The second knee in the cosmic ray spectrum observed with the surface detector of the Pierre Auger Observatory
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et al.; Institute for Cosmic Ray Research (ICRR) Univeristy of Tokyo; International Union of Pure and Applied Physics (IUPAP); JPS; Nagoya Convention and Visitors Bureau; Nagoya University
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The determination of the energy spectrum features with low systematic uncertainty is crucial for interpreting the nature of cosmic rays. In this study, we conducted a measurement of the energy spectrum at the Pierre Auger Observatory using a surface detector with a calorimetric energy scale indirectly set by a fluorescence detector. The surface detector consists of an array of water-Cherenkov detectors that extends over 3000 km2 with 1500 m spacing. Additionally, two nested arrays of the same kind with 750 m and 433 m spacing were utilized to lower the energy threshold of the measurements. This contribution presents, for the first time, the spectrum measured with the 433 m array, which reduces the energy threshold down to 63 PeV, nearly half the energy at which we previously published a steepening using the 750 m array. Our measurements include a characterization of the spectral features of the flux steepening around 230 PeV, known as the second-knee. The study benefits from a nearly 100% duty cycle and geometrical exposure. Notably, this is the first simultaneous measurement of the second knee energy and spectral indexes before and after the break, using a surface detector with an energy scale predominantly independent of air shower simulations and assumptions regarding hadronic interaction models. © Copyright owned by the author(s) under the terms of the Creative Commons.
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Cerenkov counters, Cosmic ray detectors, Cosmic ray measurement, Photons, Cosmic ray spectra, Energy scale, Energy spectrum, Energy thresholds, M-array, Measurements of, Pierre Auger observatory, Spectra features, Surface detectors, Systematic uncertainties, Cosmology
