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arXiv · 2309.16794

Electroweak Precision Measurements of a Nearly-Degenerate $Z^\prime$-$Z$ System

Dayun Qiu·Yi-Lei Tang
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Abstract

In this paper, we discuss the possibility to probe a nearly-degenerate $Z^{\prime}$-$Z$ system by analyzing the $Z$-lineshape at an electron-positron collider. Compared with the usual $Z^{\prime}$ in the literature well separated with the standard model (SM) $Z$ boson in mass, the nearly-degenerate $Z^{\prime}$-$Z$ mixing affects the observed effective ``oblique parameters'' $\tilde{S}$, $\tilde{T}$, $\tilde{U}$, and the effective deviation of ``number of neutrino species'' $\delta \tilde{N}_{\nu}$ in a more complicated way and cannot be simply computed perturbatively up to a particular order. Aiming at solving this problem, we write down a general simplified effective Lagrangian and enumerate some parameter spaces corresponding to some typical models, and suggest a method to extract the constraints by looking into the line-shape of the $Z$-like resonance at an electron-positron collider.

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Dayun Qiu, Yi-Lei Tang. 2023-09-28. Electroweak Precision Measurements of a Nearly-Degenerate $Z^\prime$-$Z$ System. https://arxiv.org/abs/2309.16794

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