1,224 research outputs found
Access to improve the muon mass and magnetic moment anomaly via the bound-muon factor
A theoretical description of the factor of a muon bound in a nuclear
potential is presented. One-loop self-energy and multi-loop vacuum polarization
corrections are calculated, taking into account the interaction with the
binding potential exactly. Nuclear effects on the bound-muon factor are
also evaluated. We put forward the measurement of the bound-muon factor via
the continuous Stern-Gerlach effect as an independent means to determine the
free muons magnetic moment anomaly and mass. The scheme presented enables to
increase the accuracy of the mass by more than an order of magnitude
Two-loop virtual light-by-light scattering corrections to the bound-electron g factor
A critical set of two-loop quantum electrodynamics corrections to the g factor of hydrogenlike ions is calculated in the Furry picture. These corrections are due to the polarization of the external magnetic field by the quantum vacuum, which is dressed by the binding field. The result obtained for the self-energy–magnetic-loop diagrams is compared with the current state-of-the-art result, derived through a perturbative expansion in the binding strength parameter Zα, with Z the atomic number and α the fine-structure constant. Agreement is found in the Z→0 limit. However, even for very light ions, the perturbative result fails to approximate the magnitude of the corresponding correction to the g factor. The total correction to the g factor coming from all diagrams considered in this work is found to be highly relevant for upcoming experimental tests of fundamental physics with highly charged ions
Theory of the two-loop self-energy correction to the g factor in nonperturbative Coulomb fields
Two-loop self-energy corrections to the bound-electron factor are investigated theoretically to all orders in the nuclear binding strength parameter . The separation of divergences is performed by dimensional regularization, and the contributing diagrams are regrouped into specific categories to yield finite results. We evaluate numerically the loop-after-loop terms, and the remaining diagrams by treating the Coulomb interaction in the electron propagators up to first order. The results show that such two-loop terms are mandatory to take into account for projected near-future stringent tests of quantum electrodynamics and for the determination of fundamental constants through the factor
QED corrections to the g factor of Li- and B-like ions
QED corrections to the factor of Li-like and B-like ions in a wide range of nuclear charges are presented. Many-electron contributions as well as radiative effects on the one-loop level are calculated. Contributions resulting from the interelectronic interaction, the self-energy effect, and most of the terms of the vacuum-polarization effect are evaluated to all orders in the nuclear coupling strength . Uncertainties resulting from nuclear size effects, numerical computations, and uncalculated effects are discussed
First analysis of anisotropic flow with Lee--Yang zeroes
We report on the first analysis of directed and elliptic flow with the new
method of Lee--Yang zeroes. Experimental data are presented for Ru+Ru reactions
at 1.69 AGeV measured with the FOPI detector at SIS/GSI. The results obtained
with several methods, based on the event-plane reconstruction, on Lee--Yang
zeroes, and on multi-particle cumulants (up to 5th order) applied for the first
time at SIS energies, are compared. They show conclusive evidence that
azimuthal correlations between nucleons and composite particles at this energy
are largely dominated by anisotropic flow.Comment: 5 pages, 3 figures, submitted to Phys. Rev. C Rapid Co
No evidence of a sudden change of spectral appearance or magnetic field strength of the O9.7V star HD 54879
Isospin dependence of relative yields of and mesons at 1.528 AGeV
Results on and meson production in Ru +
Ru and Zr + Zr collisions at a beam kinetic
energy of 1.528 GeV, measured with the FOPI detector at GSI-Darmstadt, are
investigated as a possible probe of isospin effects in high density nuclear
matter. The measured double ratio ()/() is
compared to the predictions of a thermal model and a Relativistic Mean Field
transport model using two different collision scenarios and under different
assumptions on the stiffness of the symmetry energy. We find a good agreement
with the thermal model prediction and the assumption of a soft symmetry energy
for infinite nuclear matter while more realistic transport simulations of the
collisions show a similar agreement with the data but also exhibit a reduced
sensitivity to the symmetry term.Comment: 5 pages, 3 figures. accepted for publication in Phys. Rev.
Two-proton small-angle correlations in central heavy-ion collisions: a beam-energy and system-size dependent study
Small-angle correlations of pairs of protons emitted in central collisions of
Ca + Ca, Ru + Ru and Au + Au at beam energies from 400 to 1500 MeV per nucleon
are investigated with the FOPI detector system at SIS/GSI Darmstadt.
Dependences on system size and beam energy are presented which extend the
experimental data basis of pp correlations in the SIS energy range
substantially. The size of the proton-emitting source is estimated by comparing
the experimental data with the output of a final-state interaction model which
utilizes either static Gaussian sources or the one-body phase-space
distribution of protons provided by the BUU transport approach. The trends in
the experimental data, i.e. system-size and beam energy dependences, are well
reproduced by this hybrid model. However, the pp correlation function is found
rather insensitive to the stiffness of the equation of state entering the
transport model calculations.Comment: 9 pages, 8 figures, accepted at Eur. Phys. Journ.
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