Calibration with a Kr83m source in Project 8 Phase II

The Project 8 collaboration aims to measure the neutrino mass at a sensitivity ~40 meV with the tritium endpoint method in four phases. To achieve this goal, the Project 8 collaboration has developed the Cyclotron Radiation Emission Spectroscopy (CRES) technique to measure the energy of electrons from the decay of radioactive gas sources. In Phase II, we have measured the first CRES spectrum for molecular tritium. Due to its 17.8 keV conversion electron line sitting close to the tritium endpoint at 18.6 keV, we used Kr83m as a calibration source for magnetic field calibration and instrumental response measurement. In this talk, I will present the calibration of the Phase II apparatus with Kr83m, including the linearity of the frequency-energy response and the fit results of the 17.8 keV line in a deep magnetic trap and a shallow magnetic trap. From the fit results in the shallow magnetic trap, we find the instrumental response can be as narrow as ~2 eV. I will also show how the Kr83m calibration datasets can help assess some of the systematics for the tritium data analysis.