Speaker
Description
Hyper-Kamiokande will start collecting accelerator neutrino data in 2028 to measure the leptonic CP violating phase, $\delta_{CP}$. The largest systematic uncertainty is knowledge of the ratio between the electron neutrino and antineutrino cross sections, $\Delta (\sigma_{{\nu}_e}/\sigma_{\bar{\nu}_e})$. Improper modeling could generate an ambiguous asymmetry in any measured difference between the ratios of $\nu_{\mu} \to \nu_e$ and $\bar{\nu}_{\mu} \to \bar{\nu}_e$ oscillation probabilities, thus leading to a bias in the measurement of the CP violating phase ($\delta_{CP}$). Sensitivity studies show that the magnetised near detector (ND280) currently operating at the T2K experiment, and the intermediate water-Cherenkov detector (IWCD) may constrain $\Delta (\sigma_{{\nu}_e}/\sigma_{\bar{\nu}_e})$ to about 4\%. Reducing this further would lead to an improvement in the sensitivity to $\delta_{CP}$. Hyper-Kamiokande is developing the conceptual design of a second upgrade of ND280, called ND280++, envisaged for the, post 2030, high-statistics running phase. The current ND280 subdetectors would be replaced with up to 10 tons of water and/or organic scintillator detectors and time projection chambers, increasing the neutrino target mass by a factor of three, and include a larger water content. ND280++ will permit the collection of a high-statistics sample of $\nu_e$ and $\bar{\nu}_{e}$ interactions, the precision measurement of the neutrino cross section in water and the high-resolution reconstruction of the hadronic final state, sensitive to proton momenta below 200 MeV/c. The ND280++ reference design will be presented and the status of the ongoing R\&D, ranging from scintillating fibers, 3D segmented water-based liquid scintillator to highly segmented organic scintillator, will be reported. Finally, the results of the ongoing simulation studies of the ND280++ physics potential will be discussed.