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2013 Nobel prize in Physics — The theoretical discovery of the Higgs boson

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Front view of the ATLAS detector, one of the two instruments which recently confirmed the existence of the Higgs boson

The Nobel Prize in Physics 2013 was awarded jointly to François Englert (BE) and Peter W. Higgs (UK) for the theoretical discovery of a mechanism that contributes to our understanding of the origin of mass of subatomic particles, and which recently was confirmed through the discovery of the predicted fundamental particle, by the ATLAS and CMS experiments at CERN’s Large Hadron Collider.

According to the so-called standard model of particle physics, every object in nature is built on components named fermions (a fermion displays the strange property of not being invariant under one turn around itself, but under two turns). Let us mention quarks, themselves building blocks for the protons and neutrons and constituents of the nuclei of the atoms ; and electrons, orbiting about atoms’ nuclei. The standard theory describes interactions between fermions as the result of exchanges of bosons : photons for the electromagnetic interactions, vector bosons for the weak interactions, and gluons for the strong interactions (a boson distinguishes itself from a fermion by being invariant under one turn in space).

All elegant as it was the picture turned out to be valid only for massless particles. Following early works by Y. Nambu, J. Goldstone, P. Anderson and J.S. Schwinger, a possible solution emerged with works by R. Brout, F. Englert and P. Higgs. This solution postulated the existence of scalar field filling the whole space and showing a spontaneous symmetry breaking at a specific (very large) energy giving birth to four particles. Three are responsible for the short range of weak interactions. It is through coupling to the fourth one, named the Higgs boson, that fermions have a mass. It is the one that had to be experimentally detected to confirm the entire scenario.

The experimental discovery of the Higgs boson is therefore a giant step in particle physics. No discovery ever mobilized so many efforts, due first to the very large energy of the sought particle : 125.3±0.6 GeV/c2, second to the weak probability of direct detection in electron-positron collider (LEP for Large Electron-Positron collider, the previous CERN instrument). It was necessary to consider specific decays of Higgs bosons produced in proton -proton collisions in the LHC (Large Hadron Collider, the current and new CERN instrument). The decay of Higgs bosons had to be identified out of a background of billions of other events. The discovery is the fruit of teamworks involving thousands of scientists, making use of most advanced technologies and requiring most acute and very varied skills.

Cryogenics is vital to CERN facilities for operating the superconducting accelerating cavities and bending magnets needed to achieve a closed path for the circling particles, whose high energy made possible the experimental discovery of the Higgs boson. Over the past twenty years researchers and engineers of Institut NEEL (through CRTBT, one of its founding labs) provided its support to CERN, based on their long-standing expertise in the field. They contributed to the training on-site in Geneva of about 100 CERN staff for the operation of advanced cryogenics. In turn, this collaboration led to facilities for fruitful fundamental investigations of turbulence at record-high controlled Reynold-numbers, using helium at low temperature (4K).

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