Parity Violation In Weak Interactions Research Articles

Stereoselectivity of beta irradiation of D,L-tryptophan in aqueous solution.

A POSSIBLE connection between the molecular asymmetry of living matter and the intrinsic asymmetry of elementary particles1 was first suggested by Vester2. All the experiments based essentially on the non-conservation of parity in weak interactions3,4 can be classified as follows: (1) It is assumed that L- and D-enantiomers are not exact mirror images of each other but differ in their scalar physicochemical properties5,6. Parity-violating forces originated by weak interactions could in principle give rise to different bond strengths in enantiomer molecules. If the recently discovered neutral weak currents turn out to be of vector and axialvector type—an opinion favoured by present neutrino experiments7–9—there is necessarily an interference between parity-conserving electromagnetic interaction and parity-violating weak interaction; it might, however, be very small23. The question whether a particular molecular quantum state does allow for the actual occurrence of a seizable parity-violating effect has, to our knowledge, not yet been settled. (2) It is supposed that the almost exclusive existence of one enantiomer in the biosphere is due to the asymmetric interaction of longitudinally polarised β rays with molecules (interaction either with racemic mixtures or with molecules undergoing reaction to form asymmetric compounds) during the early history of the earth. With this view it is believed that an induced optical activity is a result of the natural radiation from isotopes in the earth's crust4,10,11. Experiments which aimed to generate optical activity in this manner are summarised in Table 1.

Parity Mixing and Nuclear Structure in the Decays from OrientedGd153,159andTb161

Measurement of the angular distribution of the 363-keV $\ensuremath{\gamma}$ radiation following the decay of $^{159}\mathrm{Gd}$ oriented in Gd${\mathrm{Fe}}_{2}$ at low temperatures has yielded a vanishing value of the parity-non-conserving forward-backward asymmetry, indicating in this transition no large effect resulting from the parity-violating weak nucleon-nucleon interaction. Vanishing asymmetries were observed for other strongly hindered transitions in $^{159}\mathrm{Tb}$ and in $^{161}\mathrm{Dy}$. The 0-90\ifmmode^\circ\else\textdegree\fi{} anisotropy of the 363-keV angular distribution has yielded a value for the magnetic moment of the $^{159}\mathrm{Gd}$ ground state of $\ensuremath{\mu}=(\ensuremath{-}0.44\ifmmode\pm\else\textpm\fi{}0.03){\ensuremath{\mu}}_{N}$. The magnitude of the hyperfine field of Tb in Gd${\mathrm{Fe}}_{2}$ has been estimated to be 370 \ifmmode\pm\else\textpm\fi{} 80 kG, based on observation of the 0-90\ifmmode^\circ\else\textdegree\fi{} anisotropy of $\ensuremath{\gamma}$ transitions in $^{161}\mathrm{Dy}$. The multipole characters of various $\ensuremath{\beta}$ and $\ensuremath{\gamma}$ transitions following the decay of oriented $^{153,159}\mathrm{Gd}$ and $^{161}\mathrm{Tb}$ have been deduced.

THE HISTORY OF DOUBLE SCATTERING OF ELECTRONS AND EVIDENCE FOR THE POLARIZATION OF BETA RAYS

It is pointed out that in 1928 Cox, McIlwraith, and Kurrelmeyer (Proc. Natl. Acad. Sci. U.S. l4, 544) performed experiments in double scattering of Ra beta rays which evidence negative helicity for beta rays and, therefore, parity violation in weak interactions. Further experimentation is reviewed and discussed. (T.R.H.)

Circular polarization of bremsstrahlung from high energy electrons with arbitrary polarization

In view of the recently discovered possibilities of producing polarized electrons in parity-violating weak interactions --- BETA decay and mu -meson decay --- circular polarization of bremsstrahlung becomes of interest as a means for detecting the polarization. The bremsstrahlung circular polarization is found to be sensitive to transverse polarization; thus at high energies, E1 >> mc2, where Coulomb scattering is no longer feasible, it offers another possibility for detecting transverse electron spins. The Born approximation differential cross section was derived, and a summation over flnal electron spins and integration over final electron momenta were performed, with a result feasible for experimental application. The following general results were found: (1) bremsstrahlung is both linearly and circularly polarized; (2) the linear polarization is independent of any polarization of the initial electron; (3) circular pelarization occurs only for polarized initial electrons, (4) if this circular polarization is not observed, the radiation has the same angular distribution and spectrum as that from unpolarized electrons.

Unrenormalizable interactions and the structure of elementary particles

A possible relation of the unrenormalizable interactions to the internal structure of elementary particles is approached with the help of a simple model. A non-local, charge-independent, and CP (combined) invariant interaction is examined and a simple connection is found to emerge between the problems of parity violation in weak interactions and the divergence of self-energy. The connection involves a supposed universal fundamental length.