Project 8 has developed a novel technique, cyclotron radiation emission spectroscopy (CRES), for direct neutrino mass measurements. A CRES-based experiment on the beta spectrum of tritium has been carried out in a small-volume apparatus. We provide a detailed account of the experiment, focusing on systematic effects and analysis techniques. In a Bayesian (frequentist) analysis, we measure the tritium endpoint as $18{553}_{-19}^{+18}$ ($18{548}_{-19}^{+19}$) eV and set upper limits of 155 (152) eV (90% C.L.) on the neutrino mass. No background events are observed beyond the endpoint in 82 days of running. We also demonstrate an energy resolution of $1.66\pm 0.19\mathrm{eV}$ in a resolution-optimized magnetic trap configuration by measuring ${}^{83\mathrm{m}}\mathrm{Kr}17.8$-keV internal-conversion electrons. These measurements establish CRES as a low-background, high-resolution technique with the potential to advance neutrino mass sensitivity.

• Received 23 March 2023
• Accepted 9 January 2024

DOI:https://doi.org/10.1103/PhysRevC.109.035503