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

THE PIERRE AUGER COLLABORATION; GARCIA, B (500 AUTHORS IN ALPHABETICAL ORDER)

PHYSICAL REVIEW D

AMER PHYSICAL SOC

Lugar: New York; Año: 2017 vol. 96 p. 1 - 22

1550-7998

p { margin-bottom: 0.1in; line-height: 115%; }Wepresent a new method for probing the hadronic interaction models atultrahigh energy and extracting details about mass composition. Thisis done using the time profiles of the signals recorded with thewater-Cherenkov detectors of the Pierre Auger Observatory. Theprofiles arise from a mix of the muon and electromagnetic componentsof air showers. Using the risetimes of the recorded signals, wedefine a new parameter, which we use to compare our observations withpredictions from simulations. We find, first, inconsistencies betweenour data and predictions over a greater energy range and withsubstantially more events than in previous studies. Second, bycalibrating the new parameter with fluorescence measurements fromobservations made at the Auger Observatory, we can infer the depth ofshower maximum Xmaxfor a sample of over 81,000 events extending from 0.3 to over100 EeV. Above 30 EeV, the sample is nearly 14 times larger than whatis currently available from fluorescence measurements and extendingthe covered energy range by half a decade. The energy dependence of <Xmax> iscompared to simulations and interpreted in terms of the mean of thelogarithmic mass. We find good agreement with previous work andextend the measurement of the mean depth of shower maximum to greaterenergies than before, reducing significantlythe statistical uncertainty associated with the inferences about masscomposition