Particle physics origin of the 5 MeV bump in the reactor antineutrino spectrum?

Abstract

One of the most puzzling questions in neutrino physics is the origin of the excess at 5 MeV in the reactor antineutrino spectrum. In this paper, we explore the excess via the reaction ${}^{13}$C$(\overline{\nu },{\overline{\nu }}^{\prime }n{)}^{12}$C${}^{\ast }$ in organic scintillator detectors. The de-excitation of ${}^{12}$C${}^{\ast }$ yields a prompt $4.4$ MeV photon, while the thermalization of the product neutron causes proton recoils, which in turn yield an additional prompt energy contribution with finite width. Together, these effects can mimic an inverse beta decay event with around 5 MeV energy. We consider several non-standard neutrino interactions to produce such a process and find that the parameter space preferred by Daya Bay is disfavored by measurements of neutrino-induced deuteron disintegration and coherent elastic neutrino-nucleus scattering. While non-minimal particle physics scenarios may be viable, a nuclear physics solution to this anomaly appears more appealing.

13 pages, 5 figures, matches published version

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• Neutrino Physics Opportunities with the IsoDAR Source at Yemilab
• Constraining Sterile Neutrino Cosmology with Terrestrial Oscillation Experiments
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• Nuclear Weak Rates and Nuclear Weak Processes in Stars
• Neutrino-13C Cross Sections at Supernova Neutrino Energies
• Future searches for light sterile neutrinos at nuclear reactors
• Does the 220 PeV Event at KM3NeT Point to New Physics?
• Study of beta spectrum shapes relevant to the prediction of reactor antineutrino spectra
• Neutrino oscillation analysis of 217 live-days of Daya Bay and 500 live-days of RENO