Sensitivity Of Cosmic Ray Knee Composition Seen By A Hadron Calorimeter Plus ARGO

Ground-based air-shower experiments observe cosmic rays with energies up to 100EeV(10²⁰ eV). Measurements so far reported suggest that the slope of the all-particle spectrum in the energy range of about 100-1000TeV is somewhat flatter than that observed at lower energies, while at higher energies over several times 1000TeV the energy spectrum becomes steeper with the slope of about -3.0.The break in the overall spectrum at around 1000TeV is often referred to as the "knee"in the spectrum. It is commonly understood that the knee of the primary cosmic ray spectrum has its origin in the acceleration and propagation of high energy cosmic rays in the Galaxy.While there is no consensus on the origin of cosmic rays with energies beyond the knee, observations of cosmic rays in such a high energy region may naturally stand in need of another acceleration mechanisms or new cosmic ray source.Thus, measurements of the primary cosmic rays around the knee are very important and its composition is fundamental input for understanding the particle acceleration mechanism that pushes cosmic rays to very high energies. However, because of extremely low and steeply decreasing flux at high energies, direct measurement of primary cosmic rays on board balloons are still limited in the energy region to below a few hundred TeV. To date, the knee composition of primary cosmic rays has been studied by observing air shower with a large ground-based apparatus.In order to study the composition around the knee, measurements of muon content in each air shower or muons in deep underground , measurements of lateral distribution of air shower Cherenkov lights, or maximum depth of shower using air Cherenkov telescopes, and multiparameter measurements of air shower have been carried out and devoted to drawing a conclusion about the knee composition. In spite of great efforts so far, however, there is a divergence of conclusion on the composition from experiment to experiment and the knee composition is still the question at issue. Another approach may be required to get more direct information about the composition.