Unpolarized Deuterons Research Articles

The WASA Facility at COSY

The WASA (Wide Angle Shower Apparatus) facility is a 4π detector system for charged and neutral particles that has been designed to study production and decay of light mesons. After successful operation at CELSIUS the facility has started data taking as fixed target internal experiment at the COoler SYnchrotron and storage ring COSY [1] at Forschungszentrum Jülich in 2007. COSY delivers beams of polarized and unpolarized protons and deuterons in the momentum range between 0.3 and 3.7 GeV/c. In collisions with a hydrogen or deuterium target, mesons with masses up to the φ meson can be produced. The WASA detector setup (Figure 1) comprises a forward part to measure charged target-recoil particles and scattered projectiles, a central part to measure meson decay products, and a pellet target.

Exclusive Scattering from Unpolarized and Polarized Deuteron

We present results for exclusive electron scattering from polarized and unpolarized deuteron. We employ the Gross equation to describe the deuteron ground state, and we use the SAID parametrization of the full NN scattering amplitude to describe the final state interactions. We discuss properties of various asymmetries accessible with a polarized deuteron target and/or a polarized beam.

Measurement of azimuthal asymmetries associated with deeply virtual Compton scattering on an unpolarized deuterium target

Azimuthal asymmetries in exclusive electroproduction of a real photon from an unpolarized deuterium target are measured with respect to beam helicity and charge. They appear in the distribution of these photons in the azimuthal angle ϕ around the virtual-photon direction, relative to the lepton scattering plane. The extracted asymmetries are attributed to either the deeply virtual Compton scattering process or its interference with the Bethe–Heitler process. They are compared with earlier results on the proton target. In the measured kinematic region, the beam-charge asymmetry amplitudes and the leading amplitudes of the beam-helicity asymmetries on an unpolarized deuteron target are compatible with the results from unpolarized protons.

Parity-violating effects in elastic electron deuteron scattering

The general expressions for parity violation observables in elastic scattering of polarized and/or unpolarized electrons from unpolarized deuterons are given and are numerically evaluated for the kinematics of SAMPLE, PVA4 and G0 experiments. The dominant contribution from the interference of \( \gamma\) and Z exchange as well as the smaller contributions from strangeness (s \( \bar{{s}}\) components of the nucleon, parity odd admixtures in the deuteron wave function, anapole moments and radiative corrections are included and discussed in the context of parity-violating electron scattering experiments of present interest.

Status of the investigation of the spin structure of d, 3H, and 3He at VBLHE using polarized and unpolarized deuteron beam

The investigation of the spin structure of d, 3H, and 3He has been performed at the RIKEN acceleration research facility and VBLHE. Vector A y and tensor A yy , A xx , A xz analyzing powers for $$ \vec d $$ d → 3Hen and $$ \vec d $$ d → 3Hp are presented at 270 MeV. Themirror channels (3Hen and 3Hp) are comparedto each other in order to find possible manifestation of charge-symmetry breaking. The preliminary results on the polarization observables for $$ \vec d $$ d → 3Hp at 200MeV are also presented. The obtained data are compared with one-nucleon-exchange calculations.As a byproduct, $$ \vec d $$ d → pX and $$ \vec d $$ 12C → pX breakup reactions are investigated at 140, 200, and 270MeV. The experimental data on $$ \vec d $$ p elastic scattering were obtained at 270, 880, and 2000 MeV at the Nuclotron. The polarization of the deuteron beam was measured at 270 MeV at the internal target station. The preliminary data on the vector A y and tensor A yy , A xx analyzing powers for the $$ \vec d $$ p elastic scattering at 880 MeV are presented. The calculations on A y , A yy , and A xx analyzing powers for the $$ \vec d $$ p elastic scattering at 880 MeV were performed in the framework of the multiple-scattering model.

Measurements of the total-cross-section difference Δσ L(np) at 1.39, 1.69, 1.89, and 1.99 GeV

New accurate data of the neutron-proton spin-dependent total-cross-section difference Δσ L(np) at the neutron-beam kinetic energies 1.39, 1.69, 1.89, and 1.99 GeV are presented. In general, these data complete the measurements of energy dependence of Δσ L(np) over the Dubna Synchrophasotron energy region. Measurements were carried out at the Synchrophasotron of the Veksler and Baldin Laboratory of High Energies of the Joint Institute for Nuclear Research. The quasi-monochromatic neutron beam was produced by breakup of extracted polarized deuterons. The deuteron (and hence neutron) polarization direction was flipped every accelerator burst. The initial transverse (with respect to beam momentum) neutron polarization was changed to a longitudinal one and longitudinally polarized neutrons were transmitted through the large proton longitudinally polarized target. The target polarization direction was inverted after one to two days of measurements. Four different combinations of the beam and target parallel and antiparallel polarization directions, both oriented along the neutron-beam momentum, were used at each energy. A fast decrease in −Δσ L(np) with increasing energy above 1.1 GeV and a structure in the energy dependence around 1.8 GeV, first observed from our previous data, seem to be well revealed. The new results are also compared with model predictions and with phase-shift analysis fits. The Δσ L quantities for isosinglet state I = 0, deduced from the measured Δσ L(np) values and known Δσ L(pp) data, are also given. The results of the measurements of unpolarized total cross sections σ 0tot(np) at 1.3, 1.4, and 1.5 GeV and σ 0tot(nC) at 1.4 and 1.5 GeV are presented as well. These data were obtained using the same apparatus and high-intensity unpolarized deuteron beams extracted either from the Synchrophasotron or from the Nuclotron.

Measurement of the np total cross section difference $\Delta\sigma_{\mathrm L}(np)$ at 1.39, 1.69, 1.89 and 1.99 GeV

New accurate results of the neutron-proton spin-dependent total cross section difference \(\Delta\sigma_{\mathrm L}(np)\) at the neutron beam kinetic energies 1.39, 1.69, 1.89 and 1.99 GeV are presented. Measurements were carried out in 2001 at the Synchrophasotron of the Veksler and Baldin Laboratory of High Energies of the Joint Institute for Nuclear Research. A quasi-monochromatic neutron beam was produced by break-up of extracted polarized deuterons. The deuteron (and hence neutron) polarization direction was flipped every accelerator burst. The vertical neutron polarization direction was rotated onto the neutron beam direction and longitudinally (L) polarized neutrons were transmitted through a large proton L-polarized target. The target polarization vector was inverted after 1-2 days of measurements. The data were recorded for four different combinations of the beam and target parallel and antiparallel polarization directions at each energy. A fast decrease of \(\Delta\sigma_{\mathrm L}(np)\) with increasing energy above 1.1 GeV was confirmed. The structure in the \(\Delta\sigma_{\mathrm L}(np)\) energy dependence around 1.8 GeV, first observed from our previous data, seems to be well pronounced. The new results are also compared with model predictions and with phase shift analysis fits. The \(\Delta\sigma_{\mathrm L}\) quantities for isosinglet state I = 0, deduced from the measured \(\Delta\sigma_{\mathrm L}(np)\) values and the known \(\Delta\sigma_{\mathrm L}(pp)\) data, are also given. The results were completed by the measurements of unpolarized total cross sections \(\sigma_{0\mathrm{tot}}(np)\) at 1.3, 1.4 and 1.5 GeV and \(\sigma_{0\mathrm{tot}}(n\)C) at 1.4 and 1.5 GeV. These data were obtained using the same apparatus and high intensity unpolarized deuteron beams were extracted either from the Synchrophasotron, or from the Nuclotron.

Parity violation in deuteron photodisintegration

We analyze the energy dependence for two types of parity-non-conserving (PNC) asymmetries in the reaction $\gamma D\to np$ in the near-threshold region. The first one is the asymmetry in reaction with circularly polarized photon beam and unpolarized deuteron target. The second one corresponds to those with an unpolarized photon beam and polarized target. We find that the two asymmetries have quite different energy dependence, and their shapes are sensitive to the PNC-meson exchange coupling constants. The predictions for the future possible experiments to provide definite constraints for the PNC-coupling constants are discussed.

HERA-3

A brief review is given on the physics potential of HERA beyond the presently approved programme. Questions of particular interest include QCD in a regime of weak coupling and high partonic densities achieved in eA collisions and spin physics with polarized colliding beams. Those two distinct programmes can be naturally merged and even substantiated by using polarized and unpolarized deuterons at the starting phase of the HERA-3 run. Basic machine implications and detector requirements are also discussed.

Parity-nonconservation effects in the photodisintegration of polarized deuterons

P-odd correlations in the deuteron photodesintegration are considered. The $\pi$-meson exchange is not operative in the case of unpolarized deuterons. For polarized deuterons a P-odd correlation due to the $\pi$-meson exchange is about $3 \times 10^{-9}$. Short-distance P-odd contributions exceed essentially than the contribution of the $\pi$-meson exchange.

The study of deuteron structure at short internucleon distances in reaction with hadronic probes

The possibility to use the reaction of deuterons fragmentation into cumulative hadrons is discussed. The experimental results and the theoretical calculations for reaction with polarized and unpolarized deuteron are presented.

Coherent photo- and lepto-production of vector mesons from deuterium

We discuss the coherent photo- and lepto-production of vector mesons from deuterium at intermediate (virtual) photon energies, 3 GeV ≲ ν ≲ 30 GeV. These processes provide several options to explore the space-time evolution of small size quark-gluon configurations. Furthermore, we study the dependence of the production cross section on the energy and momentum transfer t due to variations of the finite longitudinal interaction length. Kinematic regions are determined where the production cross section is most sensitive to the final state interaction of the initially produced hadronic wave packet. For unpolarized deuteron targets this double scattering contribution can be investigated mainly at large values of the momentum transfer t. For polarized targets kinematic windows sensitive to double scattering are available also at moderate t. We suggest several methods for an investigation of color coherence effects at intermediate energies.

On the unfolding of the neutron structure functions from the deuteron data

A new method for the extraction of the neutron structure functions from the combined data on the deep inelastic lepton scattering off proton and deuteron targets is proposed. The principal advantages of the method are: (i) only analyticity of the structure functions is assumed, and (ii) the spin-dependent structure functions may be considered as well, whereas the smearing factor method does not work is this case. To make clear the capabilities of the new method, we consider its application to the real data on polarized and unpolarized deuteron.

Neutrino- and antineutrino-deuteron elastic scattering and the axial isoscalar nucleon current.

We calculate the neutrino and antineutrino elastic scattering cross section on unpolarized deuterons at energies from a few MeV to several GeV and squared momentum transfers up to 5 ${\mathrm{GeV}}^{2}$. These cross sections can be used to deduce the unknown weak SU(2) isoscalar and SU(3) flavor-scalar axial-vector coupling to nucleons. This observable can be related to the strangeness axial-vector matrix element in the absence of QCD radiative or isospin-violating corrections. We show that the unknown weak magnetic vector coupling may also be gleaned from these measurements. We use different techniques at different energies, including light-cone impulse approximation at the highest energies, and show that they connect smoothly to each other.

Relativistic and meson exchange current effects in few nucleon systems

The Bethe-Salpeter approach is discussed for the A=2 and 3 system. Using a relativistic one boson exchange model the elastic em form factors are calculated. Predictions compare well with the experimental data. Within the same dynamical model fully relativistic meson exchange current contributions are determined and the structure functions for unpolarized deuteron disintegration are studied. Boost effects and the relativistic structure of the nucleon em operators are found to be important in certain kinematic regions. Relativistic corrections to the trinucleon binding energy are discussed using separable representations of the Paris and Bonn potentials.

Radiattonal capture of neutrons by deuterons n + d ?3H + ? and P-odd nuclear forces

P-odd polarizational phenomena are considered in the radiative capture of neutrons by deuterons: n + d →3H + γ. It is shown that, in the general case, 18 different P-odd asymmetries of the angular distribution of γ quanta arise in the collision of arbitrarily polarized neutrons with a deuteron target characterized by vector and tensor polarizations. The P-odd contribution to the density matrix of the λ quanta formed in the capture of polarized neutrons by unpolarized deuterons is determined by eight real structural functions, while the P-odd dependence of the Stokes parameters of the photons on the tensor polarization of the deuterons is characterized, in the general case, by ten structural functions. In slow-neutron capture, the number of P-odd correlations is reduced.

The mass of 35P and spin-parity assignments for excited 35P states

The 36S(d,3He)35P reaction was studied with 52 MeV unpolarized and vector-polarized deuterons. The mass excess of 35P was determined to be −24859±2 keV. Angular distributions of the differential cross sections dσ(θ)dω and the analyzing powers iT11(θ) for strongly excited states were measured. Excitation energies of various proton hole states were determined and the respective values of spin and parity were assigned. The DWBA analysis shows that these states exhaust nearly the complete pickup strength of the (2s,1d) shell.

Cross section and polarization in deuteron photodisintegration: General formulas

The differential cross section and the outgoing nucleon polarization in the disintegration of unpolarized deuterons by polarized photons are given as expansions in Legendre functions.NUCLEAR REACTIONS $d(\stackrel{\ensuremath{\rightarrow}}{\ensuremath{\gamma}}, n)p$. Differential cross section and polarization. Legendre function expansion.

Polarization of recoil deuterons in ed elastic scattering at medium energies

Vector and tensor polarizations of the recoil deuteron in ed elastic scattering are calculated for θ = 0°–180° and q 2 ⩽ 8 GeV/ c. A longitudinally polarized electron beam is assumed to scatter off an unpolarized deuteron target. Calculations are made in the relativistic impulse approximation using a recently described approach based on the Bethe-Salpeter equation with the time-ordered perturbation theory. The results are different, at high q 2 even qualitatively so, from those of a non-relativistic calculation, and a relativistic calculation which takes the spectator nucleon on-mass-shell. In the light of these results, a recent suggestion that polarization measurements would throw new light on the off-shell behavior and tensor force strength of the NN interaction is reexamined. Results are also presented for the three deuteron form factors G C , G Q and G M,and the often-needed related quantities S S, S Q and S M. The latter results may have an important implication in high-momentum transfer reactions involving deuterons.

Distinguishability ofSU(2)×U(1)×U′(1) andSO(10) gauge models from the Weinberg-Salam model

The predictions ofSU(2)×U(1)×U′(1) andSO(10) gauge models for the asymmetry parametersA-,B-,CL andCR in the deep inelastic scattering of polarized electrons and positrons by unpolarized protons and deuterons are compared with those calculated in the Weinberg Salam model for different values ofy. The model based on,SU(2)×U(1)×U′(1) group has been found almost indistinguishable from the Weinberg Salam model with regard to the parametersA-,B- andCL (except forB- in the region 0≦y≦0.2) althoughCR exhibits marked distinguishability. TheSO(10) model, for certain choice of its model parameters, can be distinguished from the Weinberg Salam model through measurement of the asymmetry parameters for different values ofy.