predictions from shower simulations, we find for both of our adopted models of hadronic physics (QGSJETII-04 and EPOS-LHC) an indication that the mean cosmic-ray mass increases slowly with energy, as has been inferred from other studies. However, the mass estimates are dependent on the shower model and on the range of distance from the shower core selected. Thus the method has uncovered further deficiencies in our understanding of shower modelling that must be resolved before the mass composition can be inferred from (sec θ)max.

Tests of hadronic interactions with measurements by Pierre Auger Observatory

“…The composition interpretation of the sec θ max measurements imply, in general, the presence of heavier primaries on average, when compared to the composition expected from the X max measurements (see Ref. [18]). The difference is of order of ∆ ln A ≈ 1.…”

Report on Tests and Measurements of Hadronic Interaction Properties with Air Showers

“…Rise-time of shower front The Pierre Auger Observatory has published mass-composition measurements based on the normalized rise-time [31] and the rise-time asymmetry [32]. The rise-time is the time interval in which the collected surface detector charge rises from 10 % to 50 % of the final value.…”

Radio detection of cosmic rays with the Auger Engineering Radio Array

“…Water Cherenkov detectors (SD) AERA LPDA AERA butterfly, ext+int trig AERA butterfly, int trig AMIGA Unitary Cell beacon FD field of view HEAT field of view that this energy can be determined with a resolution of 17% or better [7]. Many different approaches exist to determine the cosmic-ray energy from radio measurements [2].…”