Hyper-K One-Year Pre-Construction Extension

The Hyper-Kamiokande experiment is the next generation flagship experiment for the
study of neutrino oscillations, nucleon decays, and astrophysical neutrinos. The detector is a third generation
underground water Cherenkov detector. It will serve as the far detector for a long baseline neutrino oscilla-
tion experiment planned for the upgraded J-PARC (Japan Proton Accelerator Research Complex) neutrino
beam as well as a detector capable of observing proton decays, atmospheric neutrinos, and neutrinos from
astronomical origins enabling measurements that far exceed the current world best measurements.
The proposed activities address the core scientific questions in STFC's roadmap 1 : What are the fun-
damental particles? (C1), Is there a unified framework? (C3) What is the origin of the matter anti-matter
asymmetry? (C7) How do the laws of physics work when driven to the extremes? (D1). Because the long
baseline neutrino experiment is capable of addressing these questions it is the highest priority of the neutrino
STFC roadmap. Furthermore, this project is also perfectly aligned with the European Strategy which recog-
nises it importance [2]: Rapid progress in neutrino oscillation physics, with significant European involvement,
has established a strong scientific case for a long-baseline neutrino programme exploring CP violation and
the mass hierarchy in the neutrino sector. CERN should develop a neutrino programme to pave the way for a
substantial European role in future long-baseline experiments. Europe should explore the possibility of major
participation in leading long-baseline neutrino projects in the US and Japan.

The Hyper-K experiment is well placed to have a significant impact on our understanding of the Universe through the measurement of a number of keenly awaited quantities most notable of which are: CP-violation in neutrinos and neutrino mass hierarchy. To achieve this project plans to contribute to the experiment by researching and developing detector components that will significantly contribute to achieving these goals. These detector components are ground-breaking in their own right and have the potential to impact fields such as Medical physics through the photosensors that will be investigated as part of the project as well as other fields and the environment (the water target needs to have a high radiopurity which will require innovation to achieve this). Perhaps the most important output of the experiment for UK industry will be the hundreds of trained postdocs and graduate students who will receive high-quality scientific training while working on the project.
Hyper-Kamiokande should provide a gold mine for public engagement in science. Any number of examples could be given of public engagement activities driven by the public's fascination with neutrino physics. It has attracted significant attention from the arts that have inspired the production of a number of works.