CERN-THESIS-2012-153 26/07/2012 - CERN Document Server

κ f FCNC partial width (GeV) FCNC BR total width (GeV)
0.6 0.71 9.8×10 −1 3.98×10 −1 2.46
0.3 0.71 2.5×10 −1 1.42×10 −1 1.72
0.1 0.71 2.7×10 −2 1.81×10 −2 1.50
0.1 0 2.7×10 −2 1.81×10 −2 1.50
0.1 1 2.7×10 −2 1.81×10 −2 1.50
0.01 0.71 2.7×10 −4 1.84×10 −4 1.48
0.001 0.71 2.7×10 −6 1.84×10 −6 1.48
Table 4.1: FCNC widths and BR obtained for several coupling values as reported by TopReX for t¯t → bWqZ.
reported by TopRex. Relevant kinematical distributions obtained with these coupling values are shown in
Figure 4.1.
The MRST2007 LO* [79] PDF set was used with the TopRex generator. All signal events were hadronized
with PYTHIA 6.421 [76]. The masses of the top quark, W-boson and Z-boson were set to 172.5 GeV,
80.4 GeV and 91.2 GeV, respectively.
To study the effect of the uncertainty due to the uncertainty on the top quark mass, samples with top
quark masses of 170 GeV and 175 GeV were also generated. The uncertainty due to initial- and final-state
radiation (ISR/FSR) was evaluated using the AcerMC generator [80] interfaced with PYTHIA, and by varying
parameters controlling ISR and FSR in a range consistent with those used in the Perugia Hard/Soft tune
variations [81] and with experimental data [82].
4.3 Background
MC simulation samples were also generated for those SM processes with final-state topologies similar to the
signal. As it will be explained in Chapter 6 these processes include events with three final state charged
leptons, events with two final state charged leptons and at least one jet being misidentified as a lepton and
events with four leptons in which one is not reconstructed.
Diboson events (WW, WZ and ZZ) were produced using ALPGEN 2.13 [83]. The CTEQ6L1 [84] PDF was
used, and up to three additional partons from the matrix element were simulated. The parton shower and
the underlying event were added using HERWIG v6.510 [85,86] and the JIMMY [87] underlying event model
with the AUET1 tune [88] to the ATLAS data.
45