The Top Quark:
Single Lepton Channel Events


As the last page showed, a proton / antiproton collision can result in positively and negatively charged W bosons. These bosons then dacay to hadron jets, leptons and other particles, which are then detected.

The type of decays whereby one W boson decays to hadrons and the other to leptons are called single lepton channel events.
 

  • The W+ boson decays to leptons
     
  • The W- boson decays to quarks and then hadrons in two 'light' jets
  • The W+ boson decays to quarks and then hadrons in two 'light' jets
     
  • The W- boson decays to leptons

 


By forming a histogram of the mass of the decay particles it is possible to estimate the mass of the top quark.

Added complication

Unlike the events used for the calculation of the Z° boson and W boson masses, there is a mixture of hadron jets and leptons in the events used to calculate the mass of the top quark. Specifically:

  • two 'heavy' hadron jets from the decayed bottom-quark and anti-bottom-quark
  • one charged lepton or charged anti-lepton
  • two 'light' hadron jets

There will also be significant missing transverse momentum due to the neutrino, as with the W boson events.

The particles all decay so quickly that they appear to come from the same point. You must associate the three decay products of the top quark together, and the three decay products of the anti-top-quark together. You can find the transverse masses of associated systems and plot them separately on the histogram.

hint: Use the charged lepton to associate the groups of particles:
 

charged lepton source associated groups
electron / muon
(negatively charged lepton)
anti-top-quark the electron / muon
neutrino (the missing momentum)
anti-bottom-quark 'heavy' hadron jet
bottom-quark 'heavy' hadron jet
two 'light' hadron jets
positron / antimuon
(positively charged lepton)
top-quark the positron / anti-muon
neutrino (the missing momentum)
bottom-quark 'heavy' hadron jet
anti-bottom-quark 'heavy' hadron jet
two 'light' hadron jets

if the associated group is blue it means the decay products are from the hadronic channel
if the associated group is green it means the decay products are from the leptonic channel


Last modified Wed 23 January 2002 . View page history
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