From Super-Kamiokande to Hyper-Kamiokande

Project Information

SK2HK

Grant agreement ID: 872549

DOI

10.3030/872549

Project closed

EC signature date 15 October 2019

Start date 1 November 2019

End date 28 February 2026

Funded under

• EXCELLENT SCIENCE - Marie Skłodowska-Curie Actions

Total cost

€ 575 000,00

EU contribution

€ 575 000,00

Coordinated by

UNIVERSIDAD AUTONOMA DE MADRID
Spain

Periodic Reporting for period 1 - SK2HK (From Super-Kamiokande to Hyper-Kamiokande)

Reporting period: 2019-11-01 to 2024-02-29

Summary of the context and overall objectives of the project

SK2HK, Super-Kamiokande (SK) to Hyper-Kamiokande (HK), is part of the ongoing global efforts to understand the most fundamental elements of matter and their interactions. We aim to investigate neutrino interactions using the existing experimental facility in Japan, the SK detector located in the Kamioka Observatory (Gifu Prefecture) and owned by the partner of this Project: the Institute for Cosmic Ray Research of the University of Tokyo (ICRR).

SK is a very big (50000 tons) instrumented pure water tank that measures the radiation Cherenkov generated by energetic charged particles traveling along its inside. External particles, for instance neutrinos, might interact with particles in the detector. The final state interaction consists of newer particles, many of them charged and therefore able to be measured by SK. From those measurements we can learn about the interaction process and the fundamental physics behind. The SK detector is located underground, approx. 1000 m overburden, to reduce the flux from cosmic ray muons arriving to the detector.

We have upgraded SK (to SuperK-Gd) by dissolving a salt of Gd on its water. The very large neutron capture cross section of the Gd, with photon emission in the process (approx. 8 MeV total energy) allows precise identification of neutrons which will be key in the discovery of the DSNB (Diffuse Supernova Neutrino Background).

We are working on the new generation neutrino experiment, the HK project. It consists of a) a huge "far detector", SK-like device (approx. 200000 tons), being built also at Kamioka, b) an upgraded neutrino beam made at JPARC (Japan Proton Accelerator Research Complex, Ibaraki prefecture) and directed to Kamioka, and c) an additional "near detector", IWCD (Intermediate Water Cherenkov Detector), to measure with unprecedented precision the characteristics of the neutrino beam at generation.

SK2HK addresses fundamental problems in Physics at different stages, by analyzing the SK data, and by designing and building HK-FD and IWCD. These are neutrino oscillations, the search for dark matter, the physics of nearby galactic supernova, the DSNB, and Grand Unification. The collaborative work with the leaders of the field (ICRR holds two Nobel Prices in Physics: M. Koshiba in 2002, and T. Kajita in 2015) provides us with invaluable experience.

Work performed from the beginning of the project to the end of the period covered by the report and main results achieved so far

The project is divided into 5 work packages (WP). Despite of the COVID19 pandemic, reasonable work has been done on all of them.

Activities around management and coordination (WP1) have been the SK2HK Kick-off meeting (held on 2020/01/17 at the REA headquarters in Brussels), the first distribution of funding (2020/02/21), the suspension because of COVID19 (2020/06/05-2021/07/01) and the amendment (AMD-872549-6, -17) prepared and signed for resuming properly the activities, the rearrangement of WUT secondments [before/after TRIUMF: 10/5, ICRC: 17/22 ], the organization of the Mid-term-Meeting (held on 2022/12/12 at LLR-EC in the Paris area), others.

To assure a smooth running of SK (WP2), we monitor its operation through various types of shifts: regular SK data-taking (before COVID19 in the SK control room, fully remotely afterwards, now first shift onsite, second and third remote) and data-Acquisition quality (High and Low energy samples) done remotely. In addition, the performance of EGADS (before it was a prototype for dissolving Gd in SK, now a Supernova small detector) is also constantly monitored remotely by 8-hours, round the clock, shifts.

To reduce the experimental uncertainties of SK (WP2), we work on 2 calibration programs: a continuous 0.01 Hz flash of a Xenon light and a monthly study of the SK response to ~9 MeV γ’s produced at the capture of neutrons by a Nickel ball. With them we monitor the properties of the SK water and the gains of the 11400 photomultipliers (PMTs) that form SK. We also work to get the maximum insight on the evolution of the reflectivity of the light inside SK.

We have also been responsible during significant periods of time of the:
- SK’s PMTs and High Voltage maintenance
- concentration of the Gd salt along the whole volume of SK;

Respecting SK data analysis and physics output (WP3) we are working on:
- full understanding of Neutron tagging with SuperK-Gd
- Hybrid (neutron and tau tagging) Neural-Network based neutrino Oscillation analyses
- expanding SK’s fiducial volume for the Atmospheric neutrino Oscillation Analyses
- a T2K + Atmospheric Joint oscillation analysis
- the Cosmogenic induced spallation background at the DSNB search with SK (PhD thesis).
- DSNB search at SK without/with (SK-IV,-V / -VI,-VII respectively) Gd salt dissolved

Activities carried out on the building and running the necessary scientific instruments (WP4) are:
- Screening of the Gd salt (close to 40 tons of Gd2(SO4)3) for SuperK-Gd (for RI and other non-desired elements)
- Development of candidate photosensor covers protecting the HK-PMTs from chain reaction after implosion; program of implosion tests on them at the “Old JAMIC” research infrastructure in Hokkaido (Japan).
- design and build of prototype multi-PMT modules for Hyper-K’s IWCD and Far detectors.
- techniques for waveform compression, to be implemented in IWCD (and its prototype WCTE) mPMT firmware, leading to minimization of data rate and data volume.
- implementation of front-end modules for Hyper-K electronics, particularly the 2nd prototype of the Multi-PMT concentrator card.

Respecting communication and training (WP5) we have finished one Master Thesis and two “Graduation Thesis” at UAM, and two PhD Thesis at LLR-CNRS. Four WUT staff were seconded to Triumf for mPMT related technology transfer Triumf-WUT. Also, we are already studying the organization in Poland of one of next year’s Hyper-Kamiokande Collaboration Meeting

Progress beyond the state of the art and expected potential impact (including the socio-economic impact and the wider societal implications of the project so far)

Our main works are purely scientific ones. The “end product” is to increase our knowledge on the fundamental interactions in Nature. Their short-term impact on Society is of course limited. In the long term, our studies on Neutrino masses and oscillations, on the Grand Unification of the known forces, on the cosmic neutrino background from all the Supernovae along the history of the Universe will, sooner or later, have a profound impact on Humanity.

On the other side, the “mid-term product” is the build and run the scientific instruments necessary for those studies. Activities carried out relevant to the World-wide scientific Community have been described previously.
About the evolution of the guiding and framework of the SK experiment and HK project, SK2HK has been always present in the work towards the main achievements, and in some cases it has been key:
- 2020/02: The HK project is officially approved by the Japanese Diet
- 2020/07: start of SuperK-Gd (phase T1); ~14 tons of Gd2(SO4)3 loaded into SK
- 2022/03: WCTE (Water Cherenkov Test Experiment) approved by CERN Research Board
- 2022/05: SuperK-Gd starts phase T1.5; ~26 additional tons of Gd2(SO4)3 loaded into SK
- Several MoUs signed towards the international participation in the funding of HK: a) 3.5M EUR for HK at Spanish General Budget 2021 b) MoU between NCBJ (Poland) and UT/KEK signed at 2022/02, c) 3.8M EUR for HK at Spanish General Budget 2022, d) budget request to the French funding agencies submitted at end 2022, e) MoU between MCIN (Spain) and UT/KEK at 2022/07, f) some Budget approved at IN2P3 (0.95M EUR) and at CEA/Irfu (0.7M EUR) in 2023

Main parts of the Project