Speaker
Description
I report the results of a search for $\bar{\nu}_{\mu} \rightarrow \bar{\nu}_{e}$ oscillations at the T2K experiment in a 3-flavour framework. An exposure of $1.49 \times 10^{21}$ Protons On Target (POT) is used in $\nu$ mode and $1.63 \times 10^{21}$ POT in $\bar{\nu}$ mode; an increase of $46\%$ in the $\bar{\nu}$ exposure compared to results reported in June 2018.
Results are reported for a joint analysis where candidate events are selected from the e-like events observed in $\bar{\nu}$ running mode. In order to obtain the best possible constraint on $\bar{\nu}_{e}$ appearance, observations from four other far detector event samples (across both $\nu$ and $\bar{\nu}$ modes) are used in conjunction with near-detector data. These observations constrain the values of the oscillation and systematic parameters, including the mass-hierarchy.
Two hypotheses are tested: a) no appearance and b) $\bar{\nu}_{e}$ appearance according to the current best knowledge of the PMNS matrix. Both rate-only and rate+shape analyses are performed, producing p-values for each hypothesis. A description is given of the method used to constrain the parameters and the treatment of priors used to generate distributions of the rate-only and rate+shape test statistics.
