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:

\eta _{q}={\frac {q}{q-1}}{\frac {P_{q}P_{{q-2}}}{P_{{q-1}}^{2}}},

where $P_{n}$ is probability of observing $n$ objects inside of some phase space regions. The bunching parameters measure deviations of the multiplicity distribution $P_{n}$ from a Poisson distribution, since for this distribution

\eta _{q}=1

.

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

F_{q}=\langle n\rangle ^{{-q}}\sum _{{n=q}}^{{\infty }}{\frac {n!}{(n-q)!}}P_{n}.

References

Chekanov, S.V.; Kuvshinov, V.I. (1994). "Bunching Parameter and Intermittency in High-Energy Collisions" (PDF). Acta Physica Polonica B. 25: 1189–1197. arXiv:hep-ph/9605379. Bibcode:1996hep.ph....5379C.
Chekanov, S.V.; Kittel, W.; Kuvshinov, V.I. (1996). "Multifractal Multiplicity Distribution in Bunching-Parameter Analysis". Journal of Physics G. 22 (5): 601–610. arXiv:hep-ph/9606202. Bibcode:1996JPhG...22..601C. doi:10.1088/0954-3899/22/5/007.
Chekanov, S.V.; Kuvshinov, V.I.; Kuvshinov, V. I. (1997). "Generalized Bunching Parameters and Multiplicity Fluctuations in Restricted Phase-Space Bins". Zeitschrift für Physik C. 74 (3): 517–529. arXiv:hep-ph/9606335. doi:10.1007/s002880050414.

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