Conserved Vector Current Predictions Research Articles

Test of the conserved vector current hypothesis by aβ-ray angular distribution measurement in the mass-8 system

The beta-ray angular correlations for the spin alignments of 8Li and 8B have been observed in order to test the conserved vector current (CVC) hypothesis. The alignment correlation terms were combined with the known beta-alpha-angular correlation terms to determine all the matrix elements contributing to the correlation terms. The weak magnetism term, 7.5\pm0.2, deduced from the beta-ray correlation terms was consistent with the CVC prediction 7.3\pm0.2, deduced from the analog-gamma-decay measurement based on the CVC hypothesis. However, there was no consistent CVC prediction for the second-forbidden term associated with the weak vector current. The experimental value for the second-forbidden term was 1.0 \pm 0.3, while the CVC prediction was 0.1 \pm 0.4 or 2.1 \pm 0.5.

Present status of e +e − → hadrons

The current status of the low energy measurements of e + e − annihilation into hadrons in Novosibirsk is described. Results of the calculations of the τ-lepton branching ratios based on the hypothesis of the conserved vector current (CVC) are presented. The consistency of CVC predictions for the branching ratios derived from e + e − data with the results from τ-lepton decays is discussed together with possible future improvements.

CVC and hadronic decays of τ lepton

Critical analysis of the tests of the conserved vector current (CVC) using data on τ -lepton decays into hadrons and e + e − → hadrons is presented. CVC predictions for the branching ratios and mass spectra derived from e + e − data are in general consistent with the data on τ decays. Limitations on the precision of CVC tests resulting from the available statistics are discussed.

The decay of theτ lepton to six pions

We present the branching ratio predictions of an isospin statistical model forτ decays to four, five and six pions. Limits on the branching ratios of the three possible six pionτ decay modes using the Conserved Vector Current (CVC) Hypothesis and thee+e−→6π cross section data are also presented. We find that the isospin model prediction is in good agreement with the well-measured four pion decay modes and consistent with the five pion decay modes. However, we find that some of the recent six pionτ measurements do not agree with the isospin model and the CVC prediction.

Measurement of the beta spectral shapes of 12B and 12N.

The spectral shapes of the {sup 12}B and {sup 12}N beta decays have been measured with a beta spectrograph specifically designed to examine the spectral effect of weak magnetism. Writing the weak magnetism correction to the beta spectra as (1+{alpha}{sub {plus minus}}{ital E}) we find the difference {alpha}{sub {minus}}{minus}{alpha}{sub +}=(1.24{plus minus}0.42)%/MeV, in agreement with the conserved vector current prediction.

Beta-alpha angular correlations in mass 8

A detailed study of the β∓-α angular correlations in the 8Li(β-) and 8B(β+) decays was performed. Since these decays proceed to the 2α continuum, detection of both alpha particles enabled determination of various correlations as functions of the final-state energy. The experimental results show a small (≈ 15% of weak magnetism) deviation from the conserved vector current prediction which is dependent on the final-state energy. An effect of this size cannot be interpreted as convincing evidence for the presence of second-class currents or a breakdown of conserved vector current theory. However, the inclusion of the vector second-forbidden terms in the nuclear weak current as predicted by the conserved vector current theory is crucial to obtain even approximate agreement with the experimental results.

Beta spectrum ofF20

The shape of the $\ensuremath{\beta}$-ray spectrum of $^{20}\mathrm{F}$ has been investigated as a test of the weak magnetism prediction of the conserved vector current theory. Using the radiative width of the analog $M1$ decay in $^{20}\mathrm{Ne}$ to determine the magnetic form factor we calculate, from conserved vector current theory, a deviation of the $\ensuremath{\beta}$ spectrum from the allowed shape of +1.23\ifmmode\pm\else\textpm\fi{}0.03% Me${\mathrm{V}}^{\ensuremath{-}1}$. Higher order terms reduce the slope to 0.94% Me${\mathrm{V}}^{\ensuremath{-}1}$. The spectrum was measured with an iron-free intermediate-image magnetic spectrometer and the deviation was found to +0.4\ifmmode\pm\else\textpm\fi{}0.5% Me${\mathrm{V}}^{\ensuremath{-}1}$ or somewhat smaller than the conserved vector current prediction.[RADIOACTIVITY $^{20}\mathrm{F}$: measured $\ensuremath{\beta}$-spectrum shape; compared with CVC prediction.]