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Higgs physics

The study of the electroweak symmetry breaking and the search for evidence of a scalar field is at the core of the LHC physics programme. This field was postulated by Robert Brout and François Englert at the ULB, and by Peter Higgs in Edinburgh. At the IIHE we are strongly engaged in this high-priority research. We address the search in three complementary ways :

  • The search for a high-mass (mH>200 GeV) scalar boson in the H -> ZZ -> l+l-nunubar channel. This channel is the most sensitive to the presence of a standard-model-like scalar particle at high mass thanks to its high branching ratio.
  • The measurement of the ZZ diboson cross-section and the tests for possible deviations from the standard model predictions.
  • The search for H -> tautau decays in the ZH associated production mode (mH around 125 GeV). The rate of H -> tautau decays is predicted by the standard model but so far data show a deficit compared to the expected rate.


Contact persons

Prof. Barbara Clerbaux
Université Libre de Bruxelles
Boulevard du Triomphe, CP230
B-1050 Bruxelles, Belgium
phone:   +32 (0)2 629 3214
fax:       +32 (0)2 629 3816
secr:    +32 (0)2 629 3202
Prof. Pascal Vanlaer
Université Libre de Bruxelles
Boulevard du Triomphe, CP230
B-1050 Bruxelles, Belgium
phone:   +32 (0)2 629 3898
fax:       +32 (0)2 629 3816
secr:    +32 (0)2 629 3202



In July 2012, CMS observed a particle which is consistent with Higg's boson.

The paper which details the observation of this new particle with a mass of around 125 GeV by the CMS experiment is available at the follwing link.

Phys. Lett. B 716 (2012) 30-61 link : cdsweb.cern.ch/record/1471016/files/plb.716.30.pdf


A number of key plots and interpretations from this paper are included below.

The diphoton invariant mass distribution is shown with each event weighted by the S/(S+B) value of its category. The lines represent the fitted background and signal, and the coloured bands represent the ±1 and ±2 standard deviation uncertainties in the background estimate. The inset shows the central part of the unweighted invariant mass distribution.


The observed local p-value for the five decay modes and the overall combination as a function of the SM Higgs boson mass. The dashed line shows the expected local p-values for a SM Higgs boson with a mass mH.