SAMURAI-APPS

Precision study of W bosons pair production in association with jets at High Energy Colliders

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 Obiettivo del progetto (Objective)

'With the beginning of the experimental programs at the LHC, the need to describe multi-particle scattering events with high accuracy has become more pressing. On the theoretical side, perturbative calculation within leading order precision cannot be sufficient, therefore accounting for effects due to Next-to-Leading Order (NLO) corrections becomes mandatory. In the last few years, tremendous progress in the computation of one-loop virtual corrections for processes involving many particles has been observed. The new ideas based on the universal four-dimensional decomposition for the numerator of the integrand for any one-loop scattering amplitudes, the four-dimensional unitarity-cuts, detecting only the (poly)logarithmic structure of the amplitude, known as the cut-constructible part, and unitarity-cuts in $d$-dimension, yielding the complete determination of dimensionally regulated one-loop amplitudes, appear to give the possibility of developing an automated multi-process evaluator for scattering amplitudes at NLO. In this context, the researcher and his collaborators merged many of the new ideas to develop a new formalism encoded in a public computer program called SAMURAI. SAMURAI is a tool designed for the automated numerical evaluation of one-loop corrections to any scattering amplitudes within the dimensional-regularization scheme. The potential of SAMURAI will be exploited into all possible high energy physics applications.'

Introduzione (Teaser)

The Standard Model, the theory of how the basic building blocks of matter interact, is currently being re-discovered at the Large Hadron Collider (LHC). EU-funded scientists have developed new analytical tools for this purpose.

Descrizione progetto (Article)

The search for the Higgs boson and the estimation of its mass needed precise extraction of the Higgs boson's signal from background processes. The main objective of the 'Precision study of W bosons pair production in association with jets at high energy colliders' (SAMURAI-APPS) fellowship was to provide largely automated tools for this purpose. In particular, the SAMURAI-APPS team developed tools for high order corrections of hadron-hadron collisions.

The software package GOSAM was developed to support the automated calculation of the scattering cross-section, describing the probability of interaction between particles. The coupling between interacting particles was visualised using Feynman diagrams. High order corrections were represented in diagrams with loops.

GOSAM was used to calculate corrections within both quantum chromodynamics (QCD) and electroweak theory. QCD is the theory of the strong interactions between elementary particles which along with the electro-weak interactions compose the Standard Model.

The user only needs to specify the details of the process to be analysed, and launch the generation of the source code and its compilation. Depending on the setup for the given process, scattering amplitudes can be deduced with different techniques. GOSAM offers the option of choosing the best approach in terms of speed and numerical stability.

On 4 July 2012, the observation of a Higgs boson with a mass around 125 GeV was announced at the European Organization for Nuclear Research (CERN). This discovery implied a great success of the Standard Model with measurements of the Higgs boson properties being consistent with the theoretical predictions.

Although the Standard Model accurately describes phenomena within its domain, some pieces of the jigsaw puzzle are still missing. Use of the SAMURAI-APPS tools with more LHC experiments could change all this. Detailed measurements of all the decay branching of the Higgs particle as well as of other new particles are expected to reveal unknown facets of the subatomic world.