Abstract

The purpose of this analysis was to explore the mass, history, and purpose of the J/psi particle. We created histograms that show where the CMS detector picked up the energy from the particle. The graphs included show the full set of data before editing, the graphs once we changed the bin, and the most significant part of the histogram once the bin was changed. Our results and conclusion comes from analyzing the data we collected and created.  We confirmed the mass of the J/psi particle as 3.097 GeV/c², and deduced the reason why this particle and data is significant.

Introduction

The J/psi particle was independently discovered by two different physicists, Burton Richter and Samuel Ting, around the same time in 1974. They both decided to announce the particle on November 11, 1974. The discovery of this particle verified the existence of a fourth quark, the charm quark, in addition to the known up, down, and strange quarks, earning them the 1976 Nobel Prize. The J/psi particle is a neutral meson particle made up of a charm quark and a charm antiquark. The universally accepted and calculated mass of the particle is 3.097 or 3.1 GeV/c², which is around 6000 times that of the electron's mass, or 3.5 times that of the proton's mass. The J/psi is also the first excited state of charmonium, which is a meson formed by the bound state of a charm and anti-charm pair. An excited state is when an electron has more energy than that of its ground state, and a bound state is when a particle has a certain amount of potential energy around it, and the energy in that particle is less than the potential energy. This causes it to be unable to move. The reason the J/psi was discovered was because of the experiments being conducted by Richter and Ting. Before their experiments, there had been predictions of a fourth quark, the charm quark. Richter was conducting an experiment with electrons and positrons to meet in head on collisions, and the J/psi appeared when conditions were perfect for it to be produced. Ting was experimenting to see how the twins of an electron and its antiquark are spawned at high energies when the particle was discovered by his team and him.  

Procedures

Our plan was to create histograms that yielded the J/psi particle. We went to the data selection and chose the data set called J/psi Data. From there we selected the muon event type to graph, and the plot selection of the muon and antimuon mass. This original histogram looked like stair steps with no significant information, but once we changed the bin size from 1.0 to 0.09, a J/psi particle was detected shown by a significant spike in the graph. This was between the masses of 3.08 to 3.1 GeV/c² because of the accepted mass of 3.09 GeV/c² for the particle. To determine exactly where the particle was and its mass, we cut out the area of the graph between 3.08 to 3.1 GeV/c², which then created a new histogram and analyzed it further. In order to get this histogram to where we could understand it and see a clearer view of the mass, we changed the bin width once again from 1.0 to 0.09. From this and adjusting the x and y axes, we were able to create graphs that show where the J/psi particle was. We then collected background information from the internet to explain the discovery and other important details about the particle. 

Results

Figure 1, shows the graph with no editing. It does not show significant information, because the bin is too large to display the smaller discrepencies in the graph. This was where we decided to change the bin size in order to create a clearer graph that actually displayed useful data. Figure 2 shows the histogram when the bin number has been changed to 0.09. Now, it is possible to see the spike in the data where a J/psi particle is present. This happens at a mass between 3.08 and 3.1 GeV/C². In figure 3, the histogram with a bin of 0.09 has been cut to show the most significant part, which is where the J/psi particle was detected based on the greatest mass measured. From this information, we were able to determine the mass of the J/psi particle as the same number measured by Richter and Ting.

Discussions & Conclusions

In conclusion, the J/psi particle was one of the most important discoveries in the studies of quarks. The discovery of this particle brought with it the discovery of the fourth unknown quark at the time, the charm and its anticharm. From the graphs we have created and analyzed, they support the known mass of J/psi particle, 3.097 GeV/c². This information views the decay of the particle going from a muon to an antimuon pair. The mass of this decay led to the discovery of the J/psi because it was the mass of a particle that had not yet been discovered.  When this mass was detected, the scientists knew that there was either a error in their detector or a huge and important discovery. It proved to be the latter, and won Richter and Ting the Nobel Prize. For further study, it is possible to create other events in which a J/psi particle is detected and determine what size bin is needed to detect the appearance of a J/psi particle. 

Bibliography

http://hyperphysics.phy-astr.gsu.edu/hbase/particles/hadron.html

http://www.britannica.com/EBchecked/topic/298573/Jpsi-particle

http://www.bnl.gov/bnlweb/history/nobel/nobel_76.asp

http://www.nobelprize.org/nobel_prizes/physics/laureates/1976/press.html