D. Melconian

Tensor interaction constraints from β-decay recoil spin asymmetry of trapped atoms

We have measured the angular distribution of recoiling daughter nuclei emitted from the Gamow-Teller {beta} decay of spin-polarized {sup 80}Rb. The asymmetry of this distribution vanishes to lowest order in the standard model (SM) in pure Gamow-Teller decays, producing an observable very sensitive to new interactions. We measure the non-SM contribution to the asymmetry to be A{sub T}=0.015{+-}0.029 (stat) {+-}0.019 (syst), consistent with the SM prediction. We constrain higher-order SM corrections using the measured momentum dependence of the asymmetry, and their remaining uncertainty dominates the systematic error. Future progress in determining the weak magnetism term theoretically or experimentally would reduce the final errors. We describe the resulting constraints on fundamental four-Fermi tensor interactions.

Electron-capture branch of {sup 100}Tc and tests of nuclear wave functions for double-{beta} decays.

We present a measurement of the electron-capture branch of {sup 100}Tc. Our value, B(EC) = (2.6 {+-} 0.4) x 10{sup -5}, implies that the {sup 100}Mo neutrino absorption cross section to the ground state of {sup 100}Tc is roughly 50% larger than previously thought. Disagreement between the experimental value and QRPA calculations relevant to double-{beta} decay matrix elements persists. We find agreement with previous measurements of the 539.5- and 590.8-keV {gamma}-ray intensities.

β decay of 32Cl: Precision γ-ray spectroscopy and a measurement of isospin-symmetry breaking

Background: Models to calculate small isospin-symmetry-breaking effects in superallowed Fermi decays have been placed under scrutiny in recent years. A stringent test of these models is to measure transitions for which the correction is predicted to be large. The decay of 32Cl decay provides such a test case. Purpose: To improve the gamma yields following the beta decay of 32Cl and to determine the ft values of the the beta branches, particularly the one to the isobaric-analogue state in 32S. Method: Reaction-produced and recoil-spectrometer-separated 32Cl is collected in tape and transported to a counting location where beta-gamma coincidences are measured with a precisely-calibrated HPGe detector. Results: The precision on the gamma yields for most of the known beta branches has been improved by about an order of magnitude, and many new transitions have been observed. We have determined 32Cl-decay transition strengths extending up to E_x~11 MeV. The ft value for the decay to the isobaric-analogue state in 32S has been measured. A comparison to a shell-model calculation shows good agreement. CONCLUSIONS: We have experimentally determined the isospin-symmetry-breaking correction to the superallowed transition of this decay to be (\delta_C-\delta_NS)_exp=5.4(9)%, significantly larger than for any other known superallowed Fermi transition. This correction agrees with a shell-model calculation, which yields \delta_C-\delta_NS=4.8(5)%. Our results also provide a way to improve the measured ft values for the beta decay of 32Ar.

The β+ decay of 37K as a multi‐faceted probe of fundamental physics

Precision β decay experiments represent an important and complimentary approach to high‐energy searches for physics outside the “Standard Model”, our current understanding of fundamental particles and their interactions. The mirror decay of 37K provides an excellent probe with which to search for new physics. The ft value of this (as well as other T = 1/2 mirror transitions) can be used to provide a measurement of the value of the Vud element of the CKM mass‐mixing matrix, complementing the value obtained from superallowed pure Fermi decays. In addition, the polarized angular distribution parameters are sensitive to a variety of possible new physics: the β and ν asymmetries can be used to search for right‐handed currents in the charged weak interaction, and their energy‐dependences are sensitive to second‐class currents forbidden in the Standard Model. Time‐reversal symmetry can also be tested by a precision measurement of the triple‐vector correlation between the initial nuclear spin and the momenta of t...

Precision half-life measurement of theβ+decay ofK37

The half-life of \tsups{37}K has been measured to be

Precision half-life measurement of the \boldmath

1.23651(94)~\mathrm{s}

\beta^+

, a value nearly an order of magnitude more precise than the best previously reported. The

decay of \tsups{37}K

\beta^+

Precision half-life measurement of the β + decay of K 37

decay of \tsups{37}K occurs mainly via a superallowed branch to the ground-state of its

{sup 3}He+{sup 4}He {yields} {sup 7}Be astrophysical S factor

T=1/2