Forschungs- & Entwicklungsinformationsdienst der Gemeinschaft - CORDIS


HIGGS@LHC Berichtzusammenfassung

Project ID: 321133
Gefördert unter: FP7-IDEAS-ERC
Land: France

Mid-Term Report Summary - HIGGS@LHC (Search and study of the Higgs bosons at the LHC)

The last three years were extremely rich and exciting for particle physics. With the historical discovery of a Higgs boson at the LHC in July 2012, crowned by a Nobel price in fall 2013, and the first probe of its fundamental properties, they witnessed a giant step in the unraveling of the mechanism that breaks electroweak symmetry and generates the fundamental particle masses. They promoted the Standard Model (SM) as the appropriate theory, up to the presently probed energy scale, to describe the electromagnetic, weak and strong forces. This triumph has also led to some frustration as the hope of observing some signs of the new physics models that were put forward to address some important problems of the SM did not materialize. The hope is that with the coming upgrade of the LHC to higher energy and luminosity, much larger mass scales than presently probed will be accessed, allowing for the first hints of this new physics to be detected.
The observation of the Higgs boson, the determination of its basic properties and the study of their implications for the SM and new physics beyond it, were the essential issues addressed by our research project. In particular, we had six main objectives: 1) to perform precise predictions for the Higgs signal at LHC, 2) to perform precise predictions for the major backgrounds, 3) to develop new search techniques and strategies at LHC, 4) to develop and improve software tools for Higgs phenomenology, 5) to investigate the phenomenology of new physics scenarios with extended Higgs sectors and 6) to study the connection of Higgs physics with cosmology and flavour physics.
The wealth of Higgs data produced by the LHC experiments allowed us to perform a large number of important and comprehensive investigations. Progress has been made in all the research domains that were planned in our original proposal. This was particularly the case for the interpretation of the measured Higgs mass and production/decay rates in the context of the SM and many of its new physics extensions (in particular in the minimal and next-to-minimal supersymmetric extensions, models with extra dimensions and/or with extended Higgs sectors) and the interplay between these results and cosmology (concerning in particular the dark matter problem) or flavour physics (like top quarks and neutrinos). Progress has also been made in the analysis of the Higgs signal and backgrounds at the LHC, with many interesting new channels being considered (like double Higgs production in the SM and beyond and Higgs decays into top quarks in supersymmetry). In addition, essential tools for Higgs studies developed by our group have received major upgrades.
One recent study can illustrate the work done in all of these topics. In a collaboration with the Rome group (L. Maiani and collaborators), we have provided a global three-dimensional fit of the couplings to fermions and gauge bosons of the observed SM-like Higgs state, proposed a new approach to parametrise the Higgs sector of the minimal supersymmetric SM extension, put forward and discussed new search channels for the heavier Higgs states in this model, in particular decays into heavy top quarks (a detailed analysis of the interference between the signal with the top-quark pair QCD background is required and under way); finally, this approach has been implemented in the basic numerical tools that describe Higgs phenomenology.
Other scientific achievements in the six research topics or objectives of the project have been described in other sections of this report. In particular, the work performed so far led to:
- The publication of more than 90 articles in the most important refereed journals of the field. Among these, eight articles were written by the PI, ten by the first postdoctoral fellow financed by the grant, ten articles by the three post-doctoral fellows hired in fall 2014, one written very recently by the PhD student and finally five articles written by members of our research group in collaboration with experimental teams (namely, CMS, D0 and Fermi-LAT). All publications are in open access and the vast majority of them explicitly acknowledge the support of the ERC grant.
- The publication of several reports in proceedings of workshops and conferences; some like the "Handbook of LHC Higgs Cross Sections" from the LHC Higgs working group, which has collected already more than 500 citations, are extremely important for Higgs physics at LHC ( we should note here that four members of our team are convening physics subgroups in this context) . In addition, two PhD theses have been defended during these two years and some of the work performed there acknowledges ERC funding.
- Besides financing the postdoctoral fellow that was hired in 2013 (and the three post-docs and one PhD student hired this fall) and the team members to attend conferences and workshops, some of the ERC funds were used to invite several collaborators and to help organize by our laboratories a few events which are directly related to Higgs physics.

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