Abstract
In the direct detection of the galactic dark matter, experiments using cryogenic solid-state detectors or noble liquids play for years a very relevant role, with increasing target mass and more and more complex detection systems. But smaller projects, based on very sensitive, advanced detectors following new technologies, could help in the exploration of the different proposed dark matter scenarios too. There are experiments focused on the observation of distinctive signatures of dark matter, like an annual modulation of the interaction rates or the directionality of the signal; other ones are intended to specifically investigate low mass dark matter candidates or particular interactions. For this kind of dark matter experiments at small scale, the physics case will be discussed and selected projects will be described, summarizing the basics of their detection methods and presenting their present status, recent results and prospects.
Highlights
According to a great deal of cosmological and astrophysical observations at different scales, there is a need of both dark energy and dark matter (DM) in the Universe; the dark matter particles could explain an important fraction of the its energy-mass budget, its nature is unknown [1,2]
The direct detection of DM was focused for years on the elastic scattering off target nuclei of Weakly Interacting Massive Particles (WIMPs), for spin-independent (SI) and spin-dependent (SD) interactions, giving rise to nuclear recoils (NR) as detectable signals; but inelastic scattering and scattering with electrons in the detector medium producing electron recoils (ER) are being considered too, as it will be shown later
DarkSide-50 has operated at Laboratori Nazionali del Gran Sasso (LNGS) a dual-phase liquid Ar detector, filled with underground Ar (UAr) with strongly suppressed 39Ar activity [29]; detecting the S2 signal only and achieving a 100 eVee energy threshold, the search for low mass DM gave the strongest limits from 1.8 to 3.5 GeV/c2 for SI DMnucleus interaction [30] and results on DM-electron interaction [31]
Summary
According to a great deal of cosmological and astrophysical observations at different scales, there is a need of both dark energy and dark matter (DM) in the Universe; the dark matter particles could explain an important fraction of the its energy-mass budget, its nature is unknown [1,2]. Assuming a particular type of interaction, the expected counting rates can be predicted considering certain astrophysical parameters (like the local density, the velocity distribution and the escape velocity of the DM particles) and properties of the DM particle [7]; the direct detection formalism is summarized, for example, in the Dark Matter section of [2] and detailed for elastic NR in [8] This direct detection mechanism is really challenging as the produced signal is rare, with very low energy and has a continuum energy spectrum (which decays almost exponentially) making it indistinguishable from backgrounds [9]. Running experiments and projects intended to identify distinctive signatures of the DM interaction will be presented, for the annual modulation in the expected rates, and, for the signal directionality Those intended to explore low mass DM using purely ionization detectors, like gas chambers or semiconductors, will be discussed in Section 4 while Section 5 will be devoted to experiments focused on SD interactions.
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