RevModPhys.84.1477】Tests of the standard electroweak model at the energy frontier

Approach discussed in sec ii where the coefcients of

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Unformatted text preview: rs invoked in the effective Lagrangian approach are unnecessary in an effective-field-theory approach. In the presence of new physics, neutral TGCs (those involving only and Z bosons) can contribute to Z and ZZ production. As described, neutral TGCs are anomalous by their very nature since these couplings are absent in the SM. For each of the diboson final states Z and ZZ, one can follow an analogous procedure to the anomalous charged TGCs (those involving a W boson) by writing down the most general effective Lagrangian that respects Lorentz invariance and electromagnetic gauge invariance (Baur and Berger, 1993; Baur and Rainwater, 2000). Using prescriptions detailed by Baur and Berger (1993) and Baur and Rainwater (2000), the effective Lagrangians introduce anomalous coupling parameters hV ðV ¼ ; Z and i ¼ 3; 4Þ i0 V and fj0 ðV ¼ ; Z and j ¼ 4; 5Þ, respectively, which can be constrained through an analysis of Z and ZZ production in high-energy collider data. It is important to note that, under the assumption of on-shell Z bosons, the Z Z couplings contributing to Z production and ZZ couplings contributing to ZZ production are completely independent (Baur and Rainwater, 2000). In general, the effects on observables from turning on anomalous TGCs are correlated. When we refer to ‘‘1D limits,’’ we refer to the limits derived on one parameter when the others are set to their SM values. There are a few important differences regarding the study of diboson physics in particle collisions at LEP, Tevatron, and the LHC that are worth pointing out at this stage:  At LEP, eþ eÀ collisions occur at a well-defined energy that is set by the accelerator. Therefore, the center-ofmass energy is known with good precision and there are no form factors in anomalous coupling analyses.  In eþ eÀ collisions, the initial state has zero electric charge. Therefore, exclusive states with net charge, such as WZ and W , cannot be produced at LEP. The WW and ZZ states can and have been produced and studied at LEP. A measurement of the WW cross section over a scan in beam energy dramatically illustrates the existence of the WWZ coupling in electroweak theory (Quigg, 2009). pffiffiffi  At hadron colliders, s is fixed for long periods of time (defining different periods of the accelerator operation pffiffiffi ^ that change very infrequently), but s varies collision byffi collision. Any anomalous couplings are likely to be pffiffi ^ s dependent. The form factor ansatz used ffiffiffi cut off the p to ^ anomalous coupling parameters at large s to preserve S-matrix unitary of the amplitude reflects this dependence. For this reason, it is reasonable to expect that, once a sufficient amount of integrated luminosity has been acquired, the higher-energy reach afforded by high-energy hadron collisions will lead to better sensitivity to anomalous couplings as compared to the limits from LEP, despite larger backgrounds in a typical hadron collision event. In other...
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