Limiting soft particle production and QCD

Understand

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.