Adiabatic expansion of nuclear matter gas to describe violation of Feynman scaling law in multiple particle production

Abstract

The main features of the rapidity density distribution of the produced hadrons in multiple particle production in nucleon collisions are; (a) the distribution in the forward region (ȳ ≥ 0) has a shape similar to the Fermi distribution, (b) the distribution in the most forward region reaches almost the maximum rapidity ymax = ln(√s/M) (M : nucleon mass), and (c) the shrinkage of the distribution from the maximum rapidity increases with the incident energy (i.e. violation of Feynman scaling law). These features are possible to be described by the assumptions that; (1) a fireball of the gas (made of nuclear matter, with the temperature Ti and with the shape of the incident nucleon with Lorentz contraction) is produced in the collision, (2) the fireball makes the adiabatic expansion, and (3) the constituent particles of the gas obey the Maxwell-Boltzmann distribution of the temperature Tf in the final state.