Higgs boson
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| |
| Composition | Elementary particle |
|---|---|
| Statistics | Bosonic |
| Status | A Higgs boson of mass ≈125 GeV has been tentatively confirmed by CERN on 14 March 2013,[1][2][3] although it is unclear as yet which model the particle best supports or whether multiple Higgs bosons exist.[2] (See: Current status) |
| Symbol | H0 |
| Theorised | R. Brout, F. Englert, P. Higgs, G. S. Guralnik, C. R. Hagen, and T. W. B. Kibble (1964) |
| Discovered | Large Hadron Collider (2011-2013) |
| Mass | 125.09±0.21 (stat.)±0.11 (syst.) GeV/c2(CMS+ATLAS)[4] |
| Mean lifetime |
1.56×10−22 s
[Note 2] (predicted) |
| Decays into | various other decays (predicted) |
| Electric charge | 0 e |
| Colour charge | 0 |
| Spin | 0 (tentatively confirmed at 125 GeV)[1] |
| Parity | +1 (tentatively confirmed at 125 GeV)[1] |
The Higgs boson is an elementary particle in the Standard Model of particle physics. It is the quantum excitation of the Higgs field[6][7]—a fundamental field of crucial importance to particle physics theory,[7] first suspected to exist in the 1960s. Unlike other known fields such as the electromagnetic field, it takes a non-zero constant value almost everywhere. The question of the Higgs field's existence has been the last unverified part of the Standard Model of particle physics and, according to some, "the central problem in particle physics".[8][9]
The presence of this field, now believed to be confirmed, explains why some fundamental particles have mass when, based on the symmetries controlling their interactions, they should be massless. The existence of the Higgs field would also resolve several other long-standing puzzles, such as the reason for the weak force's extremely short range.
Although it is hypothesized that the Higgs field permeates the entire Universe, evidence for its existence has been very difficult to obtain. In principle, the Higgs field can be detected through its excitations, manifest as Higgs particles, but these are extremely difficult to produce and detect. The importance of this fundamental question led to a 40 year search, and the construction of one of the world's most expensive and complex experimental facilities to date, CERN'sLarge Hadron Collider,[10] in an attempt to create Higgs bosons and other particles for observation and study. On 4 July 2012, the discovery of a new particle with a mass between 125 and 127 GeV/c2 was announced; physicists suspected that it was the Higgs boson.[11][12][13] Since then, the particle has been shown to behave, interact, and decay in many of the ways predicted by the Standard Model. It was also tentatively confirmed to have even parity and zero spin,[1] two fundamental attributes of a Higgs boson. This appears to be the first elementary scalar particlediscovered in nature.[14] More studies are needed to verify that the discovered particle has properties matching those predicted for the Higgs boson by the Standard Model, or whether, as predicted by some theories, multiple Higgs bosons exist.[3]
The Higgs boson is named after Peter Higgs, one of six physicists who, in 1964, proposed the mechanism that suggested the existence of such a particle. On December 10, 2013, two of them, Peter Higgs and François Englert, were awarded the Nobel Prize in Physics for their work and prediction (Englert's co-researcher Robert Brout had died in 2011 and the Nobel Prize is not ordinarily given posthumously).[15] Although Higgs's name has come to be associated with this theory, several researchers between about 1960 and 1972 independently developed different parts of it. In mainstream media the Higgs boson has often been called the "God particle", from a 1993 book on the topic; the nickname is strongly disliked by many physicists, including Higgs, who regard it as sensationalistic.[16][17][18]
In the Standard Model, the Higgs particle is a boson with no spin, electric charge, or colour charge. It is also very unstable, decaying into other particles almost immediately. It is a quantum excitation of one of the four components of the Higgs field. The latter constitutes a scalar field, with two neutral and two electrically charged components that form a complex doublet of the weak isospin SU(2) symmetry. The Higgs field is tachyonic (this does not refer to faster-than-light speeds, it means that symmetry-breaking through condensation of a particle must occur under certain conditions), and has a "Mexican hat" shaped potential with nonzero strength everywhere (including otherwise empty space), which in its vacuum state breaks the weak isospin symmetry of the electroweak interaction. When this happens, three components of the Higgs field are "absorbed" by the SU(2) and U(1) gauge bosons (the "Higgs mechanism") to become the longitudinal components of the now-massive W and Z bosons of the weak force. The remaining electrically neutral component separately couples to other particles known as fermions (via Yukawa couplings), causing these to acquire mass as well. Some versions of the theory predict more than one kind of Higgs fields and bosons. Alternative "Higgsless" models may have been considered if the Higgs boson was not discovered.
On 15 December 2015, two teams of physicists, working independently at CERN, reported preliminary hints of a possible new subatomic particle (more specifically, the ATLAS and CMS experiments, using 13 TeV proton collision data, showed a moderate excess around 750 GeV, in the two-photon spectrum): if real, one possibility is that the particle could be a heavier version of a Higgs boson.
On 4 July 2012, the ATLAS and CMS experiments at CERN's Large Hadron Collider announced they had each observed a new particle in the mass region around 126 GeV. This particle is consistent with the Higgs boson predicted by the Standard Model. The Higgs boson, as proposed within the Standard Model, is the simplest manifestation of the Brout-Englert-Higgs mechanism. Other types of Higgs bosons are predicted by other theories that go beyond the Standard Model.
On 8 October 2013 the Nobel prize in physics was awarded jointly to François Englert and Peter Higgs "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."
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Featured updates on this topic
At the 2015 LHCP conference the collaborations presented for the first time combined measurements of many properties of the Higgs boson
Updates
Do recent discoveries mean there’s nothing left? Find out what the future holds for theoretical physics in our final In Theory series installment
Today the ATLAS and CMS experiments presented for the first time a combination of their results on the mass of the Higgs boson
Recent publications from CMS use data from the LHC's first run to shed light on the properties of the Higgs boson
Without a doubt, it is a Higgs boson, but is it the Higgs boson of the Standard Model? Run 2 of the LHC find out, says theorist John Ellis
In CERN’s 60th year, the first proof of the existence of the Higgs boson earns a Guinness World Record for CERN, ATLAS and CMS
At ICHEP in Valencia, Spain, all four LHC experiments presented new results from the LHC’s first run. Run 2 physics holds much promise
Results reported by ATLAS and CMS discuss the decay of Higgs bosons directly to fermions, the particles that make up matter
Teach the machines: CERN launches competition to develop machine-learning analysis techniques for Higgs data
At the Moriond conference CMS presented the best constraint yet of the Higgs boson “width”, a parameter that determines the particle’s lifetime
On his first trip to CERN since sharing the Nobel prize in physics last year with Peter Higgs, François Englert talks Higgs bosons and supersymmetry
