  Heavy quark expansion can nicely explain the lifetime of $\Lambda_{b}$.
However, there still exist sizable uncertainties from the four-quark operator
matrix elements of $\Lambda_{b}$ in $1/m_{b}^{3}$ corrections, which describe
the spectator effects. In this work, these four-quark operator matrix elements
are investigated using full QCD sum rules for the first time. At the QCD level,
contributions from up to dimension-6 four-quark operators are considered. Our
method of calculating high-dimensional operator matrix elements is promising to
be used to resolve the $\Omega_{c}$ lifetime puzzle.
