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

H. WAHLBERG Y PIERRE AUGER COLLABORATION

PHYSICAL REVIEW D

AMER PHYSICAL SOC

Lugar: New York; Año: 2016

1550-7998

The azimuthal asymmetry in the risetime of signals in Auger surface detector stations is a source of informationon shower development. The azimuthal asymmetry is due to a combination of the longitudinal evolutionof the shower and geometrical effects related to the angles of incidence of the particles into the detectors. Themagnitude of the effect depends upon the zenith angle and state of development of the shower and thus providesa novel observable, (sec )max, sensitive to the mass composition of cosmic rays above 3 1018 eV. Bycomparing measurements with predictions from shower simulations, we find for both of our adopted models ofhadronic physics (QGSJETII-04 and EPOS-LHC) an indication that the mean cosmic-ray mass increases slowlywith energy, as has been inferred from other studies. However, the mass estimates are dependent on the showermodel and on the range of distance from the shower core selected. Thus the method has uncovered furtherdeficiencies in our understanding of shower modelling that must be resolved before the mass composition canbe inferred from (sec )max.