13,919 research outputs found
Clan structure analysis and QCD parton showers in multiparticle dynamics. An intriguing dialog between theory and experiment
This paper contains a review of the main results of a search of regularities
in collective variables properties in multiparticle dynamics, regularities
which can be considered as manifestations of the original simplicity suggested
by QCD. The method is based on a continuous dialog between experiment and
theory. The paper follows the development of this research line, from its
beginnings in the seventies to the current state of the art, discussing how it
produced both sound interpretations of the most relevant experimental facts and
intriguing perspectives for new physics signals in the TeV energy domain.Comment: 118 pages, 48 figures; table of contents fixed for hyperre
Superposition effect and clan structure in forward-backward multiplicity correlations
The main purpose of this paper is to discuss the link between
forward-backward multiplicity correlations properties and the shape of the
corresponding final charged particle multiplicity distribution in various
classes of events in different collisions. It is shown that the same mechanism
which explains the shoulder effect and the H_n vs. n oscillations in charged
particle multiplicity distributions, i.e., the weighted superposition of
different classes of events with negative binomial properties, reproduces
within experimental errors also the forward-backward multiplicity correlation
strength in e+e- annihilation at LEP energy and allows interesting predictions
for pp collisions in the TeV energy region, to be tested at LHC, for instance
with the ALICE detector. We limit ourselves at present to study substructures
properties in hadron-hadron collisions and e+e- annihilation; they are examined
as ancillary examples in the conviction that their understanding might be
relevant also in other more complex cases.Comment: 16 page
Forward-backward multiplicity correlations and leakage parameter behaviour in asymmetric high energy collisions
Continuing previous work, forward-backward multiplicity correlations are
studied in asymmetric collisions in the framework of the weighted superposition
mechanism of different classes of events. New parameters for the asymmetric
clan distribution and for the particle leakage from clans in one hemisphere to
the opposite one are introduced to effectively classify different classes of
collisions. This tool should be used to explore forward-backward multiplicity
correlations in AB and pA collisions in present and future experiments at RHIC
and LHC.Comment: 14 pages, 2 figures, latex 2e with amsmat
Quantum Clan Model description of Bose Einstein Correlations
We propose a novel numerical method of modelling Bose-Einstein correlations
(BEC) observed among identical (bosonic) particles produced in multiparticle
production reactions. We argue that the most natural approach is to work
directly in the momentum space in which the Bose statistics of secondaries
reveals itself in their tendency to bunch in a specific way in the available
phase space. Because such procedure is essentially identical to the clan model
of multiparticle distributions proposed some time ago, therefore we call it the
Quantum Clan Model.Comment: Talk given at 4th Budapest Winter School On Eavy Ion Physics (2004),
6 pages, two figures; version published in APH (HIP
What Fraction of Gravitational Lens Galaxies Lie in Groups?
We predict how the observed variations in galaxy populations with environment
affect the number and properties of gravitational lenses in different
environments. Two trends dominate: lensing strongly favors early-type galaxies,
which tend to lie in dense environments, but dense environments tend to have a
larger ratio of dwarf to giant galaxies than the field. The two effects nearly
cancel, and the distribution of environments for lens and non-lens galaxies are
not substantially different (lens galaxies are slightly less likely than
non-lens galaxies to lie in groups and clusters). We predict that about 20% of
lens galaxies are in bound groups (defined as systems with a line-of-sight
velocity dispersion sigma in the range 200 < sigma < 500 km/s), and another
roughly 3% are in rich clusters (sigma > 500 km/s). Therefore at least roughly
25% of lenses are likely to have environments that significantly perturb the
lensing potential. If such perturbations do not significantly increase the
image separation, we predict that lenses in groups have a mean image separation
that is about 0.2'' smaller than that for lenses in the field and estimate that
20-40 lenses in groups are required to test this prediction with significance.
The tail of the distribution of image separations is already illuminating.
Although lensing by galactic potential wells should rarely produce lenses with
image separations theta >~ 6'', two such lenses are seen among 49 known lenses,
suggesting that environmental perturbations of the lensing potential can be
significant. Further comparison of theory and data will offer a direct probe of
the dark halos of galaxies and groups and reveal the extent to which they
affect lensing estimates of cosmological parameters.Comment: 32 pages, 6 embedded figures; accepted for publication in Ap
Clan Properties in Parton Showers
By considering clans as genuine elementary subprocesses, i.e., intermediate
parton sources in the Simplified Parton Shower model, a generalized version of
this model is defined. It predicts analytically clan properties at parton level
in agreement with the general trends observed experimentally at hadronic level
and in Monte Carlo simulations both at partonic and hadronic level. In
particular the model shows a linear rising in rapidity of the average number of
clans at fixed energy of the initial parton and its subsequent bending for
rapidity intervals at the border of phase space, and approximate energy
independence of the average number of clans in fixed rapidity intervals. The
energy independence becomes stricter by properly normalizing the average number
of clans.Comment: (27 pages in Plain TeX plus 10 Postscript Figures, all compressed via
uufiles) DFTT 7/9
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