Researchers have successfully synthesized a strange but short-lived lambda resonance known as Λ(1405) for the first time.
Scientists at Osaka University were part of a particle accelerator experiment that produced a strange, highly unstable particle, and determined its mass. This could contribute to a better understanding of the inner workings of super-dense neutron stars.
The Standard Model of particle physics states that most particles are composed of groups of only six kinds of fundamental entities called quarks. However, there are still many unsolved mysteries, one of which is Λ (1405), the strange but fleeting lambda resonance. It was previously thought to be a specific combination of three quarks — up, down, and odd — and gaining insight into their composition could help reveal information about the incredibly dense matter in neutron stars.
Now, researchers from Osaka University are part of a team that succeeded in synthesizing Λ(1405) for the first time by combining K with– Meson and proton and determine their combined mass (mass and width). The letter K– Mesons are negatively charged particles that contain strange quarks and antiquarks.
Schematic illustration of the reaction used to synthesize Λ(1405) by combining K- (green circle) with a proton (dark blue circle), which occurs in the nucleus of the deuteron. Credit: Hiroyuki Nomi
The most common proton that makes up the matter we are familiar with has two up quarks and one down quark. The researchers demonstrated that it is best to regard Λ(1405) as a transient binding state for K.– Mesons and protons, in contrast to the three excited states of the quarks.
In a study recently published in Physics letter b, the group describes an experiment they conducted at the J-PARC accelerator. K– Mesons are fired at deuterium targets, each containing one proton and one neutron. In a successful reaction, AJ– The meson gives off a neutron, which then combines with a proton to give the desired Λ(1405). Formation of the K bound state– Mesons and protons are only possible because neutrons carry some energy,” said study author Kentaro Inoue.
called odd baryons Λ (1405) and a schematic illustration of the evolution of matter. Credit: Hiroyuki Nomi
One aspect that has baffled scientists about Λ (1405) is its extremely light overall mass, even though it contains strange quarks, which are about 40 times heavier than the upper quarks. During the experiment, the research team managed to measure the mass of the Λ(1405) complex by observing the behavior of the decay products.
(Top) Measurement of the reaction section. The horizontal axis is the backward energy of K- and proton collisions converted to mass values. Major reaction events occur at mass values that are lower than the mass sum of K- and protons, which alone indicates the presence of Λ(1405). The data measured by scattering theory are reproduced (solid lines). (Bottom) K distribution– and the proton scattering amplitude. When squared, it corresponds to the cross section of the reaction and is generally a complex number. The calculated value corresponds to the measured data. When the real part (solid line) exceeds zero, the value of the imaginary part reaches its maximum value. This is a typical distribution of the resonance states, and defines the mass of the complex. The arrows show the actual part. Credit: 2023, Hiroyuki Nomi, leading position Λ(1405) measured in d(K–n) pS reaction, Physics letter b
“We hope that advances in this type of research will lead to more accurate descriptions of the super dense matter at the heart of the planet.[{”attribute=””>neutronstar”saysShingoKawasakianotherstudyauthorThisworkimpliesthatΛ(1405)isanunusualstateconsistingoffourquarksandoneantiquarkmakingatotalof5quarksanddoesnotfittheconventionalclassificationinwhichparticleshaveeitherthreequarksoronequarkandoneantiquark[{”attribute=””>neutronstar”saysShingoKawasakianotherstudyauthorThisworkimpliesthatΛ(1405)isanunusualstateconsistingoffourquarksandoneantiquarkmakingatotalof5quarksanddoesnotfittheconventionalclassificationinwhichparticleshaveeitherthreequarksoronequarkandoneantiquark
This research may lead to a better understanding of the early formation of the Universe, shortly after the 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.
