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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 757 records · Page 42
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DOE OSTI2023

Nuclear Matrix Elements for Neutrinoless Double-Beta Decay from Lattice QCD

Neutrinoless double-beta decay (0vbb) is a hypothetical nuclear decay that is only possible if the neutrino is a Majorana fermion. Experimental searches for this process with ever-increasing sensitivity have placed strong constraints on the 0vbb half-lives of relevant isotopes. Relating these experimental half-lives to the underlying particle physics -- the effective Majorana mass of the neutrino -- requires understanding of the nuclear matrix elements for the transition. These matrix elements can be computed within a nuclear effective field theory framework, but input from lattice QCD is necessary to constrain low-energy constants relevant for the decay. This talk will discuss calculations of these matrix elements using lattice QCD and the implications for determination of nuclear EFT parameters.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2024

Dark Radiation Constraints on Heavy QCD Axions

The naturalness problem of PQ symmetry motivates study of the heavy QCD axion, with masses m a > 1 MeV generated at scales above the QCD scale, and low values of the PQ symmetry breaking scale, ƒ a . We compute the abundance of such axions in a model-independent way, assuming only that they freeze-out after reheating from inflation, and are not subsequently diluted by new physics. If these axions decay between neutrino decoupling and the last scatter era of the Cosmic Microwave Background (CMB), they dilute the neutrinos and their abundance is constrained by CMB measurements of the energy density in dark radiation, N eff . We accurately compute this bound using a numerical code to evolve the axion momentum distribution, including many key processes and effects previously ignored. We assume that the only relevant axion decays are to final states involving Standard Model particles. We determine regions of (m a , ƒ a ) that will give a signal in N eff at CMB Stage 4 experiments. We similarly compute the N eff bound and CMB Stage 4 signal for heavy axions that can decay to light mirror photons. Finally, we compute the bounds on heavy axions with mass below 1 MeV that decay after the era of CMB last scatter, from their contribution to cold or hot dark matter or N eff at this era.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2021

The JSNS 2 detector

The JSNS 2 (J-PARC Sterile Neutrino Search at J-PARC Spallation Neutron Source) experiment aims to search for oscillations involving a sterile neutrino in the eV 2 mass-splitting range. The experiment will search for the appearance of electron antineutrinos oscillated from muon antineutrinos. The electron antineutrinos are detected via the inverse beta decay process using a liquid scintillator detector. A 1 MW beam of 3 GeV protons incident on a spallation neutron target produces an intense and pulsed neutrino source from pion, muon, and kaon decay at rest. The JSNS detector is located 24 m away from the neutrino source and began operation from June 2020. The detector contains 17 tonnes of gadolinium (Gd) loaded liquid scintillator (LS) in an acrylic vessel, as a neutrino target. It is surrounded by 31 tonnes of unloaded LS in a stainless steel tank. Optical photons produced in LS are viewed by 120 R7081 Hamamatsu 10-inch Photomultiplier Tubes (PMTs). In this study, we describe the JSNS detector design, construction, and operation.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2021

Recent Neutrino Cross-section Results from MicroBooNE

MicroBooNE is a liquid argon time projection chamber that operates in the Booster Neutrino Beam at Fermilab. The detector provides high-resolution imaging of neutrino interactions with a low threshold and full angular coverage. Thanks to a high event rate and several years of continuous operation, the MicroBooNE collaboration has obtained the world’s largest dataset of neutrino-argon scattering events. A detailed understanding of these interactions, especially the impact of nuclear physics effects, will be critical to the success of future precision neutrino oscillation efforts, particularly the argon-based Deep Underground Neutrino Experiment (DUNE) and the Short-Baseline Neutrino (SBN) program. This talk presents an overview of the latest neutrino-argon cross section measurements in MicroBooNE, including measurements of protons produced in muon neutrino interactions, measurements of the electron neutrino inclusive cross section, and progress towards measurements of rare channels.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2022

Results from the Baksan Experiment on Sterile Transitions (BEST)

The Baksan Experiment on Sterile Transitions (BEST) was designed to investigate the deficit of electron neutrinos 𝜈𝑒 observed in previous gallium-based radiochemical measurements with high-intensity neutrino sources, commonly referred to as the “gallium anomaly,” which could be interpreted as evidence for oscillations between 𝜈𝑒 and sterile neutrino (𝜈 𝑠 ) states. A 3.414-MCi 51 Cr 𝜈 𝑒 source was placed at the center of two nested Ga volumes and measurements were made of the production of 71 Ge through the charged current reaction, 71 Ga ⁢(𝜈 𝑒 ,𝑒 − ) ⁢71 Ge, at two average distances. The measured production rates for the inner and the outer targets, respectively, are [54.9$^{+2.5}_{−2.4}$⁢(stat) ± 1.4⁢(syst)] and [55.6$^{+2.7}_{−2.6}$⁢(stat) ± 1.4⁢(syst)] atoms of 71 Ge/𝑑. The ratio (𝑅) of the measured rate of 71 Ge production at each distance to the expected rate from the known cross section and experimental efficiencies are 𝑅 in = 0.79 ± 0.05 and 𝑅 out = 0.77 ± 0.05. The ratio of the outer to the inner result is 0.97 ± 0.07, which is consistent with unity within uncertainty. The rates at each distance were found to be similar, but 20%–24% lower than expected, thus reaffirming the anomaly. Furthermore, these results are consistent with 𝜈 𝑒 → 𝜈 𝑠 oscillations with a relatively large Δ⁢𝑚 2 (>0.5 eV 2 ) and mixing sin 2 ⁡2⁢𝜃 (≈ 0.4).

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2025

Data-driven model validation for neutrino-nucleus cross section measurements

Neutrino-nucleus cross section measurements are needed to improve interaction modeling to meet the precision needs of neutrino experiments in efforts to measure oscillation parameters and search for physics beyond the Standard Model. We review the difficulties associated with modeling neutrino-nucleus interactions that lead to a dependence on event generators in oscillation analyses and cross section measurements alike. We then describe data-driven model validation techniques intended to address this model dependence. The method relies on utilizing various goodness-of-fit tests and the correlations between different observables and channels to probe the model for defects in the phase space relevant for the desired analysis. These techniques shed light on relevant mismodeling, allowing it to be detected before it begins to bias the cross section results. We compare more commonly used model validation methods which directly validate the model against alternative ones to these data-driven techniques and show their efficacy with fake data studies. These studies demonstrate that employing data-driven model validation in cross section measurements represents a reliable strategy to produce robust results that will stimulate the desired improvements to interaction modeling.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2025

Antenna arrays for neutrino mass measurements with cyclotron radiation emission spectroscopy

Cyclotron Radiation Emission Spectroscopy (CRES) is a technique for precision measurements of kinetic energies of charged particles, pioneered by the Project 8 experiment to measure the neutrino mass using the tritium end-point method. It was recently employed for the first time to measure the molecular tritium spectrum and place a limit on the neutrino mass using a cubic-centimeter-scale detector. Future direct neutrino mass experiments are developing the technique to overcome the systematic and statistical limitations of current detectors. Here, this paper describes one such approach, namely the use of antenna arrays for CRES in free space. Phenomenology, detector design, simulation, and performance estimates are discussed, culminating with an example design with a projected sensitivity of 𝑚 𝛽 < ⁢0.04 eV/𝑐 2 . Prototype antenna array measurements are also shown for a demonstrator-scale setup as a benchmark for the simulation. By consolidating these results, this paper serves as a comprehensive reference for the development and performance of antenna arrays for CRES.

Physics - Nuclear physics and radiation physics↗
DOE OSTI2025

First Evidence of Solar Neutrino Interactions on 13 C

The SNO+ Collaboration reports the first evidence of 8 B solar neutrinos interacting on 13 C nuclei. The charged current interaction proceeds through 13 C +𝜈 𝑒 → 13 N+𝑒 − which is followed, with a 10 minute half life, by 13 N → 13 C +𝑒 + +𝜈 𝑒 . The detection strategy is based on the delayed coincidence between the electron and the positron. Evidence for the charged current signal is presented with a significance of 4.2⁢𝜎. Using the natural abundance of 13 C present in the scintillator, 5.7 metric tons of 13 C over 231 days of data were used in this analysis. The 5.6$^{+3.0}_{−2.3}$ observed events in the data set are consistent with the expectation of 4.7$^{+0.6}_{−1.3}$ events. This result is the second real-time measurement of CC interactions of 8 B neutrinos with nuclei and constitutes the lowest energy observation of neutrino interactions on 13 C generally. This enables the first direct measurement of the CC 𝜈 𝑒 reaction to the ground state of 13 N , yielding an average cross section of (16.1$^{+8.5}_{−6.7}$⁢(stat.)$^{+1.6}_{−2.7}$⁢(syst.))×10 −43 cm 2 over the relevant 8 B solar neutrino energies.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2020

Addendum: Cosmological dependence of non-resonantly produced sterile neutrinos

In this addendum to the article JCAP 12 (2019) 047 on the cosmological dependence of non-resonantly produced sterile neutrinos we discuss, using an analytic treatment, the parameter regions of large active-sterile neutrino mixing angles where sterile neutrinos can approach thermalization. We show that these additional considerations affect only large active-sterile neutrino mixing already rejected by different limits. Hence, the allowed sterile neutrino parameter regions are unaffected.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2020

Measurement of neutron-proton capture in the $\mathrmSNO+ water phase

The SNO+ experiment collected data as a low-threshold water Cherenkov detector from September 2017 to July 2019. Measurements of the 2.2-MeV γ 's produced by neutron capture on hydrogen were made using an Am-Be calibration source, for which a large fraction of emitted neutrons are produced simultaneously with a 4.4-MeV γ. Analysis of the delayed coincidence between the 4.4-MeV γ and the 2.2-MeV capture γ revealed a neutron detection efficiency that is centered around 50% and varies at the level of 1% across the inner region of the detector, which to our knowledge is the highest efficiency achieved among pure water Cherenkov detectors. Finally, in addition, the neutron capture time constant was measured and converted to a thermal neutron-proton capture cross section of $336.3^{+1.2}_{-1.5}$ mb .

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2022

First observation of isolated nuclear recoils following neutron capture for dark matter calibration

Low-energy nuclear recoils (NRs) are hard to measure, because they produce few e - /h + pairs in solids—i.e., they have low “ionization yield.” A silicon detector was exposed to thermal neutrons over 2.5 live days, probing NRs down to 450 eV. The observation of a neutron capture-induced component of NRs at low energies is supported by the much-improved fit upon inclusion of a capture NR model. This result shows that thermal neutron calibration of very low recoil energy NRs is promising for dark matter searches, coherent neutrino experiments, and improving understanding of ionization dynamics in solids.

79 ASTRONOMY AND ASTROPHYSICS↗