Bunching parameter
In statistics as applied in particular in particle physics, when fluctuations of some observables are measured,
it is convenient to transform the multiplicity distribution to the bunching parameters:
where is probability of observing
objects inside of some phase space regions.
The bunching parameters measure deviations of
the multiplicity distribution
from a Poisson distribution, since
for this distribution
Uncorrelated particle production leads
to the Poisson statistics, thus
deviations of the bunching parameters from the Poisson values
mean correlations between particles and dynamical fluctuations.
Normalised factorial moments
have also similar properties.
They are defined as
