📄 Showing the "Simple" version — "Popular" is not ready yet. Add it to favorites to help prioritize it. Ask for the full read

Dark matter doesn't emit or reflect light, but its presence is revealed through gravitational effects. To catch even a single particle, physicists build detectors that are like very quiet rooms: inside lie crystals that flash when a particle hits them. But the flash is faint, and if light is lost along the way, the signal can be missed.

In the COSINE-100U setup, sodium iodide crystals have learned to collect light better. Previously, quartz windows stood between the crystal and the photomultiplier — the device that converts light into an electrical signal. Light passed through several boundaries and was partially reflected. Now the windows are gone, and photomultipliers are pressed directly against the crystal ends through thin silicone pads 2 millimeters thick. The edges of large crystals were beveled so that light, as if along a chute, flows to the sensors. As a result, all eight crystals now produce more light — up to 27.7 photoelectrons per kiloelectronvolt, whereas before it was about 15.

This isn't just a technical whim. The brighter the flash, the easier it is to distinguish a real dark matter signal from random noise. Moreover, the new design reduced background from radioactive contamination on the crystal surfaces. Two crystals that were previously unusable for analysis due to poor light are now back in action. Tests showed that the new packaging withstands prolonged immersion in liquid scintillator at low temperature — the harsh conditions of an underground laboratory.

So the upgraded detector is preparing for the ultimate test. The DAMA/LIBRA group has for years reported mysterious seasonal variations in its signal that could be explained by dark matter. With brighter and cleaner crystals, COSINE-100U will finally be able to confirm or refute that observation.