Astral Alchemy: Researchers encounter the mysterious Baryon

Scientists at Osaka University have been part of an explosion experiment that produced a strange and very weak substance, and determined its mass. This could contribute to a better understanding of the inner workings of high-mass neutron stars.

The Standard Model of Physics states that most particles are made up of only six basic types of particles called quarks. However, there are still many unsolved mysteries, one of which is Λ(1405), an extreme case of Lambda. It was previously believed to be a specific combination of three quarks – up, down, and strange – and gaining an understanding of its composition could help uncover information about the larger matter in the universe. neutron stars.

Now, researchers from Osaka University are part of a team that has succeeded in growing Λ(1405) for the first time by combining K.^– meson and proton and determine its complex number (mass and width). AK^– A meson is a negatively charged particle that contains a strange quark and an antiquark.

An example of the system used to synthesize Λ(1405) by combining a K- (green circle) with a proton (dark blue circle), which occurs in the nucleus of a deuteron. Credit: Hiroyuki Noumi

The most common proton that makes up the matter we use has two quarks up and down. The researchers point out that Λ(1405) is best considered as a temporary binding of K^– meson and proton, as opposed to the three-quark excited state.

In a recently published study a Physics Letters B, the group described their experiments at the J-PARC accelerator. K^– Mesons are fired in deuterium, each with one proton and one neutron. In a successful response, K^– The meson emits a neutron, which then combines with a proton to form the desired Λ(1405). “Formation of the binding state of K.”^– The meson and the proton are not possible simply because the neutron takes some of the energy,” said the study’s author, Kentaro Inoue.

The mysterious baryon called Λ(1405) and its evolutionary shape. Credit: Hiroyuki Noumi

One of the things that has puzzled scientists about Λ(1405) is its extremely light size, despite the fact that it contains a strange quark, which is about 40 times as massive as an earthquake. During the experiment, the research team managed to measure the complex parameter of Λ(1405) by observing the behavior of the corrosion material.

(Top) Cross-sectional response measurements. The horizontal axis is the K- and proton collision recovery energy converted to mass values. Major reaction events occur at mass values ​​lower than the sum of K- and proton, which itself indicates the presence of Λ(1405). The measured data are reproduced by the diffusion theory (solid line). (Lower) Distribution K^– and proton scattering amplitudes. When squared, these correspond to the cross section of the reaction and are generally complex numbers. The statistics correspond to the measured data. When the real part (solid line) crosses 0, the value of the imaginary part reaches its maximum value. This is the characteristic distribution for a resonance state, and determine the complex mass. The arrows indicate the original part. Credit: 2023, Hiroyuki Noumi, Pole position of Λ(1405) measured in d(K)^–,n) πΣ reactions, Physics Letters B

“We expect that progress in this type of research can lead to a detailed description of the ultra-high-density structure that exists in the source[{” attribute=””>neutron star,” says Shingo Kawasaki, another study author. This work implies that Λ(1405) is an unusual state consisting of four quarks and one antiquark, making a total of 5 quarks, and does not fit the conventional classification in which particles have either three quarks or one quark and one antiquark.

This research may lead to a better understanding of the early formation of the Universe, shortly after the Big Bang, as well as what happens when matter is subject to pressures and densities well beyond what we see under normal conditions.

Reference: “Pole position of Λ(1405) measured in d(K−,n)πΣ reactions” by S. Aikawa, S. Ajimura, T. Akaishi, H. Asano, G. Beer, C. Berucci, M. Bragadireanu, P. Buehler, L. Busso, M. Cargnelli, S. Choi, C. Curceanu, S. Enomoto, H. Fujioka, Y. Fujiwara, T. Fukuda, C. Guaraldo, T. Hashimoto, R.S. Hayano, T. Hiraiwa, M. Iio, M. Iliescu, K. Inoue, Y. Ishiguro, S. Ishimoto, T. Ishikawa, K. Itahashi, M. Iwai, M. Iwasaki, K. Kanno, K. Kato, Y. Kato, S. Kawasaki, P. Kienle, Y. Komatsu, H. Kou, Y. Ma, J. Marton, Y. Matsuda, Y. Mizoi, O. Morra, R. Murayama, T. Nagae, H. Noumi, H. Ohnishi, S. Okada, Z. Omar, H. Outa, K. Piscicchia, Y. Sada, A. Sakaguchi, F. Sakuma, M. Sato, A. Scordo, M. Sekimoto, H. Shi, K. Shirotori, D. Sirghi, F. Sirghi, K. Suzuki, S. Suzuki, T. Suzuki, K. Tanida, H. Tatsuno, A.O. Tokiyasu, M. Tokuda, D. Tomono, A. Toyoda, K. Tsukada, O. Vazquez-Doce, E. Widmann, T. Yamaga, T. Yamazaki, H. Yim, Q. Zhang and J. Zmeskal, 20 December 2022, Physics Letters B.
DOI: 10.1016/j.physletb.2022.137637

The study was funded by the Japan Society for the Promotion of Science, Ministry of Education, Culture, Sports, Science and Technology.