Protons quark structure

The weak interactions change quark and lepton flavors, e.g., a d-quark into -quark or a muon into an electron (this latter, e.g., in the p e Vet /i process). The quark structures of the proton and neutron as well as the properties of nucleons are presented in O Table 2.3. The baryons are built up from three (valence) quarks and massless gluons, but they contain also dynamical (or sea) quarks (quark-antiquark pairs) in a small quantity. The mesons are built up from quark-antiquark pairs and gluons. 

HADRONS. These are subatomic particles, the strong interactions of which are manifested by the forces lhal hold neutrons and protons together in the atomic nucleus. Hadrons include Ihe proton, the neutron, and pion. among others. These particles show signs of an inner structure, i.e.. they are made up of other panicles, which has led over a period of the last several years to consider the hadrons as combinations of constituents known as quarks. See also Quarks and Particles (Subatomic). 

The fundamental assumption in this work is that the three elementary units are indivisible wave structures in the vacuum. The quarks, assumed to be confined in a proton, are considered a manisfestation of the wave structure. 

We have seen that the matter around us has various levels of organization. The most fundamental substances we have discussed so far are elements. As we will see in later chapters, elements also have structure They are composed of atoms, which in turn are composed of nuclei and electrons. Even the nucleus has structure It is composed of protons and neutrons. And even these can be broken down further, into elementary particles called quarks. Flowever, we need not concern ourselves with such details at this point. Figure 1.14 summarizes our discussion of the organization of matter. 

Quarks are particles with no internal structure that are thought to be the fundamental constituents of hadrons. Neutrons and protons are hadrons that are thought to be composed of three quarks each. 

Subatomic particle research is still a major interest to modern scientists. In fact, scientists have determined that protons and neutrons have their own structures. They are composed of subatomic particles called quarks. These particles will not be covered in this textbook because scientists do not yet understand if or how they affect chemical behavior. As you will learn in later chapters, chemical behavior can be explained by considering only an atom s electrons. 

In this zoo of particles, only the electron, which was discovered even before the atomic theory was proven and the atomic structure was known, is really unseeable, stable, and isolatable. The proton also is stable and isolatable, but it is made up of two quarks up (with charge -1-2/3) and one quark down (with charge —1/3). As for the quarks, while expected to be stable, they have not been isolated. The other particle constitutive of the atomic nucleus, the neutron, is also made up of three quarks, one up and two down, but it is not stable when isolated, decaying into a proton, an electron, and an antineutrino (with a 15-min lifetime). The fermions in each of the higher two classes of the electron family (muon and tau) and of the two quark families (strange charmed and bottom/top) are unstable (and not isolatable for the quarks). Only the elusive neutrinos in the three classes, which were postulated to ensure conservation laws in weak interaction processes, are also considered as being unseeable, stable, and isolatable. 

In 1964 there were about 200 particles called elementary particles, without being systematically explained, until the naive theory (with 3 quarks q = u, d, s) of Gell-Mann for example, the proton was a combination of 3q p=uud, while the neutron has the structure n=3q=udd ... 

For all issues relevant to the chemistry and physics of atoms, molecules, clusters, and solids only electromagnetic and — to a negligible extent — weak interactions, which are responsible for the radioactive /5-decay and the nonconservation of parity, contribute. The internal structure of hadrons, i.e., protons and neutrons built up by quarks governed by strong interactions and also gravitational forces, do not play any role and are therefore not covered by this presentation. 

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