Universal properties of particle production in the soft limit p_T -> 0

Abstract

The momentum spectra of particles in different high energy processes, such as e^+e^- annihilation, pp and nuclear collisions in the limit p,p_T -> 0 exhibit similar properties because of the dominant role of coherent soft gluon bremsstrahlung. We observe the following general features: the inclusive particle density approaches a limiting behaviour and becomes independent of primary collision energy; furthermore, it becomes proportional to the QCD colour factors C_A,C_F which appear in the Born term for the respective minimal partonic processes. In this limit, nuclear collisions reach with good accuracy participant (``wounded nucleon'') scaling. Particle ratios in the low momentum region display a universal behaviour. Future measurements at the LHC will provide crucial tests for the contributions from additional incoherent multi-component processes.