91 research outputs found
Multiparticle production and perturbative QCD
The perturbative quantum chromodynamics (QCD) is quite successful in the
description of main features of multiparticle production processes. Ten most
appealing characteristics are described in this brief review talk and compared
with QCD predictions. The general perturbative QCD approach is demonstrated and
its problems are discussed. It is shown that the analytical calculations at the
parton level with the low-momentum cut-off reproduce experimental data on the
hadronic final state surprisingly accurately even though the perturbative
expansion parameter is not very small. Moreover, the perturbative QCD has been
able not only to {\it describe} the existing data but also to {\it predict}
many new bright qualitative phenomena.Comment: 22 pages, 10 Figs, LATEX. Talk given at the conference "From the
smallest to largest distances", ITEP, Moscow, 24-26 May 200
Problem of the Complete Measurement for CP-violating Parameters in Neutral B-meson Decays
Phenomenological CP-violating parameters in decays of neutral B-mesons are
discussed. Special attention is given to the degree of their measurability. We
emphasize important role of the sign of and suggest how it could
be determined experimentally.Comment: 12 pages, no figures; some small errors are corrected, publication
reference is appende
Search for Higher Flavor Multiplets in Partial Wave Analyses
The possible existence of higher multi-quark flavor multiplets of baryons is
investigated. We argue that the S-matrix should have poles with any quantum
numbers, including those which are exotic. This argument provides a novel
justification for the existence of hadrons with arbitrary exotic structure.
Though it does not constitute a proof, there are still no theoretical arguments
against exotics. We then consider KN and piN scattering. Conventional and
modified partial-wave analyses provide several sets of candidates for
correlated pairs (Theta1, Delta), each of which could label a related 27-plet.
Properties of the pairs (masses, mass orderings, spin-parity quantum numbers)
do not quite correspond to the current theoretical expectations. Decay widths
of the candidates are either wider or narrower than expected. Possible reasons
for such disagreements are briefly discussed.Comment: 12 pages, 1 figure; v2: references corrected; v3: minor changes, to
appear in Eur.Phys.J.
Detecting new physics contributions to the D0-D0bar mixing through their effects on B decays
New physics effects may yield a detectable mass difference in the D0-D0bar
system, Delta m_D. Here we show that this has an important impact on some B -->
D decays. The effect involves a new source of CP violation, which arises from
the interference between the phases in the B --> D decays and those in the
D0-D0bar system. This interference is naturally large. New physics may well
manifest itself through Delta m_D contributions to these B decays.Comment: 10 pages, Revtex, no figures. To appear in PR
Light Baryon Resonances: Restrictions and Perspectives
The problem of nucleon resonances N' with masses below the Delta is
considered. We derive bounds for the properties of such states. Some of these
are new, while others improve upon existing limits. We discuss the nature of N'
states, and their unitary partners, assuming their existence can be verified.Comment: 11 pages, 11 figur
Momentum Spectra in the Current Region of the Breit Frame in Deep Inelastic Scattering at HERA
The production of charged particles has been measured in deep inelastic
scattering (DIS) with the ZEUS detector. The evolution of the moments of the
scaled momenta distributions in and has been investigated in the
current fragmentation region of the Breit frame. The results in the current
region are compared to data and QCD analytical calculations. The
results are consistent with the universality of single-particle spectra in DIS
and annihilation at high The results at low disagree with
analytical calculations based on the modified leading log approximation (MLLA)
and local parton hadron duality (LPHD).Comment: 3 pages. 1 postscript figure + 1 postscript preprint logo + 1 LaTeX
file + 1 style fil
Comment on "Hara's theorem in the constituent quark model"
It is pointed out that current conservation alone does not suffice to prove
Hara's theorem as it was claimed recently. By explicit calculation we show that
the additional implicit assumption made in such "proofs" is that of a
sufficiently localized current.Comment: 8 pages, Late
Comment on ``Evidence for Narrow Baryon Resonances in Inelastic pp Scattering''
Compton scattering data are sensitive to the existence of low-mass resonances
reported by Tatischeff et al. We show that such states, with their reported
properties, are excluded by previous Compton scattering experiments.Comment: One page, submitted to PR
Present status of the nonstrange and other flavor partners of the exotic Theta+ baryon
Given the existing empirical information about the exotic Theta+ baryon, we
analyze possible properties of its SU(3)F-partners, paying special attention to
the nonstrange member of the antidecuplet N*. The modified piN partial-wave
analysis presents two candidate masses, 1680 MeV and 1730 MeV. In both cases,
the N* should be rather narrow and highly inelastic. Our results suggest
several directions for experimental studies that may clarify properties of the
antidecuplet baryons, and structure of their mixing with other baryons. Recent
experimental evidence from the GRAAL and STAR Collaborations could be
interpreted as observations of a candidate for the Theta+ nonstrange partner.Comment: 4 pages, 1 figure, talk given at the Topical Group on Hadron Physics
(Fermilab, Oct. 24-26, 2004
Corrections to Angular Ordering in Multiple Hadroprodroproduction
One of the key ideas in describing the multiparticle production at high
energies in the perturbative QCD is the angular ordering in successive
soft-gluon emission. We analyse the angular distribution of particles in a jet,
and investigate the corrections to the angular ordering. At a small angle from
the jet direction, the angular ordering is exact at the next-to-leading order.
At a large angle, the angular ordering overestimates the angular particle
density by a factor , where is the
anomalous dimension of the multiplicity. The correction restores
the boost invariance of the cross section.Comment: Latex fil
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