Optimization of neutrino oscillation facilities for large θ 13

Abstract

Up to now, future neutrino beam experiments have been designed and optimized in order to look for CP violation, θ 13 and the mass hierarchy under the conservative assumption that θ 13 is very small. However, the recent results from T2K and MINOS favor a θ 13 which could be as large as 8 • . In this work, we propose a re-optimization for neutrino beam experiments in case this hint is confirmed. By switching from the first to the second oscillation peak, we find that the CP discovery potential of future oscillation experiments would not only be enhanced, but it would also be less affected by systematic uncertainties. In order to illustrate the effect, we present our results for a Super-Beam experiment, comparing the results obtained at the first and the second oscillation peaks for several values of the systematic errors. We also study its combination with a β-beam facility and show that the synergy between both experiments would also be enhanced due to the larger L/E. Moreover, the increased matter effects at the longer baseline also significantly improve the sensitivity to the mass hierarchy.

ESSnuSB Neutrino Oscillation Project

“…Considering the measured value of θ 13 , the atmospheric term becomes prominant compared to the interference term at the first maximum. An interesting possibility to increase the sensitivity to CP discovery and be less sensitive to systematic errors will be to considere a longer baseline looking at the second oscillation maximum in which the interference term is enhanced [1].…”

Physics reach of CERN-based SuperBeam neutrino oscillation experiments

“…However, the small matter effects also imply no sensitivity to the mass hierarchy from the study of the oscillations of the neutrino beam alone, although some sensitivity can be gained in combination with atmospheric neutrino oscillations at the same detector [18,20]. For the large values of θ 13 currently favoured, an even more attractive option implies the observation of this low energy beam at its second oscillation peak, which would increase the CP violation discovery potential as well as the determination of the mass hierarchy, at a ∼ 650 km baseline [21]. However, as these high beam powers are not expected to be achieved in the near future, in this work we will instead assume a more modest flux of ∼ 0.8 MW, similar to what is being considered for LAGUNA-LBNO [22].…”

On the Bayesian approach to neutrino mass ordering

“…Many studies of the capabilities for doing this in different types of experiments have been performed, including atmospheric , reactor [27,[29][30][31][32][33][34][35][36][37][38][39][40][41][42][43][44][45][46], and long baseline [14,19,32,[47][48][49][50][51][52][53][54][55][56][57][58][59][60][61][62][63][64][65][66] neutrino experiments. Most of these studies take an approach where the neutrino mass ordering is determined in a frequentist manner with the typical square root of the test statistic used as a measure of the sensitivity as if the distribution of the test statistic was a χ 2 distribution with one degree of freedom.…”