#
Spring 2021 Meeting of the APS New England Section

## Volume 66, Number 4

##
Friday–Saturday, April 16–17, 2021;
Virtual; Eastern Daylight Time

### Session B01: Contributed Talks II

10:00 AM–11:12 AM,
Saturday, April 17, 2021

Chair: Richard Price, MIT

### Abstract: B01.00003 : Experimental tests of isospin symmetry breaking in superallowed beta decay

10:24 AM–10:36 AM

Preview Abstract
Abstract

####
Author:

Victor Iacob

(Texas A&M University)

In the search for physics beyond the standard model, the unitarity test of
the Cabibbo-Kobayashi-Maskawa (CKM) matrix is one of the most demanding.
Superallowed $\beta $ transitions between $J^{\pi }=0^{+}$, $T=1$ analog
states currently provide the most precise value for $V_{\mathrm{ud}}$, the
up-down quark mixing element of the CKM-matrix. Since no axial current can
contribute in first order to these transitions, they give a direct access to
the vector coupling constant $G_{\mathrm{V}}$ of the weak interaction. The
current value of $V_{\mathrm{ud}}$ is $\pm 0.03\% $ accurate [1] and is
obtained from fifteen $ft$-values for superallowed $\beta $ decays, all
measured with a precision of $0.3\% $ or better. There are four small
theoretical corrections (all of the order of $1\% )$ required in the
$V_{\mathrm{ud}}$ extraction. The current result's error is dominated by
these theoretical corrections. From the experimentalist's perspective,
precision can be further improved by testing the reliability of the
predicted corrections. A powerful experimental test comes from measurements
of mirror pair superallowed transitions [1,2] In these transitions the
predicted corrections are relatively large and the ratio of their
$ft$-values is very sensitive to the model calculation of the
isospin-symmetry-breaking corrections $\delta_{NS} $ and $\delta_{C} $.
The talk will focus on the experimental effort required, exemplifying with
the mirror pair of superallowed $0^{+}\to 0^{+}\beta $ transitions ${
}^{34}\mbox{Ar}\to { }^{34}\mbox{Cl}$ and ${ }^{34}\mbox{Cl}\to {
}^{34}\mbox{S.}$
[1] J. J. C. Hardy and I. S. Towner, Phys. Rev. C \textbf{102}, 045501
(2020)
[2] V.E. Iacob \textit{et al.} Phys. Rev. C \textbf{101}, 045501 (2020)