The Higgs boson is the newest addition to the Standard Model, first observed in 2012, although the existence of the Higgs mechanism had been first hypothesised in 1964 by three separate groups of scientists: by Peter Higgs, by François Englert and Robert Brout, and by Gerry Guralnik, C. R. Hagen, and Tom Kibble, in what has come to be known as the 1964 PRL symmetry breaking papers.
The Higgs mechanism was aimed to solve a serious flaw of the Standard Model, that according to gauge theory, all gauge bosons must be massless. This is known to be false, as the W and Z bosons have masses of 80.4GeV/c^2 and 91.2GeV/c^2 respectively. This was solved by the addition of the Higgs field, which interacts with particles via Higgs bosons. All particles, bar photons and gluons, which are massless, interact with the Higgs field. The Higgs boson is the observable part of the Higgs field, and mediates interactions with the Higgs field.
The mass of a particle is dependent on how strongly it interacts with the Higgs field, such that an electron neutrino interacts very weakly with the Higgs field, and therefore has a very low mass, while the top quark interacts very strongly with the Higgs field, and as such has a far greater mass. Since the mass of a particle does not change, regardless of where in the universe it is, the Higgs field must be uniform and permeate the entire universe, as otherwise interactions and therefore mass would vary in size, depending on where the particle was.
It is important to note that while the Higgs mechanism gives mass to fundamental particles like quarks, most of the mass in the universe (excluding dark energy and dark matter, due to the lack of current understanding of these concepts) is not a result of interactions with the Higgs field. Most mass is actually a result of the strong force acting between quarks, and the energy of this interaction is responsible for the vast majority of the mass of hadrons, such as protons and neutrons, which in turn form atoms with electrons, comprising almost the entire mass of the atom.
While all six physicists predicted the existence of a mechanism to explain the mass of W and Z bosons, only Higgs actually predicted the existence of a particle to mediate the interactions, and for this his second paper was rejected by Physics Letters, a scientific journal. Peter Higgs is a theoretical physicist, born in Newcastle, and an Emeritus Professor of Edinburgh. He received the Nobel Prize in 2013 for his contributions, along with François Englert. Sadly, Robert Brout had died in 2011, and as such was not eligible for the prize, as the Nobel Prize cannot be awarded posthumously.
The Higgs boson was estimated to have a mass of roughly 125GeV/c^2, making it the most massive elementary boson in the Standard Model. The Higgs boson was first observed at the Large Hadron Collider near Geneva, on the 4th July 2012. It was detected by both ATLAS (A Toroidal LHC ApparatuS) and CMS (Compact Muon Solenoid), both general-purpose detectors at CERN. The CMS weighs approximately 14,000 tonnes and consists of a large superconducting cable with a current passed through it, generating a magnetic field of a strength of 4 tesla. The ATLAS detector also uses magnetic fields, to alter the trajectory of particles. It then measures how much the particle trajectory is altered, and from that deduces the mass of the particle. On July 4th, CERN announced that they had observed a particle consistent with being the Higgs boson.
The detection of the Higgs boson is made harder by its very short lifetime(a Higgs boson has a mean lifetime of 1.6*10^-22s, according to the mean lifetime equation t = hbar/gamma, where hbar is Planck's constant/2π, and gamma is the decay width). This means that the detector cannot directly observe the Higgs boson, and must, therefore, try to deduce its existence from observing the particles that it decays into.
The Higgs boson can decay into a very large number of smaller particles. The Higgs is likely to decay into a fermion anti-fermion pair, as all charges are conserved(the pair cumulatively has an electrostatic charge of 0, a neutral colour charge, and so on). In general, the stronger the interaction with the Higgs field the particle has, the more likely the Higgs boson is to decay into that particle. However, the Higgs boson cannot decay into a top anti-top pair, as a single top quark has a mass of 173GeV/c^2, greater than that of the Higgs boson.
The most common decay pattern, occurring roughly 60% of the time, is as expected the decay into a bottom anti-bottom quark pair. This pattern, however, was not observed until 2018 at the LHC, and was unconfirmed until that point. The bottom quark has a lifetime of 10^-12s itself, making it difficult to observe, as it only exists briefly before decaying into a charm or strange quark by the weak interaction.
Another decay pattern of the Higgs boson is into two gauge bosons, with roughly 21.5% of all decays resulting in a W boson pair. Less common is the production of a tau-antitau pair, with a probability of 6.3%, and a Z boson pair, with a probability of 2.6%. Other decays with a probability of happening include the formation of a charm anti-charm pair, muon anti-muon pair, gluon-gluon pair, photon-photon pair, and Z boson-photon pair.
Overall, the discovery of the Higgs boson is a crucial step towards creating a unified field theory, and as such is a very important discovery, with far-reaching consequences for the field of quantum theory.
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