Ultra-Granular Calorimeter Performances for the Heavy Flavor Physics Program at the Z Peak

Various decays of the B mesons are here used to establish the performances of an ultra-granular electromagnetic calorimeter for heavy flavour physics at an electron positron accelerator running at the Z peak. The silicon-tungsten electromagnetic calorimeter of the ILD concept is used for this purpose, enhanced by a timing capability. When possible, a $\pi$ 0 mass fit of $\gamma$$\gamma$ system is performed to improve the $\pi$ 0 energy resolution. It is also shown that in the presence in the final state of a photon without a $\pi$ 0 , the identification of genuine photon(s) versus fake photon(s) coming from K L 's, neutron's, debris of hadronic shower or other high energy $\pi$ 0 , is essential. It allows for a good precision and a good signal over background ratio for this kind of physics. The possible impact for the tau physics is discussed.