Dark photon and dark Z mediated B meson decays

Abstract

We study flavor changing neutral current decays of B and K mesons in the dark U(1)D model, with the dark photon/dark Z mass between 10 MeV and 2 GeV. Although the model provides an improved fit (compared to the standard model) to the differential decay distributions of B → K(∗)ℓ+ℓ−, with ℓ = μ, e, and Bs→ ϕμ+μ−, the allowed parameter space is ruled out by measurements of atomic parity violation, K+→ μ+ + invisible decay, and $$ {B}_s-{\overline{B}}_s $$ B s − B ¯ s mixing, among others. To evade constraints from low energy data, we extend the model to allow for (1) additional invisible ZD decay, (2) a direct vector coupling of ZD to muons, and (3) a direct coupling of ZD to both muons and electrons, with the electron coupling fine-tuned to cancel the ZD coupling to electrons via mixing. We find that only the latter case survives all constraints.