FCNC transitionsc→uγands→dγinBc→Bu*γandBs→Bd*γdecays

Abstract

We propose the ${B}_{c}\ensuremath{\rightarrow}{B}_{u}^{*}\ensuremath{\gamma}$ decay as the most suitable probe for the flavor changing neutral transition $\stackrel{\ensuremath{\rightarrow}}{c}u\ensuremath{\gamma}.$ We estimate the short and long distance contributions to this decay within the standard model and we find them to be comparable; this is in contrast with radiative decays of D mesons that are completely dominated by the long distance contributions. Since the $\stackrel{\ensuremath{\rightarrow}}{c}u\ensuremath{\gamma}$ transition is very sensitive to the physics beyond the standard model, the standard model prediction ${Br(B}_{c}\ensuremath{\rightarrow}{B}_{u}^{*}\ensuremath{\gamma})\ensuremath{\sim}{10}^{\ensuremath{-}8}$ obtained here opens a new window for future experiments. The detection of ${B}_{c}\ensuremath{\rightarrow}{B}_{u}^{*}\ensuremath{\gamma}$ decay at a branching ratio well above ${10}^{\ensuremath{-}8}$ would signal new physics. In addition we study the $\stackrel{\ensuremath{\rightarrow}}{s}d\ensuremath{\gamma}$ transition in ${B}_{s}\ensuremath{\rightarrow}{B}_{d}^{*}\ensuremath{\gamma}$ decay and we find it to be dominated by the long distance contribution. We use the Isgur-Scora-Grinstein-Wise constituent quark model for the calculation of these decays.