Greisen–Zatsepin–Kuzmin limit
GZK cutoff is named after the physicists Kenneth Greisen, Georgi Sazepin and Vadim Kuzmin limit ( engl. cutoff) for energy cosmic rays of very distant sources. This limit was calculated by them in 1966.
Charged particles of very high energy 'see' the photon () of the cosmic background radiation strongly blue-shifted and can be spread by them. Proton (p), also bound in atomic nuclei, there are, elastic scattering, the two inelastic processes
And
With an energy threshold of 6 × 1019 eV for the generation of the delta resonance (), which is divided in turn into a proton or neutron and a charged () or neutral () pion. The proton loses about 20 % of its energy and changes direction. If the energy of the proton is still above this threshold, the reaction can take place again. For very distant sources, > 100 million light years, is the probability of getting through without shock, very low. One speaks of GZK suppression.
The experimental results with respect to the highest-energy cosmic rays initially appeared contradictory. While the Agasa experiment the University of Tokyo will have registered particles above the GZK energy, the data of the HiRes collaboration with the GZK cutoff are compatible. The Auger experiment has now confirmed the HiRes results. The extremely rare events beyond the GZK - limit must come from closer sources. Indeed, the observed distribution is correlated with the known direction of the optical area potential sources.
Accurate measurements in the GZK energy can confirm or refute the theory of loop quantum gravity. This says a higher energy threshold than 6 × 1019 eV ahead.