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Dark matter is detected via the interaction with ordinary matter. Energy is transferred, which is then being measured by the experiment and can used to derive the mass of dark matter particle. The amount of deposited energy also depends on the scattering partner and for light dark matter, below one GeV, the nucleon as a scattering partner results in significantly reduced deposited energy. The electron as a scattering partner is much better suited for the detection of MeV range dark matter particles, however, the fact that the electron is in a bound state hinders the relation between deposited energy and dark matter mass.
Within this R&D project we study the possibility to detect MeV dark matter by observing dark matter electron scattering in a silicon semiconductor. A low noise detector which is able to detect single electrons has the potential to discover dark matter down to a few MeV. We use a depleted p-channel field effect transistor as detector (DepFET), similar to the one being used as pixel detector for the Belle II experiment. However, in this case the detector is used with a repetitive non-destructive readout (RNDR), leading to a sub-electron noise level.
A prototype sensor with 64x64 pixels with a pixel size of 75x75 um2 is available. A test setup dedicated for dark matter searches is currently build and first low noise measurements are expected for 2018. With an exposure of 1 kg y we expect to reach a sensitivity of about 10^41 cm2 for a 10 MeV dark matter particle scattering with a free electron.
further Information: "DEPFET detectors for direct detection of MeV Dark Matter particles", A. Bähr et al., arXiv:1706.08666.