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High precision predictions and tools for LHC Physics

Periodic Reporting for period 1 - PrecisionTools4LHC (High precision predictions and tools for LHC Physics)

Reporting period: 2015-10-01 to 2017-09-30

The CERN Large Hadron Collider (LHC) has opened a new exciting era in fundamental Particle Physics, by reaching energies never probed before in a collider experiment. The data collected in 2010-2013 already led to an historical achievement, the discovery a new-particle with properties very close to those predicted for the “Standard Model” Higgs boson.
The pivotal role played by this particle calls for an extremely accurate study of its properties. Together with the search for direct signals of New Physics at the energy that the LHC can probe, this is the major topic of research in High Energy Particle Physics over the next 20 years, certainly throughout the whole duration of the LHC experiment.
LHC results not only are at the heart of our progress in the understanding of the elementary laws of Nature, but they will also play a decisive role in driving the future directions of elementary particle physics.

Especially in absence of striking signature pointing to Physics Beyond the SM (BSM), the success of this long-term programme relies on the capability of extracting precise information from the measured data. In addition to extraordinarily sophisticated experimental equipment, accurate theoretical predictions for the sought-after signals and their known backgrounds are required.

The goal of this research project has been to push the precision of Monte Carlo programs needed to interpret LHC measurements to an unprecedented level. This was achieved combining several novel techniques developed in the Monte Carlo community and results obtained in perturbative Quantum Chromodynamics (QCD). Moreover, some state-of-the-art computations for specific quantities have been performed. The achievement of the goals has allowed (and will allow) to model more reliably signal and background processes relevant to perform a variety of overriding precision studies. This permits a more solid interpretation of future measurements and, in a longer timescale, will also be instrumental in continuing to improve the accuracy of simulation tools, which play an important role in the majority of most experimental analyses at the LHC.
"The research activity carried out during the project is of theoretical nature. The overall goal of the project was to exploit our understanding of Quantum Chromodynamics, i.e. the theory of strong interactions, to push the frontier of the theoretical accuracy with which we can predict cross sections at the LHC.

In practice this has been achieved by substantially improving the theoretical predictions for several Standard Model processes (""VH production"", ""diboson"" production), through the development of ""general purpose"" event generators that include the most accurate theoretical predictions computed so far for the processes considered.
The results of this activity are not only reported in scientific papers, but they are also made available to the experimental community by means of public computer codes, thereby maximizing their impact.

Effort also went into the computation of some observables (called ""transverse"") with an unprecedented precision (N3LL+NNLO). These results are very relevant for high-precision measurements that are currently being performed at the LHC.

All these developments were published in scientific journals, and presented at several international conferences.
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The results obtained, and tools produced, have improved significantly the theoretical description of some important processes that are currently intensively studied at the LHC (namely the production of the Higgs boson, of a single vector boson (Drell-Yan), or of a pair of weak bosons).
The Monte Carlo event generators that have been developed for Higgs and vector boson pair production, as well as the all-order results obtained for Higgs and Drell-Yan production, have now become the new state-of-the-art results. Further studies have already started, with the aim of pushing the theoretical accuracy to the next frontier.