59 research outputs found
Electroproduction of pseudoscalar mesons on the deuteron
A general analysis of polarization phenomena for coherent meson
electroproduction on deuterons, , where is a
pseudoscalar or -meson, is presented. The spin structure of the
electromagnetic current for -production at threshold is parametrized in
terms of specific (inelastic) threshold electromagnetic form factors which
depend on the momentum transfer squared and the effective mass of the produced
hadronic system. We give expressions for the structure functions of the
reaction (where the deuteron target is polarized) in
terms of these threshold form factors. The spin and isospin structures of the
amplitudes (where is a virtual photon) is
established in the framework of the impulse approximation and relationships
between meson electroproduction on deuterons and on nucleons are given. The
reaction of electroproduction on deuterons is investigated in detail
both at threshold and in the region of -isobar excitation, using the
effective Lagrangian approach for the calculation of the amplitudes of the
elementary process . Special attention is devoted to the
analysis of all standard contributions to the exclusive cross section for
, which are functions of the momentum transfer square, , of
the excitation energy of the produced hadrons and of the pion production angle,
in a region of relatively large momentum transfer. The sensitivity of these
contributions to different parametrizations of the form
factor as well as to the choice of potential is discussed.Comment: 44 pages 19 figure
Coherent electroproduction on the deuteron
A general analysis of polarization phenomena for coherent pion electroproduction on deuterons is presented. The spin and isospin structures of the amplitudes (where is a virtual photon) are established and relationships between meson electroproduction on deuterons and on nucleons are given in the framework of the impulse approximation. The reaction is investigated in detail, for a relatively large value of momentum transfer, 0.5 GeV 2 GeV, both at threshold and in the region of -isobar excitation. Special attention is devoted to the sensitivity of different contributions to the exclusive cross section for , as the form factor or the potential. The predicted -dependence of the cross section agrees well with the available experimental data
Neutral weak currents in pion electroproduction on the nucleon
Parity violating asymmetry in inclusive scattering of longitudinally
polarized electrons by unpolarized protons with or meson
production, is calculated as a function of the momentum transfer squared
and the total energy of the -system. This asymmetry, which is
induced by the interference of the one-photon exchange amplitude with the
parity-odd part of the -exchange amplitude, is calculated for the
processes ( is a virtual photon and
a virtual Z-boson) considering the -contribution in the channel,
the standard Born contributions and vector meson ( and )
exchanges in the channel. Taking into account the known isotopic properties
of the hadron electromagnetic and neutral currents, we show that the P-odd term
is the sum of two contributions. The main term is model independent and it can
be calculated exactly in terms of fundamental constants. It is found to be
linear in . The second term is a relatively small correction which is
determined by the isoscalar component of the electromagnetic current. Near
threshold and in the -region, this isoscalar part is much smaller (in
absolute value) than the isovector one: its contribution to the asymmetry
depend on the polarization state (longitudinal or transverse) of the virtual
photon.Comment: 30 pages 9 figure
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