Adiabatic expansion, local equilibrium and extended Maxwell distribution for fire-ball to describe multiple particle production

Abstract

We propose a model for multiple particle production of [Formula: see text] and [Formula: see text] collisions at high energies. Most of the processes in the model are reasonable physically and/or with reasoning. A fire-ball of a gas, made of grains, is created in the collision and makes an adiabatic and approximately one-dimensional expansion along the collision axis. The fire-ball at the final state, when the grains are free in the fire-ball, is divided into several domains and the thermal equilibrium is realized in each of the domains with different temperatures. Each grain produces several hadrons at the final state. There are two processes of the grains without and with [Formula: see text] (transverse momentum), and the cross-section of the latter process increases with the incident energy. The grains in the domain at the final state obey the extended Maxwell distributions of the temperature [Formula: see text], and the hadrons in each grain do that of the temperature [Formula: see text]. The values of the adjustable parameters are determined empirically in such a way as to reproduce the data of [Formula: see text] distributions and the rapidity density distributions at various incident energies. The model describes both distributions well at the incident energy of [Formula: see text] to 7000[Formula: see text]GeV. The local equilibrium in each domain and the adiabatic expansion describe the flat plateau and the shrinkage of the forward region, respectively, of the rapidity density distribution. Another important conclusion is that a simple hydro-dynamical model does not describe the flat plateau of the rapidity density distribution of produced hadrons at high energies.