Since 1995, experiments in the Gran Sasso deep underground laboratory in Italy attempting to directly detect dark matter have observed an annual modulation in the rare events seen by their scintillation detectors which is consistent with an increased volume of dark matter passing through the detector when the Earth’s motion around the Sun adds to the Sun’s motion through the galaxy. The current DAMA/LIBRA experiment has now, combined with its predecessor, observed this signal over 14 years.
But curiously, other similar experiments which should have seen comparable results have come up empty-handed. What is going on? One immediately thinks of explanations such as Pournelle’s Law (“It’s probably a cable.”), but so far none has explained the consistently-detected signal. A 2020 paper, “Annual modulations from secular variations: relaxing DAMA?”, suggests the result could be an artefact of the data reduction procedure, but this analysis is disputed.
To rule out seasonal effects, a duplicate detector, SABRE, is under construction one kilometre underground in a gold mine in Australia, where it will experience seasons shifted six months from those in Italy but the identical motion through the supposed dark matter stream.