According to a report on the official website of the European Organization for Nuclear Research (CERN) on the 25th, in a latest study, the ATLAS collaboration team at the Large Hadron Collider (LHC) used the Z boson, an electrically neutral carrier of the weak force, to determine the strength of the strong force with record accuracy (uncertainty less than 1%). Relevant papers have been submitted to the journal Nature Physics.
The Standard Model of particle physics states that there are four fundamental forces in nature: the strong force, the electromagnetic force, the weak force and gravity, of which the strong force that binds quarks into protons, neutrons and atomic nuclei is the strongest. The strong force is carried by gluons, and its strength is called the strong coupling constant. Although scientists' understanding of the strong coupling constant has improved over many years of measurements and theoretical development, the uncertainty in its value is still several orders of magnitude greater than that of its other "companions."
Stefano Camarda, a physicist at CERN and a member of the analysis team, pointed out that the strength of the strong force is a key parameter of the standard model, but its accuracy is currently only a few percent, while the electromagnetic force, which is 15 times weaker than the strong force, has an accuracy of one part per billion.
In order to improve the accuracy of strong force strength measurement, the ATLAS collaboration team studied the Z boson produced by the proton-proton collision at the LHC with a collision energy of 8 teraelectronvolts (TeV). A Z boson is typically produced when two quarks in colliding protons annihilate. In this process, the strong force acts through gluons radiated from the annihilating quark. This radiation gives the Z boson a transverse momentum, the magnitude of which depends on the strong coupling constant. By accurately measuring the distribution of Z boson transverse momentum and comparing it with theoretical values, the strong coupling constant can be determined.
In the latest analysis, the research team accurately determined the strong coupling constant at the Z boson mass scale to be 0.1183±0.0009. The relative uncertainty of this result is only 0.8%, which is the most accurate measurement of the strong strength in a single experiment to date.
The research team pointed out that more precise measurements of strong coupling constants are of great significance: first, it can improve the accuracy of theoretical calculations of particle processes related to the strong force; second, it can help solve some important unsolved mysteries. For example, at extremely high energies, whether all fundamental forces have the same strength, and infer whether they have a potential common source, and whether there are unknown interactions that can change the strong force in certain processes or at specific energies, etc.