Higgs boson
The Higgs boson, sometimes called the Higgs particle,[9][10] is an elementary particle in the Standard Model of particle physics produced by the quantum excitation of the Higgs field,[11][12] one of the fields in particle physics theory.[12] In the Standard Model, the Higgs particle is a massive scalar boson with zero spin, even (positive) parity, no electric charge, and no colour charge that couples to (interacts with) mass.[13] It is also very unstable, decaying into other particles almost immediately upon generation.
"God Particle" redirects here. For other uses, see The God Particle (disambiguation).Composition
H0
R. Brout, F. Englert, P. Higgs, G. S. Guralnik, C. R. Hagen, and T. W. B. Kibble (1964)
Large Hadron Collider (2011–2013)
- Bottom–antibottom pair (observed)[5][6]
- Two W bosons (observed)
- Two gluons (predicted)
- Tau–antitau pair (observed)
- Two Z bosons (observed)
- Two photons (observed)
- Two leptons and a photon (Dalitz decay via virtual photon) (tentatively observed at sigma 3.2 (1 in 1000) significance)[4]
- Muon–antimuon pair (predicted)
- Various other decays (predicted)
0 e
0
−1/2
+1
The Higgs field is a scalar field with two neutral and two electrically charged components that form a complex doublet of the weak isospin SU(2) symmetry. Its "Sombrero potential" leads it to take a nonzero value everywhere (including otherwise empty space), which breaks the weak isospin symmetry of the electroweak interaction and, via the Higgs mechanism, gives a rest mass to all massive elementary particles of the Standard Model, including the Higgs boson itself.
Both the field and the boson are named after physicist Peter Higgs, who in 1964, along with five other scientists in three teams, proposed the Higgs mechanism, a way for some particles to acquire mass. (All fundamental particles known at the time[c] should be massless at very high energies, but fully explaining how some particles gain mass at lower energies had been extremely difficult.) If these ideas were correct, a particle known as a scalar boson should also exist (with certain properties). This particle was called the Higgs boson and could be used to test whether the Higgs field was the correct explanation.
After a 40-year search, a subatomic particle with the expected properties was discovered in 2012 by the ATLAS and CMS experiments at the Large Hadron Collider (LHC) at CERN near Geneva, Switzerland. The new particle was subsequently confirmed to match the expected properties of a Higgs boson. Physicists from two of the three teams, Peter Higgs and François Englert, were awarded the Nobel Prize in Physics in 2013 for their theoretical predictions. 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 the media, the Higgs boson has often been called the "God particle" after the 1993 book The God Particle by Nobel Laureate Leon Lederman.[14] The name has been criticised by physicists,[15][16] including Higgs.[17]
Properties[edit]
Properties of the Higgs field[edit]
In the Standard Model, the Higgs field is a scalar tachyonic field – scalar meaning it does not transform under Lorentz transformations, and tachyonic meaning the field (but not the particle) has imaginary mass, and in certain configurations must undergo symmetry breaking. It consists of four components: Two neutral ones and two charged component fields. Both of the charged components and one of the neutral fields are Goldstone bosons, which act as the longitudinal third-polarisation components of the massive W+, W−, and Z bosons. The quantum of the remaining neutral component corresponds to (and is theoretically realised as) the massive Higgs boson.[160] This component can interact with fermions via Yukawa coupling to give them mass as well.
Mathematically, the Higgs field has imaginary mass and is therefore a tachyonic field.[v] While tachyons (particles that move faster than light) are a purely hypothetical concept, fields with imaginary mass have come to play an important role in modern physics.[162][163] Under no circumstances do any excitations ever propagate faster than light in such theories – the presence or absence of a tachyonic mass has no effect whatsoever on the maximum velocity of signals (there is no violation of causality).[164] Instead of faster-than-light particles, the imaginary mass creates an instability: Any configuration in which one or more field excitations are tachyonic must spontaneously decay, and the resulting configuration contains no physical tachyons. This process is known as tachyon condensation, and is now believed to be the explanation for how the Higgs mechanism itself arises in nature, and therefore the reason behind electroweak symmetry breaking.
Although the notion of imaginary mass might seem troubling, it is only the field, and not the mass itself, that is quantised. Therefore, the field operators at spacelike separated points still commute (or anticommute), and information and particles still do not propagate faster than light.[165] Tachyon condensation drives a physical system that has reached a local limit – and might naively be expected to produce physical tachyons – to an alternate stable state where no physical tachyons exist. Once a tachyonic field such as the Higgs field reaches the minimum of the potential, its quanta are not tachyons any more but rather are ordinary particles such as the Higgs boson.[166]