CERN-THESIS-2012-153 26/07/2012 - CERN Document Server
CERN-THESIS-2012-153 26/07/2012 - CERN Document Server
CERN-THESIS-2012-153 26/07/2012 - CERN Document Server
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The CKM matrix is a 3 × 3 unitary matrix, V †<br />
CKM VCKM = 1, which can be parameterized by three mixing<br />
angles and a CP-violating phase. The unitarity of the CKM matrix imposes:<br />
∗<br />
i<br />
VijVik = δjk and ∗<br />
i<br />
VijVkj = δik<br />
(2.31)<br />
The current experimental values of the matrix elements are:<br />
⎛<br />
⎜<br />
⎝<br />
|Vud| |Vus| |Vub|<br />
|Vcd| |Vcs| |Vcb|<br />
|Vtd| |Vts| |Vtb|<br />
⎞<br />
⎛<br />
⎟<br />
⎠ =<br />
⎜<br />
⎝<br />
0.97427 ± 0.00015 0.22534 ± 0.00065 0.00351 +0.00015<br />
−0.00014<br />
0.22520 ± 0.00065 0.97344 ± 0.00016 0.0412 +0.0011<br />
−0.0005<br />
0.00867 +0.00029<br />
−0.00031<br />
0.0404 +0.0011<br />
−0.0005<br />
0.999146 +0.000021<br />
−0.000046<br />
⎞<br />
⎟<br />
⎠<br />
(2.32)<br />
The magnitudes of the CKM elements just quoted were extracted from Reference [20]. These are determined<br />
by a global fit that uses all available measurements and imposes the SM constraints (three generation<br />
unitarity).<br />
W- and Z-bosons Production and Decay Modes<br />
At pp colliders the electroweak gauge bosons are produced as single particles or in pairs through a parton-<br />
parton process, for example the Drell-Yan production of W- and Z-bosons, q¯q → Z and q¯q ′ → W. The<br />
Z-bosons decay into a pair of opposite charge fermions, that can either be two same-flavor leptons (e, µ, τ<br />
or ν) or two same-flavor quarks. The latter represents a hadronic final state, and it is the one with largest<br />
branching fraction (∼ 70%). The W-boson can decay to a lepton and a neutrino of the same generation, or<br />
two quarks of the first or second generation. In this case too, the hadronic final state carries most of the<br />
branching fraction (∼ 68%). Figure 2.2 shows the Feynman diagrams for the decays of these two bosons.<br />
(a) (b)<br />
Figure 2.2: Decay modes of the W- and Z-bosons. In the case of the W-boson, the lepton ℓ carry the same<br />
charge as the boson.<br />
13