Neutrino mass ordering at DUNE: An extra $\nu$ bonus

We study the possibility of extracting the neutrino mass ordering at the future Deep Underground Neutrino Experiment using atmospheric neutrinos, which will be available before the muon neutrino beam starts being operational. The large statistics of the atmospheric muon neutrino and antineutrino samples at the far detector, together with the baselines of thousands of kilometers that these atmospheric (anti)neutrinos travel, provide ideal ingredients to extract the neutrino mass ordering via matter effects in the neutrino propagation through Earth. Crucially, muon capture by argon provides excellent charge tagging, allowing us to disentangle the neutrino and antineutrino signature. This is an important extra benefit of having a liquid argon time projection chamber as a far detector, that could render an $\sim 3.5\sigma$ extraction of the mass ordering after approximately 7 yr of exposure.

Figure 1

Left panels: Survival probability $P({\nu }_{\mu }\to {\nu }_{\mu })$ as a function of the neutrino energy $E$ and the cosine of the zenith angle, $\cos {\theta }_z$, for normal (inverted) ordering in the top (bottom) line. Right panels: The same as in the left panels, but for the antineutrino channel.

Figure 2

Number of expected muon events after $400\mathrm{kt}·\mathrm{yr}$ exposure time, separating capture and decay events (first two panels) and combining all muon-type events (right panel), using the parameters in Table 1 and ${\sin }^2{\theta }_{23}=0.547$.

Figure 3

Relative neutrino energy resolution ${\sigma }_E/E_{\nu }$ (top) and absolute neutrino angular resolution ${\sigma }_{\theta }$ (bottom) as a function of neutrino energy $E_{\nu }$ assumed in this study, for ${\nu }_e$, ${\overline{\nu }}_e$, ${\nu }_{\mu }$, and ${\overline{\nu }}_{\mu }$ charged-current interactions on argon nuclei.

Figure 4

The DUNE sensitivity to the neutrino mass ordering as a function of ${\sin }^2{\theta }_{23}^{\mathrm{true}}$. Red (blue) lines correspond to analysis method A (B). Solid lines are for normal ordering as true ordering, while dashed lines show the sensitivity in the case of true inverted ordering. The gray band corresponds to the current $1\sigma$ region for the atmospheric angle.