Letter of Intent: The Hyper-Kamiokande Experiment --- Detector Design and Physics Potential --- (1109.3262v1)

Abstract: 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. (to be continued)

• The paper outlines Hyper-Kamiokande’s design strategy to enhance neutrino detection and proton decay searches using a vast, next-generation water Cherenkov detector.
• The methodology employs two large cylindrical tanks with nearly 99,000 PMTs to provide unprecedented sensitivity compared to previous facilities.
• Key projections include constraining the CP phase within 18° over five years and boosting nucleon decay and astrophysical neutrino detection capabilities.

An Overview of the Hyper-Kamiokande Experiment: Detector Design and Physics Potential

The letter of intent detailing the Hyper-Kamiokande (Hyper-K) experiment outlines the development of a next-generation underground water Cherenkov detector. The document highlights the ambitious goals of Hyper-K, which chiefly aims to advance our understanding of neutrino physics, search for proton decay, and observe neutrinos originating from both atmospheric processes and astronomical sources. Comparatively, Hyper-K is designed to supersede the Super-Kamiokande (Super-K) detector by approximately 20 times in total mass, making it a crucial tool for acquiring greater sensitivity and precision in relevant physics measurements.

Detector Design Features

Hyper-K's design capitalizes on the proven utility and technology of the Super-K facility. The detector consists of two adjacent cylindrical tanks, each with dimensions of $$48\ \text{m} \times 54\ \text{m} \times 250\ \text{m}$$. These tanks collectively hold nearly a million metric tons of water, with the detector representing a 25-fold increase in fiducial mass relative to Super-K. The tanks are equipped with 99,000 20-inch PMTs providing 20% photo-cathode coverage. Positioned approximately 295 km away from J-PARC, the Hyper-K detector is situated for optimal detection and analysis capabilities.

Neutrino Physics and CP Violation

One of Hyper-K's primary objectives is to push the boundaries of precision in neutrino oscillation measurements, with a particular focus on the CP violation ($CPV$) in the lepton sector. The letter predicts that, upon five years of exposure to the J-PARC neutrino beam, the CP phase $\delta$ could be constrained to within 18 degrees. Furthermore, the potential to establish $CPV$ with $3\sigma$ significance over a significant portion of parameter space is bold, contingent on the relatively sizable value of $\sin^2 2\theta_{13}$ being greater than 0.03. This emphasizes the experiment's capability to traverse a new frontier in understanding the underlying symmetry properties of neutrinos, which are fundamental to high-energy physics and cosmology.

Proton Decay and Astrophysical Neutrinos

The Hyper-K letter also outlines the potential to advance the sensitivity of nucleon decay searches by an order of magnitude, primarily targeting modes such as $p \rightarrow e^+ \pi^0$ and $p \rightarrow \bar{\nu} K^+$. This capability is vital given current theoretical motivations from various Grand Unified Theories (GUTs) and their supersymmetric extensions, which predict such decay modes under certain conditions.

Moreover, Hyper-K is set to contribute significantly to neutrino astronomy. Its prospects include conducting high-precision solar neutrino measurements and serving as an observatory for supernova burst and relic neutrinos, positioning Hyper-K at the forefront of detecting neutrino emissions from core-collapse supernovae. This could yield insights into stellar explosion mechanics and allow investigation of new phenomena, such as neutrino mass hierarchy and direct mass measurements from arrival time differences during a supernova burst.

Future Developments in Astrophysics and Neutrino Geophysics

In addition to its core physics goals, Hyper-K could serve an essential role in broader astrophysics, with capabilities of high-statistics detections of solar neutrinos, potential discovery of solar flare neutrinos, and dark matter searches via indirect methods. The work in neutrino geophysics, particularly concerning terrestrial density measurements, is interesting as it bridges the disciplines of particle physics and earth sciences, offering alternative approaches to interrogate the Earth's density profile using neutrinos.

Conclusion

The Hyper-Kamiokande experiment is poised to serve as a pivotal tool in the detailed paper of neutrinos and their properties. By massively increasing the available volume compared to its predecessors, Hyper-K stands ready to produce data with unprecedented precision, opening new avenues in neutrino physics and astrophysics. The prospects of detecting rare events such as proton decay and supernova neutrinos underline the potential groundbreaking nature of the experiment across multiple domains of fundamental physics.