Abstract
The Deep Underground Neutrino Experiment (DUNE) could be revolutionary for MeV neutrino astrophysics, because of its huge detector volume, unique event reconstruction capabilities, and excellent sensitivity to the $\nu_e$ flavor. However, its backgrounds are not yet known. A major background is expected due to muon spallation of argon, which produces unstable isotopes that later beta decay. We present the first comprehensive study of MeV spallation backgrounds in argon, detailing isotope production mechanisms and decay properties, analyzing beta energy and time distributions, and proposing experimental cuts. We show that above a nominal detection threshold of 5-MeV electron energy, the most important backgrounds are --- surprisingly --- due to low-A isotopes, such as Li, Be, and B, even though high-A isotopes near argon are abundantly produced. We show that spallation backgrounds can be powerfully rejected by simple cuts, with clear paths for improvements. We compare these background rates to rates of possible MeV astrophysical neutrino signals in DUNE, including solar neutrinos (detailed in a companion paper [Capozzi et al. arXiv:1808.08232 [hep-ph]]), supernova burst neutrinos, and the diffuse supernova neutrino background. Further, to aid trigger strategies, in the Appendixes we quantify the rates of single and multiple MeV events due to spallation, radiogenic neutron capture, and other backgrounds, including through pileup. Our overall conclusion is that DUNE has high potential for MeV neutrino astrophysics, but reaching this potential requires new experimental initiatives.
Highlights
Astrophysical neutrinos are uniquely penetrating probes of their sources, whose extreme physical conditions in turn allow for new tests of neutrino properties
Despite great achievements in solar neutrino studies, opportunities remain for detailed tests of astrophysics and particle physics
The Galactic core-collapse supernova will enable multiflavor neutrino measurements, revealing details of explosion physics and testing neutrino mixing at high densities
Summary
Astrophysical neutrinos are uniquely penetrating probes of their sources, whose extreme physical conditions in turn allow for new tests of neutrino properties. Building on the work of Li and Beacom [23,24,25], our goals for this paper are to calculate the spallation backgrounds for DUNE in detail, understand their physical mechanisms, and use this understanding to develop cuts to reject backgrounds We compare these background rates to the signal rates for solar neutrinos, supernova burst neutrinos, and the DSNB, finding that spallation backgrounds can be well controlled. We aim for a factor of ≈2 precision on isotope yields, which is appropriate given the hadronic uncertainties This is adequate to guide development of DUNE as a detector for MeV neutrino astrophysics. Using the projected postcut background levels, we discuss the possible MeV neutrino programs in DUNE in Sec. IV, along with new results to aid trigger development (with the details provided in the Appendixes).
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