4,370 research outputs found
On the measurement of quarkonium state in the processes and
The intermediate quarkonium state in electron-positron
annihilation to proton and antiproton as well as in antiproton-proton
annihilation to electron and positron can produce backward-forward asymmetry,
when populated through two photon exchange. We use the dispersion relation
method, which permits to express the asymmetry in terms of partial widths of
quarkonium decay. The asymmetry dependence on the center of mass energy in the
range near the resonance is presented. The comparison with a similar effect in
these reactions with the neutral -boson in the intermediate state is given.
We show that these effects are . The main source of asymmetry is
of pure QED origin () which arises from the interference between
initial and final state real photon emission
Neutron electric form factor at large momentum transfer
Based on the recent, high precision data for elastic electron scattering from
protons and deuterons, at relatively large momentum transfer , we
determine the neutron electric form factor up to GeV. The values
obtained from the data (in the framework of the nonrelativistic impulse
approximation) are larger than commonly assumed and are in good agreement with
the Gari-Kr\"umpelmann parametrization of the nucleon electromagnetic form
factors.Comment: 11 pages 2 figure
Space-time evolution of Dirac wave packets
In this work we study the dynamics of free 3D relativistic Gaussian wave
packets with different spin polarization. We analyze the connection between the
symmetry of initial state and the dynamical characteristics of moving particle.
The corresponding solutions of Dirac equation having different types of
symmetry were evaluated analytically and numerically and after that the
electron probability densities, as well as, the spin densities were visualized.
The average values of velocity of the packet center and the average spin were
calculated analytically, and the parameters of transient Zitterbewegung in
different directions were obtained. These results can be useful for the
interpretation of future experiments with trapped ions.Comment: 10 pages, 7 figure
Search for evidence of two photon contribution in elastic electron proton data
We reanalyze the most recent data on elastic electron proton scattering. We
look for a deviation from linearity of the Rosenbluth fit to the differential
cross section, which would be the signature of the presence of two photon
exchange. The two photon contribution is parametrized by a one parameter
formula, based on symmetry arguments. The present data do not show evidence for
such deviation.Comment: 15 pages 3 figures More details on the fitting procedure, more
explicit explanation
Target normal spin asymmetry and charge asymmetry for elastic scattering and the crossed processes
Two kinds of asymmetry arise from the interference of the Born amplitude and
the box-type amplitude corresponding to two virtual photons exchange, namely
charge-odd and one spin asymmetries. In case of unpolarized particles the
charge-odd correlation is calculated. It can be measured in combination of
electron muon and positron muon scattering experiments. The forward-backward
asymmetry is the corresponding quantity which can be measured for the crossed
processes. In the case of polarized muon the one-spin asymmetry for
annihilation and scattering channels has been calculated. The additional
structure function arising from the interference is shown to suffer from
infrared divergencies. The background due to electroweak interaction is
discussed.Comment: 19 pages, 5 figure
Cross section and polarization observables for the reaction
A model independent formalism for the electron positron annihilation reaction
has been derived. The differential and total cross
sections and the elements of the spin--density matrix of the -meson were
calculated in terms of the electromagnetic form factors of the corresponding
current. Simple models of form factors have been fitted
to the available cross section data and they allow to give numerical
predictions for the different observables.Comment: 19 pages, 6 figures Added formulas for axial meson decay in 3 pions
Modified version to appear in PR
Bremsstrahlung and pair production processes at low energies, multi-differential cross section and polarization phenomena
Radiative electron-proton scattering is studied in peripheral kinematics,
where the scattered electron and photon move close to the direction of the
initial electron. Even in the case of unpolarized initial electron the photon
may have a definite polarization. The differential cross sections with
longitudinally or transversal polarized initial electron are calculated. The
same phenomena are considered for the production of an electron-positron pair
by the photon, where the final positron (electron) can be also polarized.
Differential distributions for the case of polarized initial photon are given.
Both cases of unscreened and completely screened atomic targets are considered.Comment: 15 pages, 6 figure
Radiative proton-antiproton annihilation to a lepton pair
The annihilation of proton and antiproton to electron-positron pair,
including radiative corrections due to the emission of virtual and real photons
is considered. The results are generalized to leading and next-to leading
approximations. The relevant distributions are derived and numerical
applications are given in the kinematical range accessible to the PANDA
experiment at the FAIR facility.Comment: 2 figure
What does a strongly excited 't Hooft-Polyakov magnetic monopole do?
The time evolution of strongly exited SU(2) Bogomolny-Prasad-Sommerfield
(BPS) magnetic monopoles in Minkowski spacetime is investigated by means of
numerical simulations based on the technique of conformal compactification and
on the use of hyperboloidal initial value problem. It is found that an
initially static monopole does not radiate the entire energy of the exciting
pulse toward future null infinity. Rather, a long-lasting quasi-stable
`breathing state' develops in the central region and certain expanding shell
structures -- built up by very high frequency oscillations -- are formed in the
far away region.Comment: 4 pages, 6 figure
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