Research provides new insight into the mechanism of combining quarks

Science

Newswise – Quarks are basic Particle Which create visible matter in the universe. The most interesting and most surprising property of quarks is that they are never found in isolation. Instead, they can only be observed if they are confined inside mixed particles such as proton, Nuclear physicists use huge Particle accelerator Generating different types of quarks and studying how they evolve to form observable particles. Clusters of three quarks form composite particles called baryons (like the proton and the proton). neutron), while pairs of quarks form mesons. New measurements from the Large Hadron Collider Beauty (LHCb) experiment show surprising variations in the rate of baryon production, defying previous expectations.

Effect

atom nucleus The form in which all visible matter is made up of baryons (specifically, protons and neutrons), which scientists believe originated from. early universe, Baryons are stable particles inside the nucleus that do not annihilate. radioactive Decay. However, all mesons are unstable, and they rapidly decay into lighter particles that cannot form atoms. The existence of stable baryons versus unstable mesons is what makes possible the existence of atoms and the universe as we know it. The LHCb experiment has shown that the rate of formation of quarks into baryons versus mesons depends largely on the density of their environment. The discovery helps explain the formation of the first stable particles in the early universe.

Summary

The fact that quarks must be confined is the defining characteristic of strong interaction, as described by the theory of quantum chromodynamics (QCD). Calculations using QCD can estimate the total number of heavy bottom quarks produced in particle collisions but cannot describe the fraction that emerge as baryons rather than mesons. Typically, researchers tune models to match data from previous experiments involving collisions electrons with positrons, assuming that the baryon production rate is universal.

An important difference in this new research relative to previous experiments is that the collision of protons and/or nuclei at the Large Hadron Collider produces an environment with very high quark density. In this research, nuclear physicists at the LHCb experiment found that the number of baryons containing B quarks depends on the post-collision environment, and increases with higher particle density. This suggests that scientists’ assumptions about the universality of baryon production are wrong, and that the interactions between quarks produced during their evolution into visible matter influence how many baryons emerge. These new results prove that the production of baryons in dense collisional systems requires additional theoretical mechanisms, which may have been particularly important when the first protons were formed in the early universe.

Grant

This research was supported by the Department of Energy’s Office of Science, Nuclear Physics Program.