KM3NeT: Next-generation neutrino telescope in the Mediterranean Sea

International audienceThe successes of the ANTARES detector have demonstrated the feasibility and value of deep sea neutrino telescopes, as well as their versatility through Earth and Sea sciences. KM3NeT is a distributed undersea research infrastructure in the Mediterranean Sea that will host a network of next-generation neutrino telescopes. With the ORCA telescope at the KM3NeT-Fr site, the main objective is to determine the neutrinos mass hierarchy by studying atmospheric neutrino oscillations. The ARCA telescope at the KM3NeT-It site will allow for high energy neutrino astronomy. The telescopes consist of a regular 3D array of Digital Optical Modules, each composed of 31 photomultipliers, equally spaced along flexible lines anchored on the seabed. This multi-photomultipliers concept yields a factor three increase in photocathode area, compared to a design with a single 10 inch photomultiplier, leading to a significant cost reduction. Moreover, this concept allows for an accurate measurement of the light intensity and offers directional information with an almost isotropic field of view. A detailed overview of the detectors, their construction status and their physics program will be presented. The calibration techniques will be discussed, with an emphasis on time calibration, water properties and positioning measurements