The KM3NeT Collaboration aims at the construction of a distributed
research infrastructure under the Mediterranean Sea that will host two
underwater neutrino detectors: ARCA and ORCA. They are optimised to
detect neutrinos using the Cherenkov technique and will play an
important role in the detection of high energy astrophysical
neutrinos, ARCA, and in the study of the neutrino mass hierarchy
exploiting the flux of atmospheric neutrinos, ORCA.
Both detectors share the same technology: thousands digital optical
modules, each hosting 31 3-inch photomultipliers, distributed along
tall detection units. The main difference is the distance between the
optical modules, optimised to meet the requirements of the different
scientific objectives.
The reconstruction of the neutrino direction exploits the Cherenkov
photons emitted along the path of the charged particles produced in
the neutrino interactions and requires a nanosecond
synchronisation between the photomultipliers in order to get high
angular resolution. This contribution describes the accurate time
calibration procedures developed to synchronise the time references of
the photomultipliers within an optical module and of each optical
module within the detection unit and also between detection units.