J/Psi vs Z muon decay
comparison of psuedorepidity
Penny Blue and Gail Anne Aurand08/12/2016
Abstract
The purpose of the investigation is to determine if the muons produced from J/psi decay are less energetic than the muons produced from Z boson decay. Because the CMS detector is designed to ignore lower energy background muons that intersect the beam axis, the number of low energy muons recorded from the J/psi decay may be affected. Pseudorapidity, (Eta), meaures the angle between vertical, (perpendicular), to beam, and the horizontal, (parallel) to the beam. If J/psi muons are less energetic, the number of muons recorded at angles that intersect the beam will decrease significantly. Analysis of the pseudorapidity of muons recorded from J/psi decay indicates almost no muons recorded at angles that intersect the beam. The analysis suggests that the muons produced from decay of J/psi particles are low energy and many are ignored by the CMS detector.
Introduction
How do the muons from a J/Psi decay differ from those of a Z decay?
We know that the mass of the J/Psi is approximately 3 GeV/c^2 and the Z mass is approximately 91 GeV/c^2. One of the comparisons that can be made is to look at the angle of the particle relative to the beam axis. This angle is referred to as the pseudorapidity and is represented by the Greek letter "eta". Pseudorapidity angle values of 3 and 4 indicate particles traveling along the beam axis. Pseudorapidity angles nearer to 0 are traveling nearly perpendicular to the beam axia. (see Figure 5)
The conservation laws of energy and moumentum, would lead us to believe that because the J/Psi's mass is smaller than the Z boson mass, the energy of the muon daughter particles have less energy than muons produced from a Z decay. Because of the lesser J/Psi mass, the CMS detector only records the muons from a J/Psi that travel more along the beam axis. Therefore, the psuedorapidity of these muons will be nearer to 3 or -3. In comparison, muons from the Z decay are moe energetic and therefore easier for the CMS detector to record.
Procedures
The comparision of pseudorapdity graphs of J/Psi muon decay and Z muon decay should give an idea of how the muons of the two decays differ. Observatiom of the muons produced at given angles of both graphs will reveal if there is a difference in the two.
Results
THe J/Psi mass historgram (Figure 1) indicates that the mass of the J/Psi is around 3 GeV/c^2. The Z mass histogram (Figure 3) indicates that the mass of the Z boson is about 90 GeV/c^2.
Comparison of psuedorapidity of muons at the Z boson and J/Psi particle masses indicate there is a difference.
An analysis of the muons produced from Z boson decay indicate the CMS detector records events at all of the angles of psuedorapidity (Figure 4).
Analysis of pseudorapidity of the muons from the J/Psi decay indicate the CMS detector records almost no events at anlges outside the beam axis (figure 2).
Figures
Discussion and Conclusions
Although it may be true that the J/Psi muons only travel near the beam axis, a better explanation may be that the CMS detector is designed to ignore low evergy muons with pseudorapidity between -1 and 1, to eliminate background cosmic muons, etc.
In conclusion, the evidence seems to indicate that the muons produced from J/Psi energy are less energetic than Z boson decay muons.
Bibliography
J/psi meson. (2016, June 26). In Wikipedia, The Free Encyclopedia . Retrieved 16:28, August 12, 2016, from https://en.wikipedia.org/w/index.php?title=J/psi_meson&oldid=727087510
W and Z bosons. (2016, July 28). In Wikipedia, The Free Encyclopedia . Retrieved 16:29, August 12, 2016, from https://en.wikipedia.org/w/index.php?title=W_and_Z_bosons&oldid=731965180
Pseudorapidity. (2015, November 30). In Wikipedia, The Free Encyclopedia . Retrieved 16:27, August 12, 2016, from https://en.wikipedia.org/w/index.php?title=Pseudorapidity&oldid=693044407