There are four fundamental forces within the natural world: electromagnetism, gravity, the strong nuclear force, and the weak nuclear force. One of the primary windows to the inner workings of the weak nuclear force has long been found in observations of beta decay processes. Of particular interest is the form taken by the couplings involved in beta decay; prior experiments have shown that the process is dominated by a combination of vector and axial couplings, analogous to Maxwell's theory of electromagnetism --- however the possibility of a non-dominant contribution from exotic scalar or tensor couplings remains. Such a discovery would shake the foundations upon which our understanding of the weak force is built.

A precision kinematic measurement is conducted to search for- or constrain exotic couplings within the nuclear weak force by measuring an observable known as the Fierz interference, $b_{Fierz}$, within the $^{37}$K$ \rightarrow ^{37}$Ar$ + \beta^+ + \nu_e$ transition. The effect, if present, would manifest as a perturbation to the expected shape of the energy spectrum for betas emerging from a decay --- or equivalently, as an apparent change to the energy dependence of the beta asymmetry ($A_\beta$, measured with respect to nuclear polarization), which is the approach employed here. As the observable is comprised of a linear combination of scalar and tensor couplings, any non-zero value of $b_{Fierz}$ would be indicative of exotic physics.

The measurement is carried out within the TRINAT laboratory located at TRIUMF, which provides the radioactive $^{37}$K necessary for the experiment. The TRINAT apparatus provides an isotope-specific means to cool, confine, and intermittently spin-polarize $^{37}$K atoms within a magneto-optical trap. Upon decay, outgoing particles are emitted from a small central cloud into an open geometry featuring a variety of detectors. A thorough understanding of the nuclear polarization allows the superratio technique to be employed, greatly decreasing the size of many systematic errors. Geant4 simulations are used to model scattering effects and background events that could mimic the signal being searched for. The resulting measurement gives $b_{Fierz}$ = +0.033 +/- 0.084(stat) +/- 0.039(sys), consistent with the absence of exotic scalar and tensor couplings.