The $\beta$ Decay of $^{38}\mathrm{Ca}$: Sensitive Test of Isospin Symmetry-Breaking Corrections from Mirror Superallowed $0^+\rightarrow0^+$ Transitions
| Pub type: | Inproceedings |
| Citation: | park2015sensitive |
| Status: | Published |
| Journal: | JPS Conf. Proc. |
| Booktitle: | Proceedings of the Conference on Advances in Radioactive Isotope Science (ARIS2014) |
| Volume: | 6 |
| Year: | 2015 |
| Month: | June |
| Pages: | 020033 |
| Location: | Tokyo, Japan |
| Note: | June 1-6, 2014 |
| ISBN: | 978-4-89027-110-8 |
| URL: | http://journals.jps.jp/doi/10.... |
| DOI: | 10.7566/JPSCP.6.020033 |
| Abstract: | We have measured the branching-ratio for the 0+ → 0+ superallowed β-transition from 38Ca to a relative precision of ±0.2%. Combining our result, 0.7728(16), with the known QEC value and half-life, we obtain an ft value of 3062.3(68) s for the 38Ca superallowed transition. This is the first addition to the set of well-known superallowed transitions in nearly a decade. More importantly, since 38Ca is a TZ = −1 parent nucleus, our result provides the opportunity for the first time to make a high-precision comparison of the ft values from a pair of mirror superallowed decays, 38Ca → 38mK and 38mK → 38Ar. Mirror comparisons of superallowed transitions can be used to sensitively test calculations of δC, which is the isospin symmetry-breaking correction required to determine Vud, the up-down quark-mixing element of the Cabibbo–Kobayashi–Maskawa (CKM) matrix. With our new result, the measured ratio of the mirror ft values is determined to be ftCa/ftK = 1.0036(22). This agrees well with the value, 1.0020(4), predicted when Saxon–Woods (SW) radial wave functions are used to calculate δC, and disagrees with the value, 0.9998(4), predicted when Hartree-Fock (HF) radial wave functions are used. It is the SW-calculated corrections that are currently used to determine Vud, while the HF ones are used to establish an assigned “systematic” uncertainty on the Vud result. Three more mirror pairs — with A = 26, 34, and 42 — are experimentally accessible and, if these confirm and strengthen the currently observed preference for the SW corrections, it will become possible to shrink the systematic uncertainty on Vud, reduce the uncertainty on the CKM-matrix unitarity sum, and further constrain the scope for new physics beyond the Standard Model. |
| Month_val: | 6 |
| Sig contrib: | J. C. Hardy |
| Authors: | |
| Added by: | [DGM] |
| Total mark: | 0 |
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