On the determination of the leptonic CP phase
Number of Authors: 2
2015 (English)In: Journal of High Energy Physics (JHEP), ISSN 1126-6708, E-ISSN 1029-8479, no 9, 016Article in journal (Refereed) Published
The combination of data from long-baseline and reactor oscillation experiments leads to a preference of the leptonic CP phase delta(CP) in the range between pi and 2 pi. 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 delta(CP) is highly non-Gaussian and depends on the unknown true values of theta(23) and the neutrino mass ordering. Values of delta(CP) around pi/2 are disfavored at between 2 sigma and 3 sigma, depending on the unknown true values of theta(23) and the mass ordering. Typically the standard chi(2) approximation leads to over-coverage of the confidence intervals for delta(CP). For the 2-dimensional confidence region in the (delta(CP), theta(23)) plane the usual chi(2) approximation is better justified. The 2-dimensional region does not include the value delta(CP) = pi/2 up to the 86.3% (89.2%) CL assuming a true normal (inverted) mass ordering. Furthermore, we study the sensitivity to delta(CP) and theta(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.
Place, publisher, year, edition, pages
2015. no 9, 016
Neutrino Physics, CP violation
IdentifiersURN: urn:nbn:se:su:diva-123347DOI: 10.1007/JHEP09(2015)016ISI: 000363534500007OAI: oai:DiVA.org:su-123347DiVA: diva2:874070