Thanks to the improved beam and new detectors, the T2K International Collaboration, a world leader in neutrino oscillation research, has begun collecting more accurate data than ever before. ELTE physicists are also involved in the work.
Neutrinos are the most common particles in our universe. It has no electric charge, and we don't know its mass yet, but there is already evidence that it has zero mass and that it changes from one “flavor” to another. This phenomenon is called neutrino oscillation. They are now used by particle accelerators to study the physics of neutrino oscillations more precisely.
Nearly 600 researchers from 78 research institutes in 14 countries are participating in the international T2K collaboration. During the experiments, a high-intensity neutrino beam produced at the Japan Proton Accelerator Research Center (J-PARC) in Tokai, located on the east coast of the island nation, is delivered to detectors located 280 meters away and to the Super-Kamiokande Neutrino Observatory in Gifu, on After approximately 300 km; Their density and composition are measured at both places, and conclusions are drawn about their properties from the data thus obtained. T2K demonstrated for the first time in the world the appearance of electron neutrinos in a muon neutrino beam and found signs of matter-antimatter asymmetry in the neutrinos.
Neutrinos are produced from the decay of pions or other particles resulting from interactions between proton beams and a graphite target. To understand their properties and discover why the universe lacks antimatter, it is necessary to produce a large number of neutrinos and gain a deeper understanding of the interactions between neutrinos and nuclei. – says Yoshikazu Nagai, Assistant Professor in the Department of Atomic Physics ELTE, who heads the beam group in the T2K collaboration.
At the end of 2023, T2K began a new phase of the experiment, in which many tools were improved or replaced. J-PARC has upgraded the main ring accelerator to increase the power of the proton beam. The collaboration has also developed its instruments, which are fundamental to the creation of neutrinos, with which a stable neutrino beam is generated with a record high proton beam power (about 710 kW), achieving an increase of about 40% compared to the previously upgraded case. On December 25, the neutrino beam was already working with a 760-kilowatt proton beam, even larger than planned.
The pulsating electromagnetic horn, the heart of the neutrino generator, has also been improved. “The current applied to the three electromagnetic horns has been increased from 250 kA to 320 kA by upgrading the power supply and other components, thus increasing the efficiency of focusing starting particles, such as pions generated at the target,” explains Pingal Dasgupta, a postdoctoral fellow in the Department of Atomic Physics at ELTE, which contributed to the experimental process: “This has improved the quality of the neutrino beam delivered to the Super-Kamiokande detector, while increasing the number of neutrinos observed by an additional 10%,” as a beam expert.
Through October 2023, T2K has also operated three new types of neutrino detectors near the neutrino-producing target, which measure neutrino interactions more precisely than before. The newly installed detectors are the SuperFGD, which detects orbits around the neutrino interaction point inside the detector, the High-Angle TPC, which measures the momentum of emitted particles over a wide angular range, and the Time-of-Flight, which can detect incoming or outgoing particles and identify particles. By adding gadolinium to the water, the researchers also improved the neutron sensitivity of the Super-Kamiokande detector.
T2K began its measurements using the enhanced neutrino beam in December 2023, and it is already possible to observe neutrino event candidates from the newly acquired data. As a result of the update approx. The number of observed neutrino interactions can increase threefold, which also means a reduction in measurement errors caused by statistical fluctuations (so-called “statistical errors”). The new detector is able to detect large-angle scattering of neutrino interactions, and this will also lead to a better understanding of neutrino-nuclei interactions.
With the improvements, the T2K team will be able to make more precise measurements, so it can continue to investigate the behavior of neutrinos and antineutrinos with the hope of achieving important results. The high-energy proton accelerator and neutrino experiment J-PARC is expected to play a key role in the next phase of neutrino research, and the new data will help solve the mystery of missing antimatter from our universe.
Within the framework of the experiment, the neutrino physics research group ELTE led by Yoshikazu Nagai continues to search for evidence of CP violation in the lepton sector, among other things.