Heavy quarks provide a valuable guide to the study of weak interactions. Measurements of decay lifetimes and of semileptonic decay spectra of heavy, flavored mesons yield information on individual elements of the CKM matrix, as does the observation of heavy-meson particle–antiparticle transitions such as Bd–B̄d mixing. Long anticipated data involving detection of CP-violating signals have been found to be in accord with expectations of the Standard Model and have played a crucial role in constraining the sole complex phase in the CKM matrix.

Heavy-quark mass

At the level of the Standard Model lagrangian, the six quark masses are equivalent; they are all just input parameters that must each be determined experimentally. In the real world of particle phenomenology, quark mass divides into two sectors, ‘light’ (u, d, s) and ‘heavy’ (c, b, t). It is a hallmark of light-quark spectroscopy that hadron mass is not a direct reflection of quark mass. However, for hadrons which contain a heavy quark, the energy scale is set by the mass of the heavy quark. In the following, we discuss topics of special relevance to heavy-quark mass.

Running quark mass

Heretofore we have described the renormalization of quark mass in terms of the mass shift δm = m−m0, where m0 is the bare mass. We can also, for convenience, employ a multiplicative mass renormalization constant Zm with m0 = Zmm.