$^6$He-CRES: Experimental Overview and Recent Progress

The $^6$He-CRES experiment at the University of Washington CENPA aims to precisely measure the Fierz coefficient $b_{fierz}$ which parameterizes exotic currents in the weak interaction representing a violation of SM physics. A measurement of bFierz with a $10^{-3}$ uncertainty would be competitive with current LHC searches for tensor currents.

The decay of $^6{\rm He}$ has a large endpoint ($Q(^6{\rm He})\approx 3.5\,MeV$) which allows for the $m/E$ distortion, expected from a non-zero $b_{fierz}$ coefficient, to vary by about a factor of 7 over the spectrum, leading to high sensitivity. We use Cyclotron Radiation Emission Spectroscopy (CRES), a technique first demonstrated by the Project 8 collaboration aiming at a determination of the neutrino mass via a measurement of the $^3{\rm H}$ beta spectrum. The technique determines the beta energy by measuring the frequency of the cyclotron radiation of betas in a magnetic field. The $^6$He-CRES experiment will have high energy resolution and be shielded from systematics that affect traditional means of electron spectroscopy. A high level overview of the CRES technique will be followed by a discussion of preliminary results.