Confidence in the Mass Hierarchy Determination from Reactor Neutrino Experiments

In the next decade, a number of experiments will attempt to determine the neutrino mass hierarchy. We will discuss some of the challenges that these experiments will face, focusing on the reactor neutrino experiments at intermediate baselines. Here, for example, even a small nonlinear energy response can severely affect the sensitivity to the hierarchy. Using MC simulations, we will show the probability of successfully determining the hierarchy for some realistic locations of the detector. We will also show that, since the two hierarchies are non-nested hypothesis, the statistic Δχ² does not follow a one-degree-of-freedom χ² distribution and hence the sensitivity to the hierarchy cannot be estimated by taking the square root of the expected Δχ²; we will present the correct formula for the sensitivity. (paper)