QCD and hybrid NBD on oscillating moments of multiplicity distributions in lepton- and hadron-initiated reactions

QCD predictions for moments of multiplicity distributions are compared with experimental data on e+e- collisions and their two-NBD fits. Moments of the multiplicity distribution in a two-NBD model for 1.8 TeV pp collisions are considered. Three-NBD model predictions and fits for pp at LHC energies are also discussed. Analytic expressions for moments of hybrid NBD are derived and used to get insight into jet parameters and multicomponent structure of the processes. Interpretation of observed correlations is proposed.Comment: 8 pages, no figures, Phys. Lett.

Cherenkov gluons at RHIC and LHC

The coherent hadron production analogous to Cherenkov radiation of photons gives rise to the ring-like events. Being projected on the ring diameter they produce the two-bump structure recently observed for the away-side jets at RHIC. The position of the peaks and their height determine such properties of the hadronic medium as its nuclear index of refraction, the parton density, the free path length and the energy loss of Cherenkov gluons. Beside comparatively low energy gluons observed at RHIC, there could be high energy gluons at LHC, related to the high energy region of positive real part of the forward scattering amplitude and possessing different characteristics.Comment: 6 pages, talk at QM2006 modified with new reference

Soft and hard processes in QCD

QCD equations for the generating functions are applied to separate soft and hard jets in $e^+e^-$-processes of multiparticle production. The dependence of average multiplicities and higher moments of multiplicity distributions of particles created in a "newly born" soft subjets on the share of energy devoted to them is calculated in fixed coupling gluodynamics. This dependence is the same as for the total multiplicity up to a constant factor if soft jets are defined as those carrying out a fixed share of initial energy at all energies. The constant factor depends on this share in a non-trivial way. Other definitions are also proposed. The relation between these quantities for soft and hard processes is discussed.Comment: 6 pages, no Figures, LATEX, more detailed discussion of definitions and proposals for experiment is give

The two types of Cherenkov gluons at LHC energies

Beside comparatively low energy Cherenkov gluons observed at RHIC, there could be high energy gluons at LHC, related to the high energy region of positive real part of the forward scattering amplitude. In both cases they give rise to particles emitted along some cone. The characteristics of the cones produced by these two types of gluons are different. Therefore different experiments are needed to detect them. The cosmic ray event which initiated this idea is described in detail.Comment: 6 pages, talk at IWCF2006, Hangzhou, Chin

LPM Interference and Cherenkov-like Gluon Bremsstrahlung in Dense Matter

Gluon bremsstrahlung induced by multiple parton scattering in a finite dense medium has a unique angular distribution with respect to the initial parton direction. A dead-cone structure with an opening angle $\theta^2_0 \approx 2(1-z)/(zLE)$ for gluons with fractional energy $z$ arises from the Landau-Pomeranchuck-Migdal (LPM) interference. In a medium where the gluon's dielectric constant is $\epsilon >1$, the LPM interference pattern is shown to become Cherenkov-like with an increased opening angle determined by the dielectric constant $\cos^2\theta_c=z+(1-z)/\epsilon$. For a large dielectric constant $\epsilon \gg 1+2/z^2LE$, the corresponding total radiative parton energy loss is about twice that from normal gluon bremsstrahlung. Implications of this Cherenkov-like gluon bremsstrahlung to the jet correlation pattern in high-energy heavy-ion collisions is discussed.Comment: 4 pages in RevTEx with 1 postscript figur

Moments of the truncated multiplicity distributions

In experiment, the multiplicity distributions of inelastic processes are truncated due to finite energy, insufficient statistics or special choice of events. It is shown that the moments of such truncated multiplicity distributions possess some typical features.In particular, the oscillations of cumulant moments at high ranks and their negative values at the second rank can be considered as ones most indicative on specifics of these distributions. They allow to distinguish between distributions of different type.Comment: 10 pages, LaTeX, 9 ps-figure

High ET_T jets and double scattering

The recently found excess of high E$_T$ jets over current QCD predictions is attributed to gluon radiation at double scattering process inside a nucleon. The order of magnitude estimate of the cross section fits experimental findings rather well. The specific features of the process are discussed. Various similar hadronic effects related to the short radiation length are described.Comment: 6 pages, plain LaTe