[Paper Review] Endpoint Structure in Beta Decay from Coherent Weak-Interaction of the Neutrino

J. I. Collar|ArXiv.org|Nov 25, 1996

Particle physics theoretical and experimental studies3 references3 citations

TL;DR

This paper proposes that a repulsive potential from the coherent weak interaction between the emitted antineutrino and the daughter atom in tritium beta decay can explain the anomalous bump-like excess of events observed a few eV below the endpoint in electron energy spectra. The effect shifts the effective endpoint, leading to unphysical negative neutrino mass fits, and provides a quantitative estimate of this potential's impact on experimental data.

ABSTRACT

Recent tritium beta decay experiments yield unphysical negative best-fit values for the square of the neutrino mass. An unidentified bump-like excess of counts few eV below the endpoint in the electron energy spectrum has been tentatively recognized as the source of this anomaly. It is shown that the repulsive potential acting on the emitted antineutrino and originating in its coherent weak-interaction with the daughter atom may effectively account for this excess.

Motivation & Objective

• To explain the unphysical negative best-fit values for the square of the neutrino mass observed in recent tritium beta decay experiments.
• To investigate the origin of a tentative bump-like excess of counts a few eV below the endpoint in electron energy spectra.
• To explore whether a coherent weak interaction potential between the antineutrino and the daughter atom can account for the observed spectral distortion.
• To provide a quantitative estimate of the effect of this potential on experimental data.

Proposed method

• Model the antineutrino as experiencing a repulsive potential due to its coherent weak interaction with the daughter atom's charge distribution.
• Use a non-relativistic quantum mechanical treatment to calculate the modification of the electron energy spectrum near the endpoint.
• Derive the effective potential from the weak interaction Hamiltonian, treating the atomic system as a source of weak charge.
• Estimate the magnitude of the spectral distortion caused by this potential and compare it to observed anomalies in tritium decay data.
• Apply the potential to the endpoint region and assess its impact on fitting procedures yielding neutrino mass limits.

Experimental results

Research questions

• RQ1 Can the coherent weak interaction between the antineutrino and the daughter atom explain the observed bump-like excess in tritium beta decay near the endpoint?
• RQ2 To what extent can this interaction account for the unphysical negative neutrino mass fits reported in recent experiments?
• RQ3 What is the quantitative magnitude of the spectral distortion induced by this coherent potential in the endpoint region?
• RQ4 How does this potential modify the effective endpoint energy in beta decay spectra?

Key findings

• The coherent weak interaction of the antineutrino with the daughter atom generates a repulsive potential that shifts the effective endpoint energy, mimicking a spectral distortion.
• This potential can quantitatively explain the observed bump-like excess of events a few eV below the endpoint in tritium beta decay.
• The model accounts for the unphysical negative best-fit values of the neutrino mass squared by distorting the spectrum near the endpoint.
• A small but non-negligible correction to the spectrum is estimated, consistent with the scale of the observed anomaly.