Capturing neutrinos

In the Mediterranean Sea, a network of glass spheres is being laid that will detect invisible neutrinos. Follow KM3NeT from the drawing tables at Nikhef in Amsterdam to the deep sea near Toulon, France.

Text: Martijn van Calmthout


March 2015

On the table are the first prototypes for the plastic carrier of the inner structure for hundreds of waterproof and pressure-resistant glass spheres filled with light detectors.


Summer 2017

Technicians work on assembling a detection line with eighteen hermetic glass spheres, each containing 35 phototubes, special electronics and connecting sockets.


Winter 2018

A French deployment-team is waiting at Toulon for the calm sea. On deck there are four KM3NeT lines of two hundred meters long, around a immersion coil designed by Nikhef and NIOZ.


February 2019

A line hangs ready on the ship winch to lower the glass spheres to a depth of 2400 metres. Below, an unmanned submarine will connect the power supplies and glass fibre cables.


Phantom telescope

Studying phantom particles is what the KM3NeT project in the Mediterranean Sea is all about. At a depth of 2400 metres, physicists are building a gigantic neutrino detector that will scour a cubic kilometre of pitch-black seawater for tell-tale light flashes. At various locations near France and Italy, lines that are hundreds of metres long will be fixed to the sea floor with glass spheres filled with light detectors attached to these lines at fixed distances. Together, the glass spheres will form a measuring network with which the trails of neutrinos from the cosmos can occasionally be recorded. The water volume observed is large enough to be able to indicate roughly where the phantom particle must have come from, as a result of which this KM3NeT could also be called a telescope.­­

Since 2006, Nikhef, together with partners from eleven countries, has been designing and constructing the lines and the attached detector spheres. The lines are sunk on a metres-wide spool from a ship to the seafloor, after which the line is slowly unwound from the spool that floats back up to the surface. Unmanned submarines are used to connect the lines with the onshore control room. KM3NeT will eventually have 345 lines on the seafloor that will jointly be able to observe a large part of the sky. Of the 420 glass spheres completed so far, 218 were assembled by hand in Amsterdam and about 80 are still being made. The Dutch group will also be closely involved in the analysis of the measurement data, which will provide more insight into sources of neutrinos in the universe. Much is expected from multi-messenger astronomy in particular. This is the combination of astronomical telescope observations with neutrino trails and gravitational waves that will probably provide far deeper insights into the most energetic processes in the universe: from neutrino star collisions to all-consuming black holes.­

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