QCD explanation of oscillating hadron and jet multiplicity moments

Abstract

Ratios of multiplicity moments, H q (cumulant over factorial moments K q /F q ), have been observed to show an oscillatory behaviour with respect to order, q. Recent studies of e + e − annihilations at LEP have shown, moreover, that the amplitude and oscillation length vary strongly with the jet resolution parameter y cut . We study the predictions of the perturbative QCD parton cascade assuming low nonperturbative cut-off (Q 0 ∼ Λ QCD ∼ few 100 MeV) and derive the expectations as a function of the cms energy and jet resolution from threshold to very high energies. We consider numerical solutions of the evolution equations of gluodynamics in Double Logarithmic and Modified Leading Logarithmic Approximations (DLA, MLLA), as well as results from a parton MC with readjusted parameters. The main characteristics are obtained in MLLA, while a more numerically accurate description is obtained by the MC model. A unified description of correlations between hadrons and correlations between jets emerges, in particular for the transition region of small y cut .

QCD and models on multiplicities in e + e − and $$p\bar p$$ interactions

“…The same conclusions were obtained from exact solution of equations for quark and gluon jets in the framework of fixed coupling QCD [30]. A recent exact numerical solution of the gluodynamics equation in a wide energy interval [31] coincides with the qualitative features of multiplicity distributions described above. These oscillations were confirmed by experimental data for e + e − collisions and found also for hadron-initiated processes first in [32], later in [33] and most recently in [34].…”

High Order Multiplicity Moments

“…We should note, however, that the opposite conclusion was drawn from the same data [16]. The dependence of the H q moments on their order q was investigated there for the parton jets in a MC model for varying jet resolution parameter Q c .…”

Searching for a hidden sector in multiparticle production at LHC

“…QCD next-to-leading order calculations [14,15] predict that the ratios H q defined in Eq. (3) oscillate as a function of the rank q, crossing the q-axis and becoming negative with q min ≈ 5 at LHC energies, shifting to larger values at higher energies.…”