IFIRSE officially join the Super-Kamiokande experiment

On June 5th 2021, members of the Super-Kamiokande experiment cast their votes to approve the participation of the Institute for Interdisciplinary Research in Science and Education (IFIRSE) , Quy Nhơn, Việt Nam along with 40 institutes from 10 countries including Japan, the United States, Korea, China, Poland, Spain, Canada, United Kingdom, Italy, and France..

The Super-Kamiokande experiment. Taken from here

Super-Kamiokande (SK) is the World’s Largest Underground Neutrino Detector. This detector has a cylindrical shape of 41.4m in height and 39.3m in diameter containing 50,000 tons of ultra-pure water and instrumenting 13,000 photo-multipliers which is very sensitive to detect the weak interaction. A large amount of water is to increase the probability of particle interaction. Also, placing the detector 1000m underground allows SK to shield from the cosmic ray background and other natural and artificial background sources. SK construction was started in 1991, and a continuous operation has happened since 1996. In 2021, SK marked 25 years of operation with a number of revolutionary discoveries for humankind.

  • In 1998, SK discovered a so-called neutrino oscillation phenomenon with the atmospheric neutrinos (generated when the cosmic rays interact with the Earth’s atmosphere). The discovery is significant to modern physics since it shows that neutrino has mass and thus provides a piece of tangible evidence and so far unique for the incompleteness of the Standard Model of the elementary particles, smallest blocks made up our Universe. This discovery contributed to the physics Nobel prize in 2015 to Prof. Takaaki Kajita (shared with Prof. Arthur B. Mc. Donald) [1]
  • In 2001, SK confirmed the neutrino oscillation with neutrinos coming from the Sun [2] . Neutrino is created inside of the Sun via the fusion reaction 4p+ -> He +2e+ +2 νe + 26.7MeV energy . About 66 billion solar neutrinos are passing through 1cm2 in 1 second. However, you have no feeling of the neutrino existence since neutrino interacts weakly with matter. The study of solar neutrino is valuable not in terms of physics (such as confirmation of energy generation mechanism in the Sun, universality of the neutrino oscillation...), but also concerning a timely monitor of the Sun status. Neutrino induced inside of the Sun’s core takes about 8 minutes to reach the Earth, while the sunlight we see from the Earth is actually created about 100,000 years in the core. In other words, with light, we see the Sun in the past; with neutrino, it’s the Sun of the present.
  • In 2011, SK played a role as the far detector of the T2K experiment to detect a new channel of neutrino oscillation with neutrino sourced produced from the accelerator. This discovery contributed directly to the breakthrough prize in 2016 for T2K along with other neutrino experiments (SK, SNO, KamLAND, K2K, and DayaBay) [3]. This channel of neutrino oscillation is now further investigated by T2K (in Japan), NOvA (in the US), and under constructing experiments Hyper-Kamiokande (in Japan) and DUNE (in the US) to search for the CP (C for charge-conjugation and P for parity-reversal) violation in neutrinos. In 2020, the T2K experiment [4] published a hint at the CP violation in neutrino with a confidence level of 99.7%. If the more precise measurement verifies this, this symmetry violation can explain the matter-antimatter asymmetry in the observed Universe.

Furthermore, SK is the world-leading experiment in searching for Proton decay. In the Standard Model, proton decay is prohibited. However, this process is allowed by the class of the Grand Unified Theory, which is a dream of the physicists to unify all kinds of interactions with a single simple equation. Up-to-date, SK with 25-year data collection find no evidence of this process, and the proton lifetime is estimated to be larger than 1034 years [5], much larger than the age of the Universe 1010 years.

In August 2020, SK [6] introduce gadolinium into the detector, open a a new era called SK-Gd. This rare element helps to enhance the detection of neutrino induced from the interaction, and thus increase the probability to search for the neutrino from the supernova. Supernova is among of the most fascinating astrophysical phenomena and physicists believe that heavy elements are produced in the core of the start and distribute scatteringly in the Universe when a supernova happen. Thus study of the supernova is important for our understanding of the star dynamics and origin of the heavy elements on the Earth. On average, there is thousands of supernova happen per hour in the whole Universe. Most of these happens far from our galaxy and thus can not be observed directly. Our present knowledge, 99% of binding energy of the start will be released via a tremendous flux of neutrino when they die. These neutrinos travel in any direction in the Universe and with many supernova in the past which build up a diffuse supernova neutrino background in the universe. And these supernova reach to the Earth continuously but invisibly. This kind of neutrino is not discovered yet and SK-Gd is among the best to detect this kind of neutrinos.

Neutrino Group at ICISE officially formed in 2017 with a tremendous help from Japanese neutrino physicists and the Rencontre du Vietnam, contribute to the international neutrino experiment called T2K since then. By joining SK, our group hope to contribute to the search for the diffuse supernova neutrinos and the proton decay. Besides, our ultimate is to build and experimental particle and nuclear laboratory in ICISE for the research and education purpose. We are very welcome and try our best to support students working with our group and join the international experiments such as T2K and SK. If you are interest, please contact us, or register for the Internship program at ICISE. You also can register for the fifth Vietnam School on Neutrinos (Aug. 29th-Sept. 9th, 2021) organized by Japanese neutrino physicists, Rencontres du Vietnam, and Neutrino Group at ICISE.

References
Contact

Dr. Cao Văn Sơn, email cvson@ifirse.icise.vn

@Neutrino, IFIRSE 2021