Researchers of the Instituto de Física Corpuscular (IFIC) at the Universitat de València, of the Institute for High Energy Physics at the Universitat Autònoma de Barcelona (UAB), and of the Universidad Autónoma de Madrid have contributed to reveal a basic property of neutrinos, which were not measured until now. It is an important step to learn whether neutrinos behave differently in their matter and antimatter forms. The findings appear on the cover of the Nature journal.
T2K (Tokai a Kamioka) is a particle physics experiment in Japan which deals with studying neutrino oscillations and includes research teams participating from twelve countries. T2K Collaboration has published new results, which now provide the world best measurement governing the matter–antimatter symmetry-violating phase in neutrino oscillations. For the first time, the experiment starts to reveal the basic property of neutrinos which has not been measured so far. This is an important step to learn whether neutrinos and antineutrinos behave differently and asymmetrically as described by the majority of the laws of physics in this field. Based on the data gathered until 2018, the results are published in a scientific journal Nature.
The majority of physical phenomena are described in terms of laws which predict a symmetric behaviour of particles for matter and antimatter. In terms of physics, this concept is called parity-reversal symmetry or simply CP symmetry. This symmetry is obviously not universal as proven by the current composition of the universe, the antimatter contents of which is very small. The Bing-Bang theory assumes that the universe was created with the identical amounts of matter and antimatter. But to arrive at the current state of affairs, a CP symmetry violation is essential.
Until now, the CP symmetry violation has only been observed in the physics of subatomic particles called quarks; yet, the magnitude of the violation is not big enough to explain the current composition of the universe. T2K seeks a new source of CP symmetry violation in neutrino oscillations which would manifest itself as a difference in the probability of neutrino and antineutrino oscillations.
T2K uses neutrino and antineutrino beams generated with a beam of protons at the Japan Proton Accelerator Research Complex (J-PARC) in Tokai, on the east coast of Japan.
The contribution of Spain
The T2K experiment has been constructed and operated as a result of the joint international collaboration between 500 scientists from 68 institutions in 12 countries (Canada, France, Germany, Italy, Japan, Poland, Russia, Spain, Switzerland, United Kingdom, United States, and Vietnam). For the most part, it is funded by the Ministry of Education, Culture, Sports, Science and Technology (MEXT) of Japan. Spain makes its contribution with three research groups, two of which - the Institute for High Energy Physics (IFAE, Barcelona) and the Instituto de Física Corpuscular (IFIC, Valencia) - have participated in the design, construction, and operation of the experiment for more than 15 years, thus, contributing to the study of neutrino oscillations. The Universidad Autónoma de Madrid has joined the research group recently. Spain has funded the research activity with the help of the Ministry of Economy and Competitiveness of the Catalan government (Generalitat de Catalunya) and with the support of the National Center for Particle, Astroparticle and Nuclear Physics (CPAN).
On behalf of IFIC - a joint centre of the Universitat de València and the CSIC - the article is signed by the scientists M. Antonova, A. Cervera, P. Fernández, A. Izmaylov, and P. Novella.
Reference:
“Constraint on the Matter-Antimatter Symmetry-Violating Phase in Neutrino Oscillations”
DOI: 10.1038/s41586-020-2177-0
Nature Vol. 580, pp. 339-344
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