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W Pair Production
At LEP2, the three basic W-pair production diagrams contain
Z WW,
WW and t-channel
neutrino exchange (which dominates near the W-pair threshold).
The issue of directly reconstructing the mass of a heavy boson
naturally focusses on these events, since W-pairs have already been
produced in their thousands in each of the four LEP detectors.
Typical statistics of W pair events are shown in Table 1.
Table 1:
Year, e+e- centre-of-mass energy, integrated luminosity
per LEP experiment and approximate number of W-pair events per LEP
experiment.
Year |
(GeV) |
(pb-1)/expt |
NWW/expt |
1996 |
161 |
10 |
35 |
|
172 |
10 |
120 |
1997 |
183 |
57 |
850 |
1998 |
189 |
175 |
2700 |
Given that BR(W
q) 68% and that
the remaining decays are leptonic, one sees that the W pair sample subdivides
as follows: hadronic channel (WW
qq)
46%, semileptonic channels (WW
lq)
44% and the fully leptonic channels (WW
ll)
are
10%, where l denotes e, or .
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