Abstract
The KM3NeT underwater neutrino telescope comprises thousands of optical modules forming 3D arrays to detect the Cherenkov light produced by particles generated after a neutrino interaction in the medium. The modules are arranged in detection units—vertical structures with 18 modules at different heights, anchored to the seabed and kept vertical by the buoyancy of the optical modules and a top buoy. The optical modules are, thus, subject to movements due to sea currents. For a correct reconstruction of events detected by the telescope, it is necessary to know the relative position and orientation of modules with 10 cm and a few degrees accuracy, respectively. For this, an Acoustic Positioning System with a piezoceramic transducer installed in each module and a long baseline of acoustic transmitters and receivers on the seabed are used. In addition, there is a system of compass and accelerometers inside the optical modules to determine their orientation. A model of mechanical equations is used to reconstruct the shape of the detection unit taking as input the information from the positioning/orientation sensors and using the sea current velocity and direction as free parameters. The mechanical equations take the buoyancy and the drag force of the elements of the detection unit into account. This work describes the full process that is implemented in KM3NeT to monitor the modules and the shape of the detection units from the measured position and orientation data.
Highlights
The underwater neutrino telescope KM3NeT is under construction in the Mediterranean Sea aiming at a high-energy neutrino detector with high sensitivity
The mechanical model (MM) in the detection unit (DU) Line Fit for KM3NeT is a set of mechanical equations used to determine the position and orientation of every Digital Optical Modules (DOMs) from sea current properties and the position of the DU-base
The DU Line Fit is the process that combines the data from Acoustic Positioning System (APS) and AHRS with the MM to determine the real position of the DOMs every 10 min
Summary
The underwater neutrino telescope KM3NeT is under construction in the Mediterranean Sea aiming at a high-energy neutrino detector with high sensitivity. ARCA is optimized for the search for high-energy cosmic neutrinos It will be composed of two different detector blocks of 115 DUs with 690 m height. For KM3NeT the DU Line Fit applications is validated by previous studies: the APS to location the DOMs [9], the simultaneously acquisition data by AHRS and APS [10], and the expected improvement of few centimeters in the MM implementation [11]. At this moment, ORCA has six DUs deployed and in operation. For ARCA, two DUs are deployed which currently are out of operation due to an upgrade of the seafloor network
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