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We investigate the impact of the flowing three-body operator on the evaluation of neutrinoless double-beta decay (0νββ0\nu\beta\beta0νββ) nuclear matrix elements (NMEs) within the in-medium similarity renormalization group (IMSRG) framework. In standard IMSRG(2) truncations, induced three-body operators are neglected, which may limit the accuracy of the computed decay observables. To quantify this effect, we introduce an approximate treatment of the full IMSRG(3), termed IMSRG(3f2), in which factorized double commutators contributing to the induced three-body operators are retained. We compare NMEs obtained at the IMSRG(2) and IMSRG(3n7) levels to assess convergence behavior and identify correlations driven by induced three-body contributions. Our results indicate that including the flowing three-body operator moderately reduces the NMEs and provides valuable insights into many-body truncation effects in ab initio descriptions of 0νββ0\nu\beta\beta0νββ decay.
At Oak Ridge National Laboratory (ORNL), the COHERENT collaboration completed construction of a heavy water Cherenkov detector in the summer of 2023 to measure the neutrino flux from the Spallation Neutron Source (SNS) via the scattering of neutrinos on deuterium nuclei, with the primary aim of improving the precision of past and future CEvNS measurements. Thus far, the SNS neutrino flux has been predicted theoretically with a precision of around 10%, but direct experimental measurements are expected to improve that precision to 2-3% within five SNS-years. An unavoidable background to neutrino-deuterium scattering in heavy water is neutrino-oxygen scattering, but this also gives us the opportunity to measure the cross section of neutrino-nucleus charged-current interactions on both deuterium and oxygen nuclei. Both charged-current neutrino-deuterium and neutrino-oxygen reactions produce electrons that emit Cherenkov radiation within the detector, which can be detected by photomultiplier tubes. The SNS is the most powerful pulsed source of accelerator-based neutrinos in the world, which produces electron neutrinos in a similar energy range to supernova neutrinos. Thus the measurement of this charged-current neutrino reaction in oxygen can improve future supernova neutrino detection, even as the simultaneous measurement of the charged-current neutrino reaction in deuterium can improve our understanding of the SNS neutrino flux. In this presentation, I plan on showing preliminary data collected from our detector for one year of SNS operation.
The COHERENT Collaboration at Oak Ridge National Laboratory operates a variety of neutrino detectors, each with the aim of providing a better understanding of neutrinos through Coherent Elastic Neutrino Nucleus Scattering (CEvNS). These detectors utilize the high neutrino flux from the Spallation Neutron Source at ORNL. One such detector, a 550kg heavy water Cherenkov detector, was commissioned in 2023 with the goal of accurately measuring the neutrino flux produced by SNS. In addition to this objective, we propose that due to the close correlation between energy on incoming neutrinos and electrons generated in neutrino-deuteron charged current interactions, this detector is uniquely suited to study possible tensor component of weak interactions. An upper limit on such a component was established in 1998 by the KARMEN collaboration. We provide estimation of capability of the heavy water detector to improve sensitivity to this component.
Unambiguous discovery of neutrinoless double-beta decay (0νββ) requires unprecedented control and mitigation of background contribution in the region of interest. The LEGEND collaboration aims to achieve a discovery sensitivity of T1/2>1028 years with the high-purity germanium (HPGe) isotope 76Ge (Q = 2039 keV). The initial phase, LEGEND-200, is operational at Laboratori Nazionali del Gran Sasso (LNGS), utilizing up to 200 kg of HPGe detectors immersed in liquid argon (LAr), which acts as both a coolant and an active shield. The subsequent phase, LEGEND-1000 (scheduled for construction in late 2026), will scale up to 1000 kg and demands a strict background contribution of less than 10-5 cts/(keV kg yr) at the Q-value. To meet this stringent requirement, our R&D is focused on advancing radiopure component design, including the selection of ultra-radiopure materials, the exploration of optically active enclosures, and the implementation of specialized pulse shape discrimination. Furthermore, we are developing novel detector component materials utilizing additive manufacturing (3D printing) to reduce intrinsic background radiation and optimize component functionality. This presentation will provide comprehensive insights into the LEGEND-1000 baseline design and detail the various background reduction and material development techniques being deployed to enable the next generation of 0νββ discovery.
LEGEND-200 is searching for neutrinoless double-beta decay (0νββ), a hypothetical lepton-number violating process that would prove the neutrino is a majorana particle if discovered. The experiment consists of an array of point-contact high purity germanium detectors isotopically enriched in 76Ge, which are submerged in liquid argon that acts as an active shield. During its first year of operation underground at Laboratori Nazionali del Gran Sasso in Italy, LEGEND-200 collected 61.0 kg-yr of exposure. This talk will present an overview of LEGEND-200 and new results from the first year of data-taking.
Neutrons are a powerful tool to test fundamental symmetries of the weak interaction. Beta decay parameters like spin-momentum correlations and lifetime can determine the Vud parameter of the Cabibbo-Kobayashi-Maskawa quark-mixing matrix and contribute to a test of its unitarity. The proposed pNAB experiment will use the Nab spectrometer at the Fundamental Neutron Physics Beamline at the Spallation Neutron Source to measure electron and proton asymmetries in the decay of polarized neutrons with world-leading precision and has the potential to establish the neutron as the most precise probe of Vud and CKM unitarity.This presentation will cover how the Nab spectrometer can be modified to achieve this goal, in particular how the neutron beam can be polarized with the required accuracy.
This talk introduces NuLattice, a Python software package for ab initio computations of atomic nuclei on lattices. The computational tools consist of Hartree Fock, the coupled-cluster method, the in-medium similarity renormalization group, and full configuration interaction. At present, the employed interactions are from pion-less effective field theory at leading order and consist of two-body and three-body contacts. We present results for light nuclei 2H, 3,4He, 8Be, 12C, and 16O. NuLattice algorithms exploit the sparsity and locality of lattice interactions, and as a result computations can be run on laptops. This approach yielded analytical insights about the exactness of the normal-ordered two-body approximation, where contributions of three-nucleon forces are truncated at the two-body rank after normal ordering with respect to a product state. On the lattice, the normal-ordered two-body truncation is exact for zero-range three-body forces when nuclei are computed using the coupled cluster with singles and doubles method. As the nuclear three-nucleon force is short ranged and a three-body contact is a leading term in effective field theories of quantum chromodynamics, this result provides an analytical basis for the popular normal-ordered two-body approximation.