Kamioka ObservatoryICRR, The University of Tokyo

Takuya Tomiya

3rd year PhD student in the Faculty of Science & Graduate School of Science, The University of Tokyo (As of April 2025)

Searching for phenomena that no one has discovered yet, with my own hands

My research focuses on the search for proton decay, a process deeply connected to fundamental questions such as “How did the universe begin?” and “Will the universe have an end?” Protons make up the matter all around us̶including the stars in the night sky and our own bodies. I analyze data from Super-Kamiokande (SK) to study whether protons can actually decay.
Proton decay is predicted by theories in particle physics, but despite extensive searches over the years, no evidence has been found yet. A significant difficulty in this search is that neutrino interactions, which act as background events, closely resemble proton decay signal events, making it hard to tell them apart in the analysis. To achieve higher precision than previous analyses, I study the detailed behavior of particle interactions inside the SK detector and search while considering and exploring new ideas. It is very exciting and rewarding to search for a phenomenon that no one has yet discovered. In addition, we are also introducing machine learning methods such as artificial intelligence (AI) into parts of the analysis, aiming for significant performance improvements.

Not only can I focus on my research while staying at the Kamioka Observatory to study and discuss the analysis with collaborators, but I also enjoy interacting with students from other experiments and engaging in discussions beyond my field. For a refreshing break after intensive research, Toyama, about a 20-minute drive away, offers delicious sushi and other fresh seafood, making it an ideal place to relax.

Yoshino Kaminaga

2nd year PhD student in the Faculty of Science & Graduate School of Science, The University of Tokyo (As of April 2025)

World-Leading Dark Matter Search using Knowledges from Kamioka Observatory

I’m working on the XENONnT experiment, which aims to reveal the nature of dark matter. The detector is located in the underground laboratory at Gran Sasso in Italy, a mountain with an atmosphere similar to that of Kamioka. You may wonder why I’m involved in an Italian experiment while I belong to Kamioka group. Previously, the XMASS dark matter experiment was conducted in Kamioka, and many of its members, along with their expertise, have joined XENONnT. That’s why ICRR members are contributing to XENONnT from Kamioka. Dark matter is expected to exist based on multiple astrophysical observations, yet it remains undetected and mysterious. Dark matter accounts for five times the amount of ordinary matter in the universe. What is this unknown substance that fills our universe? This curiosity led me to XENONnT. In XENONnT, we use xenon (Xe), an element that emits light when it interacts with other particles. We have 8.6 tons of Xe waiting for a rare interaction with dark matter. The analysis is carried out in collaboration with researchers from many countries all over the world. With our large and low-noise detector and advanced techniques, we’re truly at the frontier of dark matter research.

I currently live in Toyama and mainly work in Kamioka, and visit the LNGS several times per year for the shifts and meetings. Kamioka is a special environment for students—quiet, focused, and surrounded by physicists passionate about the universe. While I am working for XENON, I also learn quite a lot from the Super-Kamiokande and Hyper-Kamiokande teams. I hope you’ll join us and explore new physics together!

Kotaro Otsuzuki

2nd year of master’s course in the Faculty of Science & Graduate School of Science, The University of Tokyo (As of April 2025)

I’m currently participating in the XENONnT experiment, a direct dark matter search conducted at the Gran Sasso National Laboratory in Italy. My research focuses on two main topics. The first is the analysis of liquid xenon purity. Since XENONnT uses electro n signals to distinguish incoming particles, impurities in the liquid xenon can absorb electrons and interfere with accurate detection. Maintaining high purity is therefore critical for the experiment’s sensitivity. The second topic is neutron-based detector calibration. Neutrons interact wi th xenon nuclei in ways similar to how dark matter is expected to interact. Studying these responses helps us better understand and improve the detector’ s performance. Both themes are essential for exploring the nature of dark matter and make this research deeply rewarding. Although the experiment is based in Italy, I spend most of my time in Kamioka, Japan, where I conduct related research and development. I return to the Tokyo area for about a week each month to meet friends and recharge. Kamioka is surrounded by nature and has a warm local community, making it a great place to focus on research.

The XENONnT experiment is continuously improving its sensitivity, and the next-generation XLZD experiment is expected to start within a few years. If you’re even a little curious about dark matter, I encourage you to join us in this exciting field!

Yuki Kanemura

3rd year PhD student in the Faculty of Science & Graduate School of Science, The University of Tokyo (As of April 2024)

Try to achieve more results with the methods which no one has tried ever.

have two studies. One is an experiment detecting Supernova Relic Neutrino (SRN) with a Neural Network. SK- Gd experiment started in July.2020. Thanks to that, we could achieve increasing Super-Kamiokande (SK) sensitivity to SRN. We also need an algorithm that could efficiently select the SRN signals and reject noise events. Therefore, I am trying to distinguish them with a Neural Network, which is one of the machine learning.
The other is the automation of the measurement of radon concentration in SK water. Because radon is one of the BG events for Solar neutrino analysis, we must remove it as much as possible and monitor it in SK water. As part of that work, we sample the water from the SK detector, give the radon off to pure air, and measure the concentration. By automating the work with an automatic system and ladder circuit, I try to make the work easier while maintaining accurate measurements.
Both studies are rewarding because I use methods that no one has tried in SK. 。

I live in an apartment several ten minutes from the institute. It may be inconvenient in terms of transportation, etc., but we could control SK, the Number One detector in Japan, to take and analyze the data. It is the best place for people who would like to do cosmic particle physics experiments hard. I am looking forward to doing the unique studies in SK with you. Thank you.

Shintaro Miki

1st year PhD student in the Faculty of Science & Graduate School of Science, The University of Tokyo (As of April 2022)

Enjoy forms of trial and error that nobody has ever done before

I am mainly conducting two studies, one of which is the testing of photosensors manufactured for Hyper-Kamiokande. We place the photosensors in a darkroom to test the response when a weak light is applied. Photosensors, one of the essential components of Hyper-Kamiokande, affect the overall performance of the detector and are very interesting to investigate. Further, it is exciting to imagine that the light sensor that we are investigating now will capture the light from neutrinos at the bottom of Hyper-Kamiokande in a few years. Another study is the analysis of atmospheric neutrino oscillations at Super-Kamiokande. We aim to observe neutrinos more accurately using the information from neutrons, which are now more visible due to the dissolution of gadolinium in the water of the detector in 2020. It is a series of trial and error as nobody has ever done this before. However, I enjoy seeing the results of what we have tried.

When I entered the doctoral course, I moved to an apartment about 20 minutes by car from the research institute, and I plan to make my life as a researcher in Kamioka more fulfilling. There is even no convenience store around the research center, but when I explore nature here and there, I enjoy the feeling of returning to elementary school. While walking around, I talk with neighboring residents and enjoy the relaxed lifestyle unique to countryside areas.

I hope that we can work together with many people to conduct research that will bring out the potential of the Super-Kamiokande and Hyper-Kamiokande.