Information for Teachers

This CD-ROM gives students an insight into :

the basic concepts of the frontier of knowledge in physics,
what the basic constituents of matter are and how they behave,
what it is like to do front-line research in physics,
what instruments physicists use and how they use them,
how physicists interpret results,
and the importance of statistical analysis and how statistical fluctuations in small samples even out in larger ones.
Above all, the goal of this CD-ROM is to excite your students and inspire their curiosity!.

The information is divided into several areas covering the major themes. A basic introduction can be found at the Reception, a more detailed introduction to the physics is in the Theory area, while the Accelerators and Detectors areas introduce the tools of the trade. Each area has a number of sub-headings, and the information is structured in such a way that the further you delve into each area, the deeper you dig into the subject.

The core of the CD-ROM is in the Projects area. Here you will find real physics analysis projects using real data for your students to do. They will need to be familiar with the information contained in the first pages of each of the preceeding chapters before embarking on these projects. A 'Briefing Room' at the entrance to the Projects area will allow your students to test their knowledge before starting the projects.

Care has been taken to make the CD-ROM easily navigable. It is based on the metaphor of a visit to the CERN site. The menu bar on the left will take you to wherever you want to go. A pop-up index can take you to any term you wish to return to, and clicking on the top left window will take you back to the CERN sitemap, which can also be used as an entry point to any area you wish to visit.

Introduction to the Analysis Projects

All the projects use the same program, called WIRED for World Wide Web Interactive Remote Event Display, and the same technique: visual inspection of computer reconstructed particle collisions, otherwise known as events. After passing the Briefing Room, students are given a short tutorial on how to identify different events.

The authors would be very glad to see the results of your students' analyses. This will help us to improve this CD-ROM for future versions. If you are willing to share your results with us, please send them to us using the contact details below.

Analysis Project 1: Z Branching Ratios

The purpose of this project is to study how the Z particle decays and in particular, to measure the fraction of decays into particles of different types. These fractions are called Z branching ratios. They allow us to learn what the Universe is made of.

The Z particle is neutral. This means that it can decay into pairs of oppositely charged particles like an electron-positron pair, or a muon-antimuon pair, or a tau-antitau pair, or a quark and an antiquark. It can also decay into pairs of neutral particles, neutrinos and antineutrinos. Neutrinos don't leave any traces in the detector, meaning that the Z branching ratio into neutrinos cannot be measured directly. It is, however, these "invisible" decays of the Z that allow us to work out what the Universe is made of. We'll come back to them later.

To measure the Z branching ratios into visible particles, students will look at reconstructed Z particle decays. Using what they have learned from the introduction about what different decays look like, they will identify the decays and add up the number of times the Z decays into an electron and a positron, a muon and an antimuon, a tau and an antitau, or a quark and an antiquark.

The more events your students study, the more precise their result will be. Consequently the best way to approach the task is to split the class up into teams, each with responsibility for analyzing one file of 100 events. Each group should prepare a table, like the one shown below, in which they can record their observations. An event can only be one of the four possibilities. When they have finished, they can calculate the Z branching ratios into each particle type by dividing the number of each kind of event by the total number of events they looked at.

#Event	e⁺e^-	mu⁺mu^-	tau⁺tau^-	quark-antiquark
1	X	-	-	-
2	-	-	-	X
3	-	-	-	X
4	-	-	X	-
Sum
4 evts	1	0	1	2

When each analysis team has finished you can ask them to present their branching ratios. If you plot the results from each group on the board you will find that they are not all the same, but they scatter around a central value. The next step of the analysis will be to combine all the results in a statistically meaningful way to arrive at your class' final answer, which you can then compare with CERN's published results.

After the project, there is a discussion of the significance of the branching ratio measurement, and its implications for the composition of matter in the Universe.

Click here to open the "Z branching ratio" project

As you may notice, identifying the events is not always easy. In fact, nature is such that it is not always possible to say what an event is with 100% certainty. However, to help you we have put together lists with the most probable answer for each decay. The files below correspond to each file of events:

Analysis Project 2: Measurement of the Strength of the Strong Interaction

This analysis project takes a closer look at the events identified as quark-antiquark pairs. Most of these will be so-called two-jet events, where two jets of particles emerge from the interaction point. A smaller number, however, will have three jets, and an even smaller number will have four or even more.

The reason for this is that quarks and antiquarks can radiate gluons, the carriers of the strong force, which go on to generate jets of their own. The probability that a quark or antiquark will radiate a gluon is directly related to the strength of the strong interaction. This means that by counting up the numbers of two, three, and four or more jet events, we can measure the strength of the strong interaction. That is the goal of this project, which is followed by a discussion of the relative strengths of all the interactions of nature.

The events are the same as for the previous project, but the tables that your students should keep are slightly different:

#Event	2-jets	3-jets	>3-jets
1	X	-	-
2	-	X	-
3	X	-	-
4	-	-	X
Sum
4 evts	2	1	1

Since the data sets are the same for projects 1 and 2, if the students have enough time there is nothing to stop them from doing both projects at once.

Click here to open the "Strong Coupling Constant" Project

Analysis Project 3: Rare Events with W and Z Particles

This is not so much of a project as an opportunity for relaxation after the hard work is down. The project contains files with events at several collision energies. In some of these pairs of W and Z particles are produced. Your students can amuse themselves by trying to describe the difference between these events and those they have analysed in projects 1 and 2.

Since Z decays into electron-positron pairs, muon-antimuon pairs, and tau-antitau pairs are relatively rare, one file contains just such events.

Click here to open the "Rare Events with W and Z Particles

Troubleshooting

We have tried to identify potential problems but we need your feedback. If you run into difficulties, we would be grateful if you could document them carefully. Include as much information as you can about what has gone wrong, whether it happens all the time or just occasionally, what kind of computer you are using and anything else that you think might be helpful. Send your comments to either James Gillies or Richard Jacobsson, whose contact details are given below.

The following general tips should help you get the most out of this CD-ROM:

Don't open or keep open other applications while working with the CD-ROM. This greatly enhances the performance.
When working on the analysis projects, have patience! It takes time to launch the graphical event display. It may look as though nothing is happening, but we assure you that this is not the case. Try to resist the desire to open other applications while you are waiting, this will only increase your wait. It can take several minutes for the program to load, but once it has it runs quickly. It should only take a few seconds to go on to the next event. Note that the graphical display first shows up as a grey shaded area; it takes about a minute before all the functionality appears.
If the program starts to behave strangely, or becomes increasingly slow, then the best thing to do is to quit Netscape and then restart it. It might be a good idea to restart the computer as well. Remember to make a note of the "id number" of the event the students are looking at (shown in the top right hand corner of the graphical event display) so that they can continue from where they were.

How can I get help?

If you need help with any aspect of this package, contact James Gillies or Richard Jacobsson at CERN:

James Gillies
CERN
1211 Geneva 23
Switzerland

E-mail: James.Gillies@cern.ch

Telephone: + 41 22 767 63 33
Fax: + 41 22 782 19 06

Richard Jacobsson
CERN
1211 Geneva 23
Switzerland

E-mail: Richard.Jacobsson@cern.ch

Telephone: + 41 22 767 36 19
Fax: + 41 22 782 30 84

Particle Physics Education CD-ROM Š2001 CERN