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Report

Teaser, summary, work performed and final results

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

Teaser

Summary

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

The project has made significant progress on several of the grant\'s main directions of research. The main trust has been on high-precision calculations of LHC processes. Specifically, so far we have focused our efforts on two subjects: top quark production and extraction of parton distribution functions (PDF) [these functions describe the particle content of protons and are an important input to every LHC calculation].

Regarding top quark production, a number of high-value observables were computed. These results define the state-of-the-art in the subject and are extensively utilized by the LHC experimental collaborations and by other theorists. Regarding PDF, our calculations have allowed the extraction of state-of-the-art PDFs from high precision data. This has led to the creation of new, state-of-the-art PDF sets. We have also developed new ideas relevant for the definition of PDF in processes initiated by massive quarks (like charm, bottom or top).

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 - something, which is not possible otherwise. 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.

To date, we have also made first steps towards the calculations of a new class of processes at the LHC, like three jet production, with never before achieved, cutting edge precision. We have also performed studies of physics at future high-energy colliders as well as future LHC upgrades.

Final results

\"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. Moreover, we have produced as output calculations of top-pair production with cutting edge precision using the fastNLO grids format (the first such publicly available result). Furthermore, 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.

We expect to achieve the following results until the end of the project: First, compute 2->3 LHC processes at NNLO. This includes both the derivation of the 2-loop quantum corrections as well as the computation of the measured cross-section. No such results exist at present. This result of ours will exceed what was anticipated in the grant proposal. We also expect to compute the process of dijet production at the LHC with cutting-edge precision (currently this calculation is possible only in the so-called leading color approximation). This is one of the main benchmark LHC processes. Finally, we anticipate we will develop a new format for storing theoretically predicted \"\"events\"\". This will be used in a locally built library which can be used by everyone, including the public. We will then calculate a number of high-value processes and add them to the above library.\"