Measuring W Decays: A More Difficult Measurement

If you've got this far then you're probably now an expert at identifying different types of Z⁰ and W pair events. Here is a more difficult challenge to keep you on your toes!

In the previous challenge you measured the fractions of Z⁰s that decay to each type of particle-antiparticle pair. Another important measurement is measuring the fractions of W pairs that decay into each possible class. Remember these classes are

the four-jet events: ,

the two lepton, two neutrino events:

or the lepton-neutrino, quark-anti-quark events: , , .

In this challenge you are asked to look through a list of events but be careful as there are other types of events, such as Z⁰ decays, mixed in as well. Therefore, for each event you first need to determine whether you're looking at a W pair decay or some other kind of event.

• As in the previous challenges click on the event to see it, then to see the side view click on 'side'. Having seen both these views you should be able to decide which type of event it is, and when decided, click on the type of event of your choice. If this involves a lepton then click on side again to see the information about the momenta. You should now measure the angle of the lepton and then enter this info into the angle box. (You will need to close the image of the event first.)
• Some events may have two leptons, in which case you are going to have to work out from the momenta coordinates which line of information belongs to which lepton in order to identify the charge so you can enter the angle information for both.
• Some events may look like they contain leptons but you can find no information picture - this is probably a background event so move on to the next one.
• There is a chart which will count the numbers of each type of event you decide you have seen. If you want to know exactly how many in each category you have picked you can click on the chart and then point to the column of your choice and the number will appear.

We expect the number of , and events each to be 0.29 times the number of events. We also expect to observe that the total number of events to be 0.18 times the number of events. Check your measurements are statistically consistent with these values.

A helpful hint! In Challenge V you looked at some more complicated types of events. Here you will meet some Z⁰ decays which involve the production of high energy photons in events containing a Particle-Antiparticle Pair.

If you're working toghether as a group each of you may like to look at a different set of events and you can then combine your measurements. If you are working on your own, but don't have time to look at all events you can just look at a subset.