Ultrahigh-energy cosmic rays and stable H dibaryon

It is shown that an instanton-induced interaction between quarks produces a very deeply bound H dibaryon with mass below 2M _N , viz., M _H =1718 MeV. Therefore the H dibaryon is predicted to be a stable particle. The reaction of photodisintegration of the H dibaryon to 2Λ in the course of its motion in the cosmic microwave background will result in a new possible cutoff in the cosmic-ray spectrum. This provides an explanation for the ultrahigh-energy cosmic ray events observed above the GZK cutoff as being the result of the strong interaction of high-energy H dibaryons from cosmic rays with nuclei in the Earth’s atmosphere. Pis’ma Zh. éksp. Teor. Fiz. 70, No. 8, 483–486 (25 October 1999) Published in English in the original Russian journal. Edited by Steve Torstveit.