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

THE PIERRE AUGER COLLABORATION (471 AUTHORS IN ALPHABETICAL ORDER); GARCIA, B

PHYSICAL REVIEW D

AMER PHYSICAL SOC

Lugar: New York; Año: 2016 vol. 97 p. 1 - 16

1550-7998

P { margin-bottom: 0.21cm; }Theazimuthal asymmetry in the risetime of signals in Auger surfacedetector stations is a source of information on shower development.The azimuthal asymmetry is due to a combination of the longitudinalevolution of the shower and geometrical effects related to the anglesof incidence of the particles into the detectors. The magnitude ofthe effect depends upon the zenith angle and state of development ofthe shower and thus provides a novel observable, (sec θ)max,sensitive to the mass composition of cosmic rays above3×1018eV.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-raymass increases slowly with energy, as has been inferred from otherstudies. 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 further deficiencies in ourunderstanding of shower modeling that mustbe resolved before the mass composition can be inferred from (secθ)max