Abstract
Paleo-detectors are a proposed experimental technique to search for dark matter (DM). In lieu of the conventional approach of operating a tonne-scale real-time detector to search for DM-induced nuclear recoils, paleo-detectors take advantage of small samples of naturally occurring rocks on Earth that have been deep underground (≳5 km), accumulating nuclear damage tracks from recoiling nuclei for O(1)Gyr. Modern microscopy techniques promise the capability to read out nuclear damage tracks with nanometer resolution in macroscopic samples. Thanks to their O(1)Gyr integration times, paleo-detectors could constitute nuclear recoil detectors with keV recoil energy thresholds and 100 kilotonne-yr exposures. This combination would allow paleo-detectors to probe DM-nucleon cross sections orders of magnitude below existing upper limits from conventional direct detection experiments. In this article, we use improved background modeling and a new spectral analysis technique to update the sensitivity forecast for paleo-detectors. We demonstrate the robustness of the sensitivity forecast to the (lack of) ancillary measurements of the age of the samples and the parameters controlling the backgrounds, systematic mismodeling of the spectral shape of the backgrounds, and the radiopurity of the mineral samples. Specifically, we demonstrate that even if the uranium concentration in paleo-detector samples is 10−8 (per weight), many orders of magnitude larger than what we expect in the most radiopure samples obtained from ultra basic rock or marine evaporite deposits, paleo-detectors could still probe DM-nucleon cross sections below current limits. For DM masses ≲ 10 GeV/c2, the sensitivity of paleo-detectors could still reach down all the way to the conventional neutrino floor in a Xe-based direct detection experiment.
Highlights
More than a century after evidence for the existence of Dark Matter (DM) in our universe started to emerge [1], we still do not know what dark matter (DM) is made out of
We demonstrate that even if the uranium concentration in paleo-detector samples is 10−8, many orders of magnitude larger than what we expect in the most radiopure samples obtained from ultra basic rock or marine evaporite deposits, paleo-detectors could still probe DM-nucleon cross sections below current limits
We show how the projected sensitivity changes with the radiopurity of the samples, and demonstrate that, even if the uranium concentration in paleo-detector samples is 10−8, many orders of magnitude larger than what we expect in the most radiopure samples obtained from ultra basic rock or marine evaporite deposits, paleo-detectors could still probe DM–nucleon cross sections below current limits
Summary
More than a century after evidence for the existence of Dark Matter (DM) in our universe started to emerge [1], we still do not know what DM is made out of. SAXs promises spatial resolutions of O(15) nm in O(100) g of target material [49,50] (see the discussion in References [35,36]) These advanced microscopy techniques enable paleo-detectors to reach much larger exposures with better track length resolutions than previous ideas to probe rare events using natural minerals; see References [57,58,59,60,61,62,63,64,65,66,67,68,69,70,71] and, in particular, the work by Snowden-Ifft et al searching for damage tracks from WIMP–nucleus interactions in ancient phlogopite mica samples [72,73,74,75]. We make the code used in this work available: paleoSpec [85] for the computation of the signal and background spectra, and paleoSens [86] for the sensitivity forecasts
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