Decay of the Z' gauge boson with lepton flavor violation

TL;DR

This paper investigates the decay of a hypothetical Z' gauge boson into muon and electron, analyzing constraints from various lepton flavor violation processes to estimate the decay's branching ratio in extended models.

Contribution

It provides a detailed analysis of the Z' to mu e decay, estimating its branching ratio based on experimental bounds from muon decay processes across different Z' models.

Findings

The most restrictive coupling bound comes from the Z_{LR} boson via mu-e conversion.

The Z_ ext{chi} boson provides the tightest bound from mu to 3e decay.

The predicted branching ratio can be as high as 10^{-4} or as low as 2×10^{-7} depending on the model.

Abstract

The flavor-violating decay of a new neutral massive gauge boson $Z^\prime\to\mu e$ is analyzed in the context of extended models, in which this particle emerges. By means of the analysis of the $\mu\to e\gamma$ decay, $\mu-e$ conversion process in nuclei and the $\mu \to e e^{+}e^{-}$ decay, the strength of the $Z^\prime\mu e$ coupling is estimated and used to calculate the branching ratio of the $Z^\prime\to \mu e$ decay. This is done for the so-called $Z_S,\,Z_{LR},\,Z_\chi, Z_\psi$ and $Z_\eta$ bosons. We found that, through the $\mu-e$ conversion process, the most restrictive bound for the coupling is provided by the $Z_{LR}$ boson. Meanwhile, by means of the $\mu \to e e^{+}e^{-}$ decay, the most restrictive bound for the $Z^\prime\mu e$ coupling is provided by the $Z_\chi$ boson. However, if we concentrate on the less restrictive prediction for the Br($Z^\prime\to \mu e$), this comes from the $Z_\eta$ boson and the resulting branching ratio is less than $10^{-4}$. On the other hand, if we consider the most restrictive bound, the branching ratio for the process is below $2\times 10^{-7}$, which results from the $Z_{RL}$ boson, and is obtained through the $\mu-e$ conversion process.