The Pacific Ocean Neutrino Telescope (P-ONE)
Following the breakthrough discoveries of very-high-energy neutrinos of astrophysical origin by IceCube that started in 2013, a new field of research, neutrino astronomy, was established in the previous decade. Even though two extragalactic point sources of such neutrinos have been identified by now, TXS 0506+056 and NGC 1068, the origin and processes of creating astrophysical neutrinos are still mostly unexplored. To advance quickly in this new field, more neutrino telescopes are required. This need propelled the initiative to develop the Pacific Ocean Neutrino Experiment (P-ONE) in the Pacific Ocean near Vancouver Island. The deployment of P-ONE will start in 2025, exploiting the already available deep-sea infrastructure of Ocean Networks Canada.
The Physics Goals of P-ONE
P-ONE, located in the Northern Hemisphere, will provide data complementary to IceCube, located in Antarctica, by extending the coverage of the southern sky. Its physics goals cover searching for neutrinos from known astrophysical objects and detecting unidentified sources in the sky.
The potential galactic sources are likely located mainly near the Galactic Center and the Galactic Plane and include supernova remnants, pulsars, the neighborhood of the black hole Sgr A*, and many others. According to production models, the energy spectrum of galactic neutrinos fills the energy range 103–106.
On the other hand, extra-galactic objects — Active Galactic Nuclei, Gamma-Ray Bursts, starburst galaxies, and galaxy clusters— could generate neutrinos in the energy range of 104–108 GeV or higher. P-ONE will also contribute to multi-messenger astronomy, where combined studies are chosen.
Another direction is to investigate the characteristics of the diffuse neutrino flux at energies above 104 GeV. Searches for Dark Matter particle decays are also possible with the P-ONE telescope. Tau-neutrino tagging is also possible in P-ONE, and events with other detectors may lead to higher significant muon bundle discrimination results.
Moreover, because the scattering length in water is much longer than in ice, P-ONE will also show a much better angular resolution for incoming neutrinos (with respect to IceCube) and help identify sources in the sky.
While Baikal-GVD and KM3NeT have long been under development in the Baikal Lake and the Mediterranean Sea, respectively, and, in addition, a new project, TRIDENT, is planned in the South China Sea, the Pacific Ocean Neutrino Experiment (P-ONE) is in the advanced construction phase. It will complement the sky coverage of the existing telescopes.
The Detector Design of P-ONE
Neutrinos are observed by their Cherenkov radiation, which follows a neutrino interaction in a transparent medium. Since neutrinos rarely interact with matter, and the neutrino flux drops with energy as E−2 – E−3, huge instrumented volumes of cubic kilometer scales are needed to observe astrophysical neutrinos. To this end, existing reservoirs of transparent matter, such as Antarctic ice (IceCube) or water (Baikal-GVD, KM3NeT, P-ONE), are instrumented with light sensors.
For the detector design of P-ONE, a segmented structure similar to that of Baikal-GVD was chosen because the optical attenuation length of the ocean water is much lower than that of Antarctic ice (20–40 m vs. more than 100 m), and a uniform array structure like that of IceCube would hence generate very high costs. The individual measurement units, Precision Optical Modules (P-OM), will be connected to vertical strings, where each string will host 20 such P-OMs and several calibration modules (P-CAL) and will be anchored to the bottom of the ocean. A group of 10 strings will form a cluster comprising a cylindrical structure with a radius of 200 m and 80 m distances between strings. The vertical separation between the P-OMs will be 50 m. Seven such clusters are planned for a detector volume of one cubic kilometer. The proposed baseline layout will further be optimized during the construction phase to maximize the effective area for neutrino detection and obtain the best possible angular and energy resolution while keeping costs low.
