"Internal target experiments at the VEPP-3 storage ring, Novosibirsk"
Dimitri Mitrofanovich Nikolenko
Budker Institute of Nuclear Physics
Wednesday, January 19, 2005 -11 AM - 12:00 Noon in 375 Le Conte Hall
Abstract
The deuteron, as the simplest stable nuclear, is an ideal subject
for the investigation properties of the nucleon-nucleon interaction as well as
for the study of non-nucleon degrees of freedom. The relationship of these properties
to experimental observables is especially clear in the elastic
electron-deuteron scattering where the theoretical description in terms of form
factors is well known, and obscuring effects are small because the electromagnetic
force is relatively weak. However, although great number of works only at the
recent years the measurements of tensor polarization observables in the reactions with
electromagnetic probes and deuteron were performed. In the elastic
electron-deuteron scattering the polarization observables were measured by two
techniques: polarimeters of recoil deuterons (with both electron beam and target
unpolarized) and polarized internal gas targets in a storage ring (electron beam
unpolarized).
Elastic and inelastic scattering experiments with tensor polarized deuterium
target performed at 2GeV electron storage ring VEPP-3, Novosibirsk, will be discussed.
The measurement of tensor analyzing power components T20 and T21 in eleastic
scattering in a momentum transfer range from 8.4 to 21.6 fm^-2 determine the deuteron
quadrupole and monopole charge from factors in this important range of
momentum transfer where the first node of the deuteron monopole charge form factor is
located
The preliminary results of recent measurement of tensor analyzing power in
deuteron photo disintegration in general, are compatible with the existing theoretical
predictions, but several cases are discrepancies with available calculations.
Developed internal target technique was employed for the determination of
VEPP-3 electron beam polarization (Meoller polarimeter), that was important for the
preparation of the high-precision measurement of tau-lepton mass at the
electron-positron collider VEPP-4.
The electromagnetic form factors of the proton are important properties of this
fundamental object. However, recent polarization experiments, performed in TJNAF,
yielded unexpected results, indicating that the ratio of proton form factors
electric/magnetic depends strongly on the momentum transfer, while before
(from the unpolarized measurements) it had been assumed to be nearly constant. The possible
origin of these discrepancies is the failure of the onephoton approximation to
precisely describe the results of unpolarized experiments. Since the data for
two-photon exchange contribution are very poor, we plan to measure this contribution
through the comparison of electron-proton/positron-proton scattering, using the
possibility to have both electron and positron beams at the VEPP-3.
