Reducing model dependence of spectator effects in inclusive decays of heavy baryons

TL;DR

This paper investigates how light spectator quarks influence inclusive decay rates of heavy baryons, revealing that certain assumptions about matrix elements are invalid and that lifetime differences are smaller than previously thought.

Contribution

It extends previous analyses by explicitly evaluating matrix elements of four-quark operators and shows that color antisymmetry assumptions are significantly broken, reducing predicted lifetime differences.

Findings

Color antisymmetry of matrix elements is significantly broken.

Flavor-singlet decay rate shifts are strongly suppressed.

Lifetime differences between Lambda_b and B_d are unlikely to exceed 10%.

Abstract

The dependence of inclusive weak decay rates of heavy hadrons on light spectator quarks is considered. The analysis of a previous work on relating the effects in b baryons to those in charmed baryons is extended to explicit evaluation of the matrix elements of certain four-quark operators over heavy baryons. It is shown that the usually postulated color antisymmetry of these matrix elements is significantly broken. The flavor-singlet shift of inclusive decay rates of b baryons due to the spectator effects is shown to be strongly suppressed in the leading-log approximation. Combined with the results for the flavor non-singlet splittings, this observation allows to argue, in a less model-dependent way, than before, that within the present understanding of the spectator effects it is highly unlikely that the lifetimes of the Lambda_b and the B_d can be split by more than 10%.