SM-NEWPHYSICS-LHCB · Standard Model and New Physics with the LHCb detector

Standard Model and New Physics with the LHCb detector

In 2009, the Large Hadron Collider (LHC) - the highest energy particle-accelerator ever built - started operation at the CERN laboratory for particle physics in Geneva. The main objective of the LHC is to explore the physics of fundamental particles and their interactions at unprecedented collision energies and rates. By studying the debris of proton-proton (p-p) and heavy-ions collisions at multi-TeV energies, the four main experiments at the LHC - ALICE, ATLAS, CMS, and LHCb - try to provide answers about the forces, the elementary constituents and the space-time structure of our universe. The list of open questions to be addressed at the LHC encompasses fundamental topics such as the existence or not of the Higgs boson (the only missing piece of the Standard Model of particle physics), the flavour problem (what is the origin of the observed matter-antimatter asymmetry in the Universe?), the nature of the unknown dark matter accounting for about one fourth of the mass of the Universe, the behaviour of strongly interacting matter at the highest temperatures and densities ever reached at the laboratory, the sources and nature of the highest energy cosmic-rays measured on Earth, ... The objectives of the present ERG project were to study empirically (with the LHCb experiment) and phenomenologically (with theoretical tools) a few sectors of the Standard Model of particle physics. The two most important topics covered during the 1.5 years of ERG were the study of (i) the fundamental theory of the strong interaction, Quantum Chromodynamics (QCD) that binds quarks and gluons inside of protons and dominates most of the dynamics of the hadronic collisions at the LHC, and (ii) the study of novel production mechanisms of the Higgs boson in proton-proton collisions at the LHC. A third and fourth axes of activities centred in electroweak (measurement of W and Z bosons in LHCb) and new-physics studies could not be developed as the grant was terminated at half of the total originally planned period. The project focused in particular on exploiting the very good forward detection capabilities of the LHCb experiment to carry out QCD measurements that allow one e.g. to probe the densities of partons (quarks and gluons) inside the proton via energetic photons or jets. Other QCD studies included the comparison of high transverse momentum hadron production to theoretical perturbative QCD predictions, the estimation of the amount of anisotropies in the azimuthal angle expected in head-on proton-proton collisions due to collective multi-parton interactions, and the study of the constraints that the new LHC hadron production data imposes on hadronic Monte Carlos used in high-energy cosmic-rays physics. In the Higgs sector, the work focused on novel production mechanisms of the Higgs boson in p-p collisions characterized by the exchange of photons or two-gluons in a colour-singlet state. Altogether the results obtained have had a non-negligible impact in our understanding of the physics of the strong interaction at the highest energies ever explored in the laboratory and have provided new approaches for the possible measurement and detailed characterization of the Higgs particle at the LHC.

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