Session W11: Mini-symposium: Neutrino Mass IV

Recent Results from Daya Bay

The Daya Bay Reactor Neutrino Experiment consists of eight functionally identical detectors which are distributed between three experimental halls at various baselines from six nuclear reactor cores. With the largest sample of reactor antineutrinos in the world, the experiment has leading sensitivity to the θ₁₃ and Δm₃₂² oscillation parameters, has set some of the most stringent limits for sterile neutrino mixing for Δm₄₁² < ~1 eV², and has precisely characterized the antineutrino emission from nuclear reactors. This talk will provide a brief overview and status of the experiment and highlight the most recent results.   

Correlated backgrounds for near-surface Inverse Beta Decay detectors

Aboveground antineutrino detection requires careful control of cosmogenic background sources and accurate quantification of any residual backgrounds that survive an Inverse Beta Decay (IBD) event selection. Cosmic high-energy neutrons are among the most prominent sources of background since their flux is relatively high at the Earth's surface. The PROSPECT detector was deployed at less than 10 m distance from the High Flux Isotope Reactor at Oak Ridge National Laboratory, and has demonstrated successful aboveground antineutrino measurements with a signal-to-background ratio greater than 1:1. A detailed Monte Carlo simulation code was developed to match the performance of PROSPECT during the reactor off period, when only residual backgrounds are measured. In addition to illuminating the characteristics of these residual backgrounds, this code allows us to examine the performance of a variety of notional shielding and detector configurations. In this work, we describe the performance of compact shielding configurations to provide input on cosmic neutron background reduction for future aboveground antineutrino detector designs.   

Machine Learning Methods for IBD Analysis with PROSPECT Data

The Precision Reactor OSCillation and SPECTrum experiment (PROSPECT) is a segmented multi-ton scale 6Li doped liquid scintillator detector that was deployed at Oak Ridge's High Flux Isotope Reactor in 2018 to measure the reactor antineutrino spectrum and look for potential short baseline oscillation effects due to beyond standard model interactions. Each segment of the detector was outfitted with photomultiplier tubes (PMTs) on either end for light collection enabling centimeter scale position resolution along the length of the cell. The detection mechanism utilized the inverse beta decay (IBD) of the antineutrino on hydrogen within the scintillator, which is characterized by a prompt burst of light from the positron deposition followed by a well defined signal from neutron capture on 6Li. Throughout the duration of the experiment some PMTs became inoperative and were turned off for the initial published IBD analysis. There has since been an analysis effort to recover data from segments containing a single working PMT for the purposes of improving background rejection. This presentation goes over machine learning efforts utilizing convolutional neural networks and graph neural networks to reconstruct physics variables in single-ended segments such as the position, energy, and particle ID. It will also show the impact this has on the effective statistics for an IBD selection.   

Can decay heat measurements tell us something about the Reactor Antineutrino Anomaly?

Measurements of the decay energy released as function of time following a neutron induced fission burst on ²³⁵U, ²³⁹Pu and ²⁴¹Pu were performed in the 1970s with the purpose of quantifying possible Loss Of Coolant Accident scenarios.   This decay energy, known in technical parlance as decay heat, is mainly composed of two terms, the energy from the electrons produced together with antineutrinos in the beta-minus decay of the neutron-rich fission products, and the energy from the gamma-rays, produced in the decay of excited nuclear levels.  In this work we study if this body of decay heat data can be used to assess the Reactor Antineutrino Anomaly, that is the approximately 5%  electron antineutrinos deficit produced by nuclear reactors at short distance, first deduced by Mention and collaborators in 2011, and observed by the major reactor antineutrino experiments near nuclear power plants operating in the last 10 years.    

Signal Detection Algorithms for Phase III of the Project 8 Experiment

Project 8 is a next-generation neutrino mass experiment that uses Cyclotron Radiation Emission Spectroscopy (CRES) to measure the neutrino mass. CRES is a technique for β-decay spectroscopy which measures the frequency of the cyclotron radiation produced by energetic electrons trapped in a magnetic field. The cyclotron frequency can be directly converted into the energy spectrum, which yields the neutrino mass through measurement of the spectrum endpoint. The next phase of the Project 8 experiment seeks to measure the energy spectrum of molecular tritium β-decay in an O(10 cm³)  volume, using an antenna array or an RF cavity to collect the faint radiation emitted by an electron in a magnetic field. This talk will present an overview of the signal processing algorithms that Project 8 is developing to enable free-space or cavity based CRES, including the use of matched filtering to detect the presence of CRES signals. I will also highlight progress on machine learning techniques which are designed to complement or potentially replace matched filtering as the primary detection technique.   

Antenna Chain Characterization for Project 8 Phase III Development

Studies on neutrinos have significantly progressed in the past few decadees, but we have yet to measure the absolute neutrino mass scale. Project 8 aims to achieve an electron neutrino mass upper bound of 40 meV by leveraging a new technique called Cyclotron Radiation Emission Spectroscopy (CRES), which measures the electron cyclotron frequency and energy in a uniform magnetic field. The neutrino mass could be inferred from the shape of the β-decay electron energy spectrum near the endpoint. Phase III of Project 8 will use an array of antennas around a small active volume of gaseous tritium to record the electron energies. Testing and characterization of the antenna receiving chain with a quantum-limited amplifier provides critical input for estimating sensitivity for both Phase III and Phase IV. This presentation will expand on the latest progress of integrating a prototype Phase III antenna with a Josephson Traveling Wave Parametric Amplifier (JTWPA), including the frequency response of the system and potential problems caused by impedance mismatch. We will also gauge the target signal-to-noise ratio with match-filtered injected signals.   

Atom-Source Development for Project 8

The Project 8 experiment aims to make a direct measurement sensitive to much of the unexplored range of neutrino masses. Past experiments used molecular tritium, which has a large energy smearing from its final states. Project 8 will use atomic tritium to reach m_β ≤ 40 meV. This requires ∽10²⁰ T atoms held at tens of mK in a several-cubic-meter magnetic trap. The efficiencies of cooling the atoms and their trapped lifetime require ≥ 10¹⁹ atoms/s at the source. Phase III of Project 8 will include an Atomic Tritium Demonstrator to confirm we can produce, cool, and trap sufficient atomic T for the final Phase IV experiment.

I will discuss work at the University of Mainz to develop a high-flux tritium-compatible atom source and designt he downstream elements of a full atomic-tritium experiment. Our tests extend to a hydrogen flow of 20 sccm, 20 times the previously-published values for this type of source. Recent progress includes boosting the atomic signal/background ratio 100-fold and separation of the atom signal from background via low-energy ionization. Upgrades are underway to definitively determine if the present atom source provides sufficient atomic flux for Project 8's neutrino mass sensitivity. Designs for a higher-output atom source, if needed, and the subsequent cooling and trapping stages are in progress will be tested in due course.   

Atomic hydrogen beam characterization for the Project 8 neutrino mass experiment

There have been significant gains in characterizing neutrino properties in recent decades, however the absolute neutrino mass scale continues to be elusive. The Project 8 experiment seeks to probe this property directly via kinematic analysis of atomic tritium single beta decay, using the cyclotron radiation emission spectroscopy (CRES) technique. CRES employs a frequency-based approach to measure the differential tritium beta decay spectrum in the endpoint region, where the spectral shape is most sensitive to distortions from a finite, non-zero neutrino mass. A vital component to Project 8's neutrino mass measurement with a design sensitivity of 40 meV, is the use of atomic tritium. As a first step towards achieving this goal, an atomic hydrogen test stand has been developed. Atomic hydrogen beam characterization from recent measurements with high flows, more than an order of magnitude higher than those achieved in similar previously-published setups, will be presented here.