Light sterile neutrino sensitivity at the nuSTORM facility

A facility that can deliver beams of electron and muon neutrinos from the decay of a stored muon beam has the potential to unambiguously resolve the issue of the evidence for light sterile neutrinos that arises in short-baseline neutrino oscillation experiments and from estimates of the effective number of neutrino flavors from fits to cosmological data. In this paper, we show that the nuSTORM facility, with stored muons of $3.8\mathrm{GeV}/\mathrm{c}\pm 10\%$, will be able to carry out a conclusive muon neutrino appearance search for sterile neutrinos and test the LSND and MiniBooNE experimental signals with $10\sigma$ sensitivity, even assuming conservative estimates for the systematic uncertainties. This experiment would add greatly to our knowledge of the contribution of light sterile neutrinos to the number of effective neutrino flavors from the abundance of primordial helium production and from constraints on neutrino energy density from the cosmic microwave background. The appearance search is complemented by a simultaneous muon neutrino disappearance analysis that will facilitate tests of various sterile neutrino models.

Figure 1

A schematic of the storage ring configuration. Pions are injected into a straight section and must decay into muons before the first bend or be ejected from the ring. Muons that decay in the injection straight during subsequent turns produce the neutrino beam.

Figure 2

A cross section of the prospective iron-scintillator neutrino detector (6 m in diameter and 13 m in length).

Figure 3

Efficiencies of signals and backgrounds for (a) ${\nu }_{\mu }$ appearance and (b) ${\overline{\nu }}_{\mu }$ disappearance for an iron-scintillator neutrino detector optimized for the region of interest for nuSTORM. The appearance analysis used a BDT algorithm to define the above curves, while the disappearance analysis used a neural network (MLPBNN) as described in the text.

Figure 4

Sensitivity of nuSTORM to the ${\nu }_e\to {\nu }_{\mu }$ appearance oscillation due to the presence of sterile neutrinos assuming a ($3+1$) model with anticipated and inflated systematics, compared to 99% confidence contours from global fits to the evidence for sterile neutrinos and to all available appearance experiments generated by Kopp et al. [24] (filled contours) and limits set by ICARUS [34].

Figure 5

Sensitivity of nuSTORM to ${\nu }_{\mu }$ disappearance oscillations assuming a ($3+1$) neutrino model. Contours are generated from a ${\chi }^2$ statistic assuming both the anticipated and inflated systematic uncertainties compared to the exclusion contour produced from the fit of ${\sin }^{2}2{\theta }_{\mu \mu }$ and $\mathrm{\Delta }{m}^2$ to the existing disappearance data (blue dots) [24].