Deep sea tests of a prototype of the KM3NeT digital optical module

TL;DR

This paper reports on the deployment and testing of a novel digital optical module with segmented photomultiplier tubes in the deep Mediterranean Sea, demonstrating its capabilities for neutrino detection and background suppression.

Contribution

It introduces a new design of a digital optical module with 31 photomultiplier tubes and validates its performance in situ within the ANTARES detector.

Findings

Effective background suppression and signal recognition.

Ability to identify atmospheric muons and their directions.

Localization of bioluminescent activity.

Abstract

The first prototype of a photo-detection unit of the future KM3NeT neutrino telescope has been deployed in the deep waters of the Mediterranean Sea. This digital optical module has a novel design with a very large photocathode area segmented by the use of 31 three inch photomultiplier tubes. It has been integrated in the ANTARES detector for in-situ testing and validation. This paper reports on the first months of data taking and rate measurements. The analysis results highlight the capabilities of the new module design in terms of background suppression and signal recognition. The directionality of the optical module enables the recognition of multiple Cherenkov photons from the same $^{40}$K decay and the localization bioluminescent activity in the neighbourhood. The single unit can cleanly identify atmospheric muons and provide sensitivity to the muon arrival directions.