Determination of the neutrino mass hierarchy at an intermediate baseline

It is generally believed that neutrino mass hierarchy can be determined at a long baseline experiment, often using accelerator neutrino beams. Reactor neutrino experiments at an intermediate baseline have the capability to distinguish normal or inverted hierarchy. Recently, it has been demonstrated that the mass hierarchy could possibly be identified using Fourier transform to the $L/E$ spectrum if the mixing angle ${sin}^2(2{\theta }_{13})>0.02$. In this study, a more sensitive Fourier analysis is introduced. We found that an ideal detector at an intermediate baseline ($\sim 60\mathrm{km}$) could identify the mass hierarchy for a mixing angle ${sin}^2(2{\theta }_{13})>0.005$, without requirements on accurate information of reactor neutrino spectra and the value of $\Delta m_{32}^2$.

Figure 1

Reactor neutrino spectra at a baseline of 60 km in $L/E$ space for no oscillation (dashed-dotted line), $1-P_{21}$ oscillation (dotted line) and $P_{ee}$ oscillation in the cases of NH and IH, assuming ${sin}^2(2{\theta }_{13})=0.1$.

Figure 2

FST and FCT transform spectra for $1-P_{21}$ component (dotted line), $P_{32}$ component (dashed line), $P_{31}$ component (dotted-dashed line) and all the components of $P_{ee}$ (solid line) in the cases of NH and IH.

Figure 3

Distribution of $RL$ and $PV$ values for different parameters of baseline and ${sin}^2(2{\theta }_{13})$. For each parameter to be scanned, the default baseline is 60 km and all the other parameters are the values as in Table . Two clusters of $RL$ and $PV$ values are clearly seen in the NH and IH cases.

Figure 4

The FCT and FST spectra and Fourier power spectrum for ${sin}^2(2{\theta }_{13})=0.005$. The solid line is for NH and the dashed line is for IH. The FCT and FST spectra have distinctive features to identify the mass hierarchy, which looks more sensitive than the Fourier power spectrum method.