Limits on Electron Neutrino Disappearance from the KARMEN and LSND electron neutrino - Carbon Cross Section Data

TL;DR

This work tests electron-neutrino disappearance at high Δm^2 by comparing ν_e–carbon cross sections measured in KARMEN and LSND. Using a two-neutrino oscillation framework with P = 1 - sin^2 2θ_ee sin^2(1.27 Δm^2 L / E) and two baselines (L ≈ 17.7 m, 29.8 m), the analysis derives a 95% CL exclusion in the $(Δm^2, \sin^2 2θ_{ee})$ plane from cross-section data that align with predictions of standard models $(E_ν - Q)^2$ with $Q = 17.3$ MeV. The combined fit favors a best point at $Δm^2 ≈ 7.49$ eV^2 and $\sin^2 2θ_{ee} ≈ 0.29$, while the Gallium-era best fit is excluded at 3.6σ, significantly tightening constraints on sterile-neutrino scenarios and CPT-consistent comparisons to reactor data. Overall, the results limit electron-flavor disappearance in the few eV^2 range and impact interpretations of other anomalies, such as the Reactor Anomaly and MiniBooNE excesses.

Abstract

This paper presents a combined analysis of the KARMEN and LSND nu_e-carbon cross section measurements within the context of a search for nu_e disappearance at high Delta m^2. KARMEN and LSND were located at 17.7 m and 29.8 m respectively from the neutrino source, so the consistency of the two measurements, as a function of antineutrino energy, sets strong limits on neutrino oscillations. Most of the allowed region from the nu_e disappearance analysis of the Gallium calibration data is excluded at >95% CL and the best fit point is excluded at 3.6$σ$. Assuming CPT conservation, comparisons are also made to the oscillation analyses of reactor antineutrino data.

Figures (6)

• Figure 1: Energy distribution of neutrinos in a DAR beam.
• Figure 2: The KARMEN (points) and LSND (crosses) measured cross sections with statistical errors for $\nu_e +^{12}{\rm C} \rightarrow ^{12}{\rm N}_{gs} + e^-$ compared to the theoretical prediction of Fukugita, et al. (solid line), based on the EPT model, and Kolbe, et al. (dashed line), based on the CRPA model.
• Figure 3: Comparisons of the data to various oscillation predictions for the LSND (top) and KARMEN (bottom) data using the Fukugita prediction, as described in the text.
• Figure 4: The 95% $\nu_e$ disappearance limit from the Fukugita (EPT) fit (solid, black line) compared to the predicted sensitivity (dotted line). Also shown is the 68% (darker, shaded region) and 90% (lighter, shaded region) contours from the Gallium experiments. The dashed line is the Kolbe (CRPA) fit.
• Figure 5: The 95% $\nu_e$ disappearance limit from the combined fit (solid, black line) compared to individual fits to KARMEN data (dashed) and LSND data (dotted). This is overlaid on the Gallium 90% and 68% CL allowed regions. All fits use the Fukugita model.