Robert Brout et François Englert: brilliant physicists and emeritus Professors of the ULB, from 1979 onwards they jointly directed the Theoretical Physics Service of the Faculty of Science. Their basic work in elementary particle physics was recompensed with the Wolf Prize for Physics in 2004 and the J.J. Sakurai Prize for Physics in 2010.

Their work: The two ULB professors explained the difference between basic interactions by a mechanism called symmetry breaking which led to the unified model of electromagnetic and weak interactions. Their fascinating theory presupposes a particle, the scalar boson that the LHC collider of the CERN has just discovered.

François Englert and Peter Higgs

"Unlocking the Mysteries of the Universe at CERN" with reflections by special guests of honour Prof.François Englert (and Prof.Peter Higgs) Click on the image to watch the video. © European Parliament.

Discovering a new particle!

The scalar boson predicted by Robert Brout, François Englert and Peter Higgs

There has been great excitement in the scientific world ever since the announcement on 4 July 2012 of the discovery, or at least a major advance, in the kingdom of elementary particles: it would appear that the particle has been detected that confers a mass to all the other elementary particles, the famous scalar boson, commonly known as the Brout-Englert-Higgs boson.

This missing link among the most basic components of nature was predicted 48 years ago by two physicists of the Université Libre de Bruxelles (ULB), Robert Brout pdf and François Englertpdf , and by Peter Higgs of the University of Edinburgh.

The preliminary results obtained by the ATLAS and CMS experiments of the Large Hadron Collider (LHC) of the CERN indicate the existence of a new particle with a mass of around 125 Giga electron-volts (i.e., 125 billion electron-volts or approximatively 125 the mass of a proton – or of a hydrogen atom). This is a boson, the characteristics of which are compatible with those of the famous Brout-Englert-Higgs boson. Although further analyses are necessary in order to establish its precise nature, this discovery represents a crucial step forward in our understanding of the universe and nature.

Now that the hour of truth is approaching concerning the existence of this particle, it will no doubt be useful to place in perspective the path leading to its prediction.


The original articles

The article by Englert and Brout, "Broken symmetry and the mass of Gauge vector mesons", published one month before those by Higgs during summer 1964, established the mechanism known as "broken symmetry" in the quantum theory of fields, the theory that describes all the basic interactions of nature (except gravity, to this day). This mechanism implies the existence of an auxiliary particle, a scalar boson.

Thus the work of Brout-Englert and of Higgs supplied a decisive element in the construction of the Standard Model of elementary particles. Later in 1964, G.S. Guralnik, C.R. Hagen and T.W.B. Kibble also studied these questions, and their article – which refers to those by Englert-Brout and by Higgs – discusses certain more technical aspects.

The Standard Model represents the most precise and complete theory ever constructed to understand the basic interactions of nature. The broken symmetry mechanism, which is an essential part of the Standard Model, shows how very short range interactions between elementary particles, such as the weak nuclear force responsible for radioactive decay, and long range reactions, such as infinite range electromagnetic interaction, can have a common origin. On the basis of these ideas, the theoreticians Sheldon Glashow, Abdus Salam and Steven Weinberg constructed a theory unifying electromagnetic and weak interactions, which led to their being awarded the Nobel Prize in 1979. The discovery at the CERN in 1983 of the massive W and 2 bosons predicted by this theory led to the Nobel Prize being awarded to the experimenters Carlo Rubbia and Simon van der Meer.

What a strange name for a boson! Steven Weinberg sets the record straight

In an article published in May 2012 on the site of the New York Review of books, Steven Weinberg, 1979 Nobel laureate, returns to the history: “In his book (…), Frank Close points out that a mistake of mine was in part responsible for the term “Higgs boson.” In my 1967 paper on the unification of weak and electromagnetic forces, I cited 1964 work by Peter Higgs and two other sets of theorists. (…) As to my responsibility for the name “Higgs boson,” because of a mistake in reading the dates on these three earlier papers, I thought that the earliest was the one by Higgs, so in my 1967 paper I cited Higgs first, and have done so since then. Other physicists apparently have followed my lead. But as Close points out, the earliest paper of the three I cited was actually the one by Robert Brout and François Englert. In extenuation of my mistake, I should note that Higgs and Brout and Englert did their work independently and at about the same time, as also did the third group (Gerald Guralnik, C.R. Hagen, and Tom Kibble). But the name “Higgs boson” seems to have stuck. (However, we would point out with regard to the last sentence that, in their article, Guralnik, Hagen and Kibble cite the work of Englert-Brout and Higgs).

International recognition

The exceptional merit for modern physics of the work by Brout, Englert and Higgs was recognised by the number of scientific prizes they were awarded, including the most prestigious ones – apart from the Nobel Prize to date.

  • The European Physical Society prize, High Energies and Particles division, was awarded to Brout, Englert and Higgs in 1997, "for having formulated for the first time a self-consistent theory of charged massive vector bosons, which became the basis of the electroweak theory of elementary particles".

  • The Wolf Prize in Physics was awarded to them in 2004 “for pioneering work that has led to the insight of mass generation whenever a local gauge symmetry is realised asymmetrically in the world of sub-atomic particles”.

  • It should also be observed that the unique merits of Brout, Englert and Higgs are recognised by the Nobel Committee in the article on the scientific context of the 2008 Nobel Prize for Physicspdf , published by the Swedish Royal Academy of Science.

  • Last, the J.J. Sakurai Prize for Theoretical Particle Physics presented by the American Physical Society was awarded jointly in 2010 to Brout, Englert, Guralnik, Hagen, Higgs and Kibble "for elucidation of the properties of spontaneous symmetry breaking in four-dimensional relativistic guage theory and of the mechanism for the consistent generation of vector boson masses”.

To conclude

The boson discovered at the CERN is compatible with a good number of the characteristics expected of the Brout-Englert-Higgs particle associated with the Standard Model: production rate, principal modes of decay, etc. Of course, the measurements will be narrowed and will make it possible to state precisely whether this is the “minimal” version of the model, or one of the numerous extensions that are close to it. However, it is already brilliant confirmation of the visionary work by the three researchers.
The joy of this confirmation is nevertheless tinged with sadness, since Robert Brout passed away in May 2011 without knowledge of this final verification of his already well established work.

The Brout-Englert-Higgs Boson: A nobel Prize reflecting the best of the ULB

Traces of the collision of particles under the CMS experiment. © Photograph CERN

Robert Brout.

François Englert.

The issue of Physical Review Letters in which the article by Brout and Englert was published.

The two fellow researchers.