322 research outputs found
On relativization of the Sommerfeld-Gamow-Sakharov factor
The Sommerfeld-Gamow-Sakharov factor is considered for the general case of
arbitrary masses and energies. It is shown that the scalar triangular one-loop
diagram gives the Coulomb singularity in radiative corrections at the
threshold. The singular part of the correction is factorized at the complete
Born cross section regardless of its partial wave decomposition. Different
approaches to generalize the factor are discussed.Comment: 9 pages, 4 figures; references and discussion are extende
Event Generators for Bhabha Scattering
The results obtained by the "Event Generators for Bhabha Scattering" working
group during the CERN Workshop "Physics at LEP2" (1994/1995) are presented.Comment: 70 pages, PostScript file. To appear in the Report of the Workshop on
Physics at LEP2, G. Altarelli T. Sjostrand and F. Zwirner ed
Current tensor with heavy photon for hard pair production by longitudinally polarized electron
The electron current tensor for the scattering of heavy photon on
longitudinally polarized electron accompanied with additional hard
electron-positron pair has been considered. The contribution of collinear and
semicollinear kinematics is computed. The full analysis of both, spin-dependent
and spin-independend parts of electron current tensor, is performed. The
obtained result allows to calculate the corresponding contribution into the
second order radiative correction to cross-sections of different processes with
the next-to-leading accuracy.Comment: 19p,2Fig. (Submitted to Journ.of Physics G
NNLO massive corrections to Bhabha scattering and theoretical precision of BabaYaga@NLO
We provide an exact calculation of next-to-next-to-leading order (NNLO)
massive corrections to Bhabha scattering in QED, relevant for precision
luminosity monitoring at meson factories. Using realistic reference event
selections, exact numerical results for leptonic and hadronic corrections are
given and compared with the corresponding approximate predictions of the event
generator BabaYaga@NLO. It is shown that the NNLO massive corrections are
necessary for luminosity measurements with per mille precision. At the same
time they are found to be well accounted for in the generator at an accuracy
level below the one per mille. An update of the total theoretical precision of
BabaYaga@NLO is presented and possible directions for a further error reduction
are sketched.Comment: 5 pages, 3 tables, contrib. to proceedings of International Workshop
on e+e- collisions: from Phi to Psi, PHIPSI11, BINP, Novosibirsk, Russia,
September 19-22, 201
Two-Fermion Production in Electron-Positron Collisions
This report summarizes the results of the two-fermion working group of the
LEP2-MC workshop, held at CERN from 1999 to 2000. Recent developments in the
theoretical calculations of the two fermion production process in the
electron-positron collision at LEP2 center of the mass energies are reported.
The Bhabha process and the production of muon, tau, neutrino and quark pairs is
covered. On the basis of comparison of various calculations, theoretical
uncertainties are estimated and compared with those needed for the final LEP2
data analysis. The subjects for the further studies are identified.Comment: 2-fermion working group report of the LEP2 Monte Carlo Workshop
1999/2000, 113 pages, 24 figures, 35 table
First order radiative corrections to Bhabha scattering in dimensions
The luminosity measurement at the projected International Linear
Collider ILC is planned to be performed with forward Bhabha scattering with an
accuracy of the order of . A theoretical prediction of the
differential cross-section has to include one-loop weak corrections, with
leading higher order terms, and the complete two-loop QED corrections. Here, we
present the weak part and the virtual one-loop photonic corrections. For the
photonic corrections, the expansions in are derived with
inclusion of the terms of order in order to match the two-loop
accuracy. For the photonic box master integral in dimensions we compare
several different methods of evaluation.Comment: 35 pages, 3 figures, 2 tables, uses feynmp.sty, references update
A Complete Version of the Glauber Theory for Elementary Atom - Target Atom Scattering and Its Approximations
A general formalism of the Glauber theory for elementary atom (EA) - target
atom (TA) scattering is developed. A second-order approximation of its complete
version is considered in the framework of the optical-model perturbative
approach. A `potential' approximation of a second-order optical model is
formulated neglecting the excitation effects of the TA. Its accuracy is
evaluated within the second-order approximation for the complete version of the
Glauber EA-TA scattering theory.Comment: PDFLaTeX, 10 pages, no figures; an updated versio
The quasiclassical theory of the Dirac equation with a scalar-vector interaction and its applications in the theory of heavy-light mesons
We construct a relativistic potential quark model of , , , and
mesons in which the light quark motion is described by the Dirac equation
with a scalar-vector interaction and the heavy quark is considered a local
source of the gluon field. The effective interquark interaction is described by
a combination of the perturbative one-gluon exchange potential
and the long-range Lorentz-scalar and
Lorentz-vector linear potentials and , where
. Within the quasiclassical approximation, we obtain
simple asymptotic formulas for the energy and mass spectra and for the mean
radii of , , , and mesons, which ensure a high accuracy of
calculations even for states with the radial quantum number . We
show that the fine structure of P-wave states in heavy-light mesons is
primarily sensitive to the choice of two parameters: the strong-coupling
constant and the coefficient of mixing of the long-range
scalar and vector potentials and .
The quasiclassical formulas for asymptotic coefficients of wave function at
zero and infinity are obtained.Comment: 22 pages, 6 figure
Methods to Determine Neutrino Flux at Low Energies:Investigation of the Low Method
We investigate the "low-" method (developed by the CCFR/NUTEV
collaborations) to determine the neutrino flux in a wide band neutrino beam at
very low energies, a region of interest to neutrino oscillations experiments.
Events with low hadronic final state energy (of 1, 2 and 5 GeV)
were used by the MINOS collaboration to determine the neutrino flux in their
measurements of neutrino () and antineutrino (\nub_\mu) total cross
sections. The lowest energy for which the method was used in MINOS is
3.5 GeV, and the lowest \nub_\mu energy is 6 GeV. At these energies, the
cross sections are dominated by inelastic processes. We investigate the
application of the method to determine the neutrino flux for ,
\nub_\mu energies as low as 0.7 GeV where the cross sections are dominated by
quasielastic scattering and (1232) resonance production. We find that
the method can be extended to low energies by using values of 0.25
and 0.50 GeV, which is feasible in fully active neutrino detectors such as
MINERvA.Comment: 25 pages, 32 figures, to be published in European Physics Journal
The present theoretical error on the Bhabha scattering cross section in the luminometry region at LEP
The results concerning the theoretical evaluation of the small-angle Bhabha Scattering cross section obtained during the Workshop on Physics at LEP2 (CERN, Geneva, Switzerland, 1995) by the Working Group ``Event Generators for Bhabha Scattering'' are summarized. The estimate of the theoretical error on the cross section in the luminometry region is updated
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