Scientists have discovered the strongest isospine hybridization

Recently, Xu Xinxing, a researcher at the Institute of Modern Physics of the Chinese Academy of Sciences, and his collaborators carried out high-precision measurement of the decay properties of nuclear phosphorus-26 in the proton drip line relying on the Lanzhou heavy ion accelerator large scientific device, and found the strongest isospin mixing phenomenon in β decay, which directly challenges people’s understanding of the interaction force of atomic nuclei. The research results were published in Physical Review Letters on December 8 as a highlight article editor’s recommendation.

Symmetry is ubiquitous in nature and is a central concept in modern physics. Symmetry breaks often contain new physics. In 1932, Heisenberg proposed the concept of isospin, which regarded protons and neutrons as two states of the same particle. In the case of strict symmetry of the isospin, the Fermi transition in the β decay is only distributed to the isospin similarity.

However, the isospin symmetry breaking leads to a cleavage of Fermi transition strength, not only to the isospinic similarity, but also to the excited state near the isospinic similarity. Previously, only a few cases of such isospin mixing phenomena were found experimentally, and the isospin mixed matrix elements were all less than 50 keV, which could basically explain these phenomena in theory.

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β delayed two-proton emission Image from Jian Hao

Based on the Lanzhou heavy ion accelerator radioactive beam line (HIRFL-RIBLL1), the researchers carried out correlation measurements of the β delayed twoproton emission of phosphorus-26 in the peculiar nucleus (Figure 1), and for the first time found two highly excited states 11912 keV and 13380 keV near the isospinic similar state of silicon-26.

Based on high-precision experimental data, the researchers obtained that the isospin hybrid matrix element of silicon-26 isospin similarity state 13055 keV and high excited state 13380 keV is 130 keV, which is the strongest isospin hybrid phenomenon in β decay found in experiments so far, and the physical cause behind it may be weak binding or large deformation effect. However, the isospin-mixed matrix elements calculated by various theoretical models for phosphorus-26 decay are less than 30 keV, which is much smaller than the experimental value.

Xu Xinxing introduced that the experimental results pose a strong challenge to the existing theoretical research and will promote the development of the theory of nuclear interaction force.

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Partial decay diagram of phosphorus-26 in the peculiar nucleus Figure from Physical Review Letters

It is understood that this research is led by the Institute of Modern Physics of the Chinese Academy of Sciences, and 23 scientific research units at home and abroad, such as Sun Yat-sen University and Shanghai Jiao Tong University, are cooperatively completed. This work has been supported by research funds such as the Strategic Leading Science and Technology Project of the Chinese Academy of Sciences (Category B), the National Key R&D Program, the Young Team Program of Stable Support for Basic Research Fields of the Chinese Academy of Sciences, the High-end User Project of Lanzhou Heavy Ion Accelerator National Laboratory and the National Natural Science Foundation of China. (Source: China Science News, Liu Runan, Gan Xiao)

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