TGCs and W Pair Production at LEP

LEP is an electron-positron collider which has run above the W-pair production threshold since 1996. The coupling of three gauge bosons, as shown in figure 3.1, is possible at LEP through the annihilation of the leptons into a photon or ${\rm Z}^{0}$ which then decays into two W bosons (figure 3.2). There is also a third possible process with the triple gauge vertex, the t-channel process shown in figure 3.3. The first two TGC processes produce pairs of W bosons, however, the t-channel produces only one and so is, accordingly, known as the single W channel or process.

Figure 3.2: The two W-pair production processes which contain the trilinear gauge vertex.

Figure 3.3: The t-channel single W production process which contains the trilinear gauge vertex.

There is a third channel that produces an identical final state of a pair of W bosons as the TGC W-pair production channel, but does not include the TGC vertex. This is known as the neutrino exchange, or t-channel W-pair production channel and is shown in figure 3.4. Although the single W production has fairly different characteristics to the TGC W-pair production, and so can be separated from W-pair events, the t-channel W-pair production has very similar characteristics, therefore all three W-pair production processes have to be considered together.

Figure 3.4: The t-channel W-pair production process. This is the only W-pair production process at LEP that does not contain the trilinear gauge vertex.