Measurement of the lifetime difference of B_d mesons: possible and worthwhile?

Abstract

We estimate the decay width difference ΔΓ_d/Γ_d in the B_d system including 1/m_b contributions and part of the next-to-leading order QCD corrections, and find it to be around 0.3%. We explicitly show that the time measurements of an untagged B_d decaying to a single final state isotropically can only be sensitive to quadratic terms in ΔΓ_d/Γ_d, and hence the use of at least two different final states is desired. We discuss such pairs of candidate decay channels for the final states and explore the feasibility of a ΔΓ_d/Γ_d measurement through them. The measurement of Γ_d would be essential for an accurate measurement of sin(2β) at the LHC. The nonzero width difference can also be used to identify new physics effects and to resolve a twofold discrete ambiguity in the B_d–B̅_d mixing phase. We also derive an upper bound on the value of ΔΓ_d/Γ_d in the presence of new physics, and point out some differences in the phenomenology of width differences in the B_s and B_d systems.