ESSCET · Event Shapes in Soft-Collinear Effective Theory

The aim of the project is to study jet cross sections in electron-positron, and hadron-hadron collisions. Event-shape distributions for electron-positron collisions have been measured extensively with small experimental uncertainties. On the theoretical side event shapes are accessible to high order analytic computations. This information can be used to make precise determinations of the strong coupling and the bottom mass. The theoretical framework is set up to coherently analyse data for differential event-shape distributions in electron-positron collisions, from the peak, tail, and far-tail regions, and to determine at the same time the strong coupling and a non-perturbative soft distribution function that governs soft particle radiation between the jets. Moments of this soft function are related to power corrections that can be determined in the multi-jet region. Consistency between soft function and power corrections provides another stringent test of QCD. Comparisons to other determinations constitute an important test of QCD. Event-shape distributions for hadron-hadron collisions are measured at the Tevatron, and will play a central role at the Large Hadron Collider (LHC). Although the experimental information of hadronic machines is not as accurate as in leptonic ones, one can probe higher energies, having the chance of searching for the Higgs boson, and particles beyond the Standard Model. Moreover, hadronic machines produce copious amounts of top pairs, allowing extensive studies of its properties, such as mass and decay width. On the theoretical side, studies of event shapes in hadronic collisions, employing Soft-Collinear Effective Theory (SCET) are just starting now. SCET is a new approach to jet physics based on field theory, making answers to open conceptual questions easier to achieve. This, together with the fact that the LHC is about to start, makes clear that this is the right time for making important contributions.