Recoil Polarization Research Articles

Vector meson production by and compton scattering of polarized photons off polarized nucleons

A general analysis of vector meson production by polarized photons off polarized nucleons is presented. The cross section and vector meson decay angular distribution are discussed in terms of s-channel helicity amplitudes for natural and unnatural parity exchange. For the special case of an unpolarized target the recoil polarization is also discussed. The question of experiments suitable for analyzing natural and unnatural parity exchange is investigated in detail for the case of ϱ 0-production. As a special case, Compton scattering is discussed.

Kaon photoproduction

A simple Regge model for high-energy K + photoproduction is constructed from kaon and exchange degenerate K ∗ (892) - K ∗∗ (1420) trajectories, together with absorption of the low partial waves. Use of SU(3) symmetry and vector-meson-dominance results leaves little freedom in choice of parameters. The model requires the Λ recoil polarization asymmetry to be negative in accordance with recent measurement. The main purpose however is to prepare for an attempt, by extrapolation of the photoproduction model to lower energies and spacelike photon four-momenta, to predict cross sections for K + electroproduction. This is dealt with in the following paper.

Recoil polarization in K + Λ photoproduction at 5 GeV

The Λ polarization in the reaction γp → K + Λ has been measured using the decay Λ → pπ − as an analyzer. It is found to be large and negative in the momentum transer range 0.2 ⩽ | t| ⩽ 1.0 (GeV/ c) 2.

Regge Pole Model with the Diffractive Correction. IV

We analyze a considerable amount of data on the forward π0(in detail) and π+(π-) photoproduction in terms of Regge pole model with the diffractive correction. Our results agree qualitatively well with the differential cross section ((s-m2)2dσ/ dt ( γp →π0p)) and the π0 photoproduction asymmetry with polarized photon (at 3.4 GeV). Further we predict the ratio of dσ/ dt (γp →π0p) / dσ/ dt(γn →π0n) and the recoil polarization p(t) and the polarized target asymmetry T(t).

Magnetic Moments of Short-Lived β-Radioactive Nuclei, 12B and 12N

The magnetic moments of 12 B( T 1/2 =20 ms) and 12 N( T 1/2 =11 ms) have been determined by an NMR method using the recoil polarization and the asymmetric β decay. The nuclear polarization was preserved by using a holding static magnetic field and a recoil stopper of metal foil. Several kinds of metal foils were employed. Relative shifts of the order of 10 -3 between the centers of NMR by different metals and the resonance widths comparable to the dipolar broadening were observed. The results obtained for the magnetic moments are µ( 12 B, 1 + )=+(1.003±0.001) nm and µ( 12 N, 1 + )=+(0.4571±0.0005) nm.

Nuclear Polarization in theB11(d,p)B12Reaction. II

Measurements have been made of the polarization of the ${\mathrm{B}}^{12}$ recoil nuclei resulting from the ${\mathrm{B}}^{11}(d,p){\mathrm{B}}^{12}$ reaction for ${E}_{d}$ in the range 0.90 to 3.20 MeV. The polarization is observed by measuring the $\ensuremath{\beta}$-decay asymmetries of the ${\mathrm{B}}^{12}$ recoil nuclei with respect to the reaction plane. The ${\mathrm{B}}^{12}$ recoil nuclei formed in the ground state are separated kinematically from those in excited states and are then stopped in various solids in the presence of a small magnetic field normal to the reaction plane. The sign of the observed polarization for all measurements is in the direction of the vector ${\mathbf{k}}_{d}\ifmmode\times\else\texttimes\fi{}{\mathbf{k}}_{p}$. The magnitude of the polarization is strongly dependent on ${E}_{d}$, the recoil emission angle and the material used to stop the recoils. It is found that the polarization of ${\mathrm{B}}^{12}$ nuclei can be maintained in either metallic Pd or Au at room temperature, using holding fields smaller than 20 G. For recoils stopped in Pt metal, a magnetic field of about 200 G is required to maintain the nuclear polarization. The ${\mathrm{B}}^{12}$ recoil polarization plotted as a function of ${E}_{d}$ shows definite structure. Polarization resonances are observed at 1.5, 2.1, and 3.0 MeV. At these energies the measured relative polarizations are +(8.01\ifmmode\pm\else\textpm\fi{}0.30)%, +(4.29\ifmmode\pm\else\textpm\fi{}0.30)%, and +(3.86\ifmmode\pm\else\textpm\fi{}0.27)%, respectively, for a Pt metal recoil stopper and a 49\ifmmode^\circ\else\textdegree\fi{} (lab) recoil angle. These resonances are tentatively identified with states of the ${\mathrm{C}}^{13}$ compound nucleus near 20.0 MeV and at 20.52 and 21.28 MeV. It is believed that the polarization resonances may result from an interference between direct interaction and two-particle compound resonance processes.

Nuclear Polarization in theB11(d,p)B12Reaction. I

Measurements of the polarization of the ${\mathrm{B}}^{12}$ recoils produced in the ${\mathrm{B}}^{11}(d,p){\mathrm{B}}^{12}$ reaction have been made using a variety of recoil stopping materials. A lower limit of $P\ensuremath{\ge}+(0.0436\ifmmode\pm\else\textpm\fi{}0.0021)$ is set for the recoil polarization in the direction of ${\mathbf{k}}_{d}\ifmmode\times\else\texttimes\fi{}{\mathbf{k}}_{p}$ at ${E}_{d}=3.1$ MeV and 53\ifmmode^\circ\else\textdegree\fi{} recoil angle.

Spin-zero photoproduction parity experiments beyond the threshold region

It is suggested that parity determining experiments can often be greatly simplified if one can assume that only the few lowest angular momentum states are important. The assumptions made here are not as restrictive as those made for the conventional threshold experiments, and hence the applicability of the schemes is much wider. In particular, a parity experiment is suggested in the photoproduction of spin-zero bosons which does not require polarized photons at all, and which is well within present day experimental techniques. It involves two measurements at the same energy and angle, one measuring the recoil polarization of the fermion, and the other the differential cross section from a polarized target.

Energy Dependence and Absorption in the Use of Recoil Polarization fromπ−−pScattering

The use of recoil polarization to determine angular momentum assignments for the second and third resonances in ${\ensuremath{\pi}}^{\ensuremath{-}}\ensuremath{-}p$ scattering is found to be qualitatively unaffected by the presence of absorption in the resonant states. The energy dependence of the polarized cross section in the vicinity of a resonance is shown to give some information about both the background and the resonant state. The polarized cross section is expected to increase across a resonance if $L=J+\frac{1}{2}$ and decrease if $L=J\ensuremath{-}\frac{1}{2}$.

Coulomb corrections in allowed beta transitions

Abstract Complete expressions, with all Coulomb effects taken into account, are given for the distribution functions for allowed beta decay, including recoil, nuclear orientation, and electron polarization effects. The expressions are general in that no assumptions are made as to invariance with respect to space inversion, charge conjugation, or time reversal. Simple arguments based on the behaviour of the various momenta and angular momenta under space inversion and time reversal are used to elucidate which combinations of vectors will appear when the different symmetry laws are violated, and the modifications of these arguments necessary because of the Coulomb interaction in the final state are pointed out. Various tests of time reversal invariance, previously suggested, are re-evaluated in view of the results for the Coulomb corrections.