Project: When comparing renormalization group improved predictions of QCD for electron-positron event shape distributions such as thrust, supplemented by non-perturbative corrections based on dijet factorization, one can extract the QCD strong coupling constant. In these fits the results are several standard deviations below the world average. In the project we intend to attack the puzzling situation with an anewed multi-faceted effort to push further advancement on the theoretical description of event-shape distributions. First, the theoretical ingredients are now available to extend the precision perturbative differential cross section towards , i.e. one more order with respect to the current state of the art, which will further reduce the uncertainty from the truncation of perturbation theory. Together this will enable a reassessment of the convergence of perturbation theory and the size of the perturbative uncertainties. We also plan to incorporate new more accurate numerical fixed order  non-singular results and carry out new fits to examine the impact on the value of the strong coupling. The second and key important issue that we plan to address is the nature of nonperturbative hadronization corrections in the different regions of phase space, which could potentially have caused a bias.

Research Team: Miguel Benitez (U of Slamance), Andre H. Hoang (U of Vienna), Iain Stewart (MIT, Cambridge), Zhiquan Sun (MIT, Cambridge)

Guest of the Team: Anna Ferdinand (MIT, Cambridge)