The White Rabbit time calibration system for KM3NeT/ARCA

The KM3NeT neutrino telescope consists of two detectors: ARCA, at 3500m depth offshore Capo Passero, Sicily, and ORCA, at 2500m depth offshore Toulon. Both detectors consist in a 3D-grid of Detection Units (DUs), each with 18 Digital Optical Modules (DOMs), anchored on the seabed and linked to the shore station via optical fibers. Each DOM houses 31 3-inch photomultiplier tubes (PMTs) and the relative front-end electronics. The KM3NeT neutrino detector reconstructs the Cherenkov light wavefront emitted by charged particles produced in a neutrino interaction in water. In order to guarantee the expected physics goals in terms of angular resolution and sensitivity to astrophysical sources, the time resolution and timing offsets between all PMTs must be kept at the nanosecond level, knowledge of DOM positions at circa 20 cm accuracy and orientation at few degrees. The Collaboration has recently adopted the standard White Rabbit time-synchronization technology as the optimal solution to synchronize the detector electronics. After a strict qualification process, the first 17 DUs using standard White Rabbit have been produced and, since September 2024, three of them are fully operational in the ARCA detector, showing optimal time accuracy. The novel time calibration procedure and results from the ARCA detector will be shown and discussed.