New level of theoretical precision for LHC Run 2 and beyond

Project Information

NNLOforLHC2

Grant agreement ID: 683211

DOI

10.3030/683211

Project closed

EC signature date 27 April 2016

Start date 1 October 2016

End date 30 September 2022

Funded under

• EXCELLENT SCIENCE - European Research Council (ERC)

Total cost

€ 1 713 983,00

EU contribution

€ 1 713 983,00

Coordinated by

THE CHANCELLOR MASTERS AND SCHOLARS OF THE UNIVERSITY OF CAMBRIDGE
United Kingdom

Periodic Reporting for period 4 - NNLOforLHC2 (New level of theoretical precision for LHC Run 2 and beyond)

Reporting period: 2021-04-01 to 2022-09-30

Summary of the context and overall objectives of the project

The main objective of the project is the calculation of high-precision observables that are being measured at the Large Hadron Collider (LHC) at CERN. The project aims are two: first, to produce state of the art calculations which are used in the searches for new physics at the LHC and, second, to develop new and improved tools and approaches for performing such calculations.

The results derived in this project are unique, state-of-the-art and most have no analogues, i.e. no other competing calculations exist for the same processes. A summary of the work performed, as well as the results that have been achieved, can be found under the project's website: http://www.precision.hep.phy.cam.ac.uk

Work performed from the beginning of the project to the end of the period covered by the report and main results achieved so far

The project has made significant progress on several of the grant's main directions of research. The main trust has been towards high-precision calculations for LHC processes. Specifically, the project has delivered state of the art predictions for essentially all LHC 2->2 processes. It has also produced the first ever NNLO predictions for processes with identified hadrons. In order to be able to calculate processes with flavored jets, new flavored anti-kT jet algorithm has been proposed and tested in a number of processes. The Project has furthermore pioneered the calculation of 2->3 processes and has been able to compute a number of those processes. Besides the calculation of state of the art cross sections, the project has also delivered a number of two-loop amplitudes which are the current bottleneck. The calculations performed here have become the basis for many LHC measurements as well as improved PDF, top quark mass and alpha_S determinations.

The second main trust of the grant has been the devising of new ways for making our results public. To this end our group was the first to utilize the so called fastNLO tables for calculations of highest available precision. When our results are produced in this format they are very easy to use by other researchers and, moreover, allow for extremely fast and inexpensive recalculation by changing certain parameters, which was not possible previously. Our calculations are now being produced in this format. All results made public so far are available from our webpage and are being extensively used by theorists and experimentalists alike. We have also introduced a novel concept which goes well beyond the existing state of the art in the filed: we made public the library HighTEA which allows users to perform their own NNLO calculations. The users do not need to have access to computing infrastructure or deep knowledge of a technical subject like higher order perturbative calculations in order to use it. In fact the tool can easily be used by the general public. It is meant to be a game changing addition to the ever expanding toolbox of collider physics.

Progress beyond the state of the art and expected potential impact (including the socio-economic impact and the wider societal implications of the project so far)

The work stemming from this grant has led to several results that went beyond the then-state-of-the-art. These include the calculation of all measured distributions of top quark pairs with unmatched, cutting edge precision. We have also computed, for the first time ever, top-pair production followed by top quark decay with the same cutting edge precision. This latter work has already solved a major LHC puzzle, see https://atlas.cern/updates/physics-briefing/precision-leads-puzzles as well as our project website http://www.precision.hep.phy.cam.ac.uk/results/ttbar-decay/ for more information. We have proposed a new way for solving the so-called Integration-by-Parts Identities (IBP) which are a step towards the calculation of the two-loop quantum corrections to 3-jet production. A significant part of the IBP has already been solved and published. A number of state of the art two-loop amplitudes have been computed, which has allowed the calculation of the corresponding NNLO corrections for these processes.

We have computed the first complete prediction for dijet production at the LHC and the first prediction for 3 jets at the LHC. This allowed the first ever measurement of the running of the strong coupling constant through TeV energies with NNLO precision. Additionally, performed was the first NNLO calculation of diphoton production at non-zero transverse momentum. Another state of the art calculation was the formulation and then calculation of heavy identified hadrons with NNLO precision. Our results open the possibility for a new broad research program in this subject.

The project has also pioneered the distribution of NNLO calculation in novel formats. Specifically, the so called fastNNLO tables as well as the HighTEA database which allows any user - including the general public - to easily perform state of the art NNLO0accurate calculations.

First measurement of top charge asymmetry at the LHC versus highest precision SM prediction