Research firmly assumes that dark matter exists - but it has not yet been proven. A new experiment could change that.
Gran Sasso – Dark matter theoretically represents 85 percent of the total mass of the universe. However, it has not yet been proven in practice. Only the DAMA/LIBRA experiment, which has been running since 1995, claims to have discovered dark matter, but this result is controversial. Now a new experiment, COSINUS, aims to confirm the existence of dark matter and clarify whether DAMA/LIBRA actually detected dark matter.
COSINUS is located in the same place where DAMA/LIBRA is carried out: in the Laboratori Nazionali del Gran Sasso, the largest underground laboratory in the world. It is located in the Italian mountain range Gran Sasso, about a hundred kilometers from Rome. Deep below the earth's surface, in an extensive tunnel system and protected by 1,400 meters of rock, the sensitive measurements that are intended to detect dark matter are carried out there.
Controversial experiment measured dark matter – COSINUS could confirm the result
The DAMA/LIBRA experiment had measured a signal that met the research community's expectations - an indication of dark matter? However, other experiments failed to replicate the results, something that has troubled the research community for years. “Our new project offers the chance to solve this puzzle,” says Karoline Schäffner from the Max Planck Institute for Physics (MPP).
The technical manager of the COSINUS experiment further explains: “We use sodium iodide in our detector, the same material as in the DAMA/LIBRA experiment, in order to be able to compare the results. However, our experimental setup will achieve significantly higher accuracy.”
COSINUS project takes place in Italian underground laboratory
A special instrument was developed for the COSINUS project to measure dark matter. To do this, a crystal must be cooled to extremely low temperatures (one to two hundredths of a degree above absolute zero of -273 degrees Celsius). It is supposed to indicate when it is hit by particles of dark matter. The theory behind the experiment: If dark matter consists of previously unknown particles, the Earth should collide with these particles on its journey through space. The measuring device is intended to display these collisions in two different ways.
Schäffner explains: “If our galaxy is permeated by particles of dark matter, the Earth would move through this 'nebula' sometimes faster, sometimes more slowly.” She adds: “The situation is like driving in the rain: the faster we go, the more raindrops hit the windshield. So we expect to detect different amounts of dark matter at different times.”
Dark matter is said to cause atoms in a crystal to vibrate
When the crystal is hit by particles of dark matter, the atoms of the crystal are said to vibrate. The crystal lattice should then begin to wobble and heat up - this heat energy can be measured. In addition, light should be created in the crystal that the detector can “see”. In the controversial DAMA/LIBRA experiment, only light was measured. The ability to examine two signals in the COSINUS experiment provides more precise information about the type of particles.
Schäffner emphasizes: “This is important because not every signal that is measured in such a detector is an indication of dark matter.” She adds: “For example, they can be ordinary electrons that are created by natural radioactivity. Or neutrons, which are produced by cosmic particles.”
The detector is shielded in a seven meter high water tank
In order to detect signals from dark matter, the crystal must be shielded as effectively as possible from any background noise. Hence the choice of research location in the Italian mountain range. Many highly sensitive experiments are carried out in the tunnel system of the Laboratori Nazionali del Gran Sasso. The detector is also placed in a seven meter high tank with highly pure water. The research team expects the first results in 2025/2026. The ESA space telescope “Euclid” is also looking for dark matter – but not on Earth, but in space.
(tab)