19 August 2019 – Since this spring, the KM3NeT telescopes are routinely operating with five detection units: four at the ORCA site. At both sites, commissioning of the detector units has been completed. Several first data results have been already reported on the international conferences and workshop.
For the ORCA detector, off shore the French Provencal coast, four units were installed and connected to the seabed network. An earlier deployed unit was damaged during inspection and had to be recovered for repair in the labs of the Collaboration. It will be re-deployed in a next sea campaign. Also during the Spring-campaigns, three autonomous acoustic beacons were deployed at the seabed in the vicinity of the ORCA array. They are used for acoustic positioning of the optical modules in the detection units that move with the slowly varying deep sea currents. Sea campaigns for further expansion of the ORCA detector are scheduled after the summer break.
At the site of ARCA, after a fix of the seabed network, a detection unit that was deployed three years ago, could be revived and is again taking data since. Currently, the seabed network is being re-designed to allow for the extension of the ARCA detector of more than 200 detector units. The successful though temporary fix of the existing network makes connection of more detection units possible, while waiting for the implementation of the upgraded network.
Differences between ARCA and ORCA
The technology used for the ARCA and ORCA detectors is almost identical, but one thing is striking: the difference in volume and height of the detectors. When finished, ARCA will have a volume of about 1 Gton while the volume of ORCA will be ‘only’ about 8 Mton, while the number of optical modules in ORCA is only half the number in ARCA: more than 4000 vs about 2000. In ARCA eighteen modules are distributed over a detection unit with a height of about 1000 m, in ORCA they are distributed over about 100 m. Also the horizontal spacing between detection units is different: about 90 m in ARCA vs about 20 m in ORCA. The geometrical differences reflect the main scientific purpose for which the detectors will be used and is also visible in the first character of their names: ARCA stands for Astroparticle Research with Cosmics in the Abyss. The detector is optimised for the detection of high-energy cosmic neutrinos from distant sources in the Universe. ORCA is the acronym for Oscillation Research with Cosmics in the Abyss. The detector is optimised to measure lower energy neutrinos, thus providing information for the study of neutrinos oscillating between the three known neutrino flavours.
KM3NeT: Comparison of the physical size of the ARCA and ORCA detectors.