Abstract
Abstract
The lifetimes of bottom and charmed hadrons are analyzed within the framework of the heavy quark expansion (HQE). Lifetime differences arise from the spectator effects such as weak W-annihilation and Pauli interference. Spectator effects originating from dimension-7 four-quark operators are derived. Hadronic matrix elements of four-quark operators are parameterized in a model-independent way. Using the dimension-6 bag parameters recently determined from HQET sum rules and the vacuum insertion approximation for meson matrix elements of dimension-7 operators, the calculated B meson lifetime ratios τ(B
+)/τ(B
d
0
) = 1.074
− 0.016
+ 0.017
and τ(B
s
0
)/τ(B
d
0
) = 0.9962 ± 0.0024 are in excellent agreement with experiment. Likewise, based on the quark model evaluation of baryon matrix elements, the resulting baryon lifetime ratios τ(Ξ
b
−
)/τ(Λ
b
0
), τ(Ξ
b
−
)/τ(Ξ
b
0
), τ(Ω
b
−
)/τ(Ξ
b
−
) and the Λ
b
− B
0 lifetime ratio τ(Λ
b
0
)/τ(B
d
0
) = 0.953 also agree well with the data. Contrary to the bottom hadron sector where the HQE in 1/m
b
works well, the HQE to 1/m
c
3
fails to give a satisfactory description of the lifetimes of both charmed mesons and charmed baryons. This calls for the subleading 1/m
Q
corrections to spectator effects. The relevant dimension-7 spectator effects are in the right direction for explaining the large lifetime ratio of τ(Ξ
c
+
)/τ(Λ
c
+
). However, the destructive 1/m
c
corrections to Γ(Ω
c
0
) are too large to justify the validity of the HQE, namely, the predicted Pauli interference and semileptonic rates for Ω
c
0
become negative. Demanding these rates to be positive for a sensible HQE, we find the lifetime pattern τ(Ξ
c
+
) > τ(Ω
c
0
) > τ(Λ
c
+
) > τ(Ξ
c
0
), contrary to the current hierarchy τ(Ξ
c
+
) > τ(Λ
c
+
) > τ(Ξ
c
0
) > τ(Ω
c
0
). We conclude that the Ω
c
0
, which is naively expected to be shortest-lived in the charmed baryon system owing to the large constructive Pauli interference, could live longer than the Λ
c
+
due to the suppression from 1/m
c
corrections arising from dimension-7 four-quark operators. The new charmed baryon lifetime pattern needs to be tested in forthcoming experiments.
Publisher
Springer Science and Business Media LLC
Subject
Nuclear and High Energy Physics
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