39 research outputs found
Electroweak Processes in Few-Nucleon Systems
After a brief introduction into the basic ingredients of electroweak theory
as a spontaneously broken local, non-Abelian gauge symmetry, the general
properties of the electromagnetic current and two-photon operators are
discussed. The specific forms of vector and axial one-nucleon currents are
given, together with lowest order meson exchange and isobar currents as
well as meson production currents. A brief overview is given on the most
important one- and two-boson processes. Electron scattering in the one-boson-
approximation is then considered in greater detail. Formal expressions of the
cross section for inclusive and exclusive processes are given, including parity
violating contributions from - interference as well as from parity
violating components in the hadronic wave function. Specific electromagnetic
reactions on the deuteron are then discussed with respect to the influence of
meson exchange currents, isobar configurations in the deuteron groundstate,
relativistic contributions and the role of -meson retardation.
Furthermore, recent results on coherent and incoherent - and
-photoproduction are presented as well as a discussion of the
Gerasimov-Drell-Hearn sum rule and the effect of a parity violating deuteron
component on inclusive electron scattering off the deuteron for quasifree
kinematics. The review closes with a summary and a brief outlook.Comment: 56 pages latex including 42 postscript figures, Lectures held at the
Int. Workshop on Few-Body Problems in Nuclear Physics and Related Fields,
ECT, Trento, Italy, September 8-27, 199
The GDH sum rule for the deuteron
As first topic, the GDH sume rule is discussed in the context of a more
general class of sum rules associated with the various contributions to the
total photoabsorption cross section for target and beam polarization. Then I
address the question of whether the GDH sum rule for the neutron can be
determined from the one for the deuteron. It appears that this will not be
possible in a simple manner. The spin response of the deuteron is calculated
including contributions from the photodisintegration channel and from coherent
and incoherent single pion production as well, and the GDH integral is
evaluated up to a photon energy of 550 MeV. The photodisintegration channel
converges fast enough and gives a large negative contribution, essentially from
the state near threshold and its absolute size is about the same than
the sum of proton and neutron GDH values. It is only partially cancelled by the
single pion production contribution. But the incoherent channel has not reached
convergence at 550 MeV.Comment: talk at GDH-2000 Symposium, Mainz, 14.-17.6.2000 12 pages latex
including 3 figures, needs world scientific style (ws-p8-50x6-00.cls
Coulomb effects in polarization transfer in elastic antiproton and proton electron scattering at low energies
The influence of Coulomb distortion on the polarization transfer in elastic
proton and antiproton electron scattering at low energies is calculated in a
distorted wave Born approximation. For antiproton electron scattering Coulomb
effects reduce substantially the spin transfer cross section compared to the
plane wave Born approximation whereas for proton electron scattering they lead
to a dramatic increase for kinetic proton lab energies below about 20 keV.Comment: 10 pages, 7 figures Few typos corrected, accepted for publication in
Eur. Phys. J. A, few typos corrected, last sentence of conclusions change
Analysis of the low-energy NN-dynamics within a three-body formalism
The interaction of an -meson with two nucleons is studied within a
three-body approach. The major features of the -system in the
low-energy region are accounted for by using a s-wave separable ansatz for the
two-body - and -amplitudes. The calculation is confined to the
and configurations which are assumed to be the
most promising candidates for virtual or resonant -states. The
eigenvalue three-body equation is continued analytically into the nonphysical
sheets by contour deformation. The position of the poles of the three-body
scattering matrix as a function of the -interaction strength is
investigated. The corresponding trajectory, starting on the physical sheet,
moves around the three-body threshold and continues away from the
physical area giving rise to virtual -states. The search for poles on
the nonphysical sheets adjacent directly to the upper rim of the real energy
axis gives a negative result. Thus no low-lying s-wave -resonances
were found. The possible influence of virtual poles on the low-energy -scattering is discussed.Comment: 16 pages revtex including 10 figure
Interaction of mesons with a three-nucleon system
A study of the -3N interaction in the energy region near the -^3H
elastic scattering threshold is presented. The calculational scheme is based on
the four-body scattering formalism. A manageable form of the integral equations
is achieved by using a separable ansatz for the driving two-body - and
NN-forces as well as for the subamplitudes appearing in the (1+3) and (2+2)
partitions of the -3N system. Results presented for the -^3H
scattering length point to the existence of a virtual (antibound) s-wave
-^3H state. As a consequence, a large enhancement of the cross section
for -production from three-body nuclei is predicted.Comment: 4 pages including 2 eps-figures, Contribution to MESON 2002, 7th Int.
Workshop on Production, Properties and Interaction of Mesons, Cracow, Poland,
May 24-28, 200