Search for a light SM Higgs with the ATLAS detector

par Dr Lorenzo Feligioni (CPPM)

vendredi 21 mars 2008, 14:30 → 15:30 Europe/Paris

Amphi de Recherche

While the Standard Model of strong and electroweak interactions is an extremely well tested theory, it still needs the experimental confirmation of the Higgs mechanism of electroweak symmetry breaking, which will be given by the discovery of the Higgs boson. The global fit of Higgs boson contributions to the electroweak experimental observables, computed within the Standard Model, favors a light Higgs with a mass of m_H=76⁺³³_-25 GeV, on the edge of the 95% Confidence Level region excluded at the LEP e⁺ e^- collider.
The ATLAS detector, located at the Large Hadron Collider, CERN, Switzerland, will start to be operative by the end of the summer 2008 with the aim of collecting approximately 30 fb^-1 of 14 TeV pp collision in the next three years. The case of a light Higgs boson is experimentally the most difficult scenario, where no striking signatures can lead to an early discovery. I will give a review of several analyses that if used in combination will ensure the detection of this elusive particle.
At the LHC the Higgs production mechanism with the largest cross section is gluon fusion (gg -> H). Unfortunately this channel can not be combined with the favorable decay into b-quark pairs (dominant for m_H~ 135 GeV) since the presence of a large QCD bb background. For this reason, the ttH channel, thanks to the top quark identification algorithms, is the most promising production mechanism for the detection of H ->bb and a unique possibility of accessing the top Yukawa coupling. Despite the small branching fraction, the fine segmentation of ATLAS electromagnetic calorimeter allows also to consider gg -> H in association with an Higgs decaying in two photons. In addition, the VBF production with a subsequent decay into tau pairs has been shown to be a promising channel for the low mass region. The success of these challenging analysis relies on the quality of the understanding of the ATLAS detector together with the assessment of the performance with the first data.

Slides 20080321.pdf.pdf