P-ONE second pathfinder mission: STRAW-b

Abstract

The Pacific Ocean Neutrino Explorer (P-ONE) [1] collaboration was born to build a new large-scale neutrino telescope in the Pacific Ocean, at 2600 m b.s.l. in Cascadia Basin, off Vancouver Island. The first steps aimed at the feasibility study and the characterisation of the optical properties of the site with a first pathfinder project named STRAW (STRing for Absorption length in Water) [2] [3] [4], deployed in 2018. During the last two years, a second pathfinder project has been developed: STRAW-b. The main goal of STRAW-b is to validate the attenuation length already measured by STRAW and to add new information on the background characterisation with the study of the deep sea diffused light spectrum. It consists of a 500 m mooring (electrical-optical cable communication) equipped with three Standard Modules for environmental monitoring and seven Specialised Modules for background analysis and attenuation length measurements. All the modules are hosted in spherical 13" high-pressure resistant glass housings. Its design started at the end of 2018 and after about two years it has been successfully deployed in summer 2020 in Cascadia Basin site, connected to the underwater Ocean Networks Canada infrastructure about 40 meters away from STRAW. We present all the steps from the design to the realisation of the mooring, with a special focus on the adopted technologies.

Pacific Ocean Neutrino Experiment

“…The P-ONE Collaboration has developed and deployed two pathfinder missions in the experimental site, STRAW [17] and STRAW-b [18] (STRings for Absorption in Water), in 2018 and 2020, respectively, and was decommissioned after successful operation in Summer 2023. Their purpose was to explore the optical properties of the local water, measure the possible optical background, and test solutions planned for the regular measurement lines in the future.…”

“…The modules included two LIDARs, three modules to measure environmental conditions, one muon tracker (composed of scintillator planes and SiPMs), and two spectrometer modules. The two latter ones also contained low-light cameras to register bioluminescence events in deep ocean (see Figure 5 right) [18].…”

The Wavelength-Shifting Optical Module

“…Hydrogel [ 38 ] was used as a filling material to improve the optical properties of the module. The module was deployed in the Canadian sea at a depth of within the Ocean Network Canada [ 39 ]. It operated stably at the given conditions and provided data on the local bio-luminescence.…”

Tau neutrinos in the next decade: from GeV to EeV

“…The STRAW lines include Precision Optical Calibration Modules (POCAMs) [632], calibration devices which were designed for the IceCube Upgrade, as well as digital optical modules. STRAW-b, deployed in 2020, was designed to perform a full characterization of the water optical properties and light background of the Cascadia Basin site, with a focus on the bioluminescence emission spectrum [633]. A prototype P-ONE line is under construction.…”