  A short-distance heavy quark mass depends on two parameters, the
renormalization scale mu controlling the absorption of ultraviolet fluctuations
into the mass, and a scale R controlling the absorption of infrared
fluctuations. 1/R can be thought of as the radius for perturbative corrections
that build up the mass beyond its point-like definition in the pole scheme.
Treating R as a variable gives a renormalization group equation. We argue that
the sign of this anomalous dimension is universal: increasing R to add IR modes
decreases m(R). The flow improves the stability of conversions between mass
schemes, allowing us to avoid large logs and the renormalon. The flow in R can
be used to study IR renormalons without using bubble chains, and we use it to
determine the coefficient of the LambdaQCD renormalon ambiguity of the pole
mass with a convergent sum-rule.
