Improved calculations of beta decay backgrounds to new physics in liquid xenon detectors

Understand

We present high-precision theoretical predictions for the electron energy spectra for the ground-state to ground-state $\beta$ decays of $^{214}$Pb, $^{212}$Pb, and $^{85}$Kr most relevant to the background of liquid xenon dark matter detectors.

• The effects of nuclear structure on the spectral shapes are taken into account using large-scale shell model calculations.
• Final spectra also include atomic screening and exchange effects.
• The impact of nuclear structure effects on the $^{214}$Pb and $^{212}$Pb spectra below $\approx100$ keV, pertinent for several searches for new physics, are found to be comparatively larger than those from the atomic effects alone.