Jul. 2022

Construction and Development

The Hyper-Kamiokande tunnel excavation has reached the center of the cavern dome

In the Hyper-Kamiokande construction, which is scheduled to start observation in 2027, the tunnel excavation has progressed and finally reached the center of the cavern dome on June 23rd, 2022. From here, we start the excavation of the dome.

The red and white pole indicates the center of the dome. The hole on the left side of the photo is the tunnel excavated in 2020 for the geological survey. The tunnel in this construction connected to this survey tunnel at this dome center.

The dimensions of the tunnel in the photo are approximately 9 m high and 9 m wide. Though people look quite smaller already, the completed Hyper-Kamiokande dome will become 21 m high and 69 m in diameter, much larger than this tunnel.

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Mar. 2022

Construction and Development

The excavation of the access tunnel has been completed.

The excavation of the access tunnel was completed on February 25, 2022, as scheduled, achieving another significant milestone towards the realization of the Hyper-Kamiokande project. We plan to complete the drilling of the approach and circular tunnels as well, and the excavation of the dome section of the main cavern is scheduled to begin by the end of this year.

Edge of the access tunnel. The approach tunnel will be excavated beyond this point.

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Aug. 2021

Construction and Development

Photosensor cover development by Spanish collaborators

Ultra-sensitive photosensors with a diameter of 50 cm are used in the Hyper-Kamiokande. The photosensor has adequate water pressure resistance for use in water of the detector, and installing photosensor cover will increanse safety.

Hyper-Kamiokande is an international research collaboration, with various countries sharing the research and development work. The Spanish group is playing a central role in the development and realization of the cover. The cover is currently being developed and is expected to be completed by 2021, with mass production beginning in 2022.

Prototype of the photosensor cover. UV transparent acrylic resin and 2.5mm thickness stainless steel are used. ©Autonomous University of Madrid

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May. 2021

Construction and Development

The access tunnel excavation for the Hyper Kamiokande started.

The access tunnel excavation for the Hyper-Kamiokande project just started on May 6. Following the completion of the entrance yard construction, the excavation work finally started in earnest. An approximately 2-km long tunnel will be rapidly excavated in 9 months followed by the excavation of approach tunnels and the main cavern.

We have achieved an important milestone for the realization of Hyper-Kamiokande project. With preparations going smoothly, the construction process of the Hyper-Kamiokande is accelerating, towards the start of the experiment in 2027.

The access tunnel entrance

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Jan. 2021

Construction and Development

The production of Hyper-Kamiokande photosensors started.

Charged particles generated by high-energy events such as neutrino interactions or proton decay emit Cherenkov light when they pass through the water. Hyper-Kamiokande identifies the type of particles and measures their energy and position by the photosensors attached to the wall of the tank that detect the Cherenkov light.

We have developed a new model of high-performance photosensor to improve the efficiency and the precision of the measurements. Basic properties of the new photosensors such as the detection efficiency, counting resolution, and timing resolution have been successfully improved approximately twice compared to the photosensors currently used in Super-Kamiokande.

The mass production of the photosensors for Hyper-Kamiokande has started. The first photosensors arrived at ICRR in December 2020. We will check the delivered sensors to confirm that they satisfy the performance requirements and measure their individual properties.

The mass production will be completed within six years to start the experiment in 2027.

The new photosensors arrived at ICRR

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Oct. 2020

Construction and Development

The geological surveys for the excavation is in the final stages.

Hyper-Kamiokande will be built in one of the world’s largest underground caverns and its excavation will start at the beginning of the next fiscal year. The cavern consists of a huge cylinder with an inner diameter of 69 m, a height of 73 m, and a dome on top to stabilize the huge cylinder structure. In order to make the next important advancement with the results from Kamiokande and Super-Kamiokande, this huge volume is necessary.

A water Cherenkov detector with the effective volume 8.4 times larger than that of Super-Kamiokande will be built using the full capacity of the cavern. By combining it with the upgrade of J-PARC high-intensity proton beam, we are aiming for the next breakthrough in the fields of particle and astroparticle physics. The objectives include shedding light on the origin of matter, deeper and more precise understanding of neutrino oscillations, searching for nucleon decay to directly probe the Grand Unified Theory, and observing cosmic neutrinos from single and cumulative supernova explosions. Hyper-Kamiokande is the project which will provide an international observatory for fundamental physics for more than 20 years.

Now, the geological survey for the excavation is in the final stages. In order to determine the position of the cavern, we have performed various geological surveys these past few months. In this fiscal year, we are performing a final large-scale survey including new adits that measures 96 m in length and borings that totals 725m.

The bedrock around the currently planned position of the cavern has been investigated in detail based on the adit and boring results. In July 2020, the excavation of the adit has been completed, and it reached the center position of the Hyper-Kamiokande dome. The dome will be on top of a huge water tank. At this special position, various in-situ experiments are in progress to identify the actual physical properties of the bedrock.

The boring which penetrates through the planned position of the cavern for the investigation of its neighborhood.

With the final geological surveys going smoothly, preparations are now underway for the excavation of an access tunnel and the subsequent excavation of one the world’s largest underground caverns.

The adit to investigate the geological survey of the Hyper-Kamiokande (HK) dome, where the “HK center” mark is found at the ceiling near the dead end (bottom center).

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Mar. 2020

Construction and Development

A mockup of the PMT support structure was built in Kashiwa.

A full-scale mockup of the PMT support structure for Hyper-Kamiokande was built in ICRR (Kashiwa-city, Chiba). The size of the mockup is approximately 3m in width, 3m in height, and 0.5m in thickness. This design allows up to 12 (3 in row and 4 in column) photo sensors to be installed into it.

This mockup frame is used to determine the design of the photo sensors, the mounting procedure and the anti-chain-implosion covers. 40000 photo sensors will be mounted within Hyper Kamiokande, so it is necessary to find a quick way to install this large number of sensors efficiently and accurately in order to start operations as soon as possible.

We use the mockup structure to estimate the accuracy, rigidity and efficiency of the photo sensor installation work. We also plan to determine the installation method of the black sheets dividing the tank between inner and outer detector regions.

The preliminary black sheet design will be installed to allow the measurement of performance and the stability of the light shielding.

Currently the photo sensors and covers, developed in Japan, are ready for test measurements and several types of attachment methods have been tested. The procedures to install the photo sensors and covers developed in other counties will be tested with this mockup.

A mockup of the PMT support structure

The photo sensors and covers installed with the mockup

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Feb. 2020

Overall project

The Hyper-Kamiokande project is officially approved.

The University of Tokyo
High Energy Accelerator Research Organization (KEK)
Japan Proton Accelerator Research Complex (J-PARC) Center

Hyper-Kamiokande (HK or Hyper-K) project is the world-leading international scientific research project hosted by Japan aiming to elucidate the origin of matter and the Grand Unified Theory of elementary particles. The project consists of the Hyper-K detector, which has an 8.4 times larger fiducial mass than its predecessor, Super-Kamiokande, equipped with newly developed high-sensitivity photosensors and a high-intensity neutrino beam produced by an upgraded J-PARC accelerator facility.

The supplementary budget for FY2019 which includes the first-year construction budget of 3.5 billion yen for the Hyper-Kamiokande project was approved by the Japanese Diet. The Hyper-K project has officially started. The operations will begin in 2027.

The overall Japanese contribution will include the cavern excavation, construction of the tank (water container) and its structure, half of the photosensors for the inner detector, main part of the water system, Tier 0 offline computing, together with J-PARC accelerator upgrade and construction of a new experimental facility for the near detector complex. International contributions will include the rest of photosensors for the inner detector, sensor covers and light collectors, photosensors for the outer detector, readout electronics, data acquisition system, water system upgrade, detector calibration systems, downstream offline computing system, and the near/intermediate detector complex.

We would like to work together with domestic and international colleagues in Hyper-K for the development of neutrino physics and astrophysics.

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Jul. 2018


“ICHEP2018 Satellite Meeting for Hyper-Kamiokande and KNO” was held.

On July 8th 2018, we held the “ICHEP2018 Satellite Meeting for Hyper-Kamiokande and KNO” in Seoul, Korea. About 60 researchers from Japan, Korea, and other countries attended the meeting and discussed the expected physics sensitivities, the scientific importance, and the international collaboration of the Hyper-Kamiokande project. A Korean particle physicist and astronomer, Director of J-PARC center, and Hyper-Kamiokande members gave talks, and the roundtable discussion was held at the end of the meeting. We had lively and fruitful discussions through this meeting.

We confirmed that the second Hyper-Kamiokande detector in Korea will expand Hyper-K’s unique and important studies which cannot be done by any other experiments. Participants including Korean researchers expressed great interests in early realization of the project.


The roundtable discussions

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Apr. 2018

Construction and Development

Test of improved prototype and new anti-chain-implosion covers were carried out.

The large size photo-sensor is encapsulated in a cover to prevent possible chain implosion in deep water. Deeper the detector is, the higher water pressure is.

For Hyper-Kamiokande, which have about 60m depth, it is a important item to develop a more powerful cover than that for current Super-Kamiokande (about 40m depth). To establish the cover, we need to prove actual prevention of chain implosion in deep water. We already performed a test of a prototype in 2016, and we established an anti-chain-implosion cover for Hyper-Kamiokande.

In March 2018, we tested three type of covers, improved prototype, resin-made monolithic cover, a tube-shaped stainless steel made cover which is developed by our Spanish group (Picture 1 to 3).

(Picture 1) Test system. A photosensor with cover is located at the center of the grid, and surrounded by bare photosensors. The system is lowered down to deep water. The photosensor in the cover is crashed by a special tool (“pusher”) remotely and see the effect on the surrounding photosensors. Center is photosensor with the improved prototype. We put color tapes on glasses or cover surface to identify the surface via camera.

(Picture 2) A resin-made monolithic cover. It is much lighter than current prototype made by stainless steel.

(Picture 3) A tube-shaped cover developed by our Spain group. Structure is relatively simple and cheaper production cost is expected.

We carried out the test from March 6th to March 10th in old JAMIC (Japan Microgravity Center) building in Kami-Sunagawa city, Hokkaido, Japan (Picture 4).

We proved that the covers prevents chain implosion in 80m, 40m, and 60m, respectively. We also found differences of the shockwave generation depending on the covers and different deformation of covers, which are important to understand the process of implosion of large photo-sensor in deep water. In addition to that, we tested an implosion of smaller (8 inch diameter) photosensor in deep water, and we tested a new type of test apparatus to crash photosensors.

We successfully took such valuable data in short time. This is fully supported by Kami-Sunagawa town.

(Picture 4) Old JAMIC (Japan Microgravity Center) building in Kami-Sunagawa city, Hokkaido, Japan

(Picture 5) During the test, lowest temperature in the laboratory was below minus 10 degree. This is icicles on a rope in laboratory.

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Apr. 2017

Construction and Development

Development of software towards Hyper-Kamiokande.

Development of software is absolutely needed to investigate physics potential of HK. Software plays important role to determine detailed design of the detector. For example, it is planned that HK uses about 40,000 photo sensors. There are some candidates of photo sensor, and we can measure their properties at laboratory one by one. However, it is difficult to imagine how different in neutrino observation caused by different photo sensor candidates with 40,000 installed in the detector. In such a case, we often use a method called “simulation” in which a detector is virtually built on computer and examine physics phenomena.

In this virtual experiment, there are two simulations: simulation for physics process, like how neutrino interacts with matter and produces particles, and simulation of detector which denotes how particles are detected and transformed to signal. As for physics simulation, we can use programs used in SK or T2K because physics phenomena are universal. We have to establish the detector simulation by our own including tank size and shape, optical property of water, performance of photo sensor, readout of signal, and so on. We (core members from Duke university, US) are developing water Cherenkov detector simulator for wide use based on GEANT4, a software package of CERN. This simulator can easily change tank size, number of photo sensor, and type of photo sensor and read out by modularize them. Figure 1 shows an event sample of HK simulation.

Figure 1; Event display of HK simulation in which muon is emitted from center of the tank toward side wall. Yellow dots correspond to photo sensor which detect Cherenkov light.

To understand detector performance, software which reconstructs physics variables from information of photo sensors is also needed. The conventional method used in SK determines physics variables one by one sequentially. We are developing a new method which determines all physics variables at once by fitting expected distributions to photo sensor information. The new method uses information of un-hitted photo sensors which are not used in the conventional method, and we can expect to reconstruct physics variables more precisely.

Figure 2 show momentum resolution calculated by the new method for electron and muon which are generated by HK simulation with various momentum. The new photo sensor for HK has two times better efficiency for detecting one photon than SK and if the photo sensors cover 40% of the detector wall as SK, this figure shows the momentum resolution improves much better than SK.

Figure 2; Momentum (horizontal axis) vs momentum resolution (vertical) for electron (left) and muon (right) reconstructed by the new method. Green corresponds to SK performance, red is HK tank which new photo sensors cover 14 % of detector wall, blue is 40 % coverage case.

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Mar. 2017

Construction and Development

HK group is developing a dedicated electronics module.

Hyper-Kamiokande utilizes Cherenkov light emitted by high-speed charged particles. When Cherenkov photons hit a photo-sensor in the Hyper-Kamiokande detector, an electronic pulse is produced. The integrated electric charge of the pulse is proportional to the amount of Cherenkov light, which is itself proportional to the momentum of the particle. The spatial distribution and timing distribution of the detected photons provides the position of the interaction and the direction of the produced particles. Therefore, it is necessary to use high performance electronic circuits to record the timing and charge from each photo-sensor. We are now developing a dedicated electronics module and evaluating its performance.

We have developed a custom charge-to-time converter (QTC) ASIC for Super-Kamiokande. This ASIC converts the amount of the input charge to a digital pulse, whose width is proportional to the integrated charge collected by the photo-sensor, and whose leading edge may be digitized by a TDC to determine the time the photo-sensor was hit.

LSI developed for Super-Kamiokande; CLC101(ICRR/IWATSU Electric Co. Ltd.)

In Hyper-Kamiokande, the QTC is considered as one of the primary options for instrumenting the detector. We are designing proto-type electronics board using the QTC ASIC for Super-Kamiokande. In order to measure timing, it is planned to implement the TDC function in an FPGA by programmable logic. The FPGA is commonly used in consumer products and recent development makes it possible to measure the timing very precisely. With the latest technology, the measurement accuracy is better than 10-10 seconds.

We are developing a proto-type module, which composed of these two elements with university and laboratories in the United States.

Evaluation board developed with the group in US.

We are also evaluating electronic readout based on an FADC (Flash Analog-to-Digital Converter), as another promising candidate for the signal processing. The FADC records the waveform of the input charge signal, sampling the waveform of the signal from the photo-sensor several million times per second. The recorded waveform is further processed digitally to precisely measure the timing and the charge of the signal. This system has been developed by the groups in Canada and Poland.

Through these developments, we are aiming to develop a signal processing system capable of handling signals from 50,000 photo sensors per Hyper-Kamiokande detector module, with goals of high performance, low power consumption and low cost per channel.

Evaluation board developed by the groups in Canada and Poland.

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Feb. 2017


The workshop on Supernova at Hyper-Kamiokande was held.

On 12th and 13th February, the workshop on Supernova at Hyper-Kamiokande was held at the Koshiba hall in the University of Tokyo. About 100 researchers participated and discussed the expected sensitivity and importance of astro-neutrino observation at Hyper-Kamiokande such as neutrinos from supernova, dark matters, and so on. The top-level international researchers both from the theoretical and experimental field were invited as the speakers, and had fruitful discussions.

In astro-neutrino observations, it was confirmed that the Hyper-Kamiokande has an order of magnitude better sensitivity than running experiments, and invited speakers had great expectations for the early realization of the Hyper-Kamiokande. In addition, since it is just 30 years from the neutrino observation at SN1987A, its commemorative lecture and anniversary were also held.

Participants to the workshop

The commemorative anniversary of 30 years from the neutrino observation at SN1987A. The data printout and magnetic tape which are recorded the SN1987A neutrinos were exhibited.

30 years after the detection of SN1987A neutrinos (Super-Kamiokande website)

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May. 2015

Construction and Development

A strength test of new photosensors has been commenced.

The depth of the megaton Hyper-Kamiokande detector has reached 48 m; therefore, the photosensors to be incorporated into the detector must definitely be able to withstand a high water pressure.

The new photosensors being developed for the Hyper-Kamiokande project have been greatly improved in terms of not only photodetection but also strength under a high water pressure. A strength test of these new photosensors has been commenced.

A new photosensor made of 50-cm-diameter glass has been placed into a metal cylinder, and the metal cylinder has been placed into a blue tank for a test under a high water pressure.

Thus far, we have tested a few photosensors and confirmed that they can withstand a water depth of over 100 m, which is over two times the depth of the Hyper-Kamiokande detector.

We aim to improve the capacity of the photosensors to resist a high water pressure based on the test results.

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Feb. 2015


The Inaugural Symposium of the Hyper-Kamiokande Proto-Collaboration and signing ceremony were held.

On January 31st, 2015, the Inaugural Symposium of the Hyper-Kamiokande Proto-Collaboration and signing ceremony were held at the Kashiwa-no-ha Conference Center.

The Hyper-Kamiokande project aims to address the mysteries of the origin and evolution of the Universe’s matter and to confront theories of elementary particle unification. To realize these goals, the project will combine a high-intensity neutrino beam from the Japan Proton Accelerator Research Complex (J-PARC) with a new detector based upon precision neutrino experimental techniques developed in Japan. The Hyper-Kamiokande project will be about 25 times larger than Super-Kamiokande, the research facility that was first to discover evidence for neutrino mass in 1998.

The symposium was held to commemorate and promote the proto-collaboration to advance the Hyper-Kamiokande project internationally. In addition, a signing ceremony marking an agreement to promote of the project between the Institute for Cosmic Ray Research (ICRR) of the University of Tokyo and the Institute of Particle and Nuclear Studies of the High Energy Accelerator Research Organization (KEK) took place during the symposium.

The symposium was attended by more than 100 Hyper-Kamiokande researchers, including an international steering committee and an institutional board of representatives with members from 13 countries to celebrate the event.

The symposium commenced under the chairmanship of Prof. Akira Konaka (TRIUMF/RCNP). Next, an overview of the Hyper-Kamiokande project was provided by Prof. Masato Shiozawa (Univ. of Tokyo). Prof. Takashi Kobayashi (KEK) described the J-PARC neutrino beam facility. Prof. Francesca di Lodovico (Queen Mary Univ. of London) then addressed the International proto-collaboration of the Hyper-Kamiokande project. Finally, Prof. Chris Walter (Duke Univ.) delivered a talk on the history of international cooperation since the original Kamiokande experiment.

Subsequently, the Institute for Cosmic Ray Research (ICRR) of the University of Tokyo and the Institute of Particle and Nuclear Studies of the High Energy Accelerator Research Organization (KEK) signed a memorandum of understanding for cooperation on the Hyper-Kamiokande project.

When Prof. Tsuyoshi Nakaya (Kyoto Univ.) announced the establishment of the Hyper-Kamiokande proto-collaboration, the hall was filled with great applause.

Finally, all members of the proto-collaboration took group photos and renewed their determination to realize the Hyper-Kamiokande experiment.

Programs, Presentations and MoU

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Feb. 2015


The 6th Open Meeting for the Hyper-Kamiokande Project was held.

From January 28 to January 31, 2015, the 6th Open Meeting for the Hyper-Kamiokande Project was held at the Kavli IPMU at the Kashiwa Campus of the University of Tokyo.

More than 120 researchers participated in the meeting and lively discussions were conducted.

On the last day, the laboratory for new photodetectors at the ICRR, Univ. of Tokyo was open to collaborators. The proof-of-concept experiments for the new photodetectors were explained.

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