# Project

Back to overview

## Computing multi-particle production processes at LHC

 English title Computing multi-particle production processes at LHC Gehrmann-De Ridder Aude 139192 SNSF Professorships Institut für Theoretische Physik ETH Zürich ETH Zurich - ETHZ Theoretical Physics 01.03.2012 - 28.02.2014 669'799.00
Show all

### Keywords (4)

Particle Physics; LHC; Precision observables; Monte Carlo Methods

### Lay Summary (English)

Lay summary
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.

 Direct link to Lay Summary Last update: 21.02.2013

### Responsible applicant and co-applicants

Name Institute
 Gehrmann-De Ridder Aude Institut für Theoretische Physik ETH Zürich

### Employees

Name Institute
 Abelof Gabriel Alejandro Department of Physics and Astronomy Northwestern University
 Gehrmann-De Ridder Aude Institut für Theoretische Physik ETH Zürich

### Publications

Publication
Currie James, Gehrmann-De Ridder Aude, Glover E.W.N., Pires Joao (2014), NNLO QCD corrections to jet production at hadron colliders from gluon scattering, in JHEP, 1401, 110-110.
Abelof Gabriel, Gehrmann-De Ridder Aude (2013), Double real radiation corrections to $t\bart$ production at the LHC: the all-fermion processes, in JHEP, 1204, 076-076.
Gehrmann-De Ridder Aude, Gehrmann Thomas, Glover E.W.N., Pires Joao (2013), Double Virtual corrections for gluon scattering at NNLO, in JHEP, 1302, 026-026.
Gehrmann-De Ridder Aude, Gehrmann Thomas, Glover E.W.N., Pires Joao (2013), Second order QCD corrections to jet production at hadron colliders: the all-gluon contribution, in Phys.Rev.Lett., 110(16), 162003-162003.
Gehrmann-De Ridder Aude, Gehrmann Thomas, Ritzmann Mathias (2012), Antenna subtraction at NNLO with hadronic initial states: double real initial-initial configurations, in JHEP, 1210, 047-047.
Abelof Gabriel, Dekkers Oliver, Gehrmann-De Ridder Aude (2012), Antenna subtraction with massive fermions at NNLO: Double real initial-final configurations, in JHEP, 1212, 107-107.
Abelof Gabriel, Gehrmann-De Ridder Aude (2012), Double real radiation corrections to $t\bart$ production at the LHC: the $gg\rightarrow t\bartq\barq$ channel, in JHEP, 1211, 074-074.
Abelof Gabriel, Gehrmann-De Ridder Aude (2012), Double real radiation corrections to top-antitop production at the LHC, in PoS, LL2012, 061-061.

### Collaboration

Group / person Country
Types of collaboration
 CERN Theory Group Switzerland (Europe)
 - in-depth/constructive exchanges on approaches, methods or results- Publication
 Universität Zürich Switzerland (Europe)
 - in-depth/constructive exchanges on approaches, methods or results- Publication
 University of Durham Great Britain and Northern Ireland (Europe)
 - in-depth/constructive exchanges on approaches, methods or results- Publication
 CEA Saclay, Physique Theorique France (Europe)
 - in-depth/constructive exchanges on approaches, methods or results- Publication
 RWTH Aachen Germany (Europe)
 - in-depth/constructive exchanges on approaches, methods or results- Publication- Exchange of personnel
 ETH Institute for Particle Physics Switzerland (Europe)
 - in-depth/constructive exchanges on approaches, methods or results
 Max-Planck-Institut München Germany (Europe)
 - in-depth/constructive exchanges on approaches, methods or results

### Scientific events

#### Active participation

Title Type of contribution Title of article or contribution Date Place Persons involved
 Santa Barbara Workshop: Exploring TeV Scale New Physics with LHC data, Individual talk blackboard seminar on: Antenna subtraction 08.07.2013 Kavli Institute, UCSB, Santa Barbara , United States of America Gehrmann-De Ridder Aude;
 Brookhaven Forum Talk given at a conference Review talk on Perturbative QCD 01.05.2013 Brookhaven National Laboratory , United States of America Gehrmann-De Ridder Aude;
 HP2 Workshop Talk given at a conference Towards jet cross sections at NNLO 03.09.2012 Munich, Germany, Germany Gehrmann-De Ridder Aude;
 LoopFest X1 Talk given at a conference Towards jet cross sections at NNLO for the LHC 07.05.2012 Pittsburgh,USA, United States of America Gehrmann-De Ridder Aude;

#### Self-organised

Title Date Place
 Topical workshop ZPW13 07.01.2013 Zurich, Switzerland

### Associated projects

Number Title Start Funding scheme
 141847 Particle Physics with high-quality data from the CERN LHC 01.10.2012 Sinergia
 118864 Computing multi-particle production processes at LHC 01.03.2008 SNSF Professorships

### Abstract

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.
-