Effect of field polarizations on recoil resonances

The effect field polarization has on the amplitude of recoil-induced resonances is considered for laser-cooled free atoms and for atoms in an operating magneto-optical trap. Explicit analytical expressions for the polarization dependence of resonance amplitudes in perturbation theory are obtained for all closed dipole transitions. Optimum conditions of polarization are found for the observation of resonances.     

Calculation of proton polarization in deuteron disintegration with longitudinally polarized electrons

For the reaction dependences of the proton polarization on the deuteron electromagnetic current and on the final-state interaction are studied. The possibility of separation of the structure functions contributing to this observable is discussed. Polarizations of protons in are calculated for the kinematics of a proposed measurement in the MIT-Bates research program.     

Threshold electrodisintegration of the deuteron caused by backward scattering of electrons

Using a new relativistic integral representation for the matrix element of electromagnetic current in terms of experimental phase shifts alone (representation of Shirokov RS) the cross section of the threshold electrodisintegration of the deuteron caused by backward scattered electrons is calculated for the S-wave deuteron in the interval of the four-momentum transfers squared 0.16 ? q² ? 5 fm^?2. Nucleon-nucleon interaction in the deuteron and the final state interaction (FSI) are taken into account in a unified manner and exactly. The effects of the meson exchange currents (MEC) and the inelastic n-p channels are neglected. The calculated cross section coincides with the experimental one.     

Measurement of the asymmetry in the emission of Röntgenbremsstrahlung produced by transversely polarized electrons

The asymmetric emission of Röntgenbremsstrahlung produced in the scattering of transversely polarized electrons by Au-atoms was measured at an electron energy ofE =mc ²/4 for photon emission anglesθ=60°, 100°, 145° and compared to calculations of this process based on a partial waves method.     

The Coulomb resonances and dynamics of electrodisintegration of nuclei by high-energy electrons

The effect of the Coulomb resonances and quasi-real photons on the dynamics of electrodisintegration of nuclei by high-energy electrons is investigated in the framework of the nuclear shell model.     

Active polarized target: Measurement of proton spin polarizabilities

The static (electric and magnetic) polarizabilities of the proton are known from measurements of low-energy Compton scattering of real photons. However, no experimental data are so far available about its spin polarizabilities, which describe the response of the proton spin to a varying electromagnetic field. These fundamental structure constants can be obtained in the most model-independent way from measurements of double-polarized Compton scattering at energies below the pion threshold using a polarized photon beam and a polarized proton target. An active polarized target based on polystyrene doped with a scintillator allows recoil protons to be detected directly in the target material, background from the coherent Compton effect on heavier nuclei (¹²C etc.) to be eliminated and precise data on spin polarizabilities to be obtained.     

Beta decay of polarized Λ hyperons III. Correlations in the Λ centre-of-mass system and the proton recoil spectrum

From the analysis of 817 kinematically resonstructed beta decay events of polarized Λ hyperons for the coefficient α_ν of the neutrino correlation with respect to the Λ spin, α_ν = 0.89 ± 0.08, for the coefficient α_T of the T-odd correlation σ_Λ(p_e × p_ν), α_T = ?0.14 ± 0.13. The proton recoil spectrum yields …g₁/f₁… = 0.64 ± 0.06.     

Zeeman transitions in deuterium atoms induced by ultra-relativistic electrons

We present data showing hyperfine transitions in an atomic deuterium beam induced by the (476 MHz) radio-frequency field of a 704 MeV electron beam in a storage ring. A polarized deuterium beam, produced in an atomic beam source, was crossed with a stored electron beam and analyzed with a Breit--Rabi polarimeter. Electron-beam induced transitions were singled out by injecting different combinations of hyperfine states. Transition probabilities as high as 70% were measured at large currents (~ 100 mA). All possible deuterium transitions for a radio-frequency of 476 MHz were observed. In addition, a 1--6 transition resulting from the first harmonic (952 MHz) was observed. The effects of these transitions are of general importance for the polarized internal target technique applied in nuclear and particle physics experiments. The data are reasonably described by numerical estimates. The observed mechanism can be exploited to create nuclear polarized atoms when injecting electron polarized atoms with no net nuclear polarization into a storage cell. However, when nuclear polarized atoms are injected, care should be taken to avoid this mechanism, since it would result in depolarization of the atoms. The studies enabled us to choose the magnetic guide field during our spin-dependent electron--deuteron scattering experiments, such that electron-beam induced depolarizing effects were avoided. This revised version was published online in July 2006 with corrections to the Cover Date.     

Site-specific recoil diffraction of backscattered electrons in crystals

A novel diffraction effect in high-energy electron backscattering is demonstrated: the formation of element-specific diffraction patterns via nuclear recoil. For sapphire (Al(2)O(3)), the difference in recoil energy allows us to determine if an electron scattered from aluminum or from oxygen. The angular electron distribution obtained in such measurements is a strong function of the recoiling lattice site. These element-specific recoil diffraction features are explained using the dynamical theory of electron diffraction. Our observations open up new possibilities for local, element-resolved crystallographic analysis using quasielastically backscattered electrons in scanning electron microscopy.     

Vector meson production by inelastic scattering of polarized electrons off polarized nucleons

A general analysis of vector meson production by inelastic scattering of polarized electrons (or muons) off polarized nucleons is presented. Cross section and vector meson decay angular distribution are discussed in terms of s-channel helicity amplitudes for natural and unnatural parity exchange. The question of experiments suitable for analyzing the more refined dynamical features of ?⁰-production is discussed in detail. Estimates are given for the effects to be expected from unnatural parity exchange.     

The production of roentgenbremsstrahlung by transversely polarized electrons

The production of bremsstrahlung by transversely polarized electrons shows an azimuthal asymmetry. Measurements and calculations of this effect are presented. They indicate that the partial waves method — in the form used by Tseng and Pratt — is suitable to describe this polarization correlation.     

Asymmetry of bremsstrahlung by moderately relativistic polarized electrons

The asymmetry of bremsstrahlung by transversely polarized electrons using Sommerfeld–Maue wave functions has been calculated. In order to simplify the final formula the relativistic approximation has been used. The results obtained show a linear dependence of the asymmetry on the atomic number Z for the range 4≤Z≤26. It is shown that the approach developed gives the zeroth asymmetry for ultrarelativistic energies as expected but for initial electron energies ～5 MeV the asymmetry may achieve a magnitude ～8% (for Z=26). Polarimetry of electrons with energy higher than 1 MeV (where conventional Mott polarimeters have large experimental difficulties) may be carried out using the bremsstrahlung process providing a reasonable asymmetry and high cross section.     

Jet production in polarized proton proton scattering

We propose a model of polarized partonic densities based on Regge behaviour, quark counting rules,U(1) _A Goldberger-Treiman relation and positivity constraints. The resulting polarized proton structure function is found to be in agreement with EMC and SLAC data. From this input we compute double helicity asymmetries for 1 and 2 jet inclusive production in polarized proton proton scattering at high energies. We obtain asymmetries of 10–20% at energies \(\sqrt s = 50 - 500\) GeV.     

Polarized recoil nuclei from nuclear reactions induced by polarized lithium ions

The production of vector polarized recoil nuclei was investigated for nuclear reactions initiated by vector polarized⁶Li and⁷Li beams of energies up to 20 MeV. The vector polarization was detected by theβ-asymmetry of the decaying recoil nuclei implanted into various stopper materials. Considerable polarization values were observed for⁸Li produced in the systems⁷Li+⁹Be,⁷Li+⁷Li and⁶Li+⁷Li, and for¹²B in the systems⁷Li+⁷Li and⁶Li+¹¹B. However, no polarization has been observed for heavier nuclei with unknown nuclear moments. The relaxation of the vector polarization of⁸Li implanted into various stopper materials at room temperature was investigated in detail. For a gold stopper it was found to be much larger when compared to earlier results.     

New possibilities for studying nucleon resonances in the production of π + π − pairs by polarized electrons on an unpolarized proton

The difference of the cross sections for double charged-pion production in the scattering of opposite-helicity electrons on an unpolarized proton is evaluated within the phenomenological model developed previously. The electromagnetic nucleon-resonance form factors and the parameters of nonresonance processes were taken from a fit to the latest data of the CLAS Collaboration on double charged-pion electroproduction. The effect of the longitudinal excitations of the P ₁₁(1440) and D ₁₃(1520) states on the difference of the helicity components of the cross section is studied. The sensitivity of this observable to the nucleon-resonance contribution opens the possibility of employing it both in extracting the Coulomb form factors and in seeking new baryon states. Signals from one of these states were possibly observed in the latest data of the CLAS Collaboration.