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Quark

physical science Maturity 7-9 Next article →

Quarks are fundamental constituents of matter. They are elementary particles, which means they are not made of smaller components.

Standard Model of Elementary Particles
Standard Model of Elementary Particles

Quarks combine to form composite particles called hadrons. The most stable hadrons are protons and neutrons. These particles serve as the building blocks of atomic nuclei. Most observable matter in the universe consists of up quarks, down quarks, and electrons.

Quarks are governed by a phenomenon called color confinement. This principle dictates that quarks are never found in isolation. Instead, they exist only within hadrons or in quark–gluon plasmas. There is also a theoretical possibility of more exotic phases of quark matter. Hadrons are divided into two main families: baryons and mesons. Baryons, such as protons and neutrons, contain three valence quarks. Mesons consist of one valence quark and one antiquark.

Hadron colors
Hadron colors

Quarks possess several intrinsic properties that define their behavior. They have mass, spin, and electric charge. They also possess color charge, which allows them to engage in the strong interaction. This interaction causes quarks to attract one another and form hadrons. Quarks are unique in the Standard Model of particle physics. They are the only elementary particles that experience all four fundamental interactions. These forces include electromagnetism, gravitation, the strong interaction, and the weak interaction. Furthermore, quarks are the only known particles with electric charges that are not integer multiples of the elementary charge.

Physicists classify quarks into six distinct types known as flavors. These flavors are grouped into three generations of matter. The first generation includes the up and down quarks. These are the lightest and most stable flavors. The second generation consists of the charm and strange quarks. The third generation contains the top and bottom quarks.

Quark masses as balls
Quark masses as balls

Higher-generation quarks have greater mass and less stability. They undergo particle decay, a process where a particle transforms from a higher mass state to a lower mass state. Because of this, heavy quarks like the top quark are only produced in high-energy collisions, such as those involving cosmic rays or particle accelerators.

For every quark flavor, there is a corresponding antiquark. An antiquark is an antiparticle with the same mass and spin as its quark counterpart. However, the antiquark has an electric charge with an equal magnitude but opposite sign.

Quark weak interactions
Quark weak interactions

Quarks are also classified as fermions because they have a spin of 1/2. This means they follow the Pauli exclusion principle. This principle states that no two identical fermions can occupy the same quantum state at the same time. This distinguishes them from bosons, which have integer spin.

The quark model was proposed independently in 1964 by Murray Gell-Mann and George Zweig.

MurrayGellMannJI1
MurrayGellMannJI1
George Zweig
George Zweig

At first, the scientific community was unsure if quarks were physical entities or just mathematical abstractions. Evidence for their physical existence arrived in 1968 through deep inelastic scattering experiments. These experiments were conducted at the Stanford Linear Accelerator Center. They revealed that protons contained tiny, point-like objects. In 1974, the discovery of the charm quark helped convince physicists that the model was valid. The top quark was the final flavor to be observed, discovered at Fermilab in 1995.

Studying quarks provides deep insights into the history of our universe. Heavier quarks may have been present during the quark epoch. This was a period during the first fractions of a second after the Big Bang when the universe was extremely hot and dense.

QCDphasediagram
QCDphasediagram

By using particle accelerators to recreate high-energy conditions, scientists can study these particles. This research helps us understand the fundamental forces that hold all matter together.

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🖼️ Images & Media (10)
File:Standard Model of Elementary Particles.svg
Standard Model of Elementary Particles.svg
File:MurrayGellMannJI1.jpg
MurrayGellMannJI1.jpg
File:George Zweig.jpg
George Zweig.jpg
File:Charmed-dia-w.png
Charmed-dia-w.png
File:Beta Negative Decay.svg
Beta Negative Decay.svg
File:Quark weak interactions.svg
Quark weak interactions.svg
File:Hadron colors.svg
Hadron colors.svg
File:Strong force charges.svg
Strong force charges.svg
File:Quark masses as balls.svg
Quark masses as balls.svg
File:QCDphasediagram.svg
QCDphasediagram.svg
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