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Register a new userA method to reconstruct the muon lateral distribution with an array of segmented counters with time resolution
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Despite the significant experimental effort made in the last decades, the origin of the ultra high energy cosmic rays is still unknown. The chemical composition of these energetic particles carries key astrophysical information to identify where they come from. It is well known that the muon content of the showers generated by the interaction of the cosmic rays with air molecules, is very sensitive to the primary particle type. Therefore, the measurement of the number of muons at ground level is an essential tool to infer the cosmic ray mass composition. We introduce a novel method to reconstruct the lateral distribution of muons with an array of counters buried underground like AMIGA, one of the Pierre Auger Observatory detector systems. The reconstruction builds on a previous method we recently presented by considering the detector time resolution. With the new method more events can be reconstructed than with the previous one. In addition the statistical uncertainty of the measured number of muons is reduced, allowing for a better primary mass discrimination.
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Although the origin of ultra high energy cosmic rays is still unknown, significant progress has been achieved in last decades with the construction of large arrays that are currently taking data. One of the most important pieces of information comes from the chemical composition of primary particles. It is well known that the muon content of air showers generated by the interaction of cosmic rays with the atmosphere is rather sensitive to primary mass. Therefore, the measurement of the number of muons at ground level is an essential ingredient to infer the cosmic ray mass composition. In this work we present a new method for reconstructing the muon lateral distribution function with an array of segmented counters. The energy range from .4 to 2.5 EeV is considered. For a triangular array spaced at 750 m we found that 450 m is the optimal distance to evaluate the number of muons. The corresponding statistical and systematic uncertainties of the new and of a previous reconstruction methods are compared. Since the statistical uncertainty of the new reconstruction is less than in the original one, the power to discriminate between heavy and light cosmic ray primaries is enhanced. The detector dynamic range is also extended in the new reconstruction, so events falling closer to a detector can be included in composition studies.
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.
The origin and nature of the cosmic rays is still uncertain. However, a big progress has been achieved in recent years due to the good quality data provided by current and recent cosmic-rays observatories. The cosmic ray flux decreases very fast with energy in such a way that for energies $gtrsim 10^{15}$ eV, the study of these very energetic particles is performed by using ground based detectors. These detectors are able to detect the atmospheric air showers generated by the cosmic rays as a consequence of their interactions with the molecules of the Earths atmosphere. One of the most important observables that can help to understand the origin of the cosmic rays is the composition profile as a function of primary energy. Since the primary particle cannot be observed directly, its chemical composition has to be inferred from parameters of the showers that are very sensitive to the primary mass. The two parameters more sensitive to the composition of the primary are the atmospheric depth of the shower maximum and the muon content of the showers. Past and current cosmic-rays observatories have been using muon counters with the main purpose of measuring the muon content of the showers. Motivated by this fact, in this work we study in detail the estimation of the number of muons that hit a muon counter, which is limited by the number of segments of the counters and by the pile-up effect. We consider as study cases muon counters with segmentation corresponding to the underground muon detectors of the Pierre Auger Observatory that are currently taking data, and the one corresponding to the muon counters of the AGASA Observatory, which stopped taking data in 2004.
Aiming to observe cosmic gamma rays in the 10 - 1000 TeV energy region, we propose a 10000 m^2 underground water-Cherenkov muon-detector (MD) array that operates in conjunction with the Tibet air-shower (AS) array. Significant improvement is expected in the sensitivity of the Tibet AS array towards celestial gamma-ray signals above 10 TeV by utilizing the fact that gamma-ray-induced air showers contain far fewer muons compared with cosmic-ray-induced ones. We carried out detailed Monte Carlo simulations to assess the attainable sensitivity of the Tibet AS+MD array towards celestial TeV gamma-ray signals. Based on the simulation results, the Tibet AS+MD array will be able to reject 99.99% of background events at 100 TeV, with 83% of gamma-ray events remaining. The sensitivity of the Tibet AS+MD array will be ~20 times better than that of the present Tibet AS array around 20 - 100 TeV. The Tibet AS+MD array will measure the directions of the celestial TeV gamma-ray sources and the cutoffs of their energy spectra. Furthermore, the Tibet AS+MD array, along with imaging atmospheric Cherenkov telescopes as well as the Fermi Gamma-ray Space Telescope and X-ray satellites such as Suzaku and MAXI, will make multiwavelength observations and conduct morphological studies on sources in the quest for evidence of the hadronic nature of the cosmic-ray acceleration mechanism.
The primary aim of ANTARES is neutrino astronomy with upward going muons created in charged current muon neutrino interactions in the detector and its surroundings. Downward going muons are background for neutrino searches. These muons are the decay products of cosmic-ray collisions in the Earths atmosphere far above the detector. This paper presents a method to identify and count electromagnetic showers induced along atmospheric muon tracks with the ANTARES detector. The method is applied to both cosmic muon data and simulations and its applicability to the reconstruction of muon event energies is demonstrated.
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