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

We examine the MiniBooNE neutrino, MiniBooNE antineutrino and LSND antineutrino data sets in a two-neutrino $\stackrel{\tiny{(-)}}{\nu}_{\mu}\rightarrow\stackrel{\tiny{(-)}}{\nu}_e$ 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 $\Delta m^2$ and $\sin^22\theta_{\mu e}$, 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: $\Delta m^2=0.47$ eV$^2$, $\sin^22\theta_{\mu e}=0.010$, and $A_s=2.0\times10^{-10}$ eV. The $\chi^2$-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.Comment: 19 pages, 11 figures, 1 tabl

Comparisons and Combinations of Reactor and Long-Baseline Neutrino Oscillation Measurements

We investigate how the data from various future neutrino oscillation experiments will constrain the physics parameters for a three active neutrino mixing model. The investigations properly account for the degeneracies and ambiguities associated with the phenomenology as well as estimates of experimental measurement errors. Combinations of various reactor measurements with the expected J-PARC (T2K) and NuMI offaxis (Nova) data, both with and without the increased flux associated with proton driver upgrades, are considered. The studies show how combinations of reactor and offaxis data can resolve degeneracies (e.g. the theta23 degeneracy) and give more precise information on the oscillation parameters. A primary purpose of this investigation is to establish the parameter space regions where CP violation can be discovered and where the mass hierarchy can be determined. It is found that such measurements, even with the augmented flux from proton driver upgrades, demand sin^2 (2 theta13) be fairly large and in the range where it is measurable by reactor experiments.Comment: 25 pages, 13 figures, fixed typos; 25 pages, 13 figures, updated content, references; previous 22 pages, 12 figures, added references and fixed reference display proble

Sterile Neutrino Fits to Short Baseline Neutrino Oscillation Measurements

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.Comment: Submitted to Advances in High Energy Physics Special Issue on Neutrino Physic

Sterile Neutrino Fits to Short Baseline Data

Neutrino oscillation models involving extra mass eigenstates beyond the standard three (3+N) are fit to global short baseline experimental data. We find that 3+1 has a best fit of Delta m^2_41 = 1.75 eV^2 with a Delta chi^2 [null-min] (dof) of 52.34 (3). The 3+2 fit has a Delta chi^2 [null-min] (dof) of 56.99 (7). Bayesian credible intervals are shown for the first time for a 3+1 model. These are found to be in agreement with frequentist intervals. The results of these new fits favor a higher Delta m^2 value than previous studies, which may have an impact on future sterile neutrino searches such as the Fermilab SBN program.Comment: 17 pages. This paper has been edited to remove results from the IceCube IC86 fits. The authors have withdrawn the IceCube IC86 fits section pending official release of the IceCube IC86 dat

Sterile Neutrinos: An Introduction to Experiments

This paper is written as one chapter in a collection of essays on neutrino physics for beginning graduate students. The text presents important experimental methods and issues for those interested in searches for sterile neutrinos. Other essays in the collection, written by other authors, will cover introduction to neutrinos in the Standard Model, a description of the theory, and discussion of details of detectors, thus these aspects are not covered here. However, beyond these points, this represents a self-contained tutorial on experimental studies of sterile neutrino oscillations, covering such issues as signals vs. limits, designing experiments, and performing and interpreting global fits to the oscillation data.National Science Foundation (U.S.) (Grant 1505855)National Science Foundation (U.S.) (Grant 1505858)National Science Foundation (U.S.) (Grant 1404209

Measuring Active-to-Sterile Neutrino Oscillations with Neutral Current Coherent Neutrino-Nucleus Scattering

Light sterile neutrinos have been introduced as an explanation for a number of oscillation signals at $\Delta m^2 \sim 1$ eV$^2$. Neutrino oscillations at relatively short baselines provide a probe of these possible new states. This paper describes an accelerator-based experiment using neutral current coherent neutrino-nucleus scattering to strictly search for active-to-sterile neutrino oscillations. This experiment could, thus, definitively establish the existence of sterile neutrinos and provide constraints on their mixing parameters. A cyclotron-based proton beam can be directed to multiple targets, producing a low energy pion and muon decay-at-rest neutrino source with variable distance to a single detector. Two types of detectors are considered: a germanium-based detector inspired by the CDMS design and a liquid argon detector inspired by the proposed CLEAR experiment.Comment: 10 pages, 7 figure