Regular Article - Theoretical Physics

The European Physical Journal C

, Volume 68, Issue 1, pp 141-152

First online:

Limiting soft particle emission in e + e , hadronic and nuclear collisions

  • Wolfgang OchsAffiliated withMax Planck Institut für Physik, Werner-Heisenberg-Institut Email author 
  • , Valery A. KhozeAffiliated withInstitute for Particle Physics Phenomenology, University of DurhamPetersburg Nuclear Physics Institute
  • , M. G. RyskinAffiliated withPetersburg Nuclear Physics Institute

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In e + e collisions the particle spectra at low momenta reflect the properties of the underlying “soft” QCD gluon bremsstrahlung: the particle density, in the limit p→0, becomes independent of the incoming energy \(\sqrt{s}\) and directly proportional to the colour factors C A , C F for primary gluons or quarks respectively. We find that experimental data from the pp and nuclear reactions reveal the same behaviour: in the limit p T→0 the invariant particle spectra become independent of the collision energy, and their intensities in e + e , pp and nuclear reactions are compatible with the expected colour factors C F : C A : (N part/2)C A for N part nucleons, participating in the interaction. Coherent soft gluon bremsstrahlung is, therefore, suggested to be the dominant QCD mechanism for the soft particle production in all these reactions. These “soft” particles probe the very early stage of hadron formation in the collision. Future measurements at the LHC will provide crucial tests on the contributions from possible incoherent multi-component processes.