Searching for Dark Absorption with Direct Detection Experiments

TL;DR

This study shows that direct-detection experiments sensitive to electron recoils can probe dark-sector absorption of dark photons and axion-like particles across masses from a few eV to beyond 10 keV. By recasting XENON10, XENON100, and CDMSlite data within the axioelectric and related absorption frameworks, the authors derive updated bounds on ALP-electron couplings and dark-photon kinetic mixing, and they map projected gains for upcoming detectors like SuperCDMS SNOLAB HV and scintillating targets. The work highlights substantial improvements over existing constraints, with future experiments potentially surpassing stellar cooling limits and even touching hints from white-dwarf luminosity function for ALPs. It also provides a cohesive treatment of in-medium effects and solar production that shapes the expected signals in both current and future setups, underscoring the growing reach of direct-detection experiments into the dark sector. The results collectively emphasize that lowering detector thresholds, coupled with suitable target materials and large exposures, can open new parameter space for low-mass dark-sector particles.

Abstract

We consider the absorption by bound electrons of dark matter in the form of dark photons and axion-like particles, as well as of dark photons from the Sun, in current and next-generation direct detection experiments. Experiments sensitive to electron recoils can detect such particles with masses between a few eV to more than 10 keV. For dark photon dark matter, we update a previous bound based on XENON10 data and derive new bounds based on data from XENON100 and CDMSlite. We find these experiments to disfavor previously allowed parameter space. Moreover, we derive sensitivity projections for SuperCDMS at SNOLAB for silicon and germanium targets, as well as for various possible experiments with scintillating targets (cesium iodide, sodium iodide, and gallium arsenide). The projected sensitivity can probe large new regions of parameter space. For axion-like particles, the same current direction detection data improves on previously known direct-detection constraints but does not bound new parameter space beyond known stellar cooling bounds. However, projected sensitivities of the upcoming SuperCDMS SNOLAB using germanium can go beyond these and even probe parameter space consistent with possible hints from the white dwarf luminosity function. We find similar results for dark photons from the sun. For all cases, direct-detection experiments can have unprecedented sensitivity to dark-sector particles.

Figures (4)

• Figure 1: Ionization (S2-only) data from XENON10 Angle:2011th ( left) and XENON100 Aprile:2016wwo ( right). Top plot shows the data as the number of observed electrons, while bottom plot shows the data as the number of photoelectrons (PE) on the bottom axis and the corresponding number of electrons (1e$^-$=19.7PE) on the top axis. Blue gaussian lines on each plot show two examples of the expected observed signal shape for two different DM (ALP or $A'$) masses. The blue histogram shows the signal distribution in terms of the number of electrons produced in the detector. Varying the secondary ionization model produces different signal shapes and thus different limits. We show the signal shape in pink and magenta that produces, respectively, the worst and best limit for the same two DM masses when varying the secondary ionization model. Numbers next to the blue curves give the 90% C.L. upper bound times efficiency on the number of signal events for those masses.
• Figure 3: Constraints ( shaded regions) and prospective sensitivities ( solid colored lines) for axion-like particle (ALP) dark matter ( left) and dark-photon ($A'$) dark matter ( right), assuming that the ALP/$A'$ constitutes all the dark matter. Colored regions show constraints from XENON10, XENON100, and CDMSlite, as derived in this work, as well as the DAMIC results for $A'$ from Aguilar-Arevalo:2016zop. Shaded bands around XENON10 and XENON100 limits show how the bound varies when changing the modeling of the secondary ionization in xenon. Deep- and light-purple solid lines show projected 90% C.L. sensitivities for SuperCDMS SNOLAB HV using either Ge (20 kg-years) or Si (10 kg-years) targets, respectively. Yellow, orange, and green solid lines show projected sensitivities for hypothetical experiments with the scintillating targets CsI, NaI, and GaAs, assuming an exposure of 10 kg-years. All projections assume a realistic background model discussed in the text, but zero dark counts to achieve sensitivity to low-energy electron recoils. In-medium effects are included for all $A'$ constraints and projections. Shaded gray regions show known constraints from anomalous cooling of the Sun, red giant stars (RG), white dwarf stars (WD), and/or horizontal branch stars (HB), which are independent of the ALP or $A'$ relic density. Also shown ( left) are the combined bounds from XENON100 Aprile:2014eoa, EDELWEISS Armengaud:2013rta, CDMS Ahmed:2009ht, and CoGeNT Aalseth:2008rx; and ( right) a bound derived in An:2014twa based on XENON100 data from 2014 Aprile:2014eoa. Shaded orange region in left plot is consistent with an ALP possibly explaining the white dwarf luminosity function.
• Figure 4: Constraints ( shaded regions) and prospective sensitivities ( solid colored lines) for dark-photons ($A'$) with a Stückelberg mass from the Sun via resonant production (including in-medium effects). Colored regions show constraints from XENON10, XENON100, and CDMSlite, as derived in this work. Deep- and light-purple solid lines show projected 90% C.L. sensitivities for SuperCDMS SNOLAB HV using either Ge (20 kg-years) or Si (10 kg-years) targets, respectively. Yellow, orange, and green solid lines show projected sensitivities for hypothetical experiments with the scintillating targets CsI, NaI, and GaAs, assuming an exposure of 10 kg-years. All projections assume a realistic background model discussed in the text, but zero dark counts to achieve sensitivity to low-energy electron recoils. Shaded gray regions show constraint from anomalous cooling of the Sun. Also shown ( dotted line) is the bound derived in An:2013yua based on XENON10 data Aprile:2014eoa.
• Figure 5: Couplings needed for 1 event/kg/year for ALPS ( left) and $A'$ ( right). GaAs and Ge, and Xe and CsI have very similar behaviors due to similar refractive indices.