EAS Phenomenology and Cosmic Ray Spectrum Ground Based Measurements
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ELEMENTARY PARTICLES AND FIELDS Experiment
EAS Phenomenology and Cosmic Ray Spectrum Ground Based Measurements Yu. V. Stenkin1), 2)* Received July 10, 2019; revised July 10, 2019; accepted July 10, 2019
Abstract—Primary cosmic ray energy spectrum around and above 1 PeV is of great interest due to its non-power-law behavior (“knee”) in PeV region found many years ago using the indirect EAS (Extensive Air Shower) method. The method is based on secondary particles measuring on Earth’s surface under a thick atmosphere. Traditionally, people use detectors sensitive to ionization produced mostly by secondary electromagnetic component and therefore any found changes in EAS size spectrum correspond to secondary components, which have to be recalculated to primary spectrum. Recently some new “knees” were claimed by high altitude experiments: at ∼45 TeV for all-particle spectrum (HAWC), for primary protons and helium: at ∼400 TeV (Tibet ASγ) and at ∼700 TeV (ARGO-YBJ) thus widening the “knee” region from ∼0.045 to 5 PeV. The natural explanation of such a strange spectrum behavior in a wide energy range could be found in the EAS phenomenological approach to the knee problem. DOI: 10.1134/S1063778819660475
INTRODUCTION Up to 1949 Extensive Air Shower (EAS) was considered as a pure electro-magnetic (e-m) cascade in the atmosphere. Then Zatsepin [1, 2] had shown that this simplification was not correct and EAS is a hadronic cascade, while the e-m component is produced by π 0 and K 0 decays. This results in that two components are in equilibrium and all EAS features are defined mostly by the hadronic component being a “skeleton” of the shower. The latter means one needs to study hadronic component first of all. But, due to the absence of a cheap, large, and fast enough hadron detector, up to date people measure mostly the e-m component, sometimes muonic one and very rarely hadronic one. Up to date people use the e-m theory of cascade development (NKG-function, ages, Ne , etc.) and use Ne (number of electrons) as energy estimator when recovering primary particle energy. Up to date nobody put lower limit on the primary energy when the EAS method does work properly. Probably this is a reason for appearance of at least 4 various “knees” both for light primaries at ∼400 TeV (Tibet ASγ), at ∼700 TeV (ARGO-YBJ) and for allparticle spectrum and ∼45 TeV (HAWC) at 3–5 PeV (KASCADE and many others) last years. Are all of 1)
Institute for Nuclear Research, Russian Academy of Sciences, Moscow, Russia. 2) National Research Nuclear University MEPhI (Moscow Engineering Physics Institute), Moscow, Russia. * E-mail: [email protected]
them real (astrophysical) or “artificial” (systematic or methodical)? The phenomenological approach to the “knee” problem proposed by us in 2003 [3, 4] allowed one to look to the problem from another point of view and could explain many “puzzles” observed around the “knee” during decades in cosmic ray physics, including the “multiple knees” problem. 1. EAS PHENOMENOLOGY Experimental data accumulated over a long peri
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