210 research outputs found
Four-pion production in tau decays and e+e- annihilation: an update
An improved description of four-pion production in electron-positron
annihilation and in tau lepton decays is presented. The model amplitude is
fitted to recent data from BaBar which cover a wide energy range and which were
obtained exploiting the radiative return. Predicting tau decay distributions
from e+e- data and comparing these predictions with ALEPH and CLEO results, the
validity of isospin symmetry is confirmed within the present experimental
errors. A good description of two- and three-pion sub-distributions is
obtained. Special emphasis is put on the predictions for omega pi (->
pi+pi-pi0) in e+e- annihilation and in tau decay. The model amplitude is
implemented in the Monte Carlo generator PHOKHARA.Comment: a few typos correcte
Present status of precise calculation for small-angle Bhabha scattering
The problem of obtaining a theoretical description of Bhabha scattering at small angle, to monitor the luminosity at the precision 0 .1% requested by LEP experiments, is discussed and recent results are presented
BHAGEN-1PH: A Monte Carlo event generator for radiative Bhabha scattering
BHAGEN-1PH is a FORTRAN program providing fast Monte Carlo event generation
of the process , within electroweak theory, for
both unpolarized beams and also for the longitudinally polarized electron beam.
The program is designed for final leptons outside a small cone around the
initial leptons direction and has a new algorithm allowing also for a fast
generation of non collinear initial and final emission, as well as for
asymmetric and different angular cuts for final leptons.Comment: 23 pages, plain Tex, no figure
The Pseudothreshold Expansion of the 2-loop Sunrise Selfmass Master Amplitudes
The values at pseudothreshold of two loop sunrise master amplitudes with
arbitrary masses are obtained by solving a system of differential equations.
The expansion at pseudothreshold of the amplitudes is constructed and some
lowest terms are explicitly presented.Comment: 1+22 pages, Latex, no figures, changes in Eq.(41),(44),(47
Matching perturbative and Parton Shower corrections to Bhabha process at flavour factories
We report on a high-precision calculation of the Bhabha process in Quantum
Electrodynamics, of interest for precise luminosity determination of
electron-positron colliders involved in R measurements in the region of
hadronic resonances. The calculation is based on the matching of exact
next-to-leading order corrections with a Parton Shower algorithm. The accuracy
of the approach is demonstrated in comparison with existing independent
calculations and through a detailed analysis of the main components of
theoretical uncertainty, including two-loop corrections, hadronic vacuum
polarization and light pair contributions. The calculation is implemented in an
improved version of the event generator BABAYAGA with a theoretical accuracy of
the order of 0.1%. The generator is now available for high-precision
simulations of the Bhabha process at flavour factories.Comment: 34 pages, 8 figures, uses elsart.cls. Version to appear on Nuclear
Physics
The Threshold Expansion of the 2-loop Sunrise Selfmass Master Amplitudes
The threshold behavior of the master amplitudes for two loop sunrise
self-mass graph is studied by solving the system of differential equations,
which they satisfy. The expansion at the threshold of the master amplitudes is
obtained analytically for arbitrary masses.Comment: 1+18 pages, Latex, no figures, as in Journal reference with more
changes in Eq.(31),(42),(45
Numerical evaluation of the general massive 2-loop sunrise self-mass master integrals from differential equations
The system of 4 differential equations in the external invariant satisfied by
the 4 master integrals of the general massive 2-loop sunrise self-mass diagram
is solved by the Runge-Kutta method in the complex plane. The method, whose
features are discussed in details, offers a reliable and robust approach to the
direct and precise numerical evaluation of Feynman graph integrals.Comment: 1+21 pages, Latex, 5 ps-figure
Extension and approximation of -subharmonic functions
Let be a bounded domain, and let be a
real-valued function defined on the whole topological boundary . The aim of this paper is to find a characterization of the functions
which can be extended to the inside to a -subharmonic function under
suitable assumptions on . We shall do so by using a function algebraic
approach with focus on -subharmonic functions defined on compact sets. We
end this note with some remarks on approximation of -subharmonic functions
Simulation of the process within electroweak theory with longitudinally polarized initial electrons
We present simple analytic expressions for the distributions of the Bhabha
scattering process with emission of one hard photon, including weak boson
exchanges, and with longitudinal polarization of the initial electron. The
results from the Monte Carlo generator BHAGEN-1PH, based on these expressions,
are presented and compared, for the unpolarized case, with those existing in
literature.Comment: 9 pages, plain Tex, no figures, small change in Table
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