Quarks are fermions that obey Pauli’s exclusion principle, so it might be surprising to learn that three quarks can bind together within a nucleus. Based on its quark content, the charge of the pion is

Sample mesons, including quark content and properties, are given in (Figure). Mesons are formed by two quarks-a quark-antiquark pair. It is also interesting that no baryons are believed to exist with top quarks, because top quarks decay too quickly to bind to the other quarks in their production. Evidently, the energy associated with the spin (or angular momentum) of the particle contributes to its mass energy. Similarly, the mass of with spin 3/2 is 1.3 times the mass of the proton, and the delta zero ( ) baryon with a spin 3/2 is 1.3 times the neutron mass. Interestingly, the delta plus ( ) baryon is formed from the same three quarks as the proton, but the total spin of the particle is 3/2 rather than 1/2. Sample baryons, including quark content and properties, are given in (Figure). Quarks QuarkĪs mentioned earlier, quarks bind together in groups of two or three to form hadrons. The names and properties of the six quarks are listed in (Figure). However, this number soon grew to six-interestingly, the same as the number of leptons-to include charmed ( c), bottom ( b), and top ( t).Īll quarks are spin-half fermions have a fractional charge, and have baryon number Each quark has an antiquark with the same mass but opposite charge and baryon number. (The name ‘quark’ was coined by the physicist Murray Gell-Mann, from a phrase in the James Joyce novel Finnegans Wake.) Initially, it was believed there were only three types of quarks, called up ( u), down ( d), and strange ( s). In the 1960s, particle physicists began to realize that hadrons are not elementary particles but are made of particles called quarks.

Explain the primary evidence for the existence of quarks.

Use quark composition of hadrons to determine the total charge of these particles.

Compare and contrast the six known quarks.

By the end of this section, you will be able to:

Strange quark