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SKPLUS Report Summary

Project ID: 641540
Funded under: H2020-EU.1.3.3.

Periodic Reporting for period 1 - SKPLUS (Super-Kamiokande plus)

Reporting period: 2014-12-01 to 2016-11-30

Summary of the context and overall objectives of the project

Super-Kamiokande Plus (SKPLUS, SK+) 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 Super-Kamiokande (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. Furthermore, we are working on the design and construction of new neutrino detectors planned at the Kamioka Observatory. They are SuperK-Gd (with its prototype EGADS), that is an upgrade of Super-Kamiokande that will allow it the identification of neutrons in the final state, and Hyper-Kamiokande (HK), its next-generation successor, along with nuPRISM, its accompanying intermediate detector.

SKPLUS addresses several fundamental problems in Physics at different stages: by analyzing the data from SK, by building and commissioning SuperK-Gd, and by designing HK. They are Neutrino Oscillations, the search for Dark Matter, the physics of nearby Galactic Supernova, the measurement of the Difusse Supernova Neutrino Background and Grand Unification. Our goal with all of them is to advance in the understanding of the basic interactions in Nature.

The collaborative work with the leaders of the field - the Japanese Groups and Research Facilities - provides invaluable experience for these studies, covering neutrino physics, cosmology, astrophysics, technical design, construction and operation of water Cherenkov detectors, data analysis techniques, and hardware and software development for the new generation detectors.

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

In order to assure a smooth and continuous running of the Super-Kamiokande neutrino telescope, we supervise its operation through various types of shifts: 1) regular SK data-taking in the SK control room and, 2) Data-Acquisition quality (High and Low energy samples) done remotely. In addition, the performance of the EGADS prototype is also constantly monitored remotely by 8-hours, round the clock, shifts.

In order to reduce the experimental uncertainties of SK, we are working on two calibration programs: the continuous 0.01 Hz flash of Xenon light in the center of the detector and the approximately monthly study of response to ∼9 MeV γ’s produced at the capture of neutrons by a Nickel ball inside the detector. With them we monitor the properties of the SK water and the hit rates and gains of the 11400 photomultipliers (PMTs) that form SK.

We have upgraded the real-time monitor (SKHist) that, using data streamed by the data acquisition system, is running permanently in the SK control room. We have added a better trigger histogram representations and extended management of history of detector running parameters. Also we are working towards a web service with similar monitoring capabilities as SKHist.

We are searching for Dark Matter with Super-Kamiokande in an indirect way by measuring excess of neutrino fluxes from the Earth, the Sun and in the Galactic Center and halo. We have not observed any excess above the expected background level related to atmospheric neutrinos. Due to quality of our data and our elaborated analysis procedures, we are significantly narrowing down the properties that hypothetical Dark Matter candidates could have.

We have thoroughly included neutron tagging with Hydrogen in the global oscillation analysis of atmospheric neutrinos. With it we have improved the previous constrains by Super-Kamiokande on the neutrino mass hierarchy and the leptonic charge-parity violation.

For the SuperK-Gd upgrade we are thoroughly measuring the radioactive contamination of the available samples of Gd-salts. It is crucial to minimize. A large fraction of this work has been carried out at the Canfranc Underground Laboratory (Spain). The joint efforts with a few Companies, mostly from Japan, are providing fantastic improvements.

We have developed new ideas and made new tools for maximizing the impact of neutron tagging by Gd in the physics program of water-Cherenkov detectors. Remarkably, we have developed neural-network based algorithms for discriminating neutrino versus anti-neutrino interactions in the water and to discriminate Neutral Current from Charged Current interactions.

We have developed a method to successfully use the Gd-tagged neutrons from those produced in the final state to estimate a large fraction of the otherwise non-measurable energy transferred to the nuclei or emitted as neutrino particles in the reaction.

For nuPRISM and Hyper-Kamiokande, we have performed a thorough study of timing and charge accuracy of front-end electronics utilizing digitization based on flash analog-to-digital converters.
That resulted in the development of decent models allowing for easy exploration of various variants of the electronics, without the actual need of building costly prototypes. Therefore, significant time savings in the design process can be achieved.

We are working towards the final design of the key instrument in Hyper-Kamiokande, the photo-multipliers (PMT). We are also studying the novel Hybrid-Photo-Detector option, which is proven to perform significantly better than the current baseline approach (PMT), but lacks yet systematic studies on its reliability and cost in a mass production stage. We are also working on a novel approach to the PMT protection cover to prevent the transmission of the shock wave formed after an hypothetical implosion of the PMT that would destroy all the other PMTs immersed in the water in the same tank.

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 cooperative projects with Japanese and world-wide colleagues are steadily advancing. Within the context of the global goals of the SKPLUS project we are progressing in the construction of new generation of neutrino detectors, positively impacting the careers of the engaged researchers and communicating to the community throughout obtained achievements.

On June 27, 2015, the Super-Kamiokande (SK) collaboration approved and endorsed the SuperK-Gd project. Its actual schedule, including the refurbishment of the tank and Gd-loading time is being negotiated between the Super-Kamiokande and the T2K Collaborations (T2K uses SK as far detector).

On J-PARC PAC meeting held on July 27-29, 2016, the nuPRISM experiment has been given a stage-I approval, and is now tentatively known as J-PARC Nuclear and Particle Experiment E61.

The formal request to the Japanese Ministry of Education, Culture, Sports, Science and Technology (MEXT) for funding the Hyper-Kamiokande (HK) project was submitted in the Fall 2016. The decision by MEXT to include it on its roadmap is expected by Fall 2017. However, a necessary very important milestone has already been achieved: the Science Council of Japan has officially selected Hyper-K as one of the important large-scale projects of its Masterplan 2017.

We are proud of the “Breakthrough Prize 2016 in Fundamental Physics” awarded to several SKPLUS members for former activities but very much related to this SKPLUS project.

We are delighted with the Noble Prize in Physics 2015 awarded to our colleague, Prof. Takaaki Kajita, director and leader of our Partner Institute in SKPLUS, ICRR (U. Tokyo). The awarded research was conducted with the Super-Kamiokande detector. The neutrino studies of this Project are continuation and extension of the discoveries honored with the Nobel Price 2015.
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