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Swiss National Science Foundation (SNSF)

Wildhainweg 3P.O. Box

CH-3001 Bern

Phone +41 31 308 22 22

English title | Computing multi-particle production processes at LHC |
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Applicant | Gehrmann-De Ridder Aude |

Number | 118864 |

Funding scheme | SNSF Professorships |

Research institution | Institut für Theoretische Physik ETH Zürich |

Institution of higher education | ETH Zurich - ETHZ |

Main discipline | Theoretical Physics |

Start/End | 01.03.2008 - 29.02.2012 |

Approved amount | 964'445.00 |

Discipline |
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Theoretical Physics |

Particle Physics |

Collider Physics; Perturbative QCD; Multi-particle production; Parton-level event generators; Top-quark pairs; Gauge bosons

Lead |
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Lay summary |

With the start of the physics program at the new CERN LHC proton-proton collider, particle physics research will enter into a new era of discovery, since the LHC provides access to energy scales never attained before in a laboratory. Based on a wealth of indirect information obtained at previous colliders, one expects the LHC to provide fundamental new insights in particle physics, especially on the mechanism of electroweak symmetry breaking. The Standard Model represents our present knowledge of particle physics and describes the interactions between the fundamental constituents of matter probed at distances of $10^-18$ meters. Within this framework, through the symmetry breaking mechanism, the matter particles, quarks and leptons, acquire mass. Experiments at LHC could also provide signatures for physics beyond the Standard Model. Many new physics scenarios predict the existence of new massive, short-lived particles, which could be produced at the LHC, and which decay into lighter Standard Model particles. Potential new physics effects are expected to become manifest in the production of multi-particle final states containing hadronic jets, charged leptons, photons and missing energy. Such multi-particle final states can also be produced through Standard model processes, which are thus backgrounds to the possible new signals. In order to detect signatures of new particles, it is crucial to have precise theoretical predictions for signal and background processes. In the present research proposal, we plan to evaluate hard scattering observables for multi-particle production processes for the LHC. In particular, we will study processes involving intermediate gauge bosons in association with either hadronic jets or heavy quarks. For these processes, we aim to perform precision calculations within perturbative quantum chromodynamics (pQCD). To achieve the level of precision required to match the expected quality of the data, perturbative corrections at next-to-leading order (NLO) and sometimes even next-to-next-to-leading order (NNLO) have to be included. At present, multi-particle production processes are mainly known at the leading order, and only selected processes are known at NLO. For the initial phase of this project, we have planned specific calculations. According to the information gained from the early LHC data, the further priorities of this proposal will be set. These calculations are at the forefront of theoretical elementary particle physics. To make them feasible, existing methods for higher order calculations in quantum field theory have to be considerably extended. |

Direct link to Lay Summary | Last update: 21.02.2013 |

Name | Institute |
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Publication |
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Double real radiation corrections to $t\bart$ production at the LHC: the all-fermion processes |

Real-Virtual corrections for gluon scattering at NNLO |

Timelike Dipole-Antenna Showers with Massive Fermions |

Antenna subtraction at NNLO with hadronic initial states: double real radiation for initial-initial configurations with two quark flavours |

Antenna subtraction for the production of heavy particles at hadron colliders |

Antenna subtraction at NNLO with hadronic initial states: initial-final configurations |

Antenna subtraction for two hadronic initial states at NNLO |

NNLO antenna subtraction with one hadronic initial state |

Precise determination of the strong coupling constant at NNLO in QCD from the three-jet rate in electron--positron annihilation at LEP |

Status of higher order QCD calculations |

The SM and NLO Multileg Working Group: Summary report |

Determination of the strong coupling constant using matched NNLO+NLLA predictions for hadronic event shapes in e+e- annihilations |

NLO Antenna Subtraction with Massive Fermions |

NNLO moments of event shapes in e+e- annihilation |

e+ e- ---> 3 jets and event shapes at NNLO |

Jet rates in electron-positron annihilation at O(alpha(s)**3) in QCD |

The NLO multileg working group: Summary report |

Group / person | Country |
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Types of collaboration |
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Univ. Zurich | Switzerland (Europe) |

- in-depth/constructive exchanges on approaches, methods or results - Publication |

Univ. Giessen | Germany (Europe) |

- Publication |

Univ. Durham | Great Britain and Northern Ireland (Europe) |

- in-depth/constructive exchanges on approaches, methods or results - Publication - Exchange of personnel |

CERN | Switzerland (Europe) |

- in-depth/constructive exchanges on approaches, methods or results - Publication |

CEA Saclay | France (Europe) |

- in-depth/constructive exchanges on approaches, methods or results - Publication - Exchange of personnel |

Title | Type of contribution | Title of article or contribution | Date | Place | Persons involved |
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The first year of the LHC | Talk given at a conference | Antenna subtraction at NNLO | 04.07.2011 | Santa Barbara, United States of America | Gehrmann-De Ridder Aude; |

High Precision for Hard Processes at the LHC | Talk given at a conference | Towards top-pair production at NNLO | 14.09.2010 | Firenze, Italy | Gehrmann-De Ridder Aude; |

CHIPP workshop: Physics at the High Energy Frontier | Talk given at a conference | Staus of NNLO corrections for QCD observables at LHC | 01.09.2010 | Zurich, Switzerland | Gehrmann-De Ridder Aude; |

ICHEP 2010: International Conference for High Energy Physics | Talk given at a conference | Status of NNLO corrections in perturbative QCD | 22.07.2010 | Paris, France | Gehrmann-De Ridder Aude; |

CERN Theory Institute: HO10 | Talk given at a conference | Antenna subtraction at NNLO | 05.07.2010 | Geneva, Switzerland | Gehrmann-De Ridder Aude; |

Loopfest 2009 | Talk given at a conference | Precise determination of alpha_s | 10.05.2009 | Madison, United States of America | Gehrmann-De Ridder Aude; |

Loops and Legs 2008 | Talk given at a conference | e^+e^- -> 3 jets at NNLO | 20.04.2008 | Sondershausen, Germany | Gehrmann-De Ridder Aude; |

Moriond 2008 | Talk given at a conference | 3-jet rates at LEP | 15.03.2008 | La Thuile, Italy | Gehrmann-De Ridder Aude; |

Title | Date | Place |
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The new, the rare and the beautiful | 08.01.2010 | Zurich, Switzerland |

Number | Title | Start | Funding scheme |
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139192 | Computing multi-particle production processes at LHC | 01.03.2012 | SNSF Professorships |

With the start of the physics program at the new CERN LHC proton-proton collider, particle physics research will enter into a new era of discovery, since the LHC provides access to energy scales which were never before attained in a laboratory. Based on a wealth of indirect information obtained at previous colliders, one expects the LHC to provide fundamental new insights especially on the mechanism of electroweak symmetry breaking. Also, experiments at LHC could provide direct signatures for physics beyond the StandardModel.Many new physics scenarios predict the existence of new massive, short-lived particles, which could be produced at the LHC, and which decay into lighter Standard Model particles.Potential new physics effects are expected to become manifest in multi-particle final states containing hadronic jets, charged leptons, photons and missing energy, the latter due to the presence of an undetected neutrino or another weakly interacting massive particle. However, such multi-particle final states can also be produced through Standard model processes, which are thus backgrounds to the possible new signals. In order to detect signatures of new particles, it is crucial to have precise theoretical predictions for signal and background processes. These predictions can be obtained through precision calculations of multi-particle final states at parton level (expressed by massless quarks and gluons). In the present research proposal, we plan to evaluate hard scattering observables for multi-particle production processes for the LHC. In particular, we will study processes involving intermediate gauge bosons in association with either hadronic jets or heavy quarks. For these processes, which will be measured to a very high degree of experimental accuracy at LHC, we aim to perform precision calculations within perturbative quantum chromodynamics (pQCD). To achieve the level of precision required to match the expected quality of the data, perturbative corrections at next-to-leading order (NLO) and sometimes even next-to-next-to-leading order (NNLO) have to be included. At present, multi-particle production processes are mainly known at the leading order, and only selected processes are known at NLO.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. In particular, we will focus on two types of calculations:1. benchmark reactions to NNLO accuracy:benchmark reactions are scattering processes which occur very frequently, and can thus be measured to a very high degree of experimental accuracy. To turn these precision data into measurements of fundamental physical parameters, an equally precise theoretical description is mandatory. 2. discovery reactions to NLO accuracy: to observe physics effects beyond the Standard Model, one studies in particular multi-particle production processes. These could either provide direct evidence for new particle production, or show indirect effects in the form of deviations from Standard Model couplings and structures. These studies require a reliable theoretical description of the final states under experimental consideration. For the initial phase of this project, we have planned specific calculations of each type. According to the information gained from the early LHC data, the further priorities of this proposal will be set. Both types of calculations are at the forefront of theoretical elementary particle physics. To make them feasible, existing methods for higher order calculations in quantum field theory have to be considerably extended. The major challenge of these calculations is in the treatment of infrared singularities. Those appear in all individual subprocess contributions at higher orders, and cancel only in the sum of all subprocesses for a suitably defined observable. Within this project, we aim to develop advanced techniques to perform these infrared cancellations to NLO and NNLO, and potentially to extend these techniques to encapsulate dominant terms from even higher orders.

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Phone +41 31 308 22 22

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