Off-axis beams and detector clusters: Resolving neutrino parameter degeneracies

Abstract

There are three parameter degeneracies inherent in the three-neutrino analysis of long-baseline neutrino experiments. We develop a systematic method for determining whether or not a set of measurements in neutrino oscillation appearance experiments with approximately monoenergetic beams can completely resolve these ambiguities. We then use this method to identify experimental scenarios in which the parameter degeneracies may be efficiently resolved. Generally speaking, with two appearance measurements degeneracies can occur over wide areas of the (δ, θ 13 ) parameter space; with three measurements they occur along lines in the parameter space and with four measurements they occur only at isolated points. If two detectors are placed at the same distance from the source but at different locations with respect to the main axis of the beam (a detector cluster), each detector will measure neutrinos at different energies. Then one run with neutrinos and one run with antineutrinos will give the four independent measurements that in principle can resolve all of the parameter degeneracies if sin 2 2θ 13 ≥ 0.002. We also examine scenarios with detector clusters using only neutrino beams. Without detector clusters, the measurement of neutrinos and antineutrinos at a short distance and only neutrinos at a longer distance may also work.

Determining the neutrino mass hierarchy andCP-violation inNOνAwith a second off-axis detector

“…Many studies focus on resolving such degeneracies, e.g. by combining more than one experiment [63][64][65][66][67]75], using more than one detector [53,[57][58][59][60][61], or using information from atmospheric neutrino data [68].…”

“…However, statistical errors and realistic efficiencies and backgrounds limit considerably the capabilities of this method. Another detector [53,[57][58][59][60][61][62] or the combination with another experiment [63][64][65][66][67][68][69] would, thus, be necessary. 3 The use of only a neutrino beam could help in resolving the type of hierarchy when two different long-baselines are considered [61][62][63][64].…”

NOνAplus T2K: The race for the neutrino mass hierarchy

“…In practice, statistical errors and realistic efficiencies and backgrounds limit considerably the capabilities of this method. Another detector [35,[39][40][41][42] or the combination with another experiment [43][44][45][46][47][48][49][50][51] would, thus, be necessary 4 .…”

CP and T Violation in Neutrino Oscillations

“…The possible answer is to perform experiments at two different energies and/or two different baselines [19,21,22], or to combine two different experiments [22,23,24,25,26]. Then the degeneracy will be lifted and in principle, we can uniquely determine the oscillation parameters, provided that we can measure oscillation probabilities accurately enough.…”