Composition-sensitive parameters measured with the surface detector of the Pierre Auger Observatory

THE PIERRE AUGER COLLABORATION (AUTOR 384 DE 427); M. J. TUEROS

Mérida, México

Conferencia; 30th International Cosmic Ray Conference; 2007

Instituto de Geofísica, UNAM

A key step towards the understanding of the origin of ultra-high energy cosmic rays is their mass composition. Primary photons and neutrinos produce markedly different showers from nuclei, while showers of different nuclear species are not easy to distinguish. To maximise the discrimination with the Pierre Auger Observatory ideally all mass-sensitiveobservables should be combined, but the 10% duty cycle of the fluorescence detector limitsthe use of direct measurements of shower maximum at the highest energies. Therefore, weinvestigate mass-sensitive observables accessible with the surface detectors alone. These arethe signal risetime in the Cherenkov stations, the curvature of the shower front, the muon-to- electromagnetic ratio, and the azimuthal signal asymmetry. Risetime and curvature depend mainly on the depth of the shower development in the atmosphere, and thus on primary energy and mass. The muon content of a shower depends on the primary energy and the number of nucleons, while asymmetry about the shower core is due to geometric effects and attenuation, which are dependent on the primary mass. The mass sensitivity of these variables is demonstrated and their application for composition studies is discussed.