Tensor-polarized Deuterium Target Research Articles

Measurements of the tensor analyzing power T20 of the reaction γd → dπ0

The paper presents the results of measurements of the tensor analyzing power component [Formula: see text] for the coherent neutral pion photoproduction on the deuteron. The measurements were performed in the Budker Institute of Nuclear Physics using the internal tensor polarized deuterium target at VEPP-3 storage ring. The measurements covered the region of the photon energy 240 — 420[Formula: see text]MeV and the region of the center-of-mass pion polar angle 100–140[Formula: see text]. The results of measurements were compared with the calculations performed within frameworks of several theoretical models.

Measurement of the Components of the Tensor Analyzing Power in the Reaction γD → ppπ– at Low Proton Energies

Results obtained by measuring three components of the tensor analyzing power in the reaction of π- meson photoproduction on deuterons in the range of photon energies 300–800 MeV and proton energies 15–70 MeV are presented. The experiment was performed with an internal tensor-polarized deuterium target at the VEPP-3 electron storage ring, employing the method of recording two protons in coincidence. The obtained measurement results for the tensor analyzing power are compared with theoretical predictions.

Measurement of a double spin asymmetry in the photoproduction of $\pi^{-}$ π - -mesons on deuterons

The paper presents results of a double polarization experiment to extract an asymmetry of the $\pi^{-}$ -meson photoproduction on a tensor-polarized deuteron by a linearly polarized photon. The energy of photons lies in the range (300-700) MeV. The measurements were performed on the internal tensor-polarized deuterium target in the VEPP-3 electron-positron storage ring for the electron beam energy equal to 2 GeV. In the experiment, two protons and a scattered electron were detected in coincidence. The results of the measurement are compared with theoretical predictions made in the framework of impulse approximation, taking into account the $\pi N$ and NN-rescattering in the final state.

Measurement of the Asymmetry of Photoproduction of π– Mesons on Linearly Polarized Deuterons by Linearly Polarized Photons

The first results of a double polarization experiment to extract the asymmetry of the reaction of photoproduction of a π- meson by a linearly polarized photon on a tensor-polarized deuteron in the energy range of the virtual photon (300–700 MeV) are presented. The measurements were performed on an internal tensor-polarized deuterium target in the VEPP-3 electron-positron storage ring for the electron beam energy equal to 2 GeV. The experiment employed the method of recording two protons and the scattered electron in coincidence. The obtained measurement results are compared with the theoretical predictions obtained in the momentum approximation with allowance for πN and NN rescattering in the final state.

Measuring tensor analyzing power component T 20 of the coherent photoproduction of a neutral pion on a tensor-polarized deuteron in the VEPP-3 storage ring

An experiment to measure tensor analyzing power component T 20 of the coherent photoproduction reaction of a neutral pion on a tensor-polarized deuterium target \(\left( {\gamma \vec d \to d\pi ^0 } \right)\) is described. Measurements are made in two kinematic ranges: photon energy E γ = 200–500 MeV and neutral pion escape angle \(\Theta _{\pi ^0 }^{cm} = 100^ \circ - 140^ \circ\), E γ = 300–600 MeV, and \(\Theta _{\pi ^0 }^{cm} = 40^ \circ - 70^ \circ\). A hyperfine internal gas polarized target is used in the experiment. Detectors of neutral pions and deuterons register these particles when they coincide. The degree of target polarization and experimental luminosity are measured via the registration of elastic electron scattering on a deuteron at a low momentum of transfer. The preliminary experimental results are compared to certain theoretical predictions.

Photoreactions with tensor-polarized deuterium target at VEPP–3

We give an overview of the activity in studying photoprocesses on a tensor-polarized deuterium target, which is carried out at the VEPP–3 electron storage ring. Recent experimental results on tensor asymmetries in two-body deuteron photodisintegration at the photon energy up to 500 MeV, and in coherent pion photoproduction on deuteron are presented. Plans to upgrade the facility and future experiments are discussed. Further progress is connected with the installation of a tagging system for almost-real photons. This would allow us to extend the measurements of polarization observables in photonuclear reactions on deuteron up to a photon energy of 1.5 GeV and permit to perform double polarized experiments – with linear polarized photon beams and tensor/vector polarized deuterium targets.

On the possibility to measure the imaginary part of the spin-dependent amplitude of zero-angle coherent elastic scattering in a spin-filter experiment with an unpolarized proton beam interacting with a polarized deuterium target

As deuterons pass through an unpolarized target, there appear the phenomena of spin rotation (oscillation) and spin dichroism of deuterons; both phenomena are the manifestation of the deuteron birefringence effect. The magnitude of the effect is determined by the refractive index of deuterons in matter, which depends on the spin-dependent part d1 of the amplitude of zero-angle coherent elastic scattering of the deuteron by the nucleus. Spin dichroism is determined by the imaginary part of this amplitude, and in view of the optical theorem, by the total scattering cross-section, which is different for different spin states of the deuteron. The phenomenon of spin dichroism of deuterons results in the fact that after passing through the target, the initially unpolarized deuteron beam acquires tensor polarization proportional to the difference in the total cross-sections of scattering of deuterons with different spin states by the nucleus. The stated difference was first measured for deuterons with energies up to 20 MeV, where the phenomenon of deuteron spin dichroism was experimentally revealed, and the deuteron tensor polarization was measured. The phenomenon of spin dichroism, i.e., the production of tensor polarization was also observed at high deuteron energy. In the present report we discuss the possibility that the imaginary part of the amplitude d1 of deuteron scattering by the proton may be determined experimentally by measuring the rate of the decrease in the intensity of an unpolarized proton beam in a storage ring as the beam passes through a tensor-polarized deuterium target.

Measurement of azimuthal asymmetries associated with deeply virtual Compton scattering on a longitudinally polarized deuterium target

Azimuthal asymmetries in exclusive electroproduction of a real photon from a longitudinally polarized deuterium target are measured with respect to target polarization alone and with respect to target polarization combined with beam helicity and/or beam charge. The asymmetries appear in the distribution of the real photons in the azimuthal angle ϕ around the virtual photon direction, relative to the lepton scattering plane. The asymmetries arise from the deeply virtual Compton scattering process and its interference with the Bethe–Heitler process. The results for the beam-charge and beam-helicity asymmetries from a tensor polarized deuterium target with vanishing vector polarization are shown to be compatible with those from an unpolarized deuterium target, which is expected for incoherent scattering dominant at larger momentum transfer. Furthermore, the results for the single target-spin asymmetry and for the double-spin asymmetry are found to be compatible with the corresponding asymmetries previously measured on a hydrogen target. For coherent scattering on the deuteron at small momentum transfer to the target, these findings imply that the tensor contribution to the cross section is small. Furthermore, the tensor asymmetry is found to be compatible with zero.

A first measurement of the tensor structure function b1d

The Hermes experiment studies the spin structure of the nucleon using the 27.6 GeV longitudinally polarized positron beam of HERA and an internal target of pure gases. In addition to the well-known spin structure function g 1 , measured precisely with longitudinally polarized proton and deuteron targets, the use of a tensor-polarized deuteron target provides access to the tensor structure function b 1 d . The latter, measured with an unpolarized beam, quantifies the dependence of the parton momentum distribution on the nucleon spin. Hermes had a 1-month dedicated run with a tensor-polarized deuterium target during the 2000 data taking period. Here preliminary results on the tensor structure function b 1 d are presented for the kinematic range 0.002 < χ < 0.85 and 0.1 GeV 2 < Q 2 < 20 GeV 2 .

Nucleon-nucleon correlations in the reaction of photoelectric production of a Δ isobar on a tensor-polarized deuterium target

Density matrix elements for a Δ isobar produced in the reaction γd→Δp are calculated in a relativistic momentum approximation. A correlation function is obtained for the directions of escape of the spectator proton and the nucleon from the decay Δ→Nπ. The influence of polarization of the target and of the potential of the nucleon-nucleon interaction on the correlation function is considered.

Intermediate-energy hadronic physics with the AmPS-NIKHEF facility

We report on recent experimental results obtained at the Amsterdam (700–900) MEV Pulse Stretcher and Storage ring (AmPS) at NIKHEF: high-momentum components in few-body ( 2H, 4He) and heavy-systems ( 208Pb); and two proton correlations from the (ee′pp) reaction on 16O. We discuss spin asymmetries measured with a tensor polarized deuterium target and a 100 mA beam stored in AmPS.

Physics results from the AmPS electron scattering facility

The programme in intermediate energy hadronic physics at NIKHEF (Amsterdam) with the Amsterdam Pulse Stretcher and Storage Ring (AmPS) is now in full operation. With the ring operating in stretcher mode a beam with a current of ≥ 10 μA and with a (50 – 70) % duty factor has been used to probe high momentum components in 208Pb with the quasi-free proton knockout reaction. Ongoing coincidence experiments of type ( e, e′ p) and ( e, e′2 p) with broadband proton detectors of 500 msr solid angle are presented. We discuss an experiment with the beam in storage mode interacting with a tensor-polarized deuterium target, a storage cell fed by an atomic beam source.

Polarization observables in pi d

The composite spin observable ${\ensuremath{\tau}}_{22}$\ensuremath{\equiv}(${T}_{22}$+${T}_{20}$/ \ensuremath{\surd}6 ) has been measured at five incident pion energies between 134 and 294 MeV, in an angular range between 90\ifmmode^\circ\else\textdegree\fi{} and 170\ifmmode^\circ\else\textdegree\fi{}, using a tensor-polarized deuterium target. New, accurate data for the vector analyzing power ${\mathrm{iT}}_{11}$ were obtained at the same time. In combination with the results reported in part I of this series, our measurements allow us to determine the three analyzing powers ${T}_{20}$, ${T}_{21}$, and ${T}_{22}$, separately, and compare them with existing theoretical calculations, all of which fail, in one way or another, to reproduce the entire data set.