Particle Physics Bingo

Introduction

Prior to the 1930s, the structure of matter was thought to be pretty well understood in terms of protons, neutrons and electrons. As scientists’ knowledge of nuclear structure exploded with the discoveries of nuclear fission and cosmic rays, it became clear that more fundamental particles were needed to explain the structure of matter. The burgeoning stable of fundamental particles and forces, which now includes quarks, gluons, positrons, muons, neutrinos, etc., once prompted the great physicist Enrico Fermi to famously proclaim: “If I could remember the names of these particles, I would have been a botanist!” Playing Particle Physics Bingo will help in identifying and understanding the basic building blocks of matter and the fundamental forces in the universe.

Concepts

• Standard model
• Fundamental particles vs. composite particles
• Gauge bosons
• Fermions vs. bosons

Background

The Standard Model of particle physics is a widely held compilation and organization of the various particles, their composites, and the interactions between them. As it has developed over the years, the model has been guided by both theory and experiment. In 1934, for example, physicist Hideki Yukawa predicted the existence of mesons, which were discovered 12 years later. For all its strength, the Standard Model is still incomplete and slightly flawed—there is no explanation for gravity, causing scientists to look to string theory, which posits the existence of “gravitons.” Many of the discoveries, such as that of the top quark in 1995, of the Standard Model have been made relatively recently. With the operation of the Large Hadron Collider (LHC) at CERN in Geneva, Switzerland, scientists hope to discover more new particles and pieces to the puzzle—including the famous Higgs Boson.

A fundamental particle, also called an elementary particle, is a particle that has no internal structure and thus no smaller pieces. It may be found by itself, or it may combine with other fundamental particles to form composite particles. Composite particles are made of smaller particles, and thus can theoretically be broken into pieces. The atom is an example of a composite particle. It has an internal structure, composed of electrons, neutrons, and protons. Neutrons and protons are themselves composite particles. Our current understanding indicates that they are made of fundamental particles called quarks.

There are three classes of fundamental particles in the Standard Model: quarks, leptons and force-carrier particles called gauge bosons. Quarks are distinguished by their flavor, such as “charm” and “top.” Of course, these whimsical names do not correlate with an actual flavor, but rather are easy ways to identify individual quarks. Quarks exist in pairs that belong to corresponding generations—up and down (first generation), charm and strange (second generation), and top and bottom (third generation). When quarks combine, they form composite particles called hadrons. Leptons also have flavors and exist in pairs like quarks. Each generation has a lepton and a paired neutrino, itself a lepton—electron and electron neutrino (first generation), muon and muon neutrino (second generation), and tau and tau neutrino (third generation). Leptons, unlike quarks, do not carry a color charge, which allows a particle to participate in strong force interactions—the force that holds the nucleus of an atom together. Because leptons do not participate in strong force interactions, we are very unlikely to ever find an atom with a nucleus made of electrons.

Gauge bosons, such as the photon, govern interactions between particles. There are four fundamental forces in the universe—electromagnetism, strong force, weak force, and gravity. These forces, with the possible exception of gravity, all have specific gauge bosons that are exchanged between the particles. When an electron exerts an electromagnetic repulsive force on another electron, it exchanges a short-lived particle with the other electron. A physical analogy for this process would be two individual throwing a ball at each other while on roller skates. The act of throwing the ball and the act of catching it both exert a force on the individual, resulting in each individual rolling further away from each other (see Figure 1).

The photon, the basic “unit” of light, is the force carrier for electromagnetism. The strong force, which “glues” the nucleus of an atom and even the individual quarks together, is carried by the aptly named gluon. The weak force, associated with radioactivity, has three gauge bosons associated with it—the Z boson, and both the W⁺ and W^– bosons. Gravity is the hardest force to pin down. The proposed gauge boson is called a “graviton.” The graviton has never been observed in nature, and is not predicted in the Standard Model. Instead, it’s a consequence of string theory. There is another elementary particle which is given the classification of scalar boson—the elusive Higgs Boson. Scientists hope it will explain the difference in mass between different particles, in particular the gauge bosons—the photon is massless, but strangely, the Z and W^± gauge bosons have a small but existent mass.

Quarks, as stated before, combine to form composite particles called hadrons. Hadrons are further classified into two different groups, depending on whether they are composed of two quarks or three quarks. Three quarks together form baryons; two quarks form mesons. Baryons are much more common forms of matter, as neutrons and protons are both baryons. Mesons decay very quickly and are thus much harder to observe. Experiments in so-called supercolliders or particle accelerators have led to the discovery of at least 200 different hadrons that quarks can form.

Properties of most particles include both electric charge and spin. Spin is a measure of a particle’s angular momentum, although the particle itself is not spinning. It’s a simple title used to describe a more complicated concept. Any particle that has a spin having a half integer value (e.g., 1/2, 3/2) is classified in a family called fermions. Fermions obey the Pauli exclusion principle, which states that only one particle can occupy a certain state at a time. All other particles form a family called bosons, which have integer spin values (e.g., 0, 1) and do not obey the Pauli exclusion principle. Many bosons can crowd into one state at a time if necessary. When quarks, which are fermions with a spin of ½, combine, they may become fermions or bosons, due to the complicated way the combined spins interact with each other. A proton, which is a baryon composed of three quarks, has a spin of ½ and is a fermion. A pion, which is a meson made of an up and an anti-down quark, has no spin and is a boson. A helium-4 nucleus, which is the radioactive alpha particle emitted at high energies, is composed of an even number of fermions (2 protons and 2 neutrons), making it a boson.

Materials

Prelab Preparation

1. Before beginning this activity, laminate the Particle Physics Bingo Choice Sheets or place them into sheet protectors. This will greatly increase their durability and longevity.
2. Permanently mark any items that are not covered in your curriculum with an “X” on the choice sheets. These terms may be given as free spaces for students to mark on their bingo cards.

Procedure

1. Give each student a Particle Physics Bingo Card, the Particle Physics Student Review Sheet, a Particle Physics Chart, and approximately 25 bingo chips. Small containers such as paper cups or plastic bags may be helpful for distributing and holding the bingo chips.
2. Give the name of any items on the Particle Physics Bingo Choice Sheet that were not covered in class. Instruct students to place a bingo chip on these items and use them as free spaces.
3. Remind students that they should place a bingo chip on any square that names the item being described.
4. “Bingo” may be called when five squares in a row are covered, whether vertically, horizontally or diagonally.
5. Remind students to leave their bingo chips in place after “bingo” has been called until the win has been verified by the teacher.
6. Call out the description of an item from the Particle Physics Bingo Choice Sheet. Mark the item with a light pencil mark on paper or with a transparency marking pen if the choice sheet has been laminated or is in a sheet protector. Note: For particles such as quarks, consider writing the symbol on the board to avoid giving away too much of a hint (e.g., using the symbol “b” instead of naming “the quark with bottom flavor”). Alternatively, name its generation, and the quark it shares that with—“A generation I quark, which is paired with the up quark” (Answer: Down quark).
7. Continue to call out different descriptions from the choice sheet until a win is confirmed. Erase all pencil marks on the Choice Sheet or use a damp paper towel to erase the transparency between each round.
8. The winner of each round may get extra credit points or a small prize as you deem appropriate.
9. Consider finishing the game with a “cover-all” round, where the winner is the first person to cover the entire card.

Student Worksheet PDF

12826_Teacher1.pdf

Lab Hints

• This kit includes enough materials for 30 students. This activity may reasonably be completed in one 50-minute class period.
• In order to verify understanding, encourage students to raise their hand if they can identify one of the particles or groupings, even if that item does not appear on their card.
• Use student volunteers for calling out the component descriptions. Saying the words aloud helps reinforce the terms.
• The Particle Physics Bingo Choice Sheet can also be used as an impromptu quiz. Instead of using bingo cards, simply call out 10 names and have students write the description or symbol. You may also call out the description, or write the symbol on the board, and have students fill in the name.
• Have students read through the Background information while referencing the Particle Physics chart. Use a transparency of the chart if desired.

References

Tipler, P., Llewellyn, R. Modern Physics, Ed. 5; W. H. Freeman & Company: New York, NY, 2008 pp 561–613.

The Particle Adventure: http://particleadventure.org (accessed June 2009).