FCNC in Concurrent Dark Photon and Dark $Z$ Models

TL;DR

This paper re-evaluates constraints on a light dark vector boson model from B-meson decay data, correcting previous calculations, and finds that most parameter space is excluded by existing experimental bounds.

Contribution

It provides the correct analysis of dark Z contributions to FCNC B decays and updates the constraints on the model's parameters using comprehensive experimental data.

Findings

Most of the parameter space is ruled out by experimental bounds.

Corrected calculations show smaller allowed mixing parameters.

Some bounds are relaxed with additional dark Z interactions.

Abstract

In this work we fit the available binned data of the differential decay distribution of the exclusive $B \to K^{(*)} \ell^+ \ell^-$ and $B_s \to \phi \mu^+ \mu^-$ decays to the mass and mixing parameters of a light dark vector boson model. Due to an incorrect assessment of the dominant contribution of the dark $Z$ model to the FCNC B-meson decays, a previous work in literature reported that $\mathcal{O}(1)$ mixings were allowed by the data. In this talk we report the correct calculations and constraints on the mixing parameters as well as the mass of the dark vector boson using the marginalization technique. We also study other relevant bounds on the parameter space from low energy experiments such as the atomic parity violation, $K^+ \to \mu^+ + invisible$ decay, $B_s - \overline{B}_s$ mixing etc and find that inspite of obtaining a good fit to the experimental $b \to s \ell^+ \ell^-$ data, the entire parameter space gets ruled out from some of the above bounds. In case of a model with tiny mixing and additional interaction of the dark $Z$ to the muon, some bounds are relaxed while some others are violated.