Nikhef researchers study neutrinos, which are neutral subatomic particles that pass straight through the Earth. They did so as part of a collaboration at ANTARES (a neutrino telescope on the bottom of the Mediterranean Sea) in France and now in a new international project called KM3NeT.
KM3NeT is short for ‘Cubic Kilometre Neutrino Telescope’. It is a neutrino telescope that is currently under construction to succeed ANTARES.
Neutrinos are electrically neutral subatomic particles. They have almost no mass. They also have a very weak interaction with matter, which makes them especially hard to detect. Whenever neutrinos from the cosmos hit, for example, a water mass on Earth, most of them will simply travel straight through it. Only very occasionally will they collide with water molecules. When this happens, electrically charged muons are produced, which move in nearly the same direction as the neutrinos. These muons produce light as they move through the seawater. This is called Cherenkov radiation.
ANTARES is a neutrino telescope located on the bottom of the sea at a depth of 2500 meter, 40 km from the coast near Toulon, France. There, it searches for Cherenkov radiation as footprints of neutrinos. The seabed location is selected to largely shield the detector from disturbances by particles originating from the atmosphere. ANTARES aims to study neutrinos from the cosmos.
In order to improve the sensitivity for neutrino sources, a new neutrino telescope is needed that is more sensitive than ANTARES. To achieve this, the construction of KM3NeT started several years ago. KM3NeT is a neutrino telescope larger than a cubic kilometre.
The building blocks of this detector are so-called Digital Optical Modules (DOMs). These are glass spheres filled with 31 phototubes that detect Cherenkov radiation. KM3NeT consists of hundreds of lines of about a kilometre in length. A single line contains 18 DOMs. Phase 1 of KM3NeT consists of 31 lines; 24 in Italy and 7 in France. Eventually, KM3NeT will consist of no less than 700 lines in three locations.
KM3NeT is currently under construction to detect the fingerprints of neutrinos that originate from far-away astrophysical objects. Detecting and studying neutrinos is important to learn more about their behaviour. However, they can also be used to study the properties of their sources.
Researchers hope to use KM3NeT to discover where cosmic radiation comes from and how particle accelerators in the Universe work.
The DOM, the most important component of the KM3NeT neutrino telescope, was largely designed by Nikhef, from concept to execution. Nikhef also strongly contributes to the electronics, the optical network, the software and the data analysis. The first two operational lines, sunk into place since 2015, were assembled at Nikhef. Construction of the remaining DOMs is no longer done exclusively at Nikhef; other production lines have been set up in Europe, which are joining in.
This research programme is a prime example of fundamental scientific research, aimed at gathering basic knowledge about everything around us. At the heart of this type of research is curiosity about what our Universe is made of and how it came to be. There’s much that we know already, for example that all visible matter is built up from atoms, yet many questions remain unanswered.
Fundamental research is not aimed at realizing applications in the short term. Still, one thing is for sure: no one can predict which ground-breaking applications will eventually emerge from this research. History shows that today’s fundamental knowledge forms the breeding ground for tomorrow’s discoveries.
KM3NeT (Dutch only, article in the New Scientist special about Nikhef)