arXiv subjects

B. Fenker

Publications and source records attributed to B. Fenker.

4 recordsLinked to original sources

arXiv2025

$A_{\beta}[E_{\beta}]$ in $^{37}$K decay: new physics with opposite $\beta$ helicity

By extending our analysis and simulations of our $^{37}$K $\beta$-decay data set to allow the $\beta$ asymmetry with respect to nuclear spin to vary with $\beta$ energy $E_{\beta}$, we have gained sensitivity to new physics that depends on a helicity factor for the $\beta$, $m_\beta/E_\beta$. In particular, we constrain Lorentz scalar and tensor quark-lepton interaction strengths at a sensitivity complementary to the similar Fierz interference term in neutron $\beta$ decay. Our result for that new physics is a Fierz interference term $b$ = 0.033 $\pm$ 0.084 (stat) $\pm$ 0.039 (syst), consistent with the standard model electroweak interaction value $b=0$. We consider presently achieved complementarity to $\beta$-decay and particle physics experiments, along with projectable technical improvements to our method.

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arXiv2018

Precision measurement of the $β$-asymmetry in spin-polarized $^{37}\mathrm{K}$ decay

Using TRIUMF's neutral atom trap, TRINAT, for nuclear $β$ decay, we have measured the $β$ asymmetry with respect to the initial nuclear spin in $^{37}\mathrm{K}$ to be $A_β=-0.5707(13)_\mathrm{syst}(13)_\mathrm{stat}(5)_\mathrm{pol}$, a 0.3% measurement. This is the best relative accuracy of any $β$-asymmetry measurement in a nucleus or the neutron, and is in agreement with the standard model prediction $-0.5706(7)$. We compare constraints on physics beyond the standard model with other $β$-decay measurements, and improve the value of $V_\mathrm{ud}$ measured in this mirror nucleus by a factor of 4.

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arXiv2014

Progress towards precision measurements of beta-decay correlation parameters using atom and ion traps

The correlations of the decay products following the beta decay of nuclei have a long history of providing a low-energy probe of the fundamental symmetries of our universe. Over half a century ago, the correlation of the electrons following the decay of polarized 60Co demonstrated that parity is not conserved in weak interactions. Today, the same basic idea continues to be applied to search for physics beyond the standard model: make precision measurements of correlation parameters and look for deviations compared to their standard model predictions. Efforts to measure these parameters to the 0.1% level utilizing atom and ion trapping techniques are described.

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arXiv2014

Precision half-life measurement of the \boldmath$β^+$ decay of \tsups{37}K

The half-life of \tsups{37}K has been measured to be $1.23651(94)~\mathrm{s}$, a value nearly an order of magnitude more precise than the best previously reported. The $β^+$ decay of \tsups{37}K occurs mainly via a superallowed branch to the ground-state of its $T=1/2$ mirror, \tsups{37}Ar. This transition has been used recently, together with similar transitions from four other nuclei, as an alternative test of CVC and method for determining $V_{ud}$, but the precision of its $ft$ value was limited by the relatively large half-life uncertainty. Our result corrects that situation. Another motivation for improving the $ft$ value was to determine the standard-model prediction for the $β$-decay correlation parameters, which will be compared to those currently being measured by the \trinat{} collaboration at \triumf. The new $ft$ value, $4605(8)~\mathrm{s}$, is now limited in precision by the $97.99(14)\%$ ground-state branching ratio.

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