UK engineers are now building and installing 7 square metres of silicon light detectors for an underground Italian experiment that will hunt for dark matter particles. Most of the universe’s matter is invisible. Physicists know dark matter exists because its gravity shapes galaxies, but they have never directly detected a single particle of it. The DarkSide-20k experiment, housed deep beneath a mountain to shield it from cosmic rays, will use 20 tonnes of liquid argon to catch the faint flash of light produced when a dark matter particle occasionally collides with an argon nucleus. The UK’s contribution is a quarter of the experiment’s photon detector modules—arrays of silicon photomultipliers that convert those flashes into electrical signals with extreme sensitivity and ultra-low background noise. This is fundamental science. If the detectors work as designed, they could reveal what dark matter is made of, answering one of the deepest open questions in physics. There is no immediate practical application, but the silicon photomultiplier technology developed here—large, low-background arrays with cryogenic electronics—could later find use in medical imaging, nuclear security, or other fields that need to detect single photons in hostile environments. Past detector advances for particle physics, from silicon sensors to superconducting magnets, have spun off into MRI scanners and cancer therapy.
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This proposal leverages the UK's world-leading silicon detector integration capability to grow UK leadership in large silicon photo-multiplier (SiPM) array detectors for low-background physics, through installation of UK-built SiPM readout system components for the international DarkSide-20k experiment. Low background physics experiments address some of the most fundamental open questions in science today: what is most of the matter in the universe made of? how does dark matter interact with us? why do we live in a matter-dominated universe? Experiments studying these questions at the cosmic and intensity frontiers of particle physics increasingly employ detectors filled with liquid noble gases. Liquid nobles produce scintillation light when particles interact, which is detected with arrays of photo-sensor detectors. Silicon detectors have revolutionised particle physics at the energy frontier, and are increasingly important at the intensity and cosmic frontiers. The major challenge in dark matter and low-energy neutrino physics is to maximise signal detection efficiency whilst achieving ultra-low background interaction rates. There is a growing consensus across liquid noble dark matter and neutrino experiments that silicon photo-multiplier (SiPM) detectors are the key enabling technology to meet these challenges. The importance of developing UK leadership in this area was recognised in the recent STFC Dark Matter Strategic Review: "The development of SiPMs for future large-scale direct-DM searches using noble gases provides the opportunity for the UK to invest in early R&D in order to achieve technological leadership in any future next generation experiment. R&D would focus on the design, production and testing of large SiPM tile arrays including electronics." This proposal focuses on the installation testing of large SiPM tile arrays, including signal conditioning electronics, produced in the UK for the DarkSide-20k dark matter search experiment. The state-of-the-art in integration of large SiPM tile arrays for low-background experiments today is the DarkSide-20k photon detector module (PDM). The PDM consists of an array of ~1 cm2 SiPMs ('tiles') bonded to a substrate to form a 25 cm2 photosensitive area, connected to cryogenic front end electronics that combine the signal from all tiles and condition it. The DarkSide-UK construction project is responsible for producing 7 m^2 of these PDMs to instrument the DarkSide-20k detector, representing 25% of the total. This project is the continuation of that work, to support installation of the UK's deliverables to the international project. To execute this ambitious programme we bring together a team of experts that have built silicon detectors for the Large Hadron Collider and space-based experiments, dark matter and neutrino physics experimentalists pushing the frontiers of ultra-low radioactivity, and theorists expanding the horizons for new physics searches based on advances in instrumentation. Detector development is the engine of discovery in particle physics. This proposal aims to develop new technologies to ensure vitality of our field in the UK, with outstanding discovery potential for the future.
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