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<h2>Quarks: is That All There Is?</h2>
<p>Quarks have been mentioned at various points in this text as fundamental building blocks and members of the exclusive club of truly elementary particles. Note that an elementary or <strong>fundamental particle</strong> has no substructure (it is not made of other particles) and has no finite size other than its wavelength. This does not mean that fundamental particles are stable—some decay, while others do not. Keep in mind that <em>all</em> leptons seem to be fundamental, whereas <em>no</em> hadrons are fundamental. There is strong evidence that <strong>quarks</strong> are the fundamental building blocks of hadrons as seen in <a href="#navlink_id1169737965898">this figure</a>. Quarks are the second group of fundamental particles (leptons are the first). The third and perhaps final group of fundamental particles is the carrier particles for the four basic forces. Leptons, quarks, and carrier particles may be all there is. In this module we will discuss the quark substructure of hadrons and its relationship to forces as well as indicate some remaining questions and problems.</p>
<div class="fig_container" id="navlink_id1169737965898"><img alt="The figure shows four spheres that are labeled proton, neutron, positive pion, and negative pion. The proton sphere contains a blue up quark with spin up, a green down quark with spin down, and a red up quark with spin up. Below the figure are two equations. The upper equation is labeled spin and reads one half plus one half minus one half equals one half, and the lower equation is labeled charge and reads plus two thirds plus two thirds minus one third equals one. The neutron sphere contains a green up quark with spin down, a blue down quark with spin up, and a red down quark with spin up. The corresponding spin equation reads minus one half plus one half plus one half equals one half, and the charge equation reads plus two thirds minus one third minus one third equals zero. The positive pion sphere contains a red up quark with spin up and an anti red anti down quark with spin down. The corresponding spin equation reads plus one half minus one half equals zero, and the charge equation reads plus two thirds plus one third equals plus one. The negative pion sphere contains a green anti up quark with spin up and an anti green down quark with spin down. The corresponding spin equation reads plus one half minus one half equals zero, and the charge equation reads minus two thirds minus one third equals minus one." src="https://data.ulearngo.com/assets/39a3da44-5d60-430c-9d19-4666ab07e003"/>
<p class="fig_caption">All baryons, such as the proton and neutron shown here, are composed of three quarks. All mesons, such as the pions shown here, are composed of a quark-antiquark pair. Arrows represent the spins of the quarks, which, as we shall see, are also colored. The colors are such that they need to add to white for any possible combination of quarks.</p>
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Quarks: is That All There Is?

Physics is a science discipline concerned with the nature and properties of matter and energy. Physics topics include mechanics, heat, light and radiation, sound, electricity, magnetism, the structure of atoms, and so on.

Physics

Discover the fundamental concepts and principles of Particle Physics, including particles, forces, accelerators, reactions and conservation laws, quarks, and the unification of forces.


Quarks: is That All There Is?

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