Activity Five, Student Page

Activity Five -- The Rules of the Game (Student Page)

Scientists in every field devise rules that explain what they have observed. They then use these rules to interpret new observations. This activity will give you the chance to discover rules, called conservation laws, that play a crucial role in the study of particle physics.

The most common type of observation in particle physics is called an event. An event is similar to a chemical reaction in chemistry, in the sense that one set of particles is formed from another.

The following particle charts can help you identify the types and charges of particles in a number of events given below. As indicated, each particle can have an electrical charge of +1, -1, or 0.

Note that antiparticles are denoted by a bar over the name of the particle (e.g., p-bar = antiproton, nu-bar sub-e = antielectron -- neutrino); or simply by the charges (e^- = electron, e⁺ = positron = antielectron); pi⁺ and pi^- are particle and antiparticle, and similarly K⁺ and K^-. An antiparticle has the same mass as its corresponding particle, but the opposite value for all charges.

Two sets of particle events are shown in the table at right. The set in the left column consists only of events that are known to take place, and the set in the right column consists only of events that are believed not to take place (they've never been observed). By examining the two sets, along with the preceding chart of particles, we must determine what quantities are or are not conserved in these particle physics events. These are the "rules of the game" played by nature.

All of the quantities whose conservation can be deduced from the following events can be found by counting. All such quantities are conserved in every "observed" event, but at least one of these quantities is not conserved in each "unobserved" event. Assume that the incoming particles have sufficient energy to generate the outgoing particles.

1. What is meant when we say that a quantity is "conserved?"
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2. What quantities or numbers of object types are conserved?
a) _____________________
b) _____________________
c) _______________________

3. What is an "event" in particle physics?
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4. Which of the above events are decays?
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5. For each of the unobserved events, indicate what is not conserved (there may be more than one answer).
Event #:
11: _______________ 16: _______________
12: _______________ 17: _______________
13: _______________ 18: _______________
14: _______________ 19: _______________
15: _______________ 20: _______________