Lifetimes of doubly charmed baryons

Abstract

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 Ξcc++ baryon is longest-lived in the doubly charmed baryon system owing to the destructive Pauli interference absent in the Ξcc+ and Ωcc+. In the presence of dimension-seven contributions, its lifetime is reduced from ∼5.2×10-13 s to ∼3.0×10-13 s. The Ξcc+ baryon has the shortest lifetime of order 0.45×10-13 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 Ωcc+. Contrary to Ξcc baryons, τ(Ωcc+) becomes longer in the presence of dimension-seven effects and the Pauli interference Γ+int even becomes negative. This implies that the subleading corrections are too large to justify the validity of the HQE. Demanding the rate Γ+int to be positive for a sensible HQE, we conjecture that the Ωc0 lifetime lies in the range of (0.75∼1.80)×10-13 s. The lifetime hierarchy pattern is τ(Ξcc++)>τ(Ωcc+)>τ(Ξcc+) and the lifetime ratio τ(Ξcc++)/τ(Ξcc+) is predicted to be of order 6.7.