The Higgs boson is an elementary particle in the Standard Model of particle physics , produced by the quantum excitation of the Higgs field,   one of the fields in particle physics theory.
This mechanism implies the existence of the Higgs boson. Although Higgs's name has come to be associated with this theory the Higgs mechanism , several researchers between about and independently developed different parts of it.
In mainstream media the Higgs boson has often been called the " God particle ", from a book on the topic ,  although the nickname is strongly disliked by many physicists, including Higgs himself, who regard it as sensationalism. A separate theory, general relativity , is used for gravity. In this model, the fundamental forces in nature arise from properties of our universe called gauge invariance and symmetries. The forces are transmitted by particles known as gauge bosons.
In the Standard Model, the Higgs particle is a boson with spin zero, no electric charge and no colour charge. It is also very unstable, decaying into other particles almost immediately. 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.
The Higgs field has a " Mexican hat-shaped " potential. In its ground state , this causes the field to have a nonzero value everywhere including otherwise empty space , and as a result, below a very high energy it breaks the weak isospin symmetry of the electroweak interaction.
Technically the non-zero expectation value converts the Lagrangian 's Yukawa coupling terms into mass terms. 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 either manifests as a Higgs particle, or may couple separately to other particles known as fermions via Yukawa couplings , causing these to acquire mass as well.
Field theories had been used with great success in understanding the electromagnetic field and the strong force , but by around all attempts to create a gauge invariant theory for the weak force and its combination with fundamental force electromagnetism , the electroweak interaction had consistently failed, with gauge theories thereby starting to fall into disrepute as a result.
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The problem was that the symmetry requirements in gauge theory predicted that both electromagnetism's gauge boson the photon and the weak force's gauge bosons W and Z should have zero mass. Although the photon is indeed massless, experiments show that the weak force's bosons have mass. By the late s, physicists had not resolved these issues, which were significant obstacles to developing a full-fledged theory for particle physics.
By the early s, physicists had realised that a given symmetry law might not always be followed under certain conditions, at least in some areas of physics.
Symmetry breaking can lead to surprising and unexpected results. If electroweak symmetry was somehow being broken, it might explain why electromagnetism's boson is massless, yet the weak force bosons have mass, and solve the problems.
Shortly afterwards, in , this was shown to be theoretically possible, at least for some limited non-relativistic cases. Following the and papers, three groups of researchers independently published the PRL symmetry breaking papers with similar conclusions and for all cases, not just some limited cases. They showed that the conditions for electroweak symmetry would be "broken" if an unusual type of field existed throughout the universe, and indeed, some fundamental particles would acquire mass.
The field required for this to happen which was purely hypothetical at the time became known as the Higgs field after Peter Higgs , one of the researchers and the mechanism by which it led to symmetry breaking, known as the Higgs mechanism. A key feature of the necessary field is that it would take less energy for the field to have a non-zero value than a zero value, unlike all other known fields, therefore, the Higgs field has a non-zero value or vacuum expectation everywhere.
It was the first proposal capable of showing how the weak force gauge bosons could have mass despite their governing symmetry, within a gauge invariant theory. Although these ideas did not gain much initial support or attention, by they had been developed into a comprehensive theory and proved capable of giving "sensible" results that accurately described particles known at the time, and which, with exceptional accuracy, predicted several other particles discovered during the following years.
There was not yet any direct evidence that the Higgs field existed, but even without proof of the field, the accuracy of its predictions led scientists to believe the theory might be true.
By the s the question of whether or not the Higgs field existed, and therefore whether or not the entire Standard Model was correct, had come to be regarded as one of the most important unanswered questions in particle physics. According to the Standard Model, a field of the necessary kind the Higgs field exists throughout space and breaks certain symmetry laws of the electroweak interaction.
When the weak force bosons acquire mass, this affects their range, which becomes very small.
For many decades, scientists had no way to determine whether or not the Higgs field existed, because the technology needed for its detection did not exist at that time. If the Higgs field did exist, then it would be unlike any other known fundamental field, but it also was possible that these key ideas, or even the entire Standard Model, were somehow incorrect. Unlike other known fields such as the electromagnetic field , the Higgs field is scalar and has a non-zero constant value in vacuum.
The existence of the Higgs field became the last unverified part of the Standard Model of particle physics, and for several decades was considered "the central problem in particle physics". The presence of the field, now confirmed by experimental investigation, explains why some fundamental particles have mass , despite the symmetries controlling their interactions implying that they should be massless.
It also resolves several other long-standing puzzles, such as the reason for the extremely short range of the weak force. Although the Higgs field is non-zero everywhere and its effects are ubiquitous, proving its existence was far from easy.
In principle, it can be proved to exist by detecting its excitations , which manifest as Higgs particles the Higgs boson , but these are extremely difficult to produce and detect. The importance of this fundamental question led to a year search , and the construction of one of the world's most expensive and complex experimental facilities to date, CERN 's Large Hadron Collider ,  in an attempt to create Higgs bosons and other particles for observation and study.
This also means it is the first elementary scalar particle discovered in nature.
More studies are needed to verify with higher precision that the discovered particle has all of the properties predicted, or whether, as described by some theories, multiple Higgs bosons exist. It was therefore several decades before the first evidence of the Higgs boson was found.
By March , the existence of the Higgs boson was confirmed, and therefore, the concept of some type of Higgs field throughout space is strongly supported. Various analogies have been used to describe the Higgs field and boson, including analogies with well-known symmetry-breaking effects such as the rainbow and prism , electric fields , ripples, and resistance of macro objects moving through media such as people moving through crowds or some objects moving through syrup or molasses.
Evidence of the Higgs field and its properties has been extremely significant for many reasons. The importance of the Higgs boson is largely that it is able to be examined using existing knowledge and experimental technology, as a way to confirm and study the entire Higgs field theory. The Higgs boson validates the Standard Model through the mechanism of mass generation. As more precise measurements of its properties are made, more advanced extensions may be suggested or excluded.
As experimental means to measure the field's behaviours and interactions are developed, this fundamental field may be better understood.
If the Higgs field had not been discovered, the Standard Model would have needed to be modified or superseded. Related to this, a belief generally exists among physicists that there is likely to be "new" physics beyond the Standard Model , and the Standard Model will at some point be extended or superseded.
The Higgs discovery, as well as the many measured collisions occurring at the LHC, provide physicists a sensitive tool to parse data for where the Standard Model fails, and could provide considerable evidence guiding researchers into future theoretical developments. Below an extremely high temperature, electroweak symmetry breaking causes the electroweak interaction to manifest in part as the short-ranged weak force , which is carried by massive gauge bosons.
In the history of the universe, electroweak symmetry breaking is believed to have happened shortly after the hot big bang, when the universe was at a temperature This symmetry breaking is required for atoms and other structures to form, as well as for nuclear reactions in stars, such as our Sun.
The Higgs field is responsible for this symmetry breaking. The Higgs field is pivotal in generating the masses of quarks and charged leptons through Yukawa coupling and the W and Z gauge bosons through the Higgs mechanism. It is worth noting that the Higgs field does not "create" mass out of nothing which would violate the law of conservation of energy , nor is the Higgs field responsible for the mass of all particles.
According to Rolf-Dieter Heuer , director general of CERN when the Higgs boson was discovered, this existence proof of a scalar field is almost as important as the Higgs's role in determining the mass of other particles. It suggests that other hypothetical scalar fields suggested by other theories, from the inflaton to quintessence , could perhaps exist as well. Some theories suggest that a fundamental scalar field might be responsible for this phenomenon; the Higgs field is such a field, and its existence has led to papers analysing whether it could also be the inflaton responsible for this exponential expansion of the universe during the Big Bang.
Such theories are highly tentative and face significant problems related to unitarity , but may be viable if combined with additional features such as large non-minimal coupling, a Brans—Dicke scalar, or other "new" physics, and they have received treatments suggesting that Higgs inflation models are still of interest theoretically.
In this scenario, the universe as we know it could effectively be destroyed by collapsing into a more stable vacuum state. More speculatively, the Higgs field has also been proposed as the energy of the vacuum , which at the extreme energies of the first moments of the Big Bang caused the universe to be a kind of featureless symmetry of undifferentiated, extremely high energy. In this kind of speculation, the single unified field of a Grand Unified Theory is identified as or modelled upon the Higgs field, and it is through successive symmetry breakings of the Higgs field, or some similar field, at phase transitions that the presently known forces and fields of the universe arise.
The relationship if any between the Higgs field and the presently observed vacuum energy density of the universe has also come under scientific study.
As observed, the present vacuum energy density is extremely close to zero, but the energy density expected from the Higgs field, supersymmetry, and other current theories are typically many orders of magnitude larger. It is unclear how these should be reconciled.
This cosmological constant problem remains a major unanswered problem in physics. As yet, there are no known immediate technological benefits of finding the Higgs particle.
However, a common pattern for fundamental discoveries is for practical applications to follow later, and once the discovery has been explored further, perhaps becoming the basis for new technologies of importance to society. The challenges in particle physics have furthered major technological progress of widespread importance. CERN's requirement to process massive amounts of data produced by the Large Hadron Collider also led to contributions to the fields of distributed and cloud computing [ citation needed ].
The six authors of the PRL papers , who received the J. At the beginning of the s a number of these particles had been discovered or proposed, along with theories suggesting how they relate to each other, some of which had already been reformulated as field theories in which the objects of study are not particles and forces, but quantum fields and their symmetries.
One known problem was that gauge invariant approaches, including non-abelian models such as Yang—Mills theory , which held great promise for unified theories, also seemed to predict known massive particles as massless.
By the very early sixties, people had begun to understand another source of massless particles: spontaneous symmetry breaking of a continuous symmetry.
What Philip Anderson realized and worked out in the summer of was that, when you have both gauge symmetry and spontaneous symmetry breaking, the Nambu—Goldstone massless mode can combine with the massless gauge field modes to produce a physical massive vector field.
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This is what happens in superconductivity , a subject about which Anderson was and is one of the leading experts. The Higgs mechanism is a process by which vector bosons can acquire rest mass without explicitly breaking gauge invariance , as a byproduct of spontaneous symmetry breaking.
Weinberg was the first to observe that this would also provide mass terms for the fermions. At first, these seminal papers on spontaneous breaking of gauge symmetries were largely ignored, because it was widely believed that the non-Abelian gauge theories in question were a dead-end, and in particular that they could not be renormalised. In —72, Martinus Veltman and Gerard 't Hooft proved renormalisation of Yang—Mills was possible in two papers covering massless, and then massive, fields.
For example, Coleman found in a study that "essentially no-one paid any attention" to Weinberg's paper prior to  and discussed by David Politzer in his Nobel speech. The resulting electroweak theory and Standard Model have accurately predicted among other things weak neutral currents , three bosons , the top and charm quarks , and with great precision, the mass and other properties of some of these.
A paper and comprehensive review in Reviews of Modern Physics commented that "while no one doubted the [mathematical] correctness of these arguments, no one quite believed that nature was diabolically clever enough to take advantage of them",  adding that the theory had so far produced accurate answers that accorded with experiment, but it was unknown whether the theory was fundamentally correct.
The three papers written in were each recognised as milestone papers during Physical Review Letters 's 50th anniversary celebration. Sakurai Prize for Theoretical Particle Physics for this work.
In the paper by Higgs the boson is massive, and in a closing sentence Higgs writes that "an essential feature" of the theory "is the prediction of incomplete multiplets of scalar and vector bosons ". To produce Higgs bosons , two beams of particles are accelerated to very high energies and allowed to collide within a particle detector. Occasionally, although rarely, a Higgs boson will be created fleetingly as part of the collision byproducts.
Because the Higgs boson decays very quickly, particle detectors cannot detect it directly.
Instead the detectors register all the decay products the decay signature and from the data the decay process is reconstructed. If the observed decay products match a possible decay process known as a decay channel of a Higgs boson, this indicates that a Higgs boson may have been created. In practice, many processes may produce similar decay signatures. Fortunately, the Standard Model precisely predicts the likelihood of each of these, and each known process, occurring.