1,662 research outputs found
An SU(3) model for octet baryon and meson fragmentation
The production of the octet of baryons and mesons in e^+ e^- collisions is
analysed, based on considerations of SU(3) symmetry and a simple model for
SU(3) symmetry breaking in fragmentation functions. All fragmentation
functions, D_q^h(x, Q^2), describing the fragmentation of quarks into a member
of the baryon octet (and similarly for fragmentation into members of the meson
octet) are expressed in terms of three SU(3) symmetric functions, \alpha(x,
Q^2), \beta(x, Q^2), and \gamma(x, Q^2). With the introduction of an SU(3)
breaking parameter, \lambda, the model is successful in describing
hadroproduction data at the Z pole. The fragmentation functions are then
evolved using leading order evolution equations and good fits to currently
available data at 34 GeV and at 161 GeV are obtained.Comment: 24 pages LaTeX file including 11 postscript figure file
Superconformal constraints for QCD conformal anomalies
Anomalous superconformal Ward identities and commutator algebra in N = 1
super-Yang-Mills theory give rise to constraints between the QCD special
conformal anomalies of conformal composite operators. We evaluate the
superconformal anomalies that appear in the product of renormalized conformal
operators and the trace anomaly in the supersymmetric spinor current and check
the constraints at one-loop order. In this way we prove the universality of QCD
conformal anomalies, which define the non-diagonal part of the anomalous
dimension matrix responsible for scaling violations of exclusive QCD amplitudes
at the next-to-leading order.Comment: 30 pages, 2 figures, LaTe
Pion and Kaon Production in and Collisions at Next-to-Leading Order
We present new sets of fragmentation functions for charged pions and kaons,
both at leading and next-to-leading order. They are fitted to data on inclusive
charged-hadron production in annihilation taken by TPC at PEP (~GeV) and to similar data by ALEPH at LEP, who discriminated between
events with charm, bottom, and light- flavour fragmentation in their
charged-hadron sample. We treat all partons independently and to properly
incorporate the charm and bottom thresholds. Due to the sizeable energy gap
between PEP and LEP, we are sensitive to the scaling violation in the
fragmentation process, which allows us to extract a value for the asymptotic
scale parameter of QCD, . Recent data on inclusive charged-hadron
production in tagged three-jet events by OPAL and similar data for longitudinal
electron polarization by ALEPH allow us to pin down the gluon fragmentation
functions. Our new fragmentation functions lead to an excellent description of
a multitude of other data on inclusive charged-hadron production,
ranging from ~GeV to LEP energy. In addition, they agree nicely
with the transverse-momentum spectra of single charged hadrons measured by H1
and ZEUS in photoproduction at the collider HERA, which represents a
nontrivial check of the factorization theorem of the QCD-improved parton model.Comment: 22 pages, latex, 13 compressed ps figures in separate fil
Heavy Flavour Production in Two-Photon Collisions
We review the production of charm and bottom quarks in two-photon collisions
at e+e- colliders. The next-to-leading order QCD predictions for total cross
sections and differential distributions are compared with recent experimental
results.Comment: 6 pages, 2 figures. Talk given at the UK Phenomenology Workshop on
Collider Physics, Durham, England, 19-24 Sep 199
Next-to-Leading Order Fragmentation Functions for Pions and Kaons
We present new sets of fragmentation functions for charged pions and kaons,
both at leading and next-to-leading order. They are fitted to TPC data taken at
energy ~GeV and describe excellently a wealth of other
data on charged-hadron production, ranging from ~GeV way up to
LEP~1 energy. They also agree with data on the production of neutral pions and
kaons, if one makes the natural assumption that the respective fragmentation
functions are related to the charged counterparts by SU(2) symmetry. We also
list simple parameterizations of the and dependence of our results,
which may be implemented conveniently in applications.Comment: 22 p. + 12 figures (1 compressed Ps-file), DESY 94-124 figure file
replaced by uuencoded fil
Multiplicity distributions inside parton cascades developing in a medium
The explanation of the suppression of high-pT hadron yields at RHIC in terms
of jet-quenching implies that the multiplicity distributions of particles
inside a jet and jet-like particle correlations differ strongly in
nucleus-nucleus collisions at RHIC or at the LHC from those observed at e+e- or
hadron colliders. We present a framework for describing the medium-induced
modification, which has a direct interpretation in terms of a probabilistic
medium-modified parton cascade, and which treats leading and subleading partons
on an equal footing. We show that our approach can account for the strong
suppression of single inclusive hadron spectra measured in Au-Au collisions at
RHIC, and that this implies a characteristic distortion of the single inclusive
distribution of soft partons inside the jet. We determine, as a function of the
jet energy, to what extent the soft fragments within a jet can be measured
above some momentum cut.Comment: 5 pages, 4 eps-figures; talk given at Hot Quarks 2006, Villasimius
(Sardinia, Italy), May 15-20, 200
Система торгового оборудования для винного магазина как средство формирования визуального мерчандайзинга
Statistical approach for unpolarized fragmentation functions for the octet baryons
A statistical model for the parton distributions in the nucleon has proven
its efficiency in the analysis of deep inelastic scattering data, so we propose
to extend this approach to the description of unpolarized fragmentation
functions for the octet baryons. The characteristics of the model are
determined by using some data on the inclusive production of proton and
in unpolarized deep inelastic scattering and a next-to-leading
analysis of the available experimental data on the production of unpolarized
octet baryons in annihilation. Our results show that both parton
distributions and fragmentation functions are compatible with the statistical
approach, in terms of a few free parameters, whose interpretation will be
discussed.Comment: 14 pages, 7 eps figures, to appear in Phys. Rev.
Economic growth in the post-socialist Russian Federation after 1991 : the role of institutions
The paper emphasizes the transition in Russia and the role institutions played before and during the process. In Russia, a ?big bang? approach was applied. That is to say, transition was conducted all of a sudden, omitting important underlying reforms. This practice should function as a shock therapy. Hence, the approach should leave no other chance than an abrupt adaption to the new free-market rules. These rules would then lead to fast economic growth and development, as they did in other places. However, since Russian GDP per capita and thereby living standards deteriorated dramatically in the years after the collapse of the Soviet Union, the plan did not work. At any rate, since then Russian economic indicators recovered and partly achieved their pre-1991 levels at the end of the last decade. The paper depicts Russia?s reform efforts and the subsequent developments. The close ties among the political elite, the banking sector and the old nomenklatura are demonstrated. The patrimonial system that persisted for centuries is still observable at the state level. At any rate, Russia can neither evade its historical and institutional development path nor its societal structures that are based on networks and nepotism. Russia?s systemic lack of the rule of law and therewith of secure property, the character of the Russian political system with the patriarch as the head of state and the resulting necessity of corruption and bribes inhibit the realization of its full growth potential
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