Observe Quark Transitions as a Particle Physicist Would

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Quark Transitions: Read - Watch - Answer

Concepts Addressed

Elementary Particles and Structure
Theory as Explanation and Simplification
Extended Rules of Chemistry

Classroom Use

By studying chemical behavior, scientists were able to construct the periodic table of elements, each "element"ary particle being an atom. They used subatomic particles to explain the large number of elements and the periodicity in their chemical properties. By combining protons, neutrons, and electrons together according to some basic rules, scientists were able to build hundreds of elements and isotopes from simpler principles of structure.

Students should have already worked on the first decay page before approaching this one. They can test decays and observe both the quark components of the original particle and those of the products. Only hadrons are made of quarks, the new "element"ary particle. Leptons and bosons are themselves elementary. One simple activity would be to use the page to establish what quarks are inside each hadron. That information is also provided in the table as a shortcut reference.

In a second activity, students can try three ways to build hadrons: three quarks, three antiquarks, or one quark plus one antiquark. The class can make three possible "periodic" tables of all possible combinations, based on these rules of structure, applied to three kinds of quarks (up, down, strange) and three kinds of antiquarks (anti-up, anti-down, and anti-strange).

In the end, students can match a particle from the decay page to a combination on the table(s). Not all combinations correspond to a particle (though a few mesons do double-up or triple-up on combinations, and some baryons share combinations).

A third activity for students using this page would be to have them answer the questions on the last page to infer the amount of electric charge on each quark and antiquark, given the amount of charge on the whole hadron, which has been observed experimentally. Please be warned, this strategy does not work for mass. Theorists still may be working on it.

After answering the questions, students should be able to return to the "periodic" tables to see what the charges on some of the undiscovered particles would be. You should tell them that particles with fractional charge have never been isolated, but that their existence has be inferred from experimental evidence.

One of the affective goals of this lesson (yes, "affective" is spelled correctly here) is to have science students appreciate the method of developing a good theory. The quark model is a simplification. There are fewer elementary particles and the rules of construction are few in number. It explains the presence of discovered particles as well as the absence of undiscovered ones. In this way it is analogous to the role of subatomic particles in the patterns on the periodic table.

For a challenging activity, students can look at all the possible transitions of quarks to other kinds of quarks. Then they could list which ones are observed and which ones are not observed.

What Happens on the Decay Page

The quark decay page is similar to the basic decay page. It shows a clickable menu of particles. When you click on the symbol for a particle, a decay is shown near the bottom of the page. You can clear the result, or you can click on any symbol any number of times. The difference is that this page shows newly displayed hadrons as composites of quarks and/or antiquarks. The teacher should be aware that the results do not have explicit hadron labels, so the information on the particle table should be helpful.

Background Information

For your preparation, the table shows you the particle names along with the quark constituents of each hadron.

It becomes evident why there is such a thing as an antineutron. This antiparticle is actually made of the three anti-quark counterparts to the quarks present in a neutron.

Leptons and gauge bosons are elementary as far as we know; they are not made of quarks or any other elementary particles.

Actually, there are many more hadrons than are shown on these pages. However, ones here were all discovered by the 1960s, and it was the pattern in them that first prompted scientists to develop the quark model.

Since then, more hadrons have been discovered. Now, there are six known quarks, but only three (up, down, and strange) form the hadrons you see on these pages. The others are the charm, bottom, and top.

Also, though we know about gauge bosons for the strong interaction (gluons) and weak interaction (W⁺, W^-, and Z⁰), these pages only show the boson for the electromagnetic interaction, the gamma.