# Group of Barbara Jäger

- Members
- B. Jäger, M. Billoni, A. von Manteuffel, S. C. Thier,

Our knowledge of the fundamental building blocks of our universe is summarized in the Standard Model of elementary particles. In a variety of experiments many components of this picture have been verified with great precision. Yet, the mechanism responsible for the masses of the weak gauge bosons and fermions still awaits discovery.

With the start-up of the Large Hadron Collider (LHC) at CERN, the world’s largest laboratory for high energy physics, a new era in elementary particle physics has begun. Proton-proton collisions at unprecedented energies will reveal whether extensions of the Standard Model are necessary to account for the interactions of all particles observed to date. Most imminently, the LHC provides us with unequalled opportunities for a discovery of the Higgs boson, the last missing entity of the Standard Model.

For making optimal use of the LHC’s capabilities, a precise understanding of signal and background scattering processes is needed. From the theoretician’s side this requires detailed phenomenological studies as well as the calculation of high-energy scattering processes with highest accuracy. Our research is centered around these themes:

### Phenomenology of Elementary Particles

Data from modern collider experiments such as the Tevatron at Fermilab and the CERN LHC provide us with excellent opportunities for a precise determination of the elementary particles’ properties, such as their masses and couplings. We are working on the phenomenology of processes that serve to further constrain these parameters in the context of the Standard Model, but will also help to spot signatures of new physics, such as supersymmetry or extra dimensions.

### Precision calculations for High-Energy Scattering Processes

Providing precise predictions for collider observables requires the
calculation of high-energy scattering processes beyond the lowest order in
perturbation theory in the strong and electroweak interactions. The focus of
our work is on **multi-leg** processes in the context of the Standard Model and
some of its extensions:

- NLO-QCD Corrections to Processes with Heavy Gauge Bosons
- Precision Calculations for Processes involving Supersymmetric Particles
- Interference Effects between QCD and Electroweak Processes
- NLO Electroweak Corrections to Hadronic Processes
- NLO-QCD Corrections to Polarized Scattering Processes at Hadron-Hadron and Lepton-Hadron Colliders

Matching the experimental precision of specific reference processes requires predictions beyond NLO. Our focus is on analytical results for **multi-loop** corrections to key processes within the Standard Model:

- NNLO Corrections to Top Quark Pair Production at Hadron Colliders

### Development of Monte-Carlo-Programs for Collider Experiments

A comprehensive analysis of high-energy scattering reactions greatly profits from flexible Monte-Carlo programs that allow for the simulation of collider processes within realistic settings. Computer packages we are working with are:

- VBFNLO: a flexible Monte-Carlo program for the simulation of processes with electroweak bosons
- POWHEG-BOX: a tool for merging NLO-QCD calculations with parton-shower programs

### Development of Computer Algebra Tools

Multi-loop calculations require heavy usage of modern computer algebra methods. We contribute to the development of a computer program to automate core tasks of such calculations.

- Reduze: a program to analyze Feynman graphs and reduce loop integrals.