MicroBooNE and the ${\nu }_e$ Interpretation of the MiniBooNE Low-Energy Excess

A new generation of neutrino experiments is testing the $4.7\sigma$ anomalous excess of electronlike events observed in MiniBooNE. This is of huge importance for particle physics, astrophysics, and cosmology, not only because of the potential discovery of physics beyond the standard model, but also because the lessons we will learn about neutrino-nucleus interactions will be crucial for the worldwide neutrino program. MicroBooNE has recently released results that appear to disfavor several explanations of the MiniBooNE anomaly. Here, we show quantitatively that MicroBooNE results, while a promising start, unquestionably do not probe the full parameter space of sterile neutrino models hinted at by MiniBooNE and other data, nor do they probe the ${\nu }_e$ interpretation of the MiniBooNE excess in a model-independent way.

Figure 1

Event rate at MiniBooNE (top) and MicroBooNE (bottom) as a function of reconstructed neutrino energy. We show several MiniBooNE templates, including that of the $3+1$ oscillation best-fit, as nonstacked histograms. The bottom panel shows the spectra predicted by these templates in the MicroBooNE Inclusive fully contained channel.

Figure 2

$\mathrm{\Delta }{\chi }^2$ of the MicroBooNE Inclusive analysis with respect to the no-excess hypothesis, for various templates found by our MCMC. Each point corresponds to a specific template that provides a good fit to MiniBooNE data with a $p$-value greater than 80%, 10%, and 1% (shades of blue). The stars correspond to templates 1 and 2 presented in Fig. 1.

Figure 3

MicroBooNE constraints on sterile neutrino parameter space at $3\sigma$ C.L. (blue, inclusive and orange, CCQE). For reference, we show the MiniBooNE 1-, 2-, and $3\text{−}\sigma$ preferred regions in shades of gray [26], the future sensitivity of the three SBN detectors (pink) [46], and existing constraints from KARMEN (green) [19] and OPERA (gold) [47].

Figure 4

MicroBooNE constraints on $\mathrm{\Delta }{m}_{41}^2$ and ${\sin }^2(2{\theta }_{ee})$ (left) or ${\sin }^2(2{\theta }_{\mu \mu })$ (right). In each panel, we have either fixed (solid lines) or profiled over (dashed) the unshown mixing angle. For comparison, we show existing constraints and preferred regions (see Refs. [49, 50, 51, 52, 53, 54, 55, 56, 57, 58, 59, 60, 61, 62, 63]).

Figure 5

MicroBooNE constraint on $\mathrm{\Delta }{m}_{41}^2$ and ${\sin }^2(2{\theta }_{\mu e})$ after profiling over the unshown mixing angle in a consistent four-neutrino analysis. Preferred MiniBooNE regions [64] are shown in gray. Other constraints or projections, faded for clarity, are identical to those in Fig. 3.