An Introduction to the $^6$He-CRES Experiment*

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 $b_{fierz}$ 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 to vary by about a factor of 7 over the spectrum and therefore leads to high sensitivity to $b_{fierz}$. Using Cyclotron Radiation Emission Spectroscopy (CRES) (a technique demonstrated by the Project 8 collaboration) the $^6$He-CRES experiment based at the University of Washington CENPA will have high energy resolution and be shielded from systematics that affect traditional means of electron spectroscopy. We expect to have an event rate of $\approx 1 \,{\rm event} /{\rm  ms}$ and need  $\sim 10^8$ events for a $10^{-3}$ measurement of $b_{fierz}$. With a few days of data we should have sufficient statistics for a competitive measurement. A high level overview of the $^6$He-CRES experiment will be presented as context for the discussion of the $^6$He-CRES collaboration’s first detected CRES signals (March 2021) in a subsequent talk.