Special Lectures
Marco Zaro - Accurate predictions for Higgs production at the LHC: the VBF channel - PhD defense
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Europe/Brussels
CYCL01 (Cyclotron)
CYCL01
Cyclotron
Chemin du Cyclotron, 2 1348 Louvain-la-Neuve
Description
The Standard Model of fundamental introduction is the theory that describes reality at the smallest scales which can be currently probed by experiments. It has been formulated by S. Glashow, A. Salam and S. Weinberg in the 1960's as a gauge theory which unifies electromagnetism and weak interactions. The electromagnetic and weak force, before considered as of completely different nature, are now shown to be two sides of the same coin, with weak interactions being “weak” because they are mediated by massive particles, the W and Z bosons, while electromagnetism is mediated by the massless photon. Gauge theories, however, forbid their mediators to have a mass, since any mass term in the Lagrangian would explicitly break gauge invariance. The mechanism which allows gauge bosons to acquire a mass was formulated in the same decade by P. W. Higgs, R. Brout, F. Englert, G. Guralnik, C. Hagen and T. Kibble. This mechanism allows the appearance of mass terms at the price of introducing a new scalar doublet in the theory. One component of this new scalar doublet remains in the Lagrangian as a new particle, the Higgs boson. This particle, has been sought for almost fifty years by different experiments, until the first evidence of its existence has been claimed on July 4th, 2012. On that day, ATLAS and CMS, the two experiments at the Large Hadron Collider at the CERN (Geneva), announced the observation of a new particle, with mass of about 125 GeV and with properties compatible with these predicted for the Higgs boson.
In this thesis I will focus on one production channel of the Higgs boson, the vectorboson fusion process (VBF). This is the production channel with second largest total rate. I will first present the state-of-the-art computation of the total crosssection for this process, which is currently known up to the second order (next-to-next-to-leading order) in QCD and up to the first in the weak interactions perturbation theory. Residual theoretical uncertainties are reduced at the 2-3% level. After this, I will turn to study more exclusive observables in VBF applying typical experimental cuts. The simulation for such observables includes the nextto- leading order QCD corrections, and is matched with parton-shower Monte Carlos. This makes it possible to have accurate predictions together with a realistic description of the final state in terms of hadrons.
In this thesis I will focus on one production channel of the Higgs boson, the vectorboson fusion process (VBF). This is the production channel with second largest total rate. I will first present the state-of-the-art computation of the total crosssection for this process, which is currently known up to the second order (next-to-next-to-leading order) in QCD and up to the first in the weak interactions perturbation theory. Residual theoretical uncertainties are reduced at the 2-3% level. After this, I will turn to study more exclusive observables in VBF applying typical experimental cuts. The simulation for such observables includes the nextto- leading order QCD corrections, and is matched with parton-shower Monte Carlos. This makes it possible to have accurate predictions together with a realistic description of the final state in terms of hadrons.