Leading log approximation for parton showers

We correct and extend the leading log parton shower formalism, which is widely used to compute the predictions of QCD for high-energy experiments, by including the information carried by the polarization of the partons. For observables that do not depend on the spins of the final state particles, this introduces a correlation between the azimuthal angles that is not included in current calculations. It also allows one to compute parton showers for observables that do not depend on the final state spins.