A replay of few-body reactions in particle cosmology Original Research Article

The existence of the Greisen-Zatsepin-Kuzmin (GZK) cutoff energy for protons does not preclude the possibility of accelerating protons to energies considerably higher than the GZK cutoff. Rather, it indicates that protons being accelerated to above GZK cutoff energies, subsequently propagating in the cosmic medium while interacting with cosmic background photons, become the source of producing other ultra high energy cosmic rays (UHECRʹs) — some of them, such as GZK neutrinos, could propagate with a much longer mean free path. It is therefore of critical importance to investigate experimentally the neutrino fraction in the high energy cosmic rays, as a function of the cosmic ray energy up to energies beyond the GZK cutoff. In this paper, we wish to demonstrate how the various few-body reactions, so familiar to the audience of the few-body physics community, replay themselves at the highest-energy edge of particle cosmology. As one of our initial attempts, we employ the current state-of-the-art knowledge on photo-pion nucleon reactions to investigate the propagation, in the cosmic medium, of nucleons of energy in the range of (1–6) × 1020eV, i.e. between the GZK cutoff and Λ K production threshold. A sample numerical result is given for illustration.