p-air cross-section measurement at 1018.5 eV

The interaction cross-section is one of the fundamental properties of any elementary particle. For decades, only accelerator measurements of the particle cross-sections were available. Crosssection measurements at higher and higher energy become possible as more and more powerful accelerators are introduced. However, cosmic rays not only provide a constant flux of ultra highenergy particles, but also supply particles with energies inaccessible by modern accelerators already in service or planned. Particle cross-section measurements using cosmic rays have their difficulties, however. The cosmic ray flux is very low at ultra-high energies, and there is no direct method to measure the particle cross-section using cosmic rays. These difficulties can be overcome by using cosmic ray detectors with large aperture and specially developed measurement techniques. In this work, a novel de-convolution technique to measure the p-air inelastic cross-section using cosmic ray data is discussed in detail. This technique, applied to the data from HiRes stereo fluorescence cosmic ray detector allows us to measure this cross-section at 10 eV for the first time.