Events with ${\rm q}\bar{\rm q}\ell\bar{\nu}_{\ell}$ Final States

So far, the signal processes ${\rm e}^{-}{\rm e}^{+}\rightarrow{\rm W}^{-}{\rm W}^{+}\rightarrow$ ${\rm q}\bar{\rm q}\ell\bar{\nu}_{\ell}$ have been considered. At OPAL these are not the only processes that produce a final state of ${\rm q}\bar{\rm q}\ell\bar{\nu}_{\ell}$. For example, the TGC process, seen in figure 3.3, which does not have a intermediate state of two W bosons, can also produce a final state of ${\rm q}\bar{\rm q}\ell\bar{\nu}_{\ell}$. There are many more processes which produce the same final state which do not contain the TGC vertex or an intermediate state of two W bosons [74]. It is impossible to separate out these events in the data so they are considered as part of the signal.

The processes producing a final state of ${\rm q}\bar{\rm q}\ell\bar{\nu}_{\ell}$ are called the Charged Current (CC) processes. They can be split into three sub-sets; CC03, which are the W-pair signal events shown figure 4.5. CC10, which are the processes capable of producing a final state with the lepton being an electron, a muon or a tau, this set includes the CC03 diagrams. The extra diagrams needed to complete this set are shown in figure 4.6. Finally there is the CC20 group which is all processes which produce a final state of an electron, an anti-neutrino and a quark anti-quark pair. This set includes the ten diagrams from the CC10 set plus ten more diagrams that have a final state which can have only an electron or a positron as the lepton in the final state, shown in figure 4.7.

Figure 4.5: CC03 diagrams.

Figure 4.6: This set of diagrams plus the CC03 set form the group known as CC10 diagrams.

Figure 4.7: This set of diagrams plus the CC10 set form the group known as CC20 diagrams.