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DOES THE "KNEE" IN PRIMARY COSMIC RAY SPECTRUM EXIST?
Abstract and Figures
The problem of the knee in primary cosmic ray at energy about 3–5 PeV is the most exciting problem in cosmic ray physics. Since 1958, physicists have been trying to solve this problem. In our opinion, the problem could be solved from the experimental point of view, whereas the primary spectrum would follow a pure power law. A key to the "knee" problem lies in the hadronic structure of EAS and its propagation in the Earth's atmosphere. Neither exotic processes nor new physics are used. An explanation of the approach and some results of Monte Carlo simulations are given below.
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Plain Language Summary
When very large cosmic ray showers (CRS) impact the ground, neutrons are produced in the soil that will rattle around until they become captured by soil particles and release energetic gamma‐rays. This produces a slow explosion of particles emanating from the ground following a CRS impact, and is termed a 'neutron burst'. We present recent observations of neutron bursts from a hand held sized gamma‐ray detector at the High Altitude Water Cherenkov (HAWC) array in Mexico, that exhibit interesting spectral features (the presence of positron annihilation), and an interesting time structure (hundreds of counts within a few ms). Our simulations indicate that Terrestrial gamma‐ray flashes (TGFs, bursts of gamma‐rays associated with lightning) should also produce these neutron bursts. An implication of this work is that existing deployments of ground based TGF instruments, comprised of small gamma‐ray detectors, can additionally be used to observe signatures of large cosmic ray showers on clear days.
It is shown that recent experimental data in the region of the knee in the cosmic ray spectrum are somewhat contradictory and new approaches are needed to solve the so-called knee problem. The RRISMA project that we propose is based on the simple idea of giving priority to detecting and studying hadrons as the major EAS component. Special detectors are therefore developed. The experiment should be conducted high in the mountains (the higher the better), where the number of hadrons is higher. We therefore proposed combining PRISMA and the LHAASO (Large High Altitude Air Shower Observatory) now under construction in Tibet 4300 m above sea level.
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