[Paper Review] Confronting the short-baseline oscillation anomalies with a single sterile neutrino and non-standard matter effects

G. Karagiorgi, M.H. Shaevitz+1 more|arXiv (Cornell University)|Feb 6, 2012

Neutrino Physics Research16 citations

TL;DR

This paper proposes a single sterile neutrino model with non-standard matter effects—parametrized by an L-independent effective potential $ A_s $—to simultaneously explain the MiniBooNE low-energy excess, LSND antineutrino anomalies, and MiniBooNE neutrino data. The best-fit model yields $ \Delta m^2 = 0.47 \, \text{eV}^2 $, $ \sin^2 2\theta_{\mu e} = 0.010 $, and $ A_s = 2.0 \times 10^{-10} \, \text{eV} $, significantly improving compatibility between datasets compared to the standard (3+1) sterile neutrino model.

ABSTRACT

We examine the MiniBooNE neutrino, MiniBooNE antineutrino and LSND antineutrino data sets in a two-neutrino $\stackrel{ iny{(-)}}ν_μ ightarrow\stackrel{ iny{(-)}}ν_e$ oscillation approximation subject to non-standard matter effects. We assume those effects can be parametrized by an $L$-independent effective potential, $V_s=\pm A_s$, experienced only by an intermediate, non-weakly-interacting (sterile) neutrino state which we assume participates in the oscillation, where $+/-$ corresponds to neutrino/antineutrino propagation. We discuss the mathematical framework in which such oscillations arise in detail, and derive the relevant oscillation probability as a function of the vacuum oscillation parameters $Δm^2$ and $\sin^22θ_{μe}$, and the matter effect parameter $A_s$. We are able to successfully fit all three data sets, including the MiniBooNE low energy excess, with the following best-fit model parameters: $Δm^2=0.47$ eV$^2$, $\sin^22θ_{μe}=0.010$, and $A_s=2.0 imes10^{-10}$ eV. The $χ^2$-probability for the best fit corresponds to 21.6%, to be compared to 6.8% for a fit where $A_s$ has been set to zero, corresponding to a (3+1) sterile neutrino oscillation model. We find that the compatibility between the three data sets corresponds to 17.4%, to be compared to 2.3% for $A_s=0$. Finally, given the fit results, we examine consequences for reactor, solar, and atmospheric oscillations. For this paper, the presented model is empirically driven, but the results obtained can be directly used to investigate various phenomenological interpretations such as non-standard matter effects.

Motivation & Objective

• To resolve persistent short-baseline neutrino oscillation anomalies from MiniBooNE and LSND experiments.
• To test whether non-standard matter effects—specifically an L-independent effective potential $ A_s $—can reconcile discrepancies between neutrino and antineutrino data sets.
• To assess compatibility of a single sterile neutrino model with reactor, atmospheric, and long-baseline oscillation data.
• To evaluate the potential observability of effects in the MINOS antineutrino data set under the proposed model.

Proposed method

• The model extends the (3+1) sterile neutrino framework by introducing a non-standard matter potential $ V_s = \pm A_s $, acting only on sterile neutrino states during propagation.
• The oscillation probability is derived in a two-neutrino $ \nu_\mu \to \nu_e $ approximation, incorporating vacuum mixing parameters $ \Delta m^2 $ and $ \sin^2 2\theta_{\mu e} $, and the matter effect parameter $ A_s $.
• The effective mass-squared splitting $ \Delta m^2_M $ is modified by $ A_s $, leading to energy-dependent behavior, particularly for antineutrinos where $ \Delta m^2_M $ becomes negative and $ |\Delta m^2_M| $ increases with energy beyond $ E_0 \approx 1180 \, \text{MeV} $.
• Fits are performed on MiniBooNE neutrino, MiniBooNE antineutrino, and LSND antineutrino data sets, with $ \chi^2 $-probabilities used to assess goodness of fit.
• The model’s predictions are compared to reactor, solar, and atmospheric oscillation data to test consistency.
• The MINOS antineutrino disappearance and appearance probabilities are evaluated using the best-fit parameters to assess potential detectability.

Experimental results

Research questions

• RQ1 Can a single sterile neutrino with non-standard matter effects simultaneously explain the MiniBooNE low-energy excess and LSND antineutrino anomalies?
• RQ2 How does the inclusion of a non-standard matter potential $ A_s $ improve the compatibility between MiniBooNE and LSND data sets compared to the standard (3+1) model?
• RQ3 What are the implications of the best-fit model for long-baseline and reactor neutrino experiments, particularly in light of recent short-baseline anomalies?
• RQ4 To what extent can the MINOS antineutrino data set constrain or detect the predicted effects of the model?

Key findings

• The best-fit model parameters are $ \Delta m^2 = 0.47 \, \text{eV}^2 $, $ \sin^2 2\theta_{\mu e} = 0.010 $, and $ A_s = 2.0 \times 10^{-10} \, \text{eV} $, providing a good fit to all three data sets (MiniBooNE neutrino, MiniBooNE antineutrino, LSND antineutrino).
• The $ \chi^2 $-probability for the best fit is 21.6%, significantly higher than the 6.8% obtained when $ A_s = 0 $, indicating a substantial improvement in fit quality.
• The compatibility between the three data sets improves from 2.3% (for $ A_s = 0 $) to 17.4% under the non-standard matter effect model, suggesting reduced tension between experiments.
• The model is consistent with reactor long-baseline, atmospheric, and accelerator long-baseline neutrino oscillation data, and can reasonably accommodate recent short-baseline reactor anomalies.
• The model predicts observable effects in the MINOS antineutrino data set, particularly in appearance probabilities, due to rapid energy-dependent oscillations in the $ \sim 1200 \, \text{MeV} $ range where $ |\Delta m^2_M| $ approaches atmospheric $ \Delta m^2 $.
• The effective $ \sin^2 2\theta_{\mu\mu}^M $ for antineutrinos reaches nearly maximal values near 1200 MeV, suggesting potential sensitivity in far-to-near detector comparisons if sufficient statistics are available.