Branching ratios for theβdecay ofNa21

Abstract

We have measured the beta-decay branching ratio for the transition from 21 Na to the first excited state of 21 Ne. A recently published test of the standard model, which was based on a measurement of the β-ν correlation in the decay of 21 Na, depended on this branching ratio. However, until now only relatively imprecise (and, in some cases, contradictory) values existed for it. Our new result, 4.74(4)%, reduces but does not remove the reported discrepancy with the standard model.

Precise branching ratio measurements in $^{19}$Ne beta decay and fundamental tests of the weak interaction

“…where cause of the effect of weak magnetism [38,39] on the shapecorrection factor of the latter [21]. We obtain f A /f V = 1.0142 (28) [40], where, similar to Ref.…”

“…Analogous to the approach followed in Ref. [21], we determined this factor 4 from the product of five distinct corrections that are listed in Table I and described below.…”

“…Similarly as described in Ref. [21], we obtained absolute β-decay branches to the excited 1/2 − and 3/2 + states in 19 F from the ratios of β-γ coincident counts to the total number of observed β singles. Hence, an important step in our analysis was to obtain the integrated number of β singles events (N β ) detected by the SCEPTAR array.…”

High-precision half-life measurement for the isospinT=1/2mirrorβ+decay ofNaGrinyer1, Grinyer2, Babo3 et al. 2015Phys. Rev. C142121View full textAdd to dashboardCite

“…where K/( c) 6 = 2π 3 ln2 /(m e c 2 ) 5 = 8120.271 (12) × 10 −10 GeV −4 s, G F /( c) 3 =1.1663787(6) × 10 −5 GeV −2 is the Fermi constant, C V = 1 is the vector coupling constant, |M 0 F | 2 is the Fermi matrix element and takes the value of 1 for T = 1/2 transitions, V R is a transition-independent radiative correction, f A and f V are statistical rate functions for axial-vector and vector currents, respectively, and ρ is the Gamow-Teller to Fermi mixing ratio. The value of ρ must be deduced experimentally from measurements of angular or asymmetry correlation parameters.…”

“…There has been renewed interest in the study of the β decay of 21 Na: both branching ratios and β-ν correlation parameters have been measured recently [10][11][12]; however, its experimental f t value has the lowest precision of the three mirror nuclei that dominate the determination of V ud . In particular, the Ft mirror value for 21 Na is largely limited by the uncertainty in its half-life.…”