Λblifetime puzzle in heavy-quark expansion

Lifetime differences of heavy hadrons can be consistently computed in heavy-quark expansion. The leading effects appear through spectator interactions at order ${1/m}_b^3.$ We compute a well-defined subset of ${1/m}_b^4$ corrections to the lifetime ratio of a ${\Lambda }_b$ baryon and $B_d$ meson. We find that these corrections are large and should be taken into account in the systematic analysis of heavy hadron lifetimes. We claim that they could shift the ratio ${\tau }_{{\Lambda }_b}/{\tau }_{B_d}$ by as much as $-4.5\%,$ significantly reducing the discrepancy between the theoretical predictions and experimental observations.