T2K: Neutrino oscillations and much more!

by Dr Anthony Hillairet

Neutrino oscillation has become a leading research topic in particle physics since its discovery. Until recently, the measurement of such oscillations was performed only through the observation of the disappearance of a certain neutrino flavor. The Tokai-To-Kamioka (T2K) experiment was built to study muon neutrino disappearance but also electron neutrino appearance in a muon neutrino beam. The T2K neutrino beam travels 295km in Japan between the J-Parc facility in Tokai and the Super-Kamiokande (SK) detector at the Kamioka observatory where the neutrino flavor is observed after oscillation. In 2013, T2K reached one of its design goals by discovering electron neutrino appearance by excluding the non oscillation hypothesis at 7.3 sigmas, which represents the first confirmed observation of an appearance channel in neutrino oscillation. This result confirms the possibility to measure CP violation in the neutrino sector by neutrino accelerator experiments such as T2K. One of the biggest challenge of such measurement for current and future experiments is to reduce the systematic uncertainties from the neutrino cross sections on nuclei heavier than hydrogen. T2K can directly contribute to improve the modelisation of such interactions by measuring neutrino cross sections on various types on nuclei in its near detectors, 280 m from the production target, and in SK. The near detector ND280 is a particularly interesting apparatus for these measurements because of the wide range of nuclei that compose it, but also because of the 3 gaseous TPCs in its tracker that represent the first gaseous detectors in a neutrino beam. Neutrino-gas interactions provide a unique environment for cross section measurements since all emitted charged particles are above the detection threshold. This seminar will present the latest T2K results as well as the T2K prospects in oscillation measurements. The motivation for cross section measurements in T2K will be shown and the status and potential of the analysis of neutrino-gas interactions will be detailed.