Journal of High Energy Physics

, 2015:16 | Cite as

On the determination of the leptonic CP phase

  • Jessica ElevantEmail author
  • Thomas Schwetz
Open Access
Regular Article - Theoretical Physics


The combination of data from long-baseline and reactor oscillation experiments leads to a preference of the leptonic CP phase δ CP in the range between π and 2π. We study the statistical significance of this hint by performing a Monte Carlo simulation of the relevant data. We find that the distribution of the standard test statistic used to derive confidence intervals for δ CP is highly non-Gaussian and depends on the unknown true values of θ 23 and the neutrino mass ordering. Values of δ CP around π/2 are disfavored at between 2σ and 3σ, depending on the unknown true values of θ 23 and the mass ordering. Typically the standard χ 2 approximation leads to over-coverage of the confidence intervals for δ CP. For the 2-dimensional confidence region in the (δ CP, θ 23) plane the usual χ 2 approximation is better justified. The 2-dimensional region does not include the value δ CP = π/2 up to the 86.3% (89.2%) CL assuming a true normal (inverted) mass ordering. Furthermore, we study the sensitivity to δ CP and θ 23 of an increased exposure of the T2K experiment, roughly a factor 12 larger than the current exposure and including also anti-neutrino data. Also in this case deviations from Gaussianity may be significant, especially if the mass ordering is unknown.


Neutrino Physics CP violation 


Open Access

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© The Author(s) 2015

Open AccessThis article is distributed under the terms of the Creative Commons Attribution 4.0 International License (, which permits use, duplication, adaptation, distribution, and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made.

Authors and Affiliations

  1. 1.Oskar Klein Centre for Cosmoparticle Physics, Department of PhysicsStockholm UniversityStockholmSweden
  2. 2.Institut für Kernphysik, Karlsruhe Institute of Technology (KIT)KarlsruheGermany

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