Power Law in Hadron Production

In high energy p+p interactions the mean multiplicity of neutral mesons (from eta to Upsilon) and the transverse mass spectra of pions (m_T= 1 - 15 GeV/c^2) reveal a remarkable universal behaviour: they follow, over 10 orders of magnitude, the same power law function: C m_(T)^(-P). This scaling is rather similar to that expected in the statistical description of hadron production: the parameter P plays the role of a temperature and the normalisation constant C is analogous to the system volume. The fundamental difference is, however, in the form of the distribution function. In order to reproduce the experimental results and preserve the basic structure of the statistical approach the Boltzmann factor e^(-E^*/T) appearing in standard statistical mechanics has to be substituted by a power law factor (E^*/\Lambda)^(-P).