Lifetimes of doubly charmed baryons

The lifetimes of doubly charmed hadrons are analyzed within the framework of the heavy quark expansion (HQE). Lifetime differences arise from spectator effects such as W-exchange and Pauli interference. The Xi(++)(cc) baryon is longest-lived in the doubly charmed baryon system owing to the destructive Pauli interference absent in the Xi(+)(cc) and Omega(+)(cc). In the presence of dimension-seven contributions, its lifetime is reduced from similar to 5.2 x 10(-13) s to similar to 3.0 x 10(-13) s. The Xi(+)(cc) baryon has the shortest lifetime of order 0.45 x 10(-13) s due to a large contribution from the W-exchange box diagram. It is difficult to make a precise quantitative statement on the lifetime of Omega(+)(cc). Contrary to Xi(cc) baryons, tau(Omega(+)(cc)) becomes longer in the presence of dimension-seven effects and the Pauli interference Gamma(int)(+) even becomes negative. This implies that the subleading corrections are too large to justify the validity of the HQE. Demanding the rate Gamma(int)(+) to be positive for a sensible HQE, we conjecture that the Omega(0)(c) lifetime lies in the range of (0.75 similar to 1.80) x 10(-13) s. The lifetime hierarchy pattern is tau(Omega(+)(cc)) > tau(Xi(+)(cc)) and the lifetime ratio tau(Xi(++)(cc))/tau(Xi(+)(cc)) is predicted to be of order 6.7.