[Paper Review] Letter of Intent: The Hyper-Kamiokande Experiment --- Detector Design and Physics Potential ---

K. Abe, K. Abe+39 more|arXiv (Cornell University)|Sep 15, 2011

Neutrino Physics Research1 references282 citations

TL;DR

Hyper-Kamiokande proposes a next-generation water Cherenkov detector to study neutrino oscillations and perform neutrino radiography using the MSW effect. By detecting atmospheric neutrinos in the 5–10 GeV range with high statistics, it enables high-precision density mapping of Earth's core with potential 5% accuracy, offering insights into core composition and geodynamo energy sources.

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)

Motivation & Objective

• To design a next-generation underground water Cherenkov detector for long-baseline neutrino oscillation experiments.
• To enable high-precision neutrino radiography of Earth's interior using the MSW effect on atmospheric neutrinos.
• To measure core density differences with sub-10% accuracy, improving geophysical constraints on core composition and dynamics.
• To investigate the role of light elements in the core and the symmetry of the inner core through neutrino oscillation data.
• To provide a practical alternative to km³-scale detectors by leveraging high-statistics detection of lower-energy neutrinos.

Proposed method

• Utilize a large-volume water Cherenkov detector (1.8 Mton fiducial mass) with high photodetector coverage for efficient neutrino detection.
• Leverage the MSW effect in Earth's core to modulate atmospheric neutrino oscillation probabilities, especially for νₑ in the 5–10 GeV energy range.
• Measure the ratio of νₑ flux with and without MSW effects as a function of neutrino energy and zenith angle to infer core density profiles.
• Use precisely known neutrino oscillation parameters (θ₂₃, Δm²₃₂, θ₁₃, δ) to enhance sensitivity and reduce systematic uncertainties.
• Simulate atmospheric neutrino events using known cosmic ray spectra (index ≈ 2.7) to estimate detection rates and resolution.
• Apply statistical analysis to extract core density resolution, assuming normal mass hierarchy and standard oscillation parameters.

Experimental results

Research questions

• RQ1 Can Hyper-Kamiokande achieve a core density resolution of 5% or better using the MSW effect on atmospheric neutrinos?
• RQ2 What is the sensitivity of Hyper-Kamiokande to the density difference between Earth's inner and outer core?
• RQ3 How precisely can the C₀ parameter of Roche’s law be determined to infer inner core convection and chemical homogeneity?
• RQ4 Can the detector distinguish between spherically and cylindrically symmetric inner core structures using neutrino oscillation data?
• RQ5 What is the achievable accuracy in measuring the average core density using atmospheric neutrinos over a 10-year exposure?

Key findings

• The flux of atmospheric neutrinos in the 5–10 GeV range is over 10⁶ times greater than that of very high-energy neutrinos, enabling vastly superior statistics.
• With precise oscillation parameters, Hyper-Kamiokande can achieve higher statistical precision in neutrino radiography than km³-scale detectors like IceCube or KM3NeT.
• The MSW effect induces the largest modulation in νₑ oscillation probability in the 5–10 GeV energy range, making this window optimal for radiography.
• A 5% accuracy in core density resolution is achievable, sufficient to probe the partition coefficient of light elements between inner and outer core.
• The detector can confirm the core-mantle density difference at 1σ confidence level within one year of operation using 40 strings of IceCube-like data.
• Neutrino radiography with Hyper-Kamiokande offers a viable, high-precision method to study inner core convection and asymmetry, surpassing current capabilities of existing detectors.