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EPJ C Highlight - Shedding new light on dark matter

Light yield versus energy of events passing all selection criteria. © G. Angloher and et al.

Study shows significant progress in determining what dark matter is not made of, thanks to much more sensitive detectors capable of identifying the presence of elusive particles, called WIMPs

According to astronomical observations, dark matter constitutes a five times greater proportion of the universe than ordinary matter, which only makes up 5% of the matter in the universe. The remaining 70% of the universe is known as dark energy. However, we still do not know what dark matter is made of. Indeed, none of the known elementary particles fulfil the criteria to explain dark matter. One theory suggests that it consists of as yet unknown elementary particles that interact only very weakly with ordinary matter, fittingly called WIMPs (Weakly Interacting Massive Particles). Now, members of the CRESST (Cryogenic Rare Event Search with Superconducting Thermometers) collaboration have analysed recent data showing what dark matter is not made of, from a new kind of detector for such particles. This work has recently been published in EPJ C.

In this study, scientists use what is referred to as a heat-light technique; a WIMP scattering off a calcium tungstate crystal atomic nucleus would heat up the crystal while simultaneously producing light. For the much improved detector, the team used “home-grown” calcium tungstate crystals instead of the less pure commercially available ones. They also chose a different approach, based on a kind of scintillating clamp, to hold the crystal in place.

One obvious issue with the detection of putative WIMPs is that physicists do not know their mass. The new detector is particularly good at detecting very low energies without being interfered with by background energy sources—and is therefore good at detecting very low WIMP masses currently not accessible from other experiments. This is because the lighter the WIMP, the less energy is transferred in the scattering.

As a result, this study shows what dark matter is not made of, by probing and excluding a region of parameter space in the plane created by plotting the interaction probability of WIMPs with ordinary matter as a function of the WIMP mass. Part of this region has previously not been covered by other direct dark matter searches.

Results on low mass WIMPs using an upgraded CRESST-II detector. G. Angloher et al. (2014), European Physical Journal C 74: 3184, DOI 10.1140/epjc/s10052-014-3184-9

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