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Direct coupling of the Higgs boson to the observed top quark



On July 4, 2012, two of the experiments at the Large Hadron Collider (LHC), ATLAS (A Toroidal LHC Apparatus), and CMS (Compact Muon Solenoid) at CERN reported independently on the discovery of the Higgs boson [19659002] The discovery confirmed the existence of the last missing elementary particle of the Standard Model, half a century after the Higgs boson was theoretically predicted. At the same time, the discovery also marked the beginning of an experimental program aimed at determining the properties of the newly discovered particle. Now the CMS collaboration has reached an important milestone in this program.

In the standard model, the Higgs boson can combine with the particles of matter, the fermions, with the coupling strength being proportional to the fermion mass. While associated decay processes have been observed, decay in top quarks, the heaviest known fermions, is kinematically impossible.

Therefore, alternative routes are needed for the direct investigation of the coupling of the Higgs boson to the top quark. One is through the production of a Higgs boson and a top quark antiquark pair.

This is the production mechanism that has now been observed for the first time, and thus the CMS collaboration achieved one of the main goals of The Higgs Physics Program

New Techniques Accelerate Data Extraction

The extraction of these events from the LHC Data is a challenge as there are many everyday events that you can imitate. The identification of these events requires measurements from all CMS subdetectors, which makes the reconstruction very complex.

The team of Prof. Florencia Canelli of the Institute of Physics of the University of Zurich, in collaboration with the CMS group of ETH Zurich, developed sophisticated methods that allowed the CMS to increase its sensitivity to these events.

As a consequence, this milestone was passed much earlier than expected. "The development of these techniques also opens up the possibility of increasing sensitivity in many other areas of research at the LHC," says Canelli, who also heads the physics group researching top quarks.

Search for physics beyond the standard model

The present achievement is an example of this. By observing the coupling between the two heaviest elementary particles of the Standard Model, the LHC physics program for characterizing and understanding the Higgs boson has taken an important step.

The strength of the measured coupling agrees with that of the standard model expectation, the precision of the measurement leaves room for contributions from new physics. "In the coming years, much more data will be collected and accuracy improved to see if the Higgs boson reveals the presence of physics beyond the standard model," adds Florencia Canelli.

Research Work

Related Links

University of Zurich

Understanding Space and Time



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