Anomalous $tq\gamma$ coupling effects in exclusive radiative B-meson decays

Abstract

The top-quark FCNC processes will be searched for at the CERN LHC, which are correlated with the B-meson decays. In this paper, we study the effects of top-quark anomalous interactions $tq\gamma$ in the exclusive radiative $B\to K^{\ast }\gamma$ and $B\to \rho \gamma$ decays. With the current experimental data of the branching ratios, the direct CP and the isospin asymmetries, bounds on the coupling ${\kappa }_{tcR}^{\gamma }$ from $B\to K^{\ast }\gamma$ and ${\kappa }_{tuR}^{\gamma }$ from $B\to \rho \gamma$ decays are derived, respectively. The bound on $|{\kappa }_{tcR}^{\gamma }|$ from $\mathcal{B}(B\to K^{\ast }\gamma )$ is generally compatible with that from $\mathcal{B}(B\to X_s\gamma )$. However, the isospin asymmetry $\Delta (K^{\ast }\gamma )$ further restrict the phase of ${\kappa }_{tcR}^{\gamma }$, and the combined bound results in the upper limit, $\mathcal{B}(t\to c\gamma )<0.21$, which is lower than the CDF result. For real ${\kappa }_{tcR}^{\gamma }$, the upper bound on $\mathcal{B}(t\to c\gamma )$ is about of the same order as the $5\sigma$ discovery potential of ATLAS with an integrated luminosity of $10{\mathrm{fb}}^{-1}$. For $B\to \rho \gamma$ decays, the NP contribution is enhanced by a large CKM factor $|V_{ud}/V_{td}|$, and the constraint on $tu\gamma$ coupling is rather restrictive, $\mathcal{B}(t\to u\gamma )<1.44\times 10^{-5}$. With refined measurements to be available at the LHCb and the future super-B factories, we can get close correlations between $B\to V\gamma$ and the rare $t\to q\gamma$ decays, which will be studied directly at the LHC ATLAS and CMS.

Comments: 25 pages, 15 figures, pdflatex