Initial Probe of δCP by the T2K Experiment with νμ Disappearance and νe Appearance

The T2K long-baseline neutrino oscillation experiment has observed the disappearance of nu(mu) and the appearance of nu(e) from its nu(mu) beam and it has accumulated 6.57x10(20) protons on target, similar to 8% of its goal POT. Combining its nu(mu) disappearance and nu(e) appearance measurements with the results from reactor experiments, T2K has obtained the first constraint to date on the CP-violating phase delta(CP). Two kind of joint 3-flavour oscillation analyses have been performed, based on either Frequentist or Bayesian methods, and the results from both analyses indicate that delta(CP) is consistent with -pi/2. Furthermore, the data excluded values for delta(CP): the excluded regions found at the 90% CL with the Frequentist analysis are [0.146,0.825]pi ([-0.080,1.091]pi) for normal (inverted) mass hierarchy; and the Bayesian 90% CI obtained, marginalizing over the mass hierarchy and assuming fiat priors, is [-1.13,0.14]pi. Although more T2K neutrino (and possibly anti-neutrino) data is necessary to confirm this result, whose sensitivity could be enhanced in combination with results from a new generation of long-baseline neutrino oscillation experiments and the latest reactor measurements, this first hint on CP violation opens exciting possibilities.