4,004 research outputs found

### 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

### High E$_T$ 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

### 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

### 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

### Energy dependence of ratios of multiplicities and their slopes for gluon and quark jets

The difference between the ratio of multiplicities and the ratio of their
derivatives on energy for gluon and quark jets is calculated up to
next-to-next-to leading order of perturbative QCD. Its non-zero value is
uniquely defined by the running property of the QCD coupling constant. It is
shown that this difference is rather small compared to values which can be
obtained from experimental data. This disagreement can be ascribed either to
strong non-perturbative terms or to experimental problems with a scale choice,
jets separation and inadequate assignement of soft particles to jets.Comment: 5 pages, LATEX, no Figs; submitted to JETP Let

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