Three-flavour neutrino oscillation update and comments on possible hints for a non-zero theta_{13}

TL;DR

This paper updates the global fit of three-flavour neutrino oscillation parameters, evaluates potential hints of a non-zero theta_{13}, and finds no significant evidence for it when combining all data sets.

Contribution

It provides a comprehensive update on neutrino oscillation parameters and critically assesses the robustness of hints for a non-zero theta_{13} in recent data.

Findings

Solar + KamLAND data suggest a 1.5 sigma hint for non-zero theta_{13}

Atmospheric data hints are less robust and depend on analysis details

Combined data shows theta_{13} is consistent with zero within 1 sigma

Abstract

We provide a short summary of three-flavour neutrino oscillation parameters as determined from a global fit to 2008 data, and we comment on possible hints in favour of a non-zero value of the mixing angle theta_{13} found in arXiv:0806.2649. We do confirm a hint from solar + KamLAND data at about 1.5 sigma, which can be understood from the recent SNO CC/NC measurment. However, we show that a claimed hint from atmospheric data is much less robust. It depends on details of event rate calculations and treatment of theoretical uncertainties. We could identify two data points showing an 'excess' (at the 1 sigma level) in the SK-I multi-GeV e-like data, which seem to be the origin of the slight preference for theta_{13} > 0. We point out that once SK-I and SK-II data are combined this 'excess' disappears, and irrespective of the details of the analysis, no 'hint' from atmospheric data is obtained for the SK-I and SK-II combined data set. As a result the global fit of all data leads to a best fit value of theta_{13} consistent with zero within less than 1 sigma.