On July 3th, 23, the Institute of High Energy Physics of Chinese Academy of Sciences announced at a news briefing that a new particle had recently been discovered by the International Cooperation Group of Beijing Spectrometer. The Beijing Spectrometer Cooperation Group is composed of the Institute of High Energy Physics, 17 universities and research institutions in China, and physicists and graduate students from the United States, Japan, South Korea and Britain.
this new particle was discovered by the cooperative group by analyzing the case data of 58 million J/ψ particle decay, and during the process of analyzing the radiation decay of charm particles to positive and negative protons. The paper of this research achievement has been published in the most authoritative and influential journal of the world, Physics Review Express (July 23).
The news of the discovery of new particles immediately attracted wide attention from all sides. People want to know what kind of particle it is. What is the physical significance of this new discovery? Is this another breakthrough achievement? To answer these questions, you need to know something about particle physics.
at first, people divided particles into three categories according to their mass, and gave each category a general name. Large masses are called baryons, such as protons and neutrons; Small masses are called leptons, such as electrons and neutrinos with almost no mass; The size between the two is called meson, such as π meson. Later, according to the property that baryons and mesons are strongly dominated, they are collectively called hadrons. In the early days, some physicists speculated that mesons were composed of proton and antiproton bound States, but they were replaced by quark models later. In 1964, gherman and others put forward the quark model of hadron structure. In the quark model, baryons are composed of three quarks, while mesons are composed of positive and negative quarks. In the initial quark model, there are only three kinds of quarks: U, D and S. In 1974, after the J/ψ particle was discovered independently by Professor Ding Zhaozhong and Professor Richter, the theory of three quarks could not explain this long-lived meson, so the fourth quark, charm quark C, was introduced, and J/ψ particle was composed of a charm quark (C) and an anti-charm quark. After that, the fifth quark bottom quark B and the sixth quark top quark T were introduced. By 1995, all six quarks predicted in theory had been discovered by experiments.
J/ψ particles have a high yield in electron-positron collisions, and the decay of J/ψ particles is an ideal way to study hadron spectra and find new particles. The case of 58 million J/ψ particles obtained by Beijing Spectrometer is about one order of magnitude higher than other similar experimental data in the world, which creates a good foundation for physical analysis. The life of this new particle is very short, so it is also called * * * vibration state. The so-called * * vibration state is an unstable hadron, which contains various quantum numbers of hadron, such as spin, parity and isospin. * * * Vibrating particles generally decay by force, so their life span is very short, about 1-2-1-24 seconds. According to the uncertainty principle of energy and time in quantum mechanics, unstable particles have no definite mass, and the degree of uncertainty is called width (9), which is inversely proportional to the lifetime (τ) of particles (9=η/τ). The width of * * * vibrating particles can be as high as several hundred MeV, so the newly discovered particles are very narrow. Although the mass of this newly discovered * * * vibrational state is slightly less than the sum of the masses of protons and antiprotons, it is precisely because the mass of particles in the * * * vibrational state has a certain width that a small number of particles in this * * vibrational state are still larger than the sum of the masses of protons and antiprotons, and decay into protons and antiprotons. The experimental study of particle physics has observed similar phenomena in the decay of several particles. As soon as the news of this new discovery came out, J.Ellis, a famous theoretical physicist at CERN, commented in an article on the latest international progress: "This discovery and other new experimental results in the world are amazing and of great significance to the development of strong interaction theory." Professor Li Zhengdao, winner of the Nobel Prize in Physics, also sent a letter of congratulations to Gao Neng Institute, in which he commented: "This is a very important achievement and a meaningful work in physics."
Finding multi-quark states has always been an important goal of international high-energy physics experiments. In the hundreds of meson * * * vibrational states and baryon * * * vibrational states discovered early in the experiment, there is no conclusive evidence of multi-quark states. Recently, several international experimental groups have made remarkable progress in this field. However, in the experiment on the Beijing Electron-Positron Collider, the newly discovered particle is difficult to be attributed to the usual quark-antiquark combined state because of its unique properties, especially its narrow width, so it is speculated that it may be a multi-quark state. Some physicists think that the discovered * * * vibrational state particles may be baryon anti-baryon bound states (a kind of multi-quark states).
extensive and close international cooperation is the basic feature of high-energy physics research. Since its design, the Beijing Electron Positron Collider has been strongly supported by the international high-energy physics community, especially Professor Li Zhengdao. For more than 2 years, the China Academy of Sciences and the US Department of Energy have held talks every year, focusing on their cooperation in the Beijing Electron Positron Collider and the Beijing Spectrometer. The National Natural Science Foundation of China has always given strong support to the research work of Beijing Spectrometer. After the upgrading of Beijing Electron Positron Collider and Beijing Spectrometer in early 1999, the overall comprehensive performance has been greatly improved. The amount of data obtained every day is 3-4 times that before the upgrading, and the data quality is good. The international cooperation group of Beijing Spectrometer has conducted in-depth and detailed analysis and research on these data, and the discovery of new particles this time is one of the major physical achievements of these data.
Beijing Electron Positron Collider and Beijing Spectrometer operate in the energy region of 2 billion-5 billion electron volts. Although this energy is not very high in the world, they belong to the precision measurement frontier of one of the two frontiers of international high-energy physics experimental research, which is of great physical significance, and new major achievements are constantly emerging, becoming a new hot spot of international high-energy physics research, and the competition is fierce. The relevant state departments have approved the major transformation of the Beijing Electron Positron Collider and the Beijing Spectrometer. It is expected that the data provided by the accelerator will increase by two orders of magnitude, and the performance of the detector will also be greatly improved. After the completion of this major transformation, the Beijing Electron-Positron Collider will continue to maintain its international leading position in the research fields of charm quark physics and hadron spectroscopy.
new discoveries are also new challenges. Scientists from the Institute of High Energy said: At present, our research results only confirm the existence of this new particle. To finally clarify the basic properties and physical significance of this new particle, Chinese and foreign scientists from the Beijing Spectrometer Cooperation Group need to do a lot of in-depth and detailed data analysis, and they need to work closely with theoretical physicists at home and abroad to study it carefully, and may also need more data to finally answer these questions. A few days ago, Chinese and American scientists discovered a new particle for the first time at the Beijing Electron-Positron Collider. The person in charge of the Institute of High Energy of the Chinese Academy of Sciences said that various analytical studies have confirmed that this particle is a new particle, and it may be a multi-quark particle predicted by scientists Fermi and Yang Zhenning decades ago. At present, Chinese and foreign physicists are doing more in-depth research and discussion on the properties and decay characteristics of this new particle theoretically and experimentally.
on July 1st, Beijing time, it was reported that one of the most elusive particles in the standard model of particle physics escaped people's sight again, which either indicated that the Higgs particle was suppressed or proved that it did not exist at all. This is a crucial step to understand why there are agglomerates in our universe, but the latest forecast of Fermilab, the most authoritative national accelerator laboratory in the world, shows that this research will be difficult to produce results for at least the next six years.
On July 3rd, Beijing time, Japanese physicists have discovered a new subatomic particle, which consists of five quarks instead of the usual two or three quarks. Theorists originally speculated that matter might be composed of four or more quarks, but experiments conducted in the past 3 years have shown that it is difficult to confirm this speculation. This discovery, which will be published in the July 4th issue of Physical Review, is bound to cause a sensation in the field of particle physics research, and will also help deepen people's understanding of the early universe.