Reconstruction of air shower muon densities using segmented counters with time resolution

Abstract

Despite the significant experimental effort made in the last decades, the origin of the ultra-high energy cosmic rays is still largely unknown. Key astrophysical information to identify where these energetic particles come from is provided by their chemical composition. It is well known that a very sensitive tracer of the primary particle type is the muon content of the showers generated by the interaction of the cosmic rays with air molecules. We introduce a likelihood function to reconstruct particle densities using segmented detectors with time resolution. As an example of this general method, we fit the muon distribution at ground level using an array of counters like AMIGA, one of the Pierre Auger Observatory detectors. For this particular case we compare the reconstruction performance against a previous method. With the new technique, more events can be reconstructed than before. In addition the statistical uncertainty of the measured number of muons is reduced, allowing for a better discrimination of the cosmic ray primary mass.

Direct Measurement of the Muon Density in Air Showers with the Pierre Auger Observatory

“…8. The evolution of ρ 35 has been fitted as a power law ρ 35 (E; a, b) = a(E/10 18 eV) b (6) with a maximum likelihood approach [13,14] taking into account both the threshold effect that is caused by the application of an energy cut to data, and the uncertainties in the muon density and energy estimates. The best fit solution is a = (1.75 ± 0.05(stat) ± 0.05(sys)) m −2…”

“…where N seg = 64 is the number of detector segments. The total number of muonsμ = N i=1μ i is obtained by summing over all N time windows [6].…”

An improved reconstruction method for the AMIGA detectors

“…Then, as shown in Ref. [7], the bias due to muon pile-up can be corrected by means of the unbiased statistical correction where N s,cor is the number of corrected signals and N seg = 64 is the segmentation of a module.…”

The AMIGA underground muon detector of the Pierre Auger Observatory - performance and event reconstruction

“…The AMIGA underground muon detector Ana Martina Botti SD-750 reconstruction [10]. The muon lateral distribution function (MLDF) [9] was fitted using only the counter mode. Note that the reconstruction of data with the two modes is not expected to entirely agree at this point, as the final corrections for different sources of bias (from clipping corners, noise, etc.…”