The Higgs Boson

On 4 July 2012, during a historic seminar at CERN in Geneva, the discovery of the Higgs boson was announced. It was the last missing piece in the standard model of elementary particles. The existence of this particle had been postulated some 48 years beforehand, in 1964, by the British physicist Peter Higgs and, independently, by the Belgian physicists François Englert and Robert Brout. In their studies, the scientists introduced a mechanism for generating the masses of elementary particles, known as the “Higgs mechanism”, through coupling with a scalar field, the Higgs field. As a result of this mechanism, the Higgs field describes a physical particle, the Higgs boson. This boson is weakly coupled with matter and its mass, not precisely predicted by the theory, was expected to be in the order of hundreds of GeV. Thus, while, all the particles predicted by the standard model were slowly discovered between the 1950s and halfway through the 1980s, for a long time the Higgs boson remained an experimental goal considered prohibitive.

Announcement of the discovery of the Higgs Boson, Cern 4 July 2012 (© CERN)

Event recorded with the CMS detector in 2012 at a proton-proton centre of mass energy of 8 TeV. (© CERN)

The breakthrough arrived with the building of the Large Hadron Collider (LHC) particle accelerator, inaugurated in 2008 and devised with the precise goal of finally observing the Higgs boson. The discovery announced in 2012 was obtained by the ATLAS and CMS experiments, with a decisive contribution of INFN researchers. The first observation of the Higgs boson represented a breakthrough for particle physics, successfully ending half a century of research into particles predicted by the Standard Model. It shifted the focus of research towards “new physics”, i.e. physics not contemplated by the standard model and not yet known, and verifying details of the theory not yet well understood, having (at the time) exhausted the research into known particles predicted by the standard model.

However, part of this research has the goal of more precisely determining the properties of the Higgs boson, such as, for example, its decay processes (the boson is actually an extremely unstable particle, so much so that it decays into lighter particles in an infinitesimal fraction of a second). In addition, the features of the Higgs boson could provide clues about the existence of new physics. For this reason, beyond its crucial role in the puzzle of elementary particles, the Higgs boson will still be the subject of numerous studies for a long time, both theoretical and experimental.

ATLAS detector (©CERN)

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