Characterization of the R14374-10 photomultiplier tube for the Pacific Ocean Neutrino Experiment
The Pacific Ocean Neutrino Experiment (P-ONE) is a planned cubic-kilometer-scale neutrino telescope that will be deployed in the Pacific Ocean, leveraging deep-sea infrastructure operated by Ocean Networks Canada (ONC). The first detector line will deploy 320 3-inch Hamamatsu R14374-10 photomultiplier tubes (PMTs) to detect Cherenkov light produced by charged particles propagating through water, as well as light from calibration sources and optical backgrounds. This article presents the systematic characterization of all PMTs to be integrated into the first detector line prior to deployment, ensuring compliance with all detector acceptance criteria. All PMTs satisfy the specified performance criteria: the average transit-time spread (TTS) was measured to be $1.73\pm 0.15\,$ns, and the average charge resolution at a gain of \num{5e6} was $0.43\pm 0.03\,$pC; the average after-pulse rate was measured to be around 6$\,\%$. The integrated P-ONE data acquisition (DAQ) system was also tested and cross-validated against a laboratory digitization system. The second part of the paper presents an in-depth characterization of a subset of six PMTs, focusing on the key properties required for detector simulations, including linearity, after-pulse rate, quantum efficiency, and relative collection efficiency. PMT linearity was measured at a gain of \num{5e6} using the complete P-ONE readout electronics, and the response was found to remain linear for signals up to 150 photoelectrons. After-pulse contributions from $\text{Cs}^{+}$, $\text{He}^{+}$, and other ions were identified in the subset. The peak quantum efficiency was measured to be $27.0\pm0.7\,\%$ at 395\,nm. Using measurements of the relative detection efficiency, the collection efficiency was found to differ by a wavelength-independent offset of 10--15$\%$ across the measured wavelength range.