T2K Experiment Enters New Phase of World-Leading Neutrino Oscillation Research

Data Taken with Upgraded Accelerator Neutrino Beam and New Detectors with Significantly Improved Sensitivity

Illustration of the upgraded neutrino production devices.

The T2K Collaboration, an international collaborative experiment involving approximately 570 researchers from 78 research institutions in 14 countries, has launched a new phase of an experiment developed to study neutrino oscillations using an enhanced neutrino beam and new near-detectors.

The T2K experiment sends neutrinos produced at the Japan Proton Accelerator Research Complex (J-PARC) in Tokai, Ibaraki, to the neutrino near-detectors and the Super-Kamiokande detector in Kamioka, Hida, Gifu, about 300 km away. The T2K experiment started taking data in 2010 and directly observed electron neutrino appearance for the first time in the world in 2013.

SUNY Distinguished Professor and Chair of Stony Brook University's Department of Physics and Astronomy Chang Kee Jung is the lead Principal Investigator of the T2K Collaboration for the United States.

"Absence of an antimatter or a matter dominated universe is one of the most profound mysteries in science that is directly related to our own existence," said Jung. "Discovery of CP violation in neutrinos is currently our best path to obtain a critical clue to this mystery. T2K has taken the first step in the quest of CP violation in neutrinos in 2020, and now with the upgraded J-PARC accelerator, neutrino beamline and the near detector, it is poised to take significant steps toward the discovery. I eagerly look forward to seeing what new data reveals in the next few years with a more powerful neutrino beam and new state-of-the-art detectors."

Upgraded second electromagnetic horn with improved cooling capacity to enable neutrino production by high-intensity proton beams.

"The neutrino is our most fascinating and mysterious fundamental constituent of matter," said Nobel Prize in Physics Laureate and Stony Brook University President's Distinguished Endowed Chair in Physics Professor Barry Barish. "It was proposed almost 100 years ago to explain the apparent mysterious disappearance of energy in nuclear beta decay. Since its experimental discovery, the mysterious neutrino has become both our most fascinating particle and a powerful probe of the fundamental laws of nature. The newly upgraded T2K experiment, a marvel of modern technology and large collaborative science, is poised to resolve puzzles and make new discoveries that result from the neutrinos having a very tiny unexplained mass."

Neutrinos are produced from decayed pions or other particles produced in interactions between proton beams and a graphite target. The KEK/J-PARC Center upgraded the J-PARC main ring accelerator, including the power supply for the main magnet, to increase the repetition rate of the proton beam from 2.48 seconds to 1.36 seconds, which supplies more protons to the neutrino production target. The T2K experimental group upgraded, modified, and exchanged instruments in the neutrino beam facility such as targets, electromagnetic horns, and beam monitors. The beam commissioning was started in November 2023.

The stable production of the neutrino beam has been successfully achieved at a record high beam power (about 710 kW), an increase of about 40 percent compared to before the upgrade. Furthermore, on December 25, the continuous operation of the neutrino beam has been successfully achieved at 760 kW, which is greater than the initial design beam power.

The heart of the neutrino generator is the electromagnetic horns. The current applied to the three electromagnetic horns was increased from 250 kA to 320 kA by upgrading the power supply and other components, thereby improving the focusing efficiency of parent particles such as pions produced at the target. This improves the quality of the neutrino beam delivered to the Super-Kamiokande detector while increasing the number of neutrinos observed by about another 10 percent.

In addition, the T2K Collaboration has started observation using new neutrino near-detectors at the Neutrino Monitor Building located 280 m downstream of the neutrino production target. By October 2023, three new types of detectors were installed. A new detector, SuperFGD with a mass of approximately 2 tons of sensitive volume, is located at the center of the upgraded detectors.

A photo of the new detectors.

The J-PARC high-intensity proton accelerator and neutrino experimental facility are expected to play a key role in the next generation of neutrino research. The new phase of the T2K experiment is an important step toward the next generation of experiments, and T2K is expected to continue to lead the world in neutrino research, unraveling the mystery of the missing antimatter from our universe.

The T2K experiment is supported by the Japanese Ministry for Culture, Sports, Science, and Technology (MEXT), and is jointly hosted by the High Energy Accelerator Research Organization (KEK) and the University of Tokyo's Institute for Cosmic Ray Research (ICRR). The T2K experiment was constructed and is operated by an international collaboration that includes U.S. institutions.

The current U.S. T2K collaborating team is composed of 14 institutions - Boston University; University California, Irvine; University of Colorado; Duke University; University of Housto; Lawrence Berkeley National Lab; Louisiana State University; Michigan State University; University of Pennsylvania; University of Pittsburgh; University of Rochester; South Dakota School of Mines and Technology; Stanford Linear Accelerator Center; and Stony Brook University - and is funded by the U.S. Department of Energy, Office of Science.

Most recently, a group of U.S. institutions participated in an upgrade of the T2K near detector as described above, and made significant contributions to the construction, installation and commissioning of the SuperFGD detector. The specific U.S. contributions to SuperFGD are: (1) Scintillator Cubes (Stony Brook University); (2) Wave Length Shifting Fibers (University of Rochester); (3) Photon Sensors (Louisiana State University); (4) Mechanical Structure (University of Colorado); (5) Electronics (Louisiana State University, University of Pennsylvania and University of Pittsburgh); and (6) Project Management (Stony Brook University).

Read the complete T2K press release in the Stony Brook Press Room.

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