Applying SCET to parton showers

Abstract

In this thesis we study corrections to parton showers in the context of soft collinear effective theory (SCET). Monte Carlo event generators like Pythia or Herwig are heavily used by experimentalists to simulate events and they are indispensable tools to make exclusive theoretical predictions. They are based on a leading log parton shower algorithm that allows to resum the dominant contributions in the soft and collinear radiation. In this work we construct a framework to classify corrections to the parton shower that can be used to systematically improve event generators. We formulate parton showers as a standard matching procedure between a tower of soft collinear effective field theories called SCETi. We find two different kinds of corrections: hard-scattering corrections and jet-structure corrections. To relate these different effective field theories we make use of an important symmetry of SCET, called reparametrization invariance. In order to systematically study this symmetry, we construct operators that are invariant under reparametrization and we use them to find a minimal basis of operators that are homogeneous in the power counting. Complete basis of operators are constructed for pure glue operators for deep inelasting scattering at twist-4, for production of two and three jets from e+e- and for production of two jets via gluon fusion.