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Dark Matter-electron scattering results from DAMIC

The DAMIC Collaboration presented their latest results on the search for light dark matter particles (MeV-scale masses) for the first time in the International Conference of Cosmic Rays 2019. The results were posted on arXiv [https://arxiv.org/abs/1907.12628] and will be published soon.


DAMIC (DArk Matter In CCDs) is an experiment that uses as detection technique scientific CCDs with an unprecedented sensitivity to sub-GeV dark sector DM particles. Under the hypothesis that dark matter (DM) is made of neutral and stable particles, essential to reproduce the correct relic abundance, DAMIC will mainly explore two dark matter candidates  which are well-motivated theoretically and observationally: a) low-mass WIMPs (Weakly Interactive Massive Particle) with a wide mass range to explore, and b) the dark sector where the Dark Particles have their own set of interaction forces and thus do not couple directly with (are “hidden” from) baryonic matter.

 

The DAMIC detector is currently located at SNOLAB, Sudbury (Canada), 2 Km below the surface in the Vale Creighton Mine near Sudbury. The detector features 40 g of sensitive mass and very low background.  The DAMIC CCDs produced at the Lawrence Berkeley Laboratory achieved a record thickness of 675 microns with an area of 6cm x 6cm, for a mass of 5.8 g with 4000x4000 pixels of size 15x15 mm2. These CCDs present high spatial resolution and 3D reconstruction, an excellent energy response, an unprecedentedly low energy threshold of a few tens of eV and extremely low leakage current. This allows a unique capability to identify and reject the background as spatially correlated events occurring at different times. All this makes the DAMIC CCDs a well-suited detector to identify and suppress radioactive backgrounds, having an unrivalled sensitivity to WIMPs with masses < 6 GeVc-2.

 

DAMIC reports on direct-detection constraints on light dark matter particles interacting with electrons. The results are based on a method that exploits the extremely low levels of leakage current (2-6×10−22 A cm−2) and evaluates the charge distribution of pixels that collect less than 10 e− for contributions beyond the leakage current that may be attributed to dark matter interactions. The constraints on DM are placed on a so-far unexplored parameter space for dark matter masses between 0.6 and 100 MeV c−2 for DM-electron free scattering cross section. New constraints are also placed on hidden-photon dark matter with masses in the range 1.2- 30 eVc−2. DAMIC has established the best direct-detection limits on DM-electron scattering in the mass range of 0.6 MeVc−2 to 6 MeVc−2 by exploiting the excellent charge resolution and extremely low leakage current of DAMIC CCDs. The collaboration has also placed the best direct-detection constraints on hidden-photon dark matter in the mass range 1.2–9 eVc−2.

 

IFCA belongs to the DAMIC collaboration since May 2017, and is also part of the next generation of the experiment, DAMIC-M, that will be located in Laboratoire Souterrain de Modane (LSM), Modane (France). DAMIC-M will feature a detector mass of ~1 Kg with unprecedented single-electron resolution and a large reduction of the backgrounds, and will host the most massive CCDs ever built. The experiment will consist of 50 CCDs, each having 14g of active mass and 36 Megapixels (6k x 6k). IFCA is involved in the study of backgrounds, simulations and a Data Quality Monitoring.


DAMIC-M is already approved and funded by the US National Science Foundation, and also supported by an ERC grant from the European Council. The grant was awarded to the spoke person of the experiment, Paolo Privitera, from University of Chicago and the Laboratoire de Physique Nucléaire et Hautes Énergies (LPNHE, CNRS/Sorbonne université/Université Paris Diderot) and consists of 3.5 M Euros for the next 5 years.


Figure. Left: DAMIC detector, with the CCDs Right: The 90 % C.L upper limits on the DM-electron free scattering cross section (σe) as a function of DM mass (mχ) for three different dark-matter form factors (FDM) obtained by DAMIC at SNOLAB (solid blue line).​ Other lines present results from competing experiments.

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