MASTERCLASS

WHAT WE HAVE DONE SO FAR WITH THE MASTERCLASS
To start off the second semester, we have gone from looking at muons coming from outerspace (cosmic rays) to working on finding the Z and W particles. In order for us to know how to do this, we have to take a look at the 3D detector and all of its parts. We knew from the past semester that muons can go all the way through the detector without getting stopped up by one layer. That is how we can find what is a muon and what is an electron. We know that the electron goes through the tracker, but releases all of its energy in the E-cal, which is right after the tracker. To look for the difference between a Z and a W particle, we have to understand exactly what the difference is between the two. We knew that it was around 90 GeV, but I didn't know the big difference between a Z and a W particle. I learned from going on this website (media type="custom" key="12384824") that a Z particle decays into two main particles like muons, and electrons. These are called leptons, and all of the momentum and energy is conserved as it goes to these leptons. The W also decays into a lepton, but it only decays into either a muon or an electron, while all of the missing energy decays into a neutrino, which we can't see in the detector. By using a certain program on the detector, I could see an arrow showing where all of the missing energy is going. This was very helpful when looking at certain events. Leptons are particles that can either be charged, or neutral. The three leptons that we are looking at in this Masterclass are the electrons and muons as mentioned above. Electrons are charged, and a lepton that is not charged would be a neutrino, which we see in the Z particles. These neutrinos are the missing energy and momentum that escape from the detector.

Now that I have learned what the difference between these two particles were, I could start looking at data and decide whether the particle was a Z or a W. With a excel spreadsheet, I looked at the data that matched up with the event number, and if it had two electrons or muons, I marked it under the W column, and copied the mass of the particle to the side. If it was a Z, I would mark whether I saw a muon or an electron, and I would mark whether it was a positive or negative particle. When looking at the particle coming out of the collision, it was important to realize what way it was curving. Because we could be looking at any side of the detector, I had to make sure that it was facing the z direction and coming from the right side. I was able to do this by clicking the Z button at the top of the screen. If the decaying particle was curving clockwise, we would know that the particle is positive, and if the decaying particle is curving counterclockwise in the detector, we would know that the particle is negative. By doing this in the excel sheet, we could see how many Z particles there were, and find the average mass of the particle. This is interesting because we then look at graphs to see if our data is correct with the assumptions I made up above when talking about the two different particles. == One difficulty along the way was when I looked at one particle, I saw both a muon and an electron. This is tricky because you can't have a particle just decay into a muon and an electron (that I know of). When I brought it up, we discussed that it might be a tuo decaying from the electron or muon, and producing one of the opposite particles. Hence, you would see both a muon and an electron. After learning this, I was able to understand more about how these particles interacted and worked with each other. I found it interesting that a particle can decay into particle that can then decay into yet another particle. This ongoing sequence makes it tough to tell what a particle was sometimes. I think that this makes particle physics very interesting though.

This is the data that I took from looking at the visual detector of the CMS. From doing the 100's, I saw different patterns. I noticed that the electrons to muons was about equal (45 to 49). But what I found interesting was that there was a 3:2 ratio of positive to negative W candidates, and around 2:1 ratio of W particles to Z particles in these events.

After Looking at our data, we were able to go onto Many Eyes and see for ourselves what the plots looked like for the Z particle. Our next step is to determine the difference between the J/psi particles. This will be coming up after we study the histograms and scatter plots more to find interesting things about our data set