Event shapes in Soft Colinear Effective Theory

• Applicant: Professor Dr. Vicent Mateu Barreda
• Subject Area: Nuclear and Elementary Particle Physics, Quantum Mechanics, Relativity, Fields
• Term: from 2009 to 2012
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 162126050

A traditional method for testing the theory of strong interactions (QCD) at high precision is the analysis of jet cross sections at e+e–colliders. Event-shape distributions, infrared-safe single variable distributions that represent projections of jet cross section onto the dijet limit, play a special role as they have been measured extensively with small experimental uncertainties at LEP and at all the previous e+e–collider experiments. On the theoretical side event shapes are accessible to high order analytic computations and thus have been used in many jet analyses in the past that aimed at precise determinations of the strong coupling αѕ.Generically, event-shape distributions are strongly peaked in the dijet limit where two back-to-back jets are produced, and they show a falling and flat tail in the three- and multi-jet region. All these regions require different theoretical methods to obtain accurate predictions. Prior to this work only data in the tail region between the peak in the dijet limit and the multi-jet tail region were ever used for measurements of αѕ since only in this region theoretical computations were reliable. Thus only about a third of the available data was ever analyzed. In this project the theoretical framework is set up to coherently analyse data for differential event-shape distributions from all the regions, and to determine at the same time the strong coupling αѕ and a non-perturbative soft distribution function. This function governs soft particle radiation between the jets, which is relevant to describe the distributions in the peak region. 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. This project can serve as a starting point in defining and analyzing event-shape variables in deep inelastic scattering (DIS), and at the Large Hadron Collider.

• DFG Programme: Research Grants