Rare Radiative $B_{c}\rightarrow D_{s1}(2460)\gamma$ Transition in QCD
  We investigate the radiative $B_{c} \to D_{s1} \gamma$ transition in the framework of QCD sum rules. In particular, we calculate the transition form factors responsible for this decay in both weak annihilation and electromagnetic penguin channels using the quark condensate, mixed and two-gluon condensate diagrams as well as propagation of the soft quark in the electromagnetic field as non-perturbative corrections. These form factors are then used to estimate the branching ratios of the channels under consideration. The total branching ratio of the $B_{c} \to D_{s1} \gamma$ transition is obtained to be in order of $10^{-5}$, and the dominant contribution comes from the weak annihilation channel. 
K. Azizi, N. Ghahramani, A. R. Olamaei
hep-ph