Session L12: Minisymposium: Low Energy Neutrinos V: Neutrino Mass & Reactor Neutrinos

KATRIN: Closing in on the Neutrino Mass

The absolute mass scale of the neutrino is a critical open question in nuclear/particle physics and in cosmology. This talk will explore the potential for direct measurements of this quantity using the kinematics of beta decay, with a focus on the Karlsruhe Tritium Neutrino experiment (KATRIN). In its first two scientific campaigns, KATRIN has pushed the worldwide direct laboratory limit on the neutrino mass to 0.8 eV (90\% confidence) -- and seven subsequent neutrino-mass campaigns have now been completed. I will discuss the scientific possibilities of KATRIN's existing data sets, from probing the neutrino mass to testing the Standard Model, and will share prospects for the next few years of KATRIN science.   

Cyclotron Radiation Emission Spectroscopy and the Project 8 neutrino mass experiment

Measurements of the β^- spectrum of tritium give the most precise directly measured limits on neutrino mass. The Project 8 collaboration is using Cyclotron Radiation Emission Spectroscopy (CRES), a new experimental technique that has the potential to surmount the systematic and statistical limitations of current-generation direct measurement methods to increase sensitivity. I will introduce CRES, describe Project 8's development work on CRES and on an atomic tritium source, and outline Project 8's phased research program to reach an electron-weighted antineutrino mass sensitivity of ~40 meV/c².   

Neutrino mass limit and final analysis of the first tritium spectrum recorded with CRES

The Project 8 collaboration aims for a direct measurement of the absolute neutrino mass scale from the distortion of the tritium decay spectrum near the endpoint. To this end, the collaboration has successfully established Cyclotron Radiation Emission Spectroscopy (CRES), a frequency-based approach for measuring the energy of electrons emitted in decays. To meet the goal of a final sensitivity of 40meV/c2, Project 8 has divided the development of the experiment into four phases with Phase II data collection completed in 2020. In this talk, I will present the recently published final analysis of the first tritium spectrum recorded with the Phase II CRES prototype. We have performed a Bayesian and a frequentist analysis on the tritium data, which independently determine limits on the neutrino mass. These limits are in excellent agreement with each other and with the sensitivity of the Phase II experiment. In this talk, I will focus on the frequentist analysis and provide an outlook on how the Phase II analysis informs the future of Project 8.   

Cyclotron Radiation Emission Spectroscopy in resonant cavities for the Project 8 neutrino mass experiment

Project 8 is a next-generation experiment aiming to directly measure the neutrino mass using the tritium endpoint method with a targeted sensitivity of 40 meV. The completed phases I and II have established a new measuring technique, Cyclotron Radiation Emission Spectroscopy (CRES), as a precise measuring technique of the endpoint spectrum and extracted an upper limit on the neutrino mass from a small volume of tritium. The next development phase will demonstrate CRES on a large source volume, culminating in a pilot-scale CRES experiment with atomic tritium. A promising option is a mode-filtered, cylindrical resonant cavity in which cyclotron radiation from magnetically trapped beta electrons couples only to the lowest eigenmode(s), maximizing effective volume and minimizing signal complexity. 

I will show recent progress in the experimental design, focusing on a small scale proof-of-concept cavity CRES apparatus (CCA) to demonstrate CRES in cavities at previously benchmarked CRES frequencies of ~26 GHz. In addition to 83m-Krypton transition line measurements, an electron gun will be validated as a new calibration tool for subsequent experimental setups.   

Simulation Framework for the Project 8 Neutrino Mass Experiment

Project 8 is a multi-phased experiment with an ultimate design goal to probe the neutrino mass down to 40 meV. This is done by utilizing Cyclotron Radiation Emission Spectroscopy (CRES) to make a precision measurement of the electron kinetic energy near the endpoint of tritium beta-decay. Extensive modeling and simulation efforts of the experimental setup are crucial for designing the next phases of the experiment as well as developing event reconstruction techniques. Necessary simulation features include electron dynamics in magnetic traps, emission of cyclotron radiation, and electron coupling to resonant cavity modes. This talk will present an overview of the simulation tools used for previous phases of the experiment as well as the extensions developed to optimize designs for future phases of Project 8.   

Atomic source development for the Project 8 neutrino mass experiment

The Project 8 experiment aims to determine the mass of the electron anti-neutrino, pushing below the inverted mass hierarchy scale with a sensitivity of 40 meV. In order to achieve this, Project 8 uses Cyclotron Radiation Emission Spectroscopy (CRES) to measure the energy of tritium beta-decay electrons close to the kinematic endpoint, where the signature of the neutrino mass is imprinted. One important factor in achieving a sensitivity of 40 meV is avoiding the energy broadening due to the molecular final states of T2 molecules, which improves statistical sensitivity on the neutrino mass significantly. For this purpose, Project 8 will use atomic instead of molecular tritium. In this contribution, I will present some of the advances made in developing a source of atomic tritium as it will be necessary for the Project 8 experiment, as well as lay out future steps towards reaching that goal.   

Antineutrinos at SNO+

The SNO+ Experiment is a large liquid scintillator neutrino experiment located 2 km underground in Sudbury, Ontario, Canada. SNO+ is able to study a broad range of physics topics including reactor antineutrinos and geoneutrinos. The first detection of reactor antineutrinos in liquid scintillator at SNO+, as well as the current status of an updated analysis with a fully filled detector and increased livetime are presented. The analyses constrain the neutrino oscillation parameters Δm²₂₁ and θ₁₂, and will measure the flux of geoneutrinos at SNO+. Comparison of this result to previous measurements may help resolve tension between measurements of Δm²₂₁ from solar neutrinos and from reactor antineutrinos. Projections of the sensitivity to these parameters and to the geoneutrino signal with increased livetime are also presented.   

Progress towards understanding the source of the Reactor Antineutrino Anomaly

We have reviewed the nuclear data used in the normalization of the electron spectra measured at the Institut Laue Langevin in the 1980s, concluding that they are very close to currently recommended values, except for the neutron capture cross section on 207Pb, which is 9% higher.   This would lead to an artificially larger 235U electron and antineutrino spectra, consistent with the Daya Bay Collaboration results, as well as those reported recently by Kopeikin and collaborators.  Additionally, following an analysis that employs the latest nuclear databases of the electron data measured at ORNL in the 1970s by Dickens and collaborators, we have deduced new electron and antineutrino spectra for 235U and 239,241Pu under equilibrium conditions, which are consistent with the above mentioned normalization issue, and which can better reproduce the IBD antineutrino spectrum near its maximum, thus providing a coherent explanation for the origin of the Reactor Antineutrino Anomaly.