Measuring Z0 decays


In the challenge part 2 you learned how to distinguish events in which a Z0 decays to produce the different sorts of particle-antiparticle pairs. Now you might like to try your hand at one of the important measurements we make at LEP. This is to measure the fractions of Z0s that decay to each type of particle-antiparticle pair.

In this section you will be provided with a large number of events containing particle-antiparticle pairs from Z0 decays. Look at each one and keep a separate count of the number of: electron pair, muon pair, tau pair and quark pair events.

Before proceding any further you need to multiply the number of electron pair events you have found by a factor of 1.6. Don't worry, you don't have to understand where this factor comes from in order to do this challenge. However, if you'd like to know more about this factor click here.

Once you have classified all the events there are a number of interesting questions to ask yourself:

Note: in order to decide whether or not two numbers are "statistically consistent" you need to have some idea about "statistical errors" or "statistical uncertainties". Here is some help if this is unfamiliar to you.

Here are the events. Don't worry if you don't have time to look at them all. You can make measurements even if you look only at a subset. Of course, your measurements will be more accurate the larger the number of events you do look at. Another way might be to collaborate with a few of your friends: you could each scan a different set of events and then combine your results.

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Terry Wyatt. March 1997.