With the CERN LHC a new proton-proton collider has started taking data at the end of 2009. Compared to previous facilities, the LHC will attain collision energies never probed before in a laboratory. With this higher energy reach, the LHC could uncover new physics effects and provide answers to some of the most intriguing questions in fundamental physics.
In order to establish experimental signatures of new physics effects, it is mandatory to have a very solid and precise theoretical understanding of known Standard Model processes yielding similar final state signatures. Depending on the final state under consideration, these predictions are obtained either through precision calculations of multi-particle final states in perturbation theory or within the context of parton showers. In either approach, the theory description of collider reactions relies on an accurate knowledge of the Standard Model parameters and of the structure of the colliding protons.
Precise determinations of these quantities require accurate measurements of benchmark cross sections, combined with equally precise theoretical predictions, involving higher order quantum field theory corrections. Within the project proposed here, we aim to compute higher order corrections to next-to-next-to-leading order (NNLO) in perturbation theory to the following benchmark cross sections:
1. pp -> 2j: the production of di-jet final states is the most basic 2-> 2 QCD scattering processes at hadron colliders; it allows for precision tests of the theory of strong interactions, i.e. QCD.
2. pp -> V+j: the production of a massive vector boson (W+- or Z0) in association with a hadronic jet. This process has multiple applications both in view of direct and indirect searches for new physics effects, precision determinations of physics parameters (electroweak couplings, parton distributions) and calibration of experimental conditions (jet energy scale, luminosity).
3. pp -> tt: top quark pair production. With the large number of top quark pairs produced at the LHC, the study of the top quark properties will become precision physics.
For each of the processes considered, we will develop a parton-level event generator, which is a Monte Carlo program generating events with full kinematical information on all final state particles. This program will contain all partonic channels relevant at a given order and will allow to apply the precise experimental definitions to all observables which can be constructed from a given final state. The calculations are based on the antenna subtraction method, which we developed as a theoretical tool to handle multi-parton final states at higher orders in perturbation theory.
A different application of the antenna formalism is the description of multi-particle final states through parton showers. The VINCIA parton-shower event generator program uses antenna functions to obtain a reliable description of single particle emissions, which are then exponentiated to obtain a full event description. Within this project, we aim to contribute to the further development of VINCIA by including particle mass effects, and by developing a matching of this antenna-based parton shower onto fixed order matrix elements including higher-order perturbative corrections.