Analysis of D-Zero Data From Fermi National Accelerator Laboratory
The diagram below shows the collision for the event labeled Run 92704 Event 14022. The other data plots can be represented by diagrams similar to this but may not have exactly the same debris, going in the directions shown here.
While this event looks complex at first, it may be summarized by noting that a proton and antiproton collide to create a top antitop pair that exist for a very short time. Almost immediately the very massive top and antitop decay into the constituents that are known to be their signature. These include four "jets" (large blasts of particles) that are the result of decays of W bosons and some less massive quarks. It is important to note that one of the jets will often contain a low energy or "soft" muon. The soft muon helps identify the jet as a bottom quark jet. In addition, a muon and neutrino come out as debris from the collision. You can see it in the upper right part of the diagram.
You will notice that there is no information given about the neutrino except the magenta tower indicating its direction on the color plot. While scientists can predict with confidence that it comes out of the collision, it cannot be detected very easily. Still, a careful consideration of the momenta before the collision and after the collision may give you a clue as to how much momentum this particle has!
Make a momentum vector diagram to determine the momentum of the neutrino. Be sure to remember that the total momentum of the system must be zero so any "missing" momentum must belong to the muon neutrino.
Question 1. What is the momentum of the missing neutrino?
This shows, then, that the total energy that came from the two top quarks that were formed is equal to the numerical sum of all the momenta discovered in the collision. Fill in all the momentum values from your color plot in the table below. Finally add the measured value for the neutrino that you just determined at the end of this table.
Question 2. What do you determine the mass of the top quark to be?