182 research outputs found
The radiative return at phi- and B-factories: FSR for muon pair production at next-to-leading order
Muon pair production through the radiative return is of importance for a
measurement of the hadronic production cross section in two ways: it provides
an independent calibration and it may give rise to an important background for
a measurement of the pion form factor. With this motivation the Monte Carlo
event generator PHOKHARA is extended to include next-to-leading order radiative
corrections to the reaction . Furthermore, virtual
ISR corrections to FSR from pions are introduced, which extends the
applicability of the generator into a new kinematical regime. Finally, the
effect of photon vacuum polarization is introduced into this new version of the
generator.Comment: 11 pages, 15 figure
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
Nucleon form factors, B-meson factories and the radiative return
The feasibility of a measurement of the electric and magnetic nucleon form
factors at -meson factories through the radiative return is studied. Angular
distributions allow a separation of the contributions from the two form
factors. The distributions are presented for the laboratory and the hadronic
rest frame, and the advantages of different coordinate systems are
investigated. It is demonstrated that values up to 8 or even 9 GeV
are within reach. The Monte Carlo event generator PHOKHARA is extended to
nucleon final states, and results are presented which include Next-to-Leading
Order radiative corrections from initial-state radiation. The impact of angular
cuts on rates and distributions is investigated and the relative importance of
radiative corrections is analysed.Comment: 9 pages, 11 figures. Final version to appear in Eur. Phys. J.
Electron-positron annihilation into three pions and the radiative return
The Monte Carlo event generator PHOKHARA, which simulates hadron and muon production at electron-positron colliders through radiative return, has been extended to final states with three pions. A model for the form factor based on generalized vector dominance has been employed, which is consistent with presently available experimental observations
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
Simulation of electron-positron annihilation into hadrons with the event generator PHOKHARA
The precise determination of the cross section for electron-positron annihilation into hadrons is one of the central tasks of ongoing experiments at low energy colliders. These measurements have to be complemented by Monte Carlo generators which simulate a large number of final states and include higher order radiative corrections. With this motivation in mind the generator PHOKHARA is extended to version 8.0, thus allowing for the simulation of final states with zero, one or two real photons. At the same time corrections from the emission of one or two virtual photons are included, such that a full next-to-next-to leading order generator is available. The stability and consistency of the program is tested. The results (for muon-pair final states) are compared to the programs KKMC and MCGPJ and implications for the analysis of various hadronic final states are investigated
Radiative return at e+e- factories
The energy dependence of the electron - positron hadronic cross section can
be measured not only by a straightforward energy scan, but also by means of the
radiative return method. To provide extensive comparisons between theory and
experiment a Monte Carlo event generator is an indispensable tool. We have
developed such a generator called PHOKHARA, which simulates e+e- -> mesons +
photon(s) processes. In this paper we present its latest tests and upgrades.Comment: 5 pages, 7 figures, presented at RADCOR 2002, Kloster Banz, Sept.
8-13, 200
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
The radiative return at phi- and B-factories: FSR at next-to-leading order
The measurement of the pion form factor and, more generally, of the cross
section for electron--positron annihilation into hadrons through the radiative
return has become an important task for high luminosity colliders such as the
- or -meson factories. For detailed understanding and analysis of this
reaction, the construction of a Monte Carlo program, PHOKHARA, has been
undertaken. Version 2.0 was based on a next-to-leading order (NLO) treatment of
the corrections from initial-state radiation (ISR). In the present paper a
further extension of PHOKHARA (version 3.0) is described, which incorporates
NLO corrections to final-state radiation (FSR). The impact of combined ISR and
FSR on various distributions is investigated and methods are presented, which
will allow the extraction of the form factor, and even give access to inclusive
photon emission due to FSR. The dependence of the results on the model for FSR
is discussed and the impact of this contribution on the anomalous magnetic
moment of the muon is evaluated.Comment: 15 pages, 17 figures. Final version to appear in Eur. Phys. J.
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