D0 dimuon charge asymmetry from B_s system with Z' couplings and the recent LHCb result

TL;DR

This paper investigates whether flavor-changing Z' couplings can explain the D0 dimuon charge asymmetry anomaly, analyzing experimental constraints and showing the necessity of fine-tuning or additional contributions.

Contribution

It provides new limits on Z' couplings and demonstrates the difficulty of explaining the asymmetry within current constraints without fine-tuning or additional effects.

Findings

Z' couplings are highly constrained by LHCb data.

Impossible to fit the asymmetry within 1σ without new contributions in B_d.

Fine-tuned parameter regions are required for Z' explanations.

Abstract

The D0 collaboration has announced the observation of the like-sign dimuon charge asymmetry since 2010, which has more than 3\sigma deviation from the Standard Model prediction. One of the promising explanation is considering the existence of flavor changing Z' couplings to the b and s quarks which can contribute to the off-diagonal decay width in the B_s - \bar{B}_s mixing. Model construction is highly constrained by the recent LHCb data of 1fb^{-1} integrated luminosity . In this paper, we analyze the experimental constraints in constructing new physics models to explain the dimuon charge asymmetry from the CP violation of the B_s system. We present limits on Z' couplings and show that it is impossible to obtain the 1\sigma range of the dimuon charge asymmetry without the new contribution in the B_d system. Even with arbitrary contribution in the B_d system, the new couplings must be in the fine tuned region.