Abstract
A program of high-precision half-life and branching-ratio measurements for superallowed Fermi emitters is being carried out at TRIUMF's Isotope Separator and Accelerator (ISAC) radioactive ion beam facility. Recent half-life measurements for the superallowed decays of 14 O, 18 Ne, and 26 Al m , as well as branching-ratio measurements for 26 Al m and 74 Rb are reported. These results provide demanding tests of the Standard Model and the theoretical isospin symmetry breaking (ISB) corrections in superallowed Fermi decays.
Highlights
A program at the Isotope Separator and Accelerator (ISAC) facility at TRIUMF, Canada’s national laboratory for particle and nuclear physics, is in place to perform high-precision half-life, branchingratio, and Q value studies for these superallowed β emitters. These experiments are performed using TRIUMF’s Ion Trap for Atomic and Nuclear Science (TITAN) [13]; a 4π gas proportional β counter; and the 8π γ-ray Spectrometer [14], a spherical array consisting of 20 Compton-suppressed high-purity germanium (HPGe) detectors, with ancillary detection systems including the Zero-Degree Scintillator (ZDS), the Scintillating Electron-Positron Tagging Array (SCEPTAR), and the Pentagonal Array for Conversion Electron Spectroscopy (PACES) [15]
With the capability of measuring all experimental quantities required for determining superallowed f t values, ISAC is providing crucial data to help distinguish between the theoretical models used for calculating isospin symmetry breaking (ISB) corrections
The resulting Ft values for these decays remain in excellent agreement with those of the other precisely measured superallowed emitters when using the Woods-Saxon radial overlap corrections of Ref. [3], supporting the accuracy of these calculations, but provide a rigorous test of the conserved vector current (CVC) hypothesis
Summary
EPJ Web of Conferences with muon decay, currently provide the most precise determination of Vud, by far the most precisely measured element of the Cabibbo-Kobayashi-Maskawa (CKM) matrix, and, when combined with Vus and Vub, confirm CKM unitarity to a precision of ±0.06% [1, 2] These fundamental tests require theoretical radiative and isospin symmetry breaking (ISB) corrections [3] to be applied to the experimentally measured f t values in order to obtain “corrected” f t values, denoted Ft; according to the CVC hypothesis, the Ft values should be constant for all superallowed decays involving states of a given isospin T. With the capability of measuring all experimental quantities required for determining superallowed f t values, ISAC is providing crucial data to help distinguish between the theoretical models used for calculating ISB corrections
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