Speaker
Dr
Hiroyuki Sekiya
(Kamioka Observatory ICRR University of Tokyo)
Description
We propose the Hyper-Kamiokande (Hyper-K) detector as a next generation underground water Cherenkov detector. It will serve as a far detector of a long baseline neutrino oscillation experiment envisioned for the upgraded J-PARC, and as a detector capable of observing -- far beyond the sensitivity of the Super-Kamiokande (Super-K) detector -- proton decays, atmospheric neutrinos, and neutrinos from astronomical origins. The baseline design of Hyper-K is based on the highly successful Super-K, taking full advantage of a well-proven technology.
Hyper-K consists of two cylindrical tanks lying side-by-side, the outer dimensions of each tank being 48 m (W) x 54 m (H) x 250 m (L). The total (fiducial) mass of the detector is 0.99 (0.56) million metric tons, which is about 20 (25) times larger than that of Super-K. A proposed location for Hyper-K is about 8 km south of Super-K (and 295 km away from J-PARC) at an underground depth of 1,750 meters water equivalent (m.w.e.). The inner detector region of the Hyper-K detector is viewed by 99,000 20-inch PMTs, corresponding to the PMT density of 20% photo-cathode coverage (one half of that of Super-K).
Hyper-K presents the potential for determination of the CP phase $\delta$ in the 3-flavor framework and therefore has discovery reach for CP violation in the lepton sector. With a total exposure of 5 years (one year being equal to 10$^7$ sec) to a 2.5 degree off-axis neutrino beam produced by the 1.66 MW J-PARC proton synchrotron, it is expected that the CP phase $\delta$ can be determined to better than 18 degrees for all possible $\delta$ values of and CP violation can be established with a statistical significance of 3$\sigma$ for 70% of the $\delta$ parameter space assuming the recent measured $\theta_{13}$ by T2K, Daya Bay, and RENO, and a known mass hierarchy. The mass hierarchy itself can be determined with more than 3$\sigma$ statistical significance for 46% of the $\delta$ parameter space. Furthermore, Hyper-K’s high statistics data sample of atmospheric neutrinos will allow us to extract additional information on the mass hierarchy and the octant of $\theta_{23}$. With a full 10 year duration of data taking, the significance for the mass hierarchy determination is expected to reach 3$\sigma$ or greater if $sin^2\theta_{23} > 0.4$.
Hyper-K will extend the sensitivity to nucleon decays beyond what can be achieved by Super-K by an order of magnitude or more. The sensitivities to the partial lifetime of protons for the decay modes p →$e^+ \pi^0$ and p→$\var{\nu}K^+$ are expected to exceed 1x$10^{35}$ years and 2x$10&^{34}$ years, respectively. This is the only known, realistic detector option capable of reaching such a sensitivity for the p→$e^+\pi^0$ mode.
The scope of studies at Hyper-K also covers high precision measurements of solar neutrinos, observation of both supernova burst neutrinos and supernova relic neutrinos, and dark matter searches.
Author
Dr
Hiroyuki Sekiya
(Kamioka Observatory ICRR University of Tokyo)
