The purpose of the first exercise is to analyse pictures of collisions of Z0-decays to measure the branching ratios of the Z0 particle. The branching ratios tell how often the Z0-decays into different kinds of particles.
A Z0 particle can decay into either two electrons, two muons, two tau particles, two neutrinos or into two quarks. The frequencies of the different kinds of decays can be calculated theoretically with the Standard Model. We can with help of Wired measure how often the different decays occurs and compare the results with the theoretical predictions.
To measure the branching ratios of the Z0 particle we need to look at a large number of collisions. In the "Collision library" there is a page with ten links. Each link contains 100 collisions with Z0-decays.
The results of this exercise can be used later in the second exercise to measure the strong coupling constant.
On the next page it is explained how to identify the different types of Z0-decays. You should also read the picture captions under the pictures in the middle frame, and the pages about particle identification in the chapter "Picture analysis".