Weak decays of doubly heavy baryons: decay constants

Inspired by the recent observation of the Xi(++)(cc) by the LHCb Collaboration, we explore the decay constants of doubly heavy baryons in the framework of QCD sum rules. With the Xi(cc), Xi(bc), Xi(bb), and Omega(cc), Omega(bc), Omega(bb) baryons interpolated by three-quark operators, we calculate the correlation functions using the operator product expansion and include the contributions from operators up to dimension six. On the hadron side, we consider both contributions from the lowest-lying states with J(P) =1/2(+) and from negative parity baryons with J(P) =1/2(-). We fi nd that the results are stable and the contaminations from negative parity baryons are not severe. These results are ingredients for the QCD study of weak decays and other properties of doubly-heavy baryons.