Latest Developments for KM3NeT

Written by katrinlink on 11th February 2015. Posted in

11 February 2015

The first KM3NeT string: 18 DOMs are visible, each containing 31 sensitive light detectors (photomultipliers). The DOMs are interconnected with a 40 m cable consisting of glass fibres for the data transport (Photos: Nikhef)

On January 19, 2015, the first detection string of the new KM3NeT neutrino telescope was shipped from Nikhef, Amsterdam to the Centre de Physique des Particules de Marseille (CPPM, a laboratory of CNRS) in France. At CPPM the instrument will be further tested and calibrated, to be deployed in the Mediterranean Sea, at 2.4 km depth off the coast of France. The sea floor network and a 40 km cable which will carry the signal from this detector to the shore were already installed earlier.

On December 17, 2014, the main electro-optic cable of the MEUST (Mediterranean EuroCentre for Underwater Science and Technologies) observatory was successfully deployed to a depth of 2475 m near Toulon, France. The 40 km long cable was the first major component of the second generation deep-sea infrastructure, KM3NeT, which will supersede the ANTARES neutrino telescope.

Like its predecessor, the KM3NeT telescope will operate by detecting the faint light that occurs in natural sea water when passing neutrinos of cosmic origin undergo an interaction with the water. Neutrinos are known for their low interaction probability, which means that cubic kilometres of sea water must be instrumented to detect enough of them. At its completion KM3NeT will be the largest astrophysical neutrino telescope operating in the northern hemisphere.

Following the successful integration of a prototype detector in May 2014, Nikhef researchers and engineers have been working hard in the last six months to prepare the first part of the KM3NeT detector (a 700 metre long line with 18 glass spheres). The building blocks of the detection unit are 18 Digital Optical Modules (DOMs). The KM3NeT DOMs each consist of pressure resistant glass spheres containing 31 photomultiplier tubes each. These are very sensitive light detectors that will register the faint flashes caused by secondaries created by interacions of cosmic neutrinos in the deep sea.

(Photos: Nikhef)

This Multi-PMT design represents a large increase in efficiency compared to the conventional design where each sphere contains one single, large PMT. Other innovations in the detector include optical data communication network, which transmits the detected signals to the shore, and the deployment mechanism, which was developed in collaboration with the Dutch institute for sea science, NIOZ.

“The detector is largely a Nikhef design, from the concept of the DOMs to the deployment technique. We also contributed significantly to the electronics, optical network and the software”, said Els Koffeman, Nikhef researcher and technical coordinator. Ronald Bruijn, Nikhef’s coordinator of the DOM production said: “The first line was assembled at Nikhef. We are very proud that we managed to do this within strict deadlines. Building the other DOMs no longer happens only at Nikhef; there are already four production lines set up in Europe to be completed soon”.

The detector line, which is now being shipped to France, is the first line of the first phase of KM3NeT. This phase will consist of 31 strings, 24 to be deployed in Italy and 7 in France. An alternative “tower-like” geometry is also under test in Italy. Aart Heijboer, KM3NeT program leader at Nikhef said: “These 31 strings are a first step that will validate the technology, a prerequisite to secure future funding for the next step (phase 2.0). The first detection line represents a major milestone for this. Ultimately we aim to build and deploy 700 strings, to realize all our scientific ambitions.”

Claude Vallée, scientific responsible of the project at CPPM, said: “We hope to receive funding to immerse 30-40 strings (the cost will be about 10 million euros) in the next couple of years. The long-term objective is to deploy hundreds of strings, providing we receive funding through the European cooperation”.

Deployment of the main electro-optic cable of the MEUST to a depth of 2475m near Toulon, France, on December 17, 2014 (Photos M.G.)

“The success of today represents another important step towards building KM3NeT-It, the Italian node within the European research infrastructure,” said Giacomo Cuttone, project manager of KM3NeT-It and director of the Southern National Laboratories (LNS) of Italy’s National Institute of Nuclear Physics (INFN).On November 18, 2014, the first tower of the KM3NeT Neutrino Observatory was laid and anchored to the seabed, at a depth of 3500 metres, off-shore Portopalo di Capo Passero, Sicily, Italy. The apparatus employs detection structures of different types, such as towers and strings, to optimize the response to the widest possible energy range of the particles to be studied. The experiment, in the final configuration of this phase, will be constituted by a total of eight towers and twenty-four strings, forming a three-dimensional matrix of sensors for the detection and measurement of high energy astrophysical neutrinos.

“Both the design and construction of the equipment and installation operations are particularly complex due to the very hostile operating environment: we are three and a half kilometres deep under the surface without the ability to conduct system maintenance”, explains Mario Musumeci, coordinator of the integration activities.

“The installation operations led to the perfect coordination between the team working at the data acquisition land station and the team on the ship”, emphasized Cuttone. “A special thanks to the INFN team, composed by Klaus Leismuller, Nunzio Randazzo and Giorgio Riccobene, who coordinated the operations from the ship Ambrosious Tide under not always ideal weather and sea conditions”.

The undertaking involved nine groups of INFN (Bari, Bologna, Catania, Genoa, LNF, LNS, Naples, Pisa, Rome) in collaboration and synergy with geophysical and oceanographic and marine biology institutes (INGV, CNR, CIBRA, NURC).

The tower is being laid and anchored to the seabed, at a depth of 3500 metres, off-shore Portopalo di Capo Passero, Sicily, Italy.

The KM3NeT Project

Remotely Operated Vehicle (ROV), an unmanned remotely controlled underwater robot connected to the surface via an electrical cable (Source INFN).

KM3NeT is an international collaboration which consists of physicists and engineers from many European countries: Cyprus, France, Germany, Greece, Ireland, Italy Netherlands, United Kingdom, Romania, and Spain. The collaboration, aims to build and deploy hundreds of strings over the coming years, thereby realizing several cubic kilometres of instrumented volume.

In its final configuration the experiment will consist of a ‘forest’ of structures. The towers and strings serve as support for tens of thousands of optical sensors (photomultipliers), highly sensitive electronic ‘eyes’ that will form an underwater antenna that can detect the trail of bluish light (called “Cherenkov radiation”) produced by the rare interactions of neutrinos of astrophysical origin in the seabed.

With this detector, which will be hosted in both Italy and France, it will be possible to detect with unprecedented accuracy high energy neutrinos which travelled through deep space carrying information about their cosmic origins while remaining almost intact. It will yield a new way to do astrophysics and to study neutrino properties. These can also be studied with what are known as atmospheric neutrinos, which will provide information on the pattern of neutrino masses.

Nikhef researcher Maarten de Jong, spokesman for the international KM3NeT collaboration, explained: “Our primary goal is to measure cosmic neutrinos. Thus, we can learn a lot about extremely energetic processes in astrophysical objects. We hope for example to trace the origin of cosmic rays, 100 years after their discovery. This astronomy side is very relevant, especially since in 2013 the Ice Cube Neutrino Observatory at the South Pole found evidence for the existence of such cosmic neutrinos. In addition, the collaboration will focus on the measurement of one of the still unknown properties of neutrinos, their intrinsic mass hierarchy. To do this, the same technology can be used, but the glass spheres and the strings have to be placed closer together. The good thing is that the technology developed here at Nikhef can be used for both research directions.”

In France, the infrastructure will also host a variety of environmental sensors for the Earth and Sea sciences community. The cable will be connected to a line of observation of marine fauna and to an observational module of the marine environment. “With MEUST, we work on hydrology (monitoring the temperature of the oceans and their oxygen content), the bio-marine (listening and studying marine mammals), and seismology (monitoring tsunamis and earthquakes)”, explained Dominique Lefevre of the Mediterranean Oceanographic Institute in France.

Why at the Bottom of the Sea

Detection principle by the KM3NeT underwater neutrino detector. (Source: KM3NeT collaboration).

The peculiarity of neutrinos resides in their extremely low probability of interacting with matter: this characteristic allows them to remain unabsorbed by the background radiation and to travel without being perturbed through regions which are opaque to electromagnetic radiation (e.g. the interior of astrophysical sources). Also, being neutral particles, they do not undergo deflections caused by the galactic and intergalactic magnetic fields which would prevent us from tracking their direction of origin. The price to pay for observing these elusive particles is the need to build detectors of enormous dimensions. Also, to protect themselves from the rain of cosmic radiation that hits the Earth, these detectors must be installed in heavily shielded places. However, it is evident that devices of this size cannot be placed in underground laboratories. A possible solution then, is to use large volumes of a natural medium, to install the appropriate instrumentation.

Maarten de Jong said: “Neutrinos have the infamous property that they are very difficult to detect. In order to do so, the detector must be very heavy and thus also very big, literally cubic kilometers. Of course that doesn’t fit into a standard laboratory but can certainly fit in the sea. We therefore build a huge but unmanned laboratory at the bottom of the sea.”

In a transparent medium, such as deep sea water or polar ice, it is possible to reveal the Cherenkov radiation produced by secondary particles (notably muons), generated by the interactions of neutrinos with matter. Since these have a direction almost identical to that of the neutrinos that generated them, their detection allows in fact to also reveal the source of neutrinos. Moreover, if we place the detector in the deep sea (or under-polar ice), the overlying matter acts as a shield against the background of cosmic particles, which otherwise would “blind” a detector placed on the surface. The water (or ice) thus has a triple function: protective shield from cosmic rays, target for the interaction with neutrinos and transparent medium through which the Cherenkov radiation may propagate.

The KM3NeT project has so far been largely financed by EU structural funds and is included in the list of European RIs by the European Strategy Forum on RIs (ESFRI).

Submitted by Eleni Chatzichristou
APPEC Communications Office

Further reading:

KM3NeT collaboration
Nikhef’s Press Release: “Eerste bouwsteen KM3NeT-detector klaar”
INFN’s Press Release: “Nuovo Successo per Km3NeT: Agganciata in Fondo al Mare la Prima dell Otto Torri”