Inclusive and exclusive decays of heavy mesons

Abstract

From our undergraduate physics courses, we are all familiar with nuclear decay processes: we know that alpha ray decay is actually the emission of alpha particles (which consist of pairs of protons and neutrons), that beta ray decay is actually the emission of an electron, and that gamma ray decay is actually the emission of a gamma ray photon, all from an unstable atomic nucleus. What we might not have learned from our undergraduate physics is that these decays correspond to nuclear strong decay, weak decay and electromagnetic decay, respectively, or that quantum field theory can be used to determine these decay rates. In practice, it is easier to determine the decay rates for individual hadrons (which are particles. including protons and neutrons, which consist of quarks). This is done by calculating the decay rates of individual quarks and then either calculating, determining or estimating other factors that are related to the interactions between quarks. The best data comes from measurements of weak decays, mainly because weakly decaying particles, including those consisting of heavy quarks, exist long enough for their lifetimes to be measured. This then allows us to estimate parameters in the standard model for quark decays, parameters which place limits on the degree to which forward-back time symmetry is allowed to be broken within the confines of the standard model.