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

TL;DR

This paper discusses the universal properties of particle production in the soft limit across various high-energy processes, highlighting energy independence, proportionality to QCD color factors, and universal particle ratios, with implications for future LHC measurements.

Contribution

It reveals universal features of soft particle production in high-energy collisions, emphasizing the role of coherent soft gluon bremsstrahlung and scaling behaviors.

Findings

Particle density approaches a universal limit independent of collision energy.

Particle ratios in the low momentum region are universal.

Nuclear collisions follow participant scaling with good accuracy.

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.