[Paper Review] Sterile Neutrino Fits to Short Baseline Neutrino Oscillation Measurements

J. M. Conrad, C. Ignarra+3 more|arXiv (Cornell University)|Jul 19, 2012

Neutrino Physics Research11 references16 citations

TL;DR

This paper evaluates short-baseline neutrino oscillation data within sterile neutrino models, finding that a (3+3) model—three active and three sterile neutrinos—provides the best fit with 67% goodness of fit and 90% compatibility among data sets, significantly improving over (3+1) and (3+2) models, though it still fails to explain the MiniBooNE low-energy appearance excess.

ABSTRACT

This paper reviews short baseline oscillation experiments as interpreted within the context of one, two, and three sterile neutrino models associated with additional neutrino mass states in the ~1 eV range. Appearance and disappearance signals and limits are considered. We show that fitting short baseline data sets to a (3+3) model, defined by three active and three sterile neutrinos, results in an overall goodness of fit of 67%, and a compatibility of 90% among all data sets -- to be compared to the compatibility of 0.043% and 13% for a (3+1) and a (3+2) model, respectively. While the (3+3) fit yields the highest quality overall, it still finds inconsistencies with the MiniBooNE appearance data sets; in particular, the global fit fails to account for the observed MiniBooNE low-energy excess. Given the overall improvement, we recommend using the results of (3+2) and (3+3) fits, rather than (3+1) fits, for future neutrino oscillation phenomenology. These results motivate the pursuit of further short baseline experiments, such as those reviewed in this paper.

Motivation & Objective

• To assess the compatibility of short-baseline neutrino oscillation data across multiple experiments within sterile neutrino models.
• To resolve persistent tensions between appearance and disappearance data sets observed in (3+1) and (3+2) models.
• To determine whether a (3+3) model—three active and three sterile neutrinos—can consistently describe both appearance and disappearance signals.
• To recommend future phenomenological focus on (3+2) and (3+3) models over (3+1) models for sterile neutrino studies.
• To motivate future experiments by identifying unresolved discrepancies, particularly in the MiniBooNE appearance data.

Proposed method

• Global fitting of short-baseline neutrino oscillation data using χ² minimization across (3+1), (3+2), and (3+3) models.
• Incorporation of appearance and disappearance signals from LSND, MiniBooNE, reactor, and other SBL experiments into a unified likelihood framework.
• Use of extended neutrino mixing matrices with additional mixing angles and mass splittings in the ~1 eV² range for sterile states.
• Evaluation of goodness-of-fit and data set compatibility using χ²-probability and compatibility metrics across models.
• Comparison of results against null hypothesis (no oscillations) and previous fits to assess improvement in consistency.
• Incorporation of cosmological constraints and reactor-based disappearance data to test model robustness.

Experimental results

Research questions

• RQ1 Can a (3+3) sterile neutrino model consistently explain both appearance and disappearance data from short-baseline experiments?
• RQ2 How does the compatibility of data sets compare across (3+1), (3+2), and (3+3) models in fitting short-baseline oscillation data?
• RQ3 Why does the (3+3) model still fail to describe the MiniBooNE low-energy appearance excess despite improved overall compatibility?
• RQ4 What is the significance of the (3+3) model’s goodness-of-fit compared to the (3+1) and (3+2) models?
• RQ5 Which sterile neutrino model provides the most robust foundation for future phenomenological and experimental work?

Key findings

• The (3+3) model achieves a goodness-of-fit probability of 67%, significantly higher than the 2.1% for the null hypothesis and 55% for the (3+1) model.
• The compatibility among all data sets in the (3+3) model is 90%, compared to only 0.043% for the (3+1) model and 0.0082% for the (3+2) model.
• Despite improved compatibility, the (3+3) model fails to account for the MiniBooNE low-energy appearance excess, indicating a persistent tension.
• The (3+2) model shows a compatibility of 69% and a goodness-of-fit of 55%, indicating moderate improvement over (3+1) but still inconsistent with data compatibility.
• The (3+1) model exhibits poor compatibility (0.043%) and low goodness-of-fit, highlighting its inability to consistently describe the full data set.
• The authors recommend prioritizing (3+2) and (3+3) models over (3+1) for future sterile neutrino phenomenology due to superior consistency and fit quality.