Mass composition of high-energy cosmic rays and scaling violation in their interactions

Abstract

There has long been controversy over the question of mass composition and interaction characteristics of cosmic rays with energies above ∼10¹² eV since in this region direct determination of particle mass has not been possible and accelerator data on interaction mechanisms have been scarce. Accelerator results in the 1970s led to the suggestion that particle interactions could be represented by the so-called scaling of the type enunciated by Feynman¹. In this model² an asymptotic condition is reached by 10¹¹ eV such that most interaction energy is carried off by a small, constant number of secondaries. Studies of cosmic rays showed that by 10¹⁵ eV if scaling remained valid then the primary mass composition must have changed considerably. An alternative model³ assumes that the mass composition remains unchanged, in which case the interaction characteristics would have to be very different⁴. The advent of the pp̄ collider results, corresponding to an energy (with respect to a stationary target) of ∼2×10¹⁴ eV, now allows us to make a distinction between the two models. Here we present evidence supporting the view that the mass composition of high-energy cosmic rays is not much different from that of lower energy rays, but the scaling model is invalid.