Inferences on mass composition and tests of hadronic interactions from 0.3 to 100 EeV using the water-Cherenkov detectors of the Pierre Auger Observatory

H. WAHLBERG Y PIERRE AUGER COLLABORATION

PHYSICAL REVIEW D

AMER PHYSICAL SOC

Lugar: New York; Año: 2017

1550-7998

We present a new method for probing the hadronic interaction models at ultra-high energy and extracting details about mass composition. This is done using the time profiles of the signals recordedwith the water-Cherenkov detectors of the Pierre Auger Observatory. The profiles arise from a mixof the muon and electromagnetic components of air-showers. Using the risetimes of the recordedsignals we define a new parameter, which we use to compare our observations with predictions fromsimulations. We find, firstly, inconsistencies between our data and predictions over a greater energyrange and with substantially more events than in previous studies. Secondly, by calibrating the newparameter with fluorescence measurements from observations made at the Auger Observatory, wecan infer the depth of shower maximum Xmax for a sample of over 81,000 events extending from 0.3EeV to over 100 EeV. Above 30 EeV, the sample is nearly fourteen times larger than currently available from fluorescence measurements and extending the covered energy range by half a decade. Theenergy dependence of hXmaxi is compared to simulations and interpreted in terms of the mean ofthe logarithmic mass. We find good agreement with previous work and extend the measurementof the mean depth of shower maximum to greater energies than before, reducing significantly thestatistical uncertainty associated with the inferences about mass composition.