Multiplicity Fluctuations in Dis

The studies of multiplicity fluctuations in restricted domains of the phase space reveal the nature of particle correlations and are sensitive to the dynamics of the underlying process. The hadronic final state in DIS is a result of a hard partonic scattering at a large momentum transfersQ ≫ Λ. A subsequent parton cascade development down to some QCD cut-off Q0 and fragmentation occuring at small momentum transfers lead to the observed hadrons. The characteristic QCD scale Λ is of the order of a few hundred MeV. At present there are two main approaches for the description of the hadronic final state: the QCD-based Monte Carlo programs and analytic perturbative QCD calculations 1 in conjunction with the Local Parton-Hadron Duality (LPHD) hypothesis . In Monte Carlo programs, the partonic final state is generated according to the pQCD picture and below Q0 ≃ 1 GeV the transition from partons to hadrons is performed by applying non-perturbative models. In analytic calculations, the parton cascade develops down to Q0, close to Λ. In this case the direct comparison of the spectra of partons with those of hadrons becomes possible, without involving any hadronization model. In the multiplicity fluctuations studies, the method of normalized factorial moments, Fq, was used . Experimentally, the moments of order q were calculated by counting n, the number of charged particles in a restricted region of phase space, Ω: Fq(Ω) = < n > −q < n(n− 1) . . . (n− q + 1) >, (1)