New physics contributions to Bˉs→π0(ρ0) η(′)\bar{B}_s \rightarrow \pi^0(\rho^0 )\,\eta^{(')} decays

The decay modes $\bar{B}_s \rightarrow \pi^0(\rho^0 )\,\eta^{(')}$ are dominated by electroweak penguins that are small in the standard model. In this work we investigate the contributions to these penguins from a model with an additional $U(1)'$ gauge symmetry and show there effects on the branching ratios of $\bar{B}_s \rightarrow \pi^0(\rho^0 )\,\eta^{(')}$. In a scenario of the model, where $Z^\prime$ couplings to the left-handed quarks vanish, we show that the maximum enhancement occurs in the branching ratio of $\bar B^0_s\to \,\pi^0\,\eta'$ where it can reach $6$ times the SM prediction. On the other hand, in a scenario of the model where $Z^\prime$ couplings to both left-handed and right-handed quarks do not vanish, we find that $Z^\prime$ contributions can enhance the branching ratio of $B^0_s\to\,\rho^0\,\eta$ up to one order of magnitude comparing to the SM prediction for several sets of the parameter space where both $\Delta M_{B_s}$ and $S_{\psi\phi}$ constraints are satisfied. This kind of enhancement occurs for a rather fine-tuned point where $\Delta M_{B_s}$ constraint on $\mid S_{SM} (B_s) + S_{Z'} (B_s)\mid$ is fulfilled by overcompensating the SM via $S_{Z'} (B_s) \simeq -2 S_{SM} (B_s)$.Comment: 25 pages, 7 figures. Version accepted for publication in European Physical Journal

Charged Higgs contribution to Bˉs→ϕπ0\bar{B}_s \rightarrow \phi \pi^0 and Bˉs→ϕρ0\bar{B}_s \rightarrow \phi \rho^0

We study the decay modes $\bar{B}_s\to \phi \pi^0$ and $\bar{B}_s\to \phi \rho^0$ within the frameworks of two-Higgs doublet models type-II and typ-III. We adopt in our study Soft Collinear Effective Theory as a framework for the calculation of the amplitudes. We derive the contributions of the charged Higgs mediation to the weak effective Hamiltonian governing the decay processes in both models. Moreover we analyze the effect of the charged Higgs mediation on the Wilson coefficients of the electrowek penguins and on the branching ratios of $\bar{B}_s\to \phi \pi^0$ and $\bar{B}_s\to \phi \rho^0$ decays. We show that wthin two-Higgs doublet models type-II and type-III the Wilson coefficients corresponding to the electroweak penguins can be enhanced due to the contributions from the charged Higgs mediation leading into enhancement in the branching ratios of $\bar{B}_s\to \phi \pi^0$ and $\bar{B}_s\to \phi \rho^0$ decays. We find that, within two-Higgs doublet models type-II, the enhancement in the branching ratio of $\bar{B}_s\to \phi \pi^0$ can not exceed $18\%$ with respect to the SM predictions. For the branching ratio of $\bar{B}_s\to \phi \rho^0$, we find that the charged Higgs contribution in this case is small where the branching ratio of $\bar{B}_s\to \phi \rho^0$ can be enhanced or reduced by about $4\%$ with respect to the SM predictions. For the case of the two-Higgs doublet models type-III we show that the branching ratio of $\bar{B}_s\to \phi \pi^0$ can be enhanced by about a factor $2$ of its value within two-Higgs doublet models type-II. However no sizable enhancement with respect to the SM predictions can be obtained for both $\bar{B}_s\to \phi \pi^0$ and $\bar{B}_s\to \phi \rho^0$ decays.Comment: 22 pages,4 figures. Accepted version for publication in Physics Letters

Connecting b→sℓℓˉb\to s\ell\bar\ell anomalies to enhanced rare nonleptonic Bˉs0\bar{B}_s^0 decays in Z′Z' model

The present data on a number of observables in $b\to s\mu^+\mu^-$ processes manifest some tensions with the standard model (SM). Assuming that these anomalies have a new physics origin, we consider the possibility that a $Z'$ boson is responsible for them. We further assume that its interactions with quarks also affect rare nonleptonic decays of the $\bar B_s^0$ meson which are purely isospin-violating and tend to be dominated by electroweak-penguin contributions, namely $\bar B_s^0\to(\eta,\eta',\phi)(\pi^0,\rho^0)$. Most of these decays are not yet observed, and their rates are expected to be relatively small in the SM. Taking into account constraints from various measurements, including the evidence for $\bar B_s^0\to\phi\rho^0$ recently seen by LHCb, we find that the $Z'$ effects on $\bar B_s^0\to(\eta,\phi)\pi^0$ can make their rates bigger than the SM predictions by up to an order of magnitude. For $\bar B_s^0\to\eta'\pi^0,(\eta,\eta')\rho^0$, the enhancement factors are at most a few. Since the $Z'$ contributions to the different channels depend on different combinations of its couplings, observations of more of these decays in future experiments, along with improved $b\to s\mu^+\mu^-$ data, will probe this $Z'$ scenario more thoroughly.Comment: 17 pages, 4 figures, somewhat revised, comments & references added, matches publicatio