Abstract
New heavy neutral gauge bosons Z' are predicted by many models of physics beyond the Standard Model. It is quite possible that Z's are heavy enough to lie beyond the discovery reach of the CERN Large Hadron Collider LHC, in which case only indirect signatures of Z' exchanges may emerge at future colliders, through deviations of the measured cross sections from the Standard Model predictions. We discuss in this context the foreseeable sensitivity to Z's of W^\pm-pair production cross sections at the e^+e^- International Linear Collider (ILC), especially as regards the potential of distinguishing observable effects of the Z' from analogous ones due to competitor models with anomalous trilinear gauge couplings (AGC) that can lead to the same or similar new physics experimental signatures at the ILC. The sensitivity of the ILC for probing the Z-Z' mixing and its capability to distinguish these two new physics scenarios is substantially enhanced when the polarization of the initial beams and the produced W^\pm bosons are considered. A model independent analysis of the Z' effects in the process e^+e^- \to W^+W^- allows to differentiate the full class of vector Z' models from those with anomalous trilinear gauge couplings, with one notable exception: the sequential SM (SSM)-like models can in this process not be distinguished from anomalous gauge couplings. Results of model dependent analysis of a specific Z' are expressed in terms of discovery and identification reaches on the Z-Z' mixing angle and the Z' mass.
Highlights
The W ± boson pair production process e+ + e− → W + + W − (1)is a crucial one for studying the electroweak gauge symmetry in e+e− annihilation
Detailed examination of (1) at the International Linear Collider (ILC) will both test this sector of the standard model (SM) with the highest accuracy and throw light on New Physics (NP) that may appear beyond the SM
This reaction is sensitive to both the leptonic vertices and the trilinear couplings to W +W − of the SM Z and of any new heavy neutral boson that can be exchanged in the s-channel
Summary
Is a crucial one for studying the electroweak gauge symmetry in e+e− annihilation. Properties of the weak gauge bosons are closely related to electroweak symmetry breaking and the structure of the gauge sector in general. Two extra, heavy neutral gauge bosons appear as consequence of the symmetry breaking and, generally, only the lightest is assumed to be within reach of the collider It is defined, in terms of a new mixing angle β, by the linear combination. In the case of extended models considered here, e.g. E6, v′ and a′ are explicitly parametrized in terms of the angle β which characterizes the direction of the Z′-related extra U(1)′ generator in the E6 group space, and reflects the pattern of symmetry breaking to SU(2)L ×U(1)Y [1, 2, 4, 6]: v′ = cos√β ; cW 6 a′ = 1√ cos β + 2cW 6.
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