BEXCO - Room B(103/104/105)
[CRI260] Impact of muon detection thresholds on the separability of primary cosmic rays
Knowledge of the mass composition of cosmic rays in the transition region of galactic to extragalactic cosmic rays would allow for the discrimination of different astrophysical models on their origin, acceleration, and propagation. An important observable to separate different mass groups of cosmic rays is the number of muons in extensive air showers. Currently, both the Pierre Auger and the Telescope Array observatories are planning to extend their experiments with muon detectors to access this crucial shower quantity. The threshold values of the different detector types cover a range from a few MeV up to approximately 1 GeV. We performed a CORSIKA simulation study to analyze the impact of the detection threshold of muons on the separation quality of different primary cosmic rays in the energy region of the ankle. Using only the number of muons as composition-sensitive variable, we find a clear dependence of the separation power on the detection threshold for ideal measurements. Although the number of detected muons increases when lowering the threshold, the discrimination power is reduced. If statistical fluctuations for muon detectors of limited size are taken into account, the threshold dependence remains qualitatively the same for small distances to the shower core but is reduced for large core distances. We interpret the impact of the detection threshold of muons on the composition sensitivity by the change of the correlation of the number of muons N_μ with the shower maximum X_max as function of the muon energy as a result of the underlying hadronic interactions and the shower geometry. We further investigate the role of muons produced by photon-air interactions and conclude that, in addition to the effect of the N_μ − X_max correlation, the separability of primaries is reduced as a consequence of the presence of more muons from photonuclear reactions in proton than in iron showers.