882 research outputs found
Two-photon-exchange effects in the electro-excitation of the resonance
We evaluate the two-photon exchange contribution to the process at large momentum transfer with the aim of a
precision study of the ratios of electric quadrupole (E2) and Coulomb
quadrupole (C2) to the magnetic dipole (M1) transitions. We
relate the two-photon exchange amplitude to the generalized
parton distributions and obtain a quantitative estimate of the two-photon
effects. The two-photon exchange corrections to the C2/M1 ratio depend strongly
on whether this quantity is obtained from an interference cross section or from
the Rosenbluth-type cross sections, in similarity with the elastic, , process.Comment: 4 pages, 4 figure
Beam normal spin asymmetry for the process
We calculate the single spin asymmetry for the
process, for an electron beam polarized normal to the scattering plane. Such
single spin asymmetries vanish in the one-photon exchange approximation, and
are directly proportional to the absorptive part of a two-photon exchange
amplitude. As the intermediate state in such two-photon exchange process is on
its mass shell, the asymmetry allows one to access for the first time the
on-shell as well as electromagnetic
transitions. We present the general formalism to describe the beam normal spin asymmetry, and provide a numerical estimate of its
value using the nucleon, , , and
intermediate states. We compare our results with the first data from the
Qweak@JLab experiment and give predictions for the A4@MAMI experiment.Comment: 18 pages, 9 figure
Empirical transverse charge densities in the deuteron
Using the recent empirical information on the deuteron electromagnetic form
factors we map out the transverse charge density in the deuteron as viewed from
a light front moving towards the deuteron. The charge densities for a
transversely polarized deuteron are characterized by monopole, dipole and
quadrupole patterns.Comment: 4 pages, 2 figure
Two- photon exchange correction to 2S-2P splitting in muonic He-3 ions
We calculate the two-photon exchange correction to the Lamb shift in muonic He-3 ions within the dispersion relations framework. Part of the effort entailed making analytic fits to the electron-He-3 quasielastic scattering data set, for purposes of doing the dispersion integrals. Our result is that the energy of the 2S state is shifted downwards by two-photon exchange effects by 15.14(49) meV
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