Precision event shapes with massive quarks

Resum

In the quest of searching for physics beyond the Standard Model, increasing the control and precision on the theoretical predictions is of utmost importance to understand the origin of the discrepancies found when comparing to experimental data. In this sense, QCD is the sector in which more effort has to be invested due to the slow convergence of the associated perturbative series and its non-perturbative aspects, which are always present no matter how large the energy is. The differential cross section distributions in terms of observables called event shapes, which contain information about the geometric properties of the particles’ momenta in the final state, are very sensitive to QCD dynamics and therefore have been studied for many years to determine the parameters involved in these interactions. In high-energy experiments, most of the time it is sufficient to use the approximation that all particles in the final state are massless, but for high-precision calculations or if one is interested in cases where the quark mass is a dominant effect, this approximation is no longer valid. While the theoretical computation for massless quarks at e+e− colliders has been pushed to unprecedented precision in recent years, computations for massive quarks remain at a lower precision and therefore the goal of this thesis is to fill in that gap. Considering non-vanishing masses opens the possibility to varying the scheme in the definition of an event shape, so we first study each of the possible schemes in the collinear limit and obtain the corresponding distribution for different observables. Next, we analyze the production of heavy quarks when measuring also the orientation of the final state with respect to the beam axis. Then the computation of the effects of this parameter on virtual quantum corrections is presented through the standard method, and finally the development of a simpler procedure based on series expansions is discussed