![]() In 1971, ’t Hooft and Veltman 14, 15 showed how indeed this theory could be renormalized. ![]() Salam and Weinberg had further conjectured that the model they put forward might be renormalizable (that is, give finite answers). The impact is far reaching: for example, electrons become massive, allowing atoms to form, and endowing our Universe with the observed complexity. Thus, the elementary particles interacting with the BEH field acquire mass. An additional feature of this model is that it provides a mechanism for granting masses to fermions as well, through the so-called Yukawa interactions 10, 13. The key element in this work was the conjecture that nature possesses an electroweak symmetry, mathematically described by the Lagrangian of the theory, which is spontaneously broken, granting mass to the W and Z bosons. In 1967, Weinberg 10 and Salam 11, extending the 1961 work of Glashow 12, proposed the use of the BEH mechanism for a theory of the unification of the electromagnetic and weak interactions, labelled as the electroweak interaction. Further details of the mechanism were presented in 1966 by Higgs 8 and in 1967 by Kibble 9. The BEH mechanism was first proposed in 1964 in the works of Brout and Englert 4, Higgs 5, 6, and Guralnik, Hagen and Kibble 7. The same map, where instead the wind speed and direction are shown, would correspond to a vector field. An analogy can be drawn of a map of an area where temperature is shown at various positions mimicking a scalar field. ![]() Scalar fields are described only by a number at every point in space that is invariant under Lorentz transformations. Its quantum manifestation is known as the SM Higgs boson. In the SM, this mechanism, labelled as the Brout–Englert–Higgs (BEH) mechanism, introduces a complex scalar (spin-0) field that permeates the entire Universe. The Higgs boson is a prediction of a mechanism that took place in the early Universe, less than a picosecond after the Big Bang, which led to the electromagnetic and the weak interactions becoming distinct in their actions. In 2012, the final missing particle of the SM, the Higgs boson, was observed by the ATLAS 1 and CMS 2, 3 collaborations at CERN. ![]() The SM has been very successful in providing accurate predictions for essentially all particle physics experiments carried out so far. These vector bosons are the massless photons (gluons) for the electromagnetic (strong) interaction, and the heavy W and Z bosons for the weak interaction. (In quantum mechanics, spin is an intrinsic form of angular momentum carried by elementary particles). The established theory of elementary particle physics, commonly referred to as the standard model (SM), provides a complete description of the electromagnetic, weak and strong interactions of matter particles, which are spin-1/2 fermions, through three different sets of mediators, which are spin-1 bosons. An order of magnitude larger number of Higgs bosons, expected to be examined over the next 15 years, will help deepen our understanding of this crucial sector. Several of the standard model issues originate in the sector of Higgs boson physics. Much evidence points to the fact that the standard model is a low-energy approximation of a more comprehensive theory. Within the uncertainties, all these observations are compatible with the predictions of the standard model of elementary particle physics. Here the CMS Collaboration reports the most up-to-date combination of results on the properties of the Higgs boson, including the most stringent limit on the cross-section for the production of a pair of Higgs bosons, on the basis of data from proton–proton collisions at a centre-of-mass energy of 13 teraelectronvolts. The CMS experiment has observed the Higgs boson in numerous fermionic and bosonic decay channels, established its spin–parity quantum numbers, determined its mass and measured its production cross-sections in various modes. Ten years later, and with the data corresponding to the production of a 30-times larger number of Higgs bosons, we have learnt much more about the properties of the Higgs boson. In July 2012, the ATLAS and CMS collaborations at the CERN Large Hadron Collider announced the observation of a Higgs boson at a mass of around 125 gigaelectronvolts.
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