Projected sensitivity of the SuperCDMS SNOLAB experiment

Abstract

SuperCDMS SNOLAB will be a next-generation experiment aimed at directly detecting low-mass particles (with masses $\ensuremath{\le}10\text{ }\text{ }\mathrm{GeV}/{\mathrm{c}}^{2}$) that may constitute dark matter by using cryogenic detectors of two types (HV and iZIP) and two target materials (germanium and silicon). The experiment is being designed with an initial sensitivity to nuclear recoil cross sections $\ensuremath{\sim}1\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}43}\text{ }\text{ }{\mathrm{cm}}^{2}$ for a dark matter particle mass of $1\text{ }\text{ }\mathrm{GeV}/{\mathrm{c}}^{2}$, and with capacity to continue exploration to both smaller masses and better sensitivities. The phonon sensitivity of the HV detectors will be sufficient to detect nuclear recoils from sub-GeV dark matter. A detailed calibration of the detector response to low-energy recoils will be needed to optimize running conditions of the HV detectors and to interpret their data for dark matter searches. Low-activity shielding, and the depth of SNOLAB, will reduce most backgrounds, but cosmogenically produced $^{3}\mathrm{H}$ and naturally occurring $^{32}\mathrm{Si}$ will be present in the detectors at some level. Even if these backgrounds are 10 times higher than expected, the science reach of the HV detectors would be over 3 orders of magnitude beyond current results for a dark matter mass of $1\text{ }\text{ }\mathrm{GeV}/{\mathrm{c}}^{2}$. The iZIP detectors are relatively insensitive to variations in detector response and backgrounds, and will provide better sensitivity for dark matter particles with masses $\ensuremath{\gtrsim}5\text{ }\text{ }\mathrm{GeV}/{\mathrm{c}}^{2}$. The mix of detector types (HV and iZIP), and targets (germanium and silicon), planned for the experiment, as well as flexibility in how the detectors are operated, will allow us to maximize the low-mass reach, and understand the backgrounds that the experiment will encounter. Upgrades to the experiment, perhaps with a variety of ultra-low-background cryogenic detectors, will extend dark matter sensitivity down to the ``neutrino floor,'' where coherent scatters of solar neutrinos become a limiting background.