Science and Technology Daily, Nanjing, July 10 (Reporter Jin Feng) The reporter learned from Nanjing Normal University on the 10th that at the 41st International Conference on High Energy Physics held on the 9th, CERN's Large Hadron Collider (LHC). The Compact Muon Coils (CMS) Collaborative Group reports the discovery of an exotic family of particles that may consist of four charm quarks.
Yi Kai, the head of the "Tsinghua-Nanjing Normal University" CMS team and a professor at Nanjing Normal University, introduced on behalf of the CMS cooperation team that these particles may be composed of four heavy-flavored quarks of the same kind, and the physical images are relatively simple and easy to understand.
"This is the first time that the Chinese experimental team has led the observation of possible all-charm tetraquark particles at the LHC, and it is also the first time that China has led the discovery of new particles in the CMS experiment." Yi Kai said.
Quark is an elementary particle, and there are currently known six types: up quark, down quark, strange quark, charm quark, top quark, and bottom quark.
"Particles are generally composed of 2-3 quarks. For example, mesons are composed of a quark and an antiquark, and baryons are composed of 3 quarks or 3 antiquarks. They are called traditional hadrons; but there is another class of particles that may be composed of The mixture of 4, 5 quarks or quark gluons is also called strange hadron because it is relatively rare." Yi Kai said.
Theorists have predicted the existence of traditional hadrons and exotic hadrons decades ago, but only in the last 20 years have scientists experimentally observed more explicit tetra- or penta-quark exotic hadrons.
"But the strange hadron family composed entirely of heavy-flavor quarks, that is, strange particles composed of charm quarks or bottom quarks, has not been discovered before," Yi Kai said.
Based on analysis of all proton-proton collision data collected by CMS from 2016 to 2018, the CMS collaboration then observed a new family of particles in the invariant mass spectra of two charm quarks.
"Each of these particles may be composed of four sympathetic heavy quarks, and the three formants in this family are tentatively named X(6600), X(6900) and X(7300) according to their mass. X(6600) and The X(7300) particles were observed for the first time in the world." Yi Kai said.
"This is the first time to experimentally observe a family of strange particles that may be composed of pure heavy-flavor quarks." Yi Kai emphasized, "Although scientists have discovered dozens of strange hadrons in the past 20 years, what are these strange hadrons? How it formed is still a mystery. The strange family of particles discovered in this study, the composition of quarks is relatively simple, and we can then understand the formation mode of these particles based on this relatively simple combination."
Yi Kai said that the CMS detector collects a large amount of data and has a good mass resolution, and is expected to make more contributions in this direction.
The CMS cooperation group consists of more than 4,000 members from more than 50 countries and about 240 units. Among them, the Chinese group members are from the Institute of High Energy Physics, Chinese Academy of Sciences, Peking University, University of Science and Technology of China, Beihang University, Tsinghua University, Nanjing Normal University and many other units.
In recent years, the Chinese CMS group has made outstanding achievements in Higgs particle property measurement and multi-boson research.