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Sterile Neutrino Fits to Short Baseline Neutrino Oscillation Measurements

J. M. Conrad, C. M. Ignarra, G. Karagiorgi, M. H. Shaevitz, J. Spitz

TL;DR

This paper evaluates short-baseline neutrino oscillation data within (3+1), (3+2), and (3+3) sterile neutrino frameworks. It demonstrates that adding three sterile states ((3+3)) yields the best global compatibility (≈90%) and improves the overall goodness-of-fit (≈67%), compared with (3+1) and (3+2). Nevertheless, the MiniBooNE low-energy appearance excess remains unresolved in the global fits, highlighting residual tensions between appearance and disappearance datasets. The authors advocate prioritizing (3+2) and (3+3) interpretations for phenomenology and emphasize the need for diverse, new short-baseline experiments to map the $L/E$ dependence and conclusively test sterile-neutrino scenarios.

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.

Sterile Neutrino Fits to Short Baseline Neutrino Oscillation Measurements

TL;DR

This paper evaluates short-baseline neutrino oscillation data within (3+1), (3+2), and (3+3) sterile neutrino frameworks. It demonstrates that adding three sterile states ((3+3)) yields the best global compatibility (≈90%) and improves the overall goodness-of-fit (≈67%), compared with (3+1) and (3+2). Nevertheless, the MiniBooNE low-energy appearance excess remains unresolved in the global fits, highlighting residual tensions between appearance and disappearance datasets. The authors advocate prioritizing (3+2) and (3+3) interpretations for phenomenology and emphasize the need for diverse, new short-baseline experiments to map the dependence and conclusively test sterile-neutrino scenarios.

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.

Paper Structure

This paper contains 33 sections, 22 equations, 16 figures, 4 tables.

Table of Contents

  1. Introduction
  2. Oscillations Involving Sterile Neutrinos
  3. Light Sterile States
  4. The Basic Oscillation Formalism
  5. (3+$N$) Oscillation Formalism
  6. Experimental Data Sets
  7. Sources and Detectors Used in Short Baseline Neutrino Experiments
  8. Sources of Neutrinos for Short Baseline Experiments
  9. Short Baseline Neutrino Detectors
  10. Data Used in The Sterile Neutrino Fits
  11. Experimental Results from Decay at Rest Studies
  12. The MiniBooNE Experimental Results
  13. Results from Multi-GeV Conventional Short baseline $\nu_\mu$ Beams
  14. Reactor and Source Experiments
  15. Long Baseline Experimental Results Contributing to the Fits
  16. ...and 18 more sections

Figures (16)

  • Figure 1: Summary of $\bar{\nu}_\mu \rightarrow \bar{\nu}_e$ and $\nu_\mu \rightarrow \nu_e$ results, shown at 95% CL. Top row: LSND, KARMEN, BNB-MB($\nu$app); Bottom row: BNB-MB($\bar{\nu}$app), NuMI-MB($\nu$app), NOMAD. See Sec. \ref{['fitexps']} for details and references.
  • Figure 2: Summary of $\bar{\nu}_\mu \rightarrow \bar{\nu}_\mu$ and $\nu_\mu \rightarrow \nu_\mu$ results, shown at 95% CL. Top row: BNB-MB($\nu$dis), CCFR84, CDHS; Bottom row: MINOS-CC, ATM. See Sec. \ref{['fitexps']} for details and references.
  • Figure 3: Summary of $\bar{\nu}_e\rightarrow \bar{\nu}_e$ and $\nu_e \rightarrow \nu_e$ results, shown at 95% CL. From left: KARMEN/LSND(xsec), Bugey, and Gallium. See Sec. \ref{['fitexps']} for details and references.
  • Figure 4: The $\Delta m^2_{41}$ vs. $\sin^2 2\theta_{\mu e}$ allowed space from fits to all data---neutrino and antineutrino---in a (3+1) model.
  • Figure 5: The $\Delta m^2_{41}$ vs. $\sin^2 2\theta_{\mu e}$ allowed space from fits to neutrino (left) and antineutrino (right) data in a (3+1) model.
  • ...and 11 more figures