Session D12: Sub-GeV and Other Light Dark Matter, and Calibrations for These Scales

Live

The DAMIC (Dark Matter in CCDs) experiment uses thick scientific grade silicon charge-coupled devices (CCDs) to detect potential ionization signals from dark matter interactions. These devices feature an impressively low leakage current ($<10^{-21}$ A cm$^2$) and a very low energy threshold (40 eV$_{\rm{ee}}$), making them ideal low-mass dark matter detectors. In addition, their unique spatial resolution provides for effective identification and mitigation of environmental backgrounds. In this talk I will summarize recent dark matter constraints from the experiment at SNOLAB, discuss the kg-size next generation DAMIC-M detector funded for operation, and show results from "Skipper” instrumented CCDs – a novel readout technique that allows for counting of individual charges, with a demonstrated resolution of 0.07 e$^-$, which ushers in a new era of sensitivity to low-energy interactions.   

Live

Superfluid He-4 is a promising target material for direct detection of light (\textless 1 GeV) dark matter. Signal channels for dark matter - nucleus interactions in superfluid He include prompt photons, triplet excimers, rotons and phonons, but measurement of these signal strengths have yet to be performed for low energy nuclear recoils. A measurement of the prompt scintillation yield from electronic and nuclear recoils was carried out in superfluid He-4 at 1.75 Kelvin, with deposited energy in the range of 10-1000 keV. The scintillation from a 16 cm$^{\mathrm{3}}$ volume of superfluid He-4, with tetraphenyl butadiene as wavelength shifter deposited on thin quartz panels, was read out by six R8520-06 MOD PMTs immersed in the superfluid, each individually biased by a Cockcroft-Walton generator. Elastic scattering of 2.8 MeV neutrons (generated by a deuterium-deuterium neutron generator) from superfluid He-4, with a liquid organic scintillator module used as far-side detector, was used to determine the scintillation signal yield for a variety of nuclear recoil energies. For comparison, Compton scattering of Cs-137 gamma-rays with the superfluid He-4, with NaI scintillators used as far-side detectors, was used to determine the scintillation signal yield of electronic recoils.   

Live

Dual-phase liquid xenon time projection chambers, like XENON1T, are leading in sensitivity to search for rare events such as those expected from WIMP dark matter. However, the sensitivity of these detectors to sub-GeV mass dark matter is limited by single- and few-electron ionization signals. These backgrounds are observed at timescales of 100s of milliseconds after high energy interactions in the detector. In this talk, I will present a characterization of these background events in XENON1T, present possible origins, and discuss the implications they have for future experiments.   

Live

The Super Cryogenic Dark Matter Search (SuperCDMS) uses high-sensitivity silicon and germanium detectors to directly search for interactions from galactic dark matter (DM). New devices instrumented with ultra-high-resolution phonon sensors exhibit single-charge sensitivity, making it possible to search for sub-GeV-mass DM candidates such as electron-recoiling DM, dark photons and axion-like particles. Improved sensitivity to very small energy depositions is achieved thanks to new phonon-sensor designs and through use of the Neganov-Trofimov-Luke effect, which enables amplification of the phonon signal via application of an electric field.~ Because of the phenomenal energy sensitivity, new searches for sub-GeV DM candidates are possible, even with these devices operated in an above-ground (unshielded) laboratory. In this talk, I will present results from a new search for sub-GeV DM candidates using a modest 1.3 gram-day exposure, acquired with a new 1-gram silicon device characterized by a 3 eV baseline energy resolution and with a charge resolution equal to 0.03 of a single electron-hole pair.   

Live

The latest developments in the search for low-mass dark matter with the snowball chamber technology, essentially a reverse bubble chamber using supercooled water instead of superheating, will be presented. The latest calibration data sets with neutron and gamma-ray radioactive calibration sources will be discussed, with implications reviewed on the extremely low energy threshold expected (sub-keV) and background discrimination as a function of thermodynamic conditions. The most recent three-dimensional image analysis will be shown with position reconstruction and multiple scattering. Information gathered from all prototypes will be analyzed together to form a projected sensitivity curve for both spin-independent and spin-dependent (proton) coupling.   

Live

The coherent elastic neutrino-nucleus scattering (CEvNS) process was first observed in 2017, over 40 years after its prediction due to the difficulty in detecting the low-energy nuclear recoil signature, by the COHERENT collaboration using a pion decay-at-rest neutrino beam produced at the Spallation Neutron Source (SNS). CEvNS is a powerful tool for testing fundamental physics in detectors with a sufficiently low threshold. We will discuss COHERENT's sensitivity to test sub-GeV WIMP dark matter candidates that may be produced at the SNS and would scatter coherently with target nuclei. A modest-scale liquid argon scintillation detector could test the cosmologically observed dark matter concentration in parameter space complementary to limits set by direct detection experiments.   

On Demand

The constituents of dark matter are still unknown, and the viable possibilities span a very large mass range. The natural scenario where dark matter originates from thermal contact with familiar matter in the early Universe requires the DM mass to lie within about an MeV to 100 TeV. Considerable experimental attention has been given to exploring Weakly Interacting Massive Particles in the upper end of this range (few GeV – ~TeV), while the region ~MeV to ~GeV is largely unexplored. If there is an interaction between light DM and ordinary matter, as there must be in the case of a thermal origin, then there necessarily is a production mechanism in accelerator-based experiments. The most sensitive way, (if the interaction is not electron-phobic) to search for this production is to use a primary electron beam to produce DM in fixed-target collisions. The Light Dark Matter eXperiment (LDMX) is a planned electron-beam fixed-target missing-momentum experiment that has unique sensitivity to light DM in the sub-GeV range. This contribution will give an overview of the theoretical motivation, the main experimental challenges and how they are addressed, as well as projected sensitivities in comparison to other experiments.   

Light Dark Matter Search in XENON1T

Liquid xenon detectors are leading the direct search for dark matter (DM) at masses above $5~\mathrm{GeV}$ thanks to excellent background discrimination power, using scintillation and ionization signals. However, requiring a scintillation signal results in a relatively high energy threshold, which limits the sensitivity to low-energy recoils from light DM. In this talk, we report results from a search for light DM signals using only the ionisation signal in the XENON1T detector. Strong event selections were developed to mitigate instrumental backgrounds, reaching $\sim20~\mathrm{events}/ (\mathrm{tonne}\cdot\mathrm{day}\cdot\mathrm{keVee}$) at $0.2~\mathrm{keVee}$. The selected data improves on current limits for DM-nucleus scattering at DM masses within $3-6~\mathrm{GeV}$. When electronic recoils induced by the Migdal effect are considered, constraints can be extended to DM masses as low as $85~\mathrm{MeV}$.   

On Demand

We propose a novel direct detection concept to search for dark matter with 100 keV to 100 MeV masses. Here, dark matter scatters off molecules in the gas phase transferring part of its kinetic energy to the internal degrees of freedom of the molecule. The excited molecule decays emitting a multiple infrared photons, which are detected externally with ultrasensitive photodetectors. We discuss in detail carbon monoxide at a temperature of 50K and with a high vapor pressure, leading to efficient photon emission. Using different isotopes of the molecule, the target is also sensitive to spin-dependent dark matter interactions with the neutron. Moreover, we also consider a target made of hydrogen halides, which probe spin-dependent dark matter interactions with the proton. The present detection concept can be realized with near-term technology and allows for the exploration of orders of magnitude of new dark matter parameter space.