Speaker
Ms
Jessica Elevant
(OKC, Stockholm University)
Description
The combination of data from long-baseline and reactor
oscillation experiments leads to a preference of the leptonic CP
phase $\delta_{\rm CP}$ 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
$\delta_{\rm CP}$ is highly non-Gaussian and depends on the unknown true
values of $\theta_{23}$ and the neutrino mass ordering. Values of
$\delta_{\rm CP}$ 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
$\delta_{\rm CP}$. For the 2-dimensional confidence region in the
($\delta_{\rm CP},\theta_{23}$) plane the usual $\chi^2$ approximation is
better justified. The 2-dimensional region does not include the
value $\delta_{\rm CP} = \pi/2$ up to the 86.3 % (89.2 %) CL assuming a true normal (inverted) mass ordering. Furthermore, we study the
sensitivity to $\delta_{\rm CP}$ 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.
Authors
Ms
Jessica Elevant
(OKC, Stockholm University)
Prof.
Thomas Schwetz-Mangold
(KIT)
