Finding Mass of W From Decay Products

Mass of W Correlation to Energy of Decay Products

Cherie B



Looking at the decay of a W boson into a muon and neutrino, and observing the missing energy due to the neutrino created in the process, creates a graph with 2 peaks, or at least favorable energies. Attempting to make any sense out of why some energies are preferred over others in the decay of the W boson.


The W boson decay produces either a muon or an electron, in addition to a neutrino. The muon or electron that is produced can be picked up by the detector, and the amount of energy of either particle can be measured and read out by the detector. The neutrino that is produced ecapes the detector unseen and undetected, so is only knowable by the amount of missing transverse energy (using conservation of momentum). We'd expect the total energy and momentum before the decay to equal the total energy and momentum after the decay of the W boson.


I first created a plot of the missing transverse energy of a W decay into a muon and neutrino. Noticing 2 peaks, I then plotted the Total Energy of the Lepton (the muon in this case). Finally, I plotted the total transverse mass.


The graph of missing transverse energy due to the neutrino created in the decay of the W seems to indicate that there are preferable energies that the neutrino would take away from the decay process, and thereby favorable energies the muon would have following the decay as well. When I looked at the total energy of the lepton (the muon) I noticed peaks at similiar energies. If we can equate energy to transverse mass, then the peaks at 10 GeV and 40 Gev may correlate respectively to the peaks at 40Gev and 70GeV; adding to a total of around 80GeV which is the mass of the W boson.


Discussion and Conclusions

It seems that maybe we can take the energies of each of the products of the W boson decay to approximatly get the mass of the W boson before the decay. I am still unsure of why there would be peaks in the energy of the lepton (muon) created in the process.