What are quarks and gluons?

Quarks and gluons are the building blocks of protons and neutrons, which in turn are the building blocks of atomic nuclei. Scientists now understand that quarks and gluons are indivisible – they cannot be broken down into smaller components. They are the only fundamental particles that have something called a color charge.

In addition to having a positive or negative electrical charge (like protons and neutrons), quarks and gluons can have three additional states of charge: positive and negative redness, greenness, and blue. These so-called color charges are just names – they are not related to actual colors.

The force that connects the positive and negative color charges is called the strong nuclear force. This powerful nuclear force is the most powerful force involved in holding matter together. It is much stronger than the other three fundamental forces: gravity, electromagnetism, and weak nuclear forces. Because the strong nuclear force is so powerful, it is extremely difficult to separate quarks and gluons. For this reason, quarks and gluons are bound inside composite particles. The only way to separate these particles is to create a state of matter called quark-gluon. plasma.

In this plasma, the density and temperature are so high that protons and neutrons melt. This soup of quarks and gluons permeated the entire universe until a few fractions of a second after the big Bang, when the universe has cooled down enough for quarks and gluons to congeal into protons and neutrons.

Today, scientists are studying this quark-gluon plasma at special facilities such as the Relativistic Heavy Ion Collider (RHIC) at Brookhaven National Laboratory.

Quark and Gluon Information

• There are six different types of quarks with a wide range of masses. They are named high, low, charm, strange, high and low.
• Quarks are the only elementary particles to undergo all the known forces of nature and to have a fractional electric charge.
• The interaction between quarks and gluons is responsible for almost all of the perceived mass of protons and neutrons and so this is where we get our mass.

DOE Science Office: Contributions to Quarks and Gluons

The DOE supports research into the interaction of quarks and gluons, how they combine into composite particles called hadrons, and how they behave at high temperature and density. Scientists are studying these topics at DOE acceleration facilities such as RHIC and the Continuous Electron Beam Accelerator (CEBAF) facility at the Thomas Jefferson National Accelerator Facility.

The theory that describes the strong nuclear force known as quantum chromodynamics is notoriously difficult to solve. However, it can be simulated on supercomputers built and maintained at DOE facilities. The DOE has been a leader in the study of quarks and gluons since the 1960s. The idea of ​​quarks was proposed in 1964, and evidence for their existence was observed in experiments in 1968 at the Stanford Linear Accelerator Center (SLAC). The heaviest and latest quark to be discovered was first observed at Fermilab in 1995.