UZH > Department of Physics > Particle Theory Group
UZH > Department of Physics > Particle Theory

Collider Physics

The Large Hadron Collider (LHC) probes elementary particle interactions at unprecedented energies. Besides producing heavy short-lived particles, such as top quarks and electroweak gauge bosons, LHC opens the possibility to discover yet unobserved particles postulated in new physics models, such as for instance the supersymmetric partners of known particles or more exotic phenomena. Research carried out here investigates prospects for searching new phenomena at hadron colliders, as well as their implications for astrophysics and cosmology.

Higgs physics

After the Higgs boson discovery in July 2012, a new frontier to high energy physics is ahead of us. Our group is deeply involved in the physics of the Higgs boson, by providing accurate theoretical predictions for the Higgs production cross section and for the associated kinematical distributions. A crucial aspect is the study of the Higgs properties, in order to verify if the observed state is indeed the Higgs boson predicted in the Standard Model or maybe something different.

Top-quark physics

The top quark is the heaviest of the six quarks and was discovered in 1995 at the Fermilab Tevatron. Owing to its large mass, it is believed to be closely related to the mechanism of mass generation and electroweak symmetry breaking in particle physics. LHC is expected to collect data on millions of top-quark events, which will enable us to perform precision studies on top-quark physics. To match such high experimental precision in the data, it is important to count on accurate theoretical predictions: our research activities aim at improving the theoretical accuracy for top-quark production and decay.

Higher-order QCD and EW calculations

In order to fully exploit the quality of the LHC measurements and to discriminate between different new physics models, theoretical calculations must include quantum corrections at least to the next-to-leading order (NLO). The complexity of traditional NLO approaches grows very fast with the number of scattering particles, and the abundant production of multi-particle final states at the LHC poses new challenges. New NLO algorithms allow us to perform NLO calculations for a wide spectrum of multi-particle processes in a highly flexible, numerically stable, and automatic way. For selected benchmark processes, we are able to compute the QCD radiative effects to the next perturbative order (NNLO).

Soft-gluon resummations

For hard scattering processes the QCD perturbative series is controlled by a small expansion parameter. Perturbative calculations at the NLO or NNLO thus provide accurate predictions to be compared to the experimental data. In some regions of the phase space, however, fixed-order calculations are not enough, since they are affected by large logarithmic contributions that spoil the convergence of the perturbative series. In these regions a resummation of the large logarithmic terms to all orders is necessary.

Monte Carlo simulations

Monte Carlo event generators are essential tools for the analysis and the interpretation of experimental data from high-energy colliders. Through the complete simulation of all the stages of the hadronic collision they offer a realistic description of the hadronic events. Members of our group are involved in Monte Carlo generators and in the interface of perturbative calculations to Monte Carlo simulations.

Computer algebra

The analytic determination of higher order corrections in perturbative quantum field theory requires extensive use of computer algebra. Calculations are implemented into computer algebra programmes such as FORM, Mathematica or Maple, and specialized packages for applications in particle theory are developed. These tools are applied in the analytical calculation of multi-loop corrections to Feynman amplitudes, relevant to precision applications in collider physics.