Measurement of the Proton-Air Cross Section with Telescope Arrays Black Rock, Long Ridge, and Surface Array in Hybrid Mode

Ultra High Energy Cosmic Ray (UHECR) detectors have been reporting on the proton-air cross section measurement beyond the capability of particle accelerators since 1984. The knowledge of this fundamental particle property is vital for our understanding of high energy particle interactions and could possibly hold the key to new physics. The data used in this work was collected over eight years using the hybrid events of Black Rock (BR) and Long Ridge (LR) fluorescence detectors as well as the Telescope Array Surface Detector (TASD). The proton-air cross section is determined at √s = 73 TeV by fitting the exponential tail of the X_max distribution of these events. The proton-air cross section is then inferred from the exponential tail fit and from the most updated high energy interaction models. σ_p^inel_−air is observed to be 520.1 ± 35.8 [Stat.] ⁺₋²⁵₄₂³₉[Sys.] mb. This is the second proton-air cross section work reported by the Telescope Array collaboration.