Limiting soft particle production and QCD

TL;DR

This paper discusses how soft particle production in high-energy collisions can be understood through perturbative QCD, predicting universal features like energy independence of particle density at low momentum, supported by existing data.

Contribution

It extends the understanding of soft particle spectra from e+e- to pp and nuclear collisions, highlighting universal features predicted by perturbative QCD.

Findings

Energy independence of particle density at low momentum confirmed by data

Universal features of soft gluon bremsstrahlung observed across collision types

Predictions applicable to future LHC energy regimes

Abstract

We present some basic elements of the treatment of particle multiplicities in jets from high energy collisions within perturbative QCD. Then we discuss the universal features of the inclusive particle spectrum for the limiting case of momentum p\to 0 (or p_T\to 0) as expected from soft QCD gluon bremsstrahlung. The energy independence of the invariant particle density in this limit I_0=E dN/d^3p|_{p\to 0} is predicted as well as the dependence of this quantity on the the colour factors characteristic of the underlying partonic processes. These properties are first recalled from e+e- collisions and then extended to pp and nuclear collisions according to Ref. 1. Present data support these predictions. It will be interesting to see whether new incoherent contributions show up in the new energy regime of LHC.