Background in the search for dark photon in e+e− annihilation

An important ingredient in the search for new particles and rare phenomena is the correct estimation of the expected contribution from processes originating from the Standard Model. The search for a new vector degree of freedom, the Dark photon, is affected by the precise knowledge of the electromagnetic interactions. In the case of invisibly decaying Dark photon produced in e+e− annihilation the evaluation of the background should be performed with less than 1% uncertainty since the sensitivity of the proposed experiments depend lineary on it. The present status of the background estimation and the considered processes are reviewed and discussed, with a special attention devoted to the possible unresolved issues