Theory 
Standard Model of Physics| CONTENT - A fine explanation of the Standard Model of Physics. A tutorial part of our science extras |
Evolution of knowledge about matter and Universe led in the 1970s to what is termed the Standard Model, or Standard Model of physics, which is the general explanation of how matter works, on Earth, and in the Universe, at atomic scale. To bring order to a plethora of recently discovered subatomic particles, in 1961 physicist Murray Gell-Mann proposed a set of rules based on symmetries in the fundamental forces of nature. The rules classified into eight groups, a scheme he named the eightfold way in a reference to Buddhist philosophy. He named fundamental particles quarks, inspired by a quote --'Three quarks for Muster Mark!' -- from James Joyce’s 1939 novel Finnegans Wake. He also posited the existence of gluons. He received the Nobel Prize in 1969. Gell-Mann was born in New York City in 1929, and did much of his work at the California Institute of Technology in Pasadena, where he taught from 1955 to 1993. The Standard Model is a 1970s synthesis of what was known then and since has been the basis for following experiments. It is successfull to describe the physical world. Technically speaking, the Standard Model is the quantum theory including the theory of strong interactions (QCD, quantum chromodynamics) and the unified theory of weak and electromagnetic forces (electroweak). The standard model of particle physics describes the fundamental particles and their interactions via the strong, electromagnetic and weak forces. The Standard Model, generally, works upon that all matter is made of two basic class of particles, the quarks and leptons along with forces acting upon those. Boson particles are carriers of forces, photons are related to electromagnetism as matter is formed by fermions. In the perspective of how the matter is distributed in the Universe, the Standard Model fails to account for dark matter as it only explains about 5 percent of it. Of note that mass and energy are used interchangeably in particle physics
Matter is made of base constituents, of forces by which these constituents interact. These forces are carried by force carriers. Matter, generally, sorts into hadrons, which are quark-based particles like baryons and mesons -- mostly the constituents of a atom -- and leptons which are particles like the electrons and neutrinos, for example. Any baryon contains at most one heavy quark as a particle with two heavy quarks (two charm et one up), called cascade-c-c-double-plus was discovered by 2017. A general principle rules matter: the Pauli Exclusion Principle. It states that two particles in the same state (color charge, intrinsic angular momentum -or spin, etc) cannot exist in the same place at the same time. Particles subject to this principle are said fermions. Fermions are matter fundamental constituents (like quarks, or electrons). Particles not subject to this principle are said bosons. Bosons are force carriers. Constituents of matter are fermions, as force carriers are bosons. Moreover any atom with an odd number of electrons, protons, and neutrons is a fermion (protons and neutrons are collectively named 'neutrons.'); any atom with an even number of electrons, protons, and neutrons is a boson. For each any particle there is an antiparticle having the same characteristics but with opposite charge. In the world of particles, light speed, or 'c,' is a unsurpassable constant of Nature and the speed of physical interactions, gravity included, in void or the upper limit to masses acceleration. Fleeting extra-heavy strange 'baryons' are predicted by the Standard Model and freezing out from other subatomic particles in a plasma soup of free quarks and gluons carrying the strong force, that mimics conditions in the Universe a few moments after the Big Bang, or a 'quark-gluon plasma'
How the Boson Got Its Name!
Satyendranath Bose, is a Indian physicist after whom the boson particle is named.The Kolkata-born scientist's had worked in the 1920s with Albert Einstein in defining
one of two basic classes of subatomic particles, describing how photons
can be considered particles as well as waves. Any
particles that follow such behavior are called
'bosons.' By then, Bose was living in his Indian city of Kolkata after 25 years running
the physics department at Dacca University, in nowadays Bangladesh. Bose died in 1974, aged 80
Matter Fundamental Constituents, or Fermions. They are subject to the Pauli Exclusion Principle. Fermions in turn are divided into quarks or leptons
All these elementary particles have a spin (angular momentum), an electric charge -in units of the proton's charge, energy (in electronvolt (eV)) and mass (in GeV/c2). Electrons' spin is the angular momentun of those around the atom's nucleus as it comes into two flavors, up and down. Physicists are still thinking about how flavor combinations of quarks can fit together to form particles as such interactions are described by the theory called 'quantum chromodynamics' (QCD). Physicists however can't do any calculation upon QCD because it is too complicated. The 'quantum state' of a particle are numbers describing its characteristics. The very act of measuring a quantum state however change the characteristics as maths of it can be complex. 'Disallowed' states that does not follow the laws of physics further has to be discarded. Charged particles like electrons will spiral in a magnetic field and give off radiation Interacting electrons in some materials can be 'fractionized' into independent particles carrying spin and charge, respectively — an unusual behaviour known as spin–charge separation
Four types of forces mediate matter interactions: the strong interaction force, the electromagnetic force, the weak force, the gravity. All these forces, except the gravity, work on the basis of quantum field theories
 | It is through such colliding events that physicists study deepest levels of matter. Accelerators make particles collide and yield others. This colliding event particularly has been produced at the Relativistic Heavy Ion Collider (RHIC) at Brookhaven National Laboratory, USA. This accelerator is specially dedicated to produce primeval states of matter, as they are believed to have existed in the early Universe. courtesy RHIC, Brookhaven National Laboratory |
Forces are carried between particles due to "force carriers". Force carriers are particles specially dedicated to transport of forces. Particles are interacting between themselves due to interactions. Interactions are exchange of force carrying particles: the latter are exerting a force of a somehow newtonian type on particles receiving them (action-reaction). Force carriers are not subject to the Pauli Exclusion Principle. Technically all interactions may be said mediated (carried) by integer-spin or Boson field quanta. Force carriers are bosons. Odd spin bosons mediate repulsive forces; even spin bosons mediate attractive forces
All these matter constituents, forces, and force-carriers are the building blocks of atoms. Quarks unite to form protons or neutrons. Protons and neutrons, which are formed of three quarks bound tight together by gluons, which are carriers of the strong force, unite to form atom nucleus. Electrons are orbiting the nucleus (atoms then form elements as elements in turn form molecules). Atom is held together due to forces mediated by force carriers: quarks are linked together by the strong force which is carried by gluons. Protons and neutrons are linked together inside the nucleus by a residual strong force emanating from their quarks constituents. Electrons are linked to nucleus by the electromagnetic force. Further, weak force acting on quarks constituents and electrons bring natural atom decay. Of interest, let's point to that, from the largest to the smallest, here is how particles or concepts rank in terms of size: electron; proton and neutron; weak force range; up, down and strange quark; charm quark; bottom quark; high energy neutrino; top quark; neutrino; and, after a much long interval the quantum foam, the Planck length and a superstring theory string. Above a critical temperature, protons and neutrons and other forms of hadronic matter melt into a hot, dense soup. Subatomic particles in an atom's nucleus take different forms at different temperatures
 | click to a diagram of the Standard Model of physics |
All this is of importance and show a tremendous variety of particles and forces at work in matter: electrons and quarks belong to the same level of matter building blocks. Both are fermions subject to the Pauli Exclusion Principle. Quarks interact via the strong force only. Electrons are subject to the electromagnetic force only. Interaction between quarks composites like protons and neutrons is mediated by mesons which are formed of quarks themselves, by-products of quarks and gluons. Electrons are linked to the atom nucleus through the electromagnetic force. Result is an atom where if protons and neutrons were 10 cm across, quarks and electrons would be 0.1 mm wide as the outer limit of electrons orbits would be 10 km away from the nucleus! The electron's mass is one of a few key parameters that govern the structure and properties of atoms. The electron' intrinsic angular momentum, or spin, acts like tiny bar magnet, which, when exposed to a magnetic field, rotate around the field's axis
Most of matter in the Universe is made of up (u) and down (d) quarks which are the most massive quarks, and of electrons which are the most massive leptons. This is called the first generation of particles, most stable of them. These are light particles. They are the by-products of second and third generation of particles decay. These particles are heavier, unstable, and decay. Above a critical temperature, protons and neutrons and other forms of matter melt into a soup of free quarks and gluons, which is named the 'quark-gluon plasma.' In the first ten-millionths of a second after the Big Bang, the Universe was hot enough to keep quarks apart. Since quarks and gluons can interact with each other in extraordinarily complex ways, physicists can write down the mathematical law governing its properties in a single line, as they still do not understand its microscopic structure. Maths that could allow are still lacking. Scientists have been able however to recreate the quark-gluon plasma in laboratories as they had expected quark-gluon plasmas to behave more like a gas. It works like a liquid instead. Like a liquid means that constituents interact more strongly with each other. A state of matter that may exist before quark-gluon plasmas form is featuring a dense mix of gluons known as a 'glasma.' In another pecular state of matter, or the Bose-Einstein condensate state of matter, many atoms work together to essentially behave as giant super-atoms
Since the Standard Model has been elaborated, it remained a pertaining theoretical model as the experiments which have been -and are- performed upon it are inserting themselves, for example, in a logics. Albeit the current handbook to physicians, the Standard Model nevertheless might have some holes according to some. At the effect of testing the Standard Model before moving to any physics going beyong, physicists are mapping out all the particles that should come from different quark combination. A question to the Standard Model are how particles got their masses. It is the famous question of the Higgs boson. The theory of the Higgs boson is linked to the one of the 'Higgs mechanism', or 'electroweak gauge symmetry,' which is a verified mechanism proposed in 1964 by Peter Higgs, by which vector bosons (force carriers particles like the photon, gluon, W and Z particles) can get a mass or their couplings among themselves and with fermions, which are quarks and leptons. The Higgs boson was proposed by one of the physicists' teams which discovered the Higgs mechanism as it remains the only Standard Model particle still unobserved in experiments. Peter Higgs, a British physicist, had proposed a first contribution about the Higgs boson by 1964, which was refused by the Physics Letters review which at the time was managed by the CERN. The Large Hadron Collider (LHC) at the CERN in Geneva, Switzerland indeed, 40 years later, is supposed to be power-able to determine if the Higgs boson exists or not and discriminate between varied theories making use of it. The Higgs boson particle is supposed to belong a class of particles know as 'scalar bosons', with spin 0 at the opposite of vector bosons which have a spin 1. The Higgs boson is thought to give particles their mass as it possesses a scalar field, or the 'Higgs field', a non-zero vacuum (and that is why the Higgs boson has no spin), every particle coupling to that field -by just travelling through the field- have that non-zero vacuum to cling, including the Higgs boson itself. The idea behind the Higgs boson is that our Universe is bathed in a invisible field, or the Higgs field, similar to a magnetic field. If a particle can move through with little or no interaction, there will be no drag and that particle will have little or no mass. If a particle interacts significantly with the Higgs field, it will have a higher mass. As there cannot be a field in physics without a particle, the Higgs boson is the one associated to that field. For instance, the particle associated with the electromagnetic field is the photon. With a mass, particles can eventually form a atom. Of note is that the proton has no mass (the best estimation of the proton's maximal mass is at most at 1.1 electronvolt, as of 2019). As related to the Big Bang, Higgs field, or a field of force, along the Higgs boson appeared after that, in a beginning, no any particle in the nascent Universe had a mass, as the Universe got colder below a critical threshold. If proved, the Higgs boson also would have its antiparticle. At a mass between 115 and 180 GeV/c2, the Higgs boson would have the Standard Model be valid at energy scales all the way up to the Planck scale (1016 TeV), a mass at 1.4 TeV, for exemple would render the Standard Model inconsistent. Masses in-between likely would move the Standard Model into the direction of unification's GUT theories. In the early moments of the Big Bang, the Higgs boson likely allowed particles to aggregate between themselves for cause they acquired a mass. The LHC might expect to check the Higgs boson through several combinations of particles, like two gluons decay into a top/anti-top pair, which then combine to make a neutral Higgs or two quarks each emit a W or Z boson, which combine to make a neutral Higgs. The LHC was built like a successor to the LEP collider at CERN which already had checked results which might hint to the boson at the time. With 7 TeV the LHC should readily discovered the boson as such a power is well above that at which detection should occur. The Higgs boson is a very unstable particle which vanishes as soon as it forms! The LHC is colliding protons. The US Fermilab Tevatron also is researching the Higgs boson. 'God particle' terms used by media to qualify the Higgs boson, are considered in the science community like overstating the Higgs boson role as even its discovery would leave questions unanswered, for example, about the unification of the Electroweak interaction and gravity, or the ultimate origin of the Universe. In the Standard Model, in terms of quantum vacuum, the non-zero vacuum expectation value of the Higgs field, arising from spontaneous symmetry breaking, is the mechanism by which the other fields in the theory acquire mass. The Higgs boson, generally, is pertaining to the question of matter/antimatter, the relationship between quantum physics and Einstein's Relativity, and to the question of empty fields
The Latest About the Higgs Boson!
On Wednesday, July 4th 2012, scientists at the CERN in Geneva, Switzerland announced that, using the Large Hadron Collider (LHC), they have discovered a new particle the properties of which could match the Higgs boson. That marks the first time since 1995 that a new fundamental particle had been
unearthed, confirming a decades-old
prediction of how the Universe works and that constitutes the last piece in the Standard Model of Physics. The advance also leaves particle physics at a crossroads as, if no new particles or phenomena show up, the discovery of
the Higgs boson could mark the end of the road. The Higgs boson is the seal to the Standard Model which includes the whole of the explanation of Nature, the force of gravity excepted as that particle gives any other its shape and size. The new mission of the LHC, now, is to pin down the properties of
the Higgs boson, which has been found with a mass 130 times the one of a proton. Higgs and other physicists who proposed the existence of the Higgs boson -Gerald Guralnik, François Englert and Carl Hagen, or Tom Kibble also had predicted in 1964 the existence of such a Higgs boson- already had solved one of the toughest physics problems then, in the early 1960s! Two of the four fundamental forces that govern the behaviour of particles
were known and nearly identical mathematically. The main difference between them was that
the particles associated with one force had mass, whereas those associated with
the other did not. Only the Higgs field explained the split. In the very early Universe, the theory
goes, the Higgs field was zero, and the two forces were as one. Shortly
after the Big Bang, the field assumed a non-zero value and the forces split
apart. One, which became electromagnetism, is mediated by massless particles of
light known as photons, which ignore the Higgs field. The other force became the
weak nuclear force, which causes certain kinds of radioactive decay, and works
through heavy particles called W and Z bosons. These interact with the Higgs
field and gain mass. Ordinary matter derives most of its mass from subsequent
interactions between particles such as quarks. The Higgs boson itself can be thought of as an excited ripple in the Higgs
field. The Higgs boson and field are needed mainly in calculations to explain how the electromagnetic and weak nuclear forces unify into the single ‘electroweak,' which in turn predicts the properties of other particles or conversely, by explaining the difference in the masses of the photons and bosons, the
Higgs boson allowed physicists to unite the electromagnetic and the weak nuclear force into a single
'electroweak' one. The likely Higgs particle has been found with a less than a one-in-a-million chance of getting these data
by chance, or around so-called 'five standard deviations.' Now what? Physicists, mostly because the CERN physicists are proponents of the speculative supercords theories, now might also looks for hints about a new theory beyond the Standard Model, or a more comprehensive theory that
could lead physicists towards a unified understanding of the Universe! For one thing, for example, the newly found particle
seems to decay into pairs of photons about twice as often as the Standard Model
predicts — and it decays less often than expected into particles known as taus
and W bosons. Such discrepancies are far from being statistically significant
right now, but if the evidence grows as more data are gathered, they could point
to physics beyond the Standard Model. It may be that the detected boson by the summer of 2012 is actually a composite, made up
of smaller particles, or that it is the first of a new class of bosons -a
'Higgs family.' Any more accute details about the Higgs boson should be released by late 2012. On a other hand, the mass of the Higgs boson generally remains a puzzle however. According to
Standard Model calculations, the Higgs should be very heavy and unstable
unless a large and improbable correction is applied to the equations. A theory
known as supersymmetry, embraced by many physicists, predicts a lighter Higgs. So far, no signals of supersymmetry have shown up
inside the LHC however. Moreover, the mass of 130 GeV in the reported data is too heavy
for the simplest supersymmetric models. The whole Standard Model generally, since long, had been thought it wouldn't fit
together nicely if the Higgs boson wasn't there. The new boson should have a spin zero as the way in which the new particle decays into other particles will also be key
to verifying its precise nature. The Higgs boson allows to explain why, for example, the photon which carries the electromagnetic force, has no mass at the difference of particles carrying the weak force. Such a dissymetry was incompatible with the fundamental, 'gauge' symmetry upon which the Standard Model is based
Like all fundamental particles, the Higgs has a fixed and quantized amount of angular momentum or spin. It also has a property of symmetry called parity, which can be either even or odd and which affects, for example, the way the Higgs can decay into other particles. According to the standard model, the Higgs should have -and actually has- zero spin and positive parity. By 2018, physicists observed the Higgs boson decaying to a pair of elementary particles known as bottom quarks, which confirmed the role of the Higgs field -- the quantum field associated with the Higgs boson -- in providing particles of matter with mass. The Higgs boson decays almost immediately after it is produced. By 2018 too, CERN physicists found that Higgs boson particle fragments yielded by smashing protons into each other, interact in terms of strength with the top quark in a manner consistent with the expectation of Standard Model
The Higgs boson and field, on a other hand, might be at the origin of a possible end of the Universe. As the Higgs boson is a excited state of the Higgs field -which pervades the whole Universe. Any particle in the Standard Model is acquiring its mass because of its interaction with the Higgs field. Now, a quantum field, like any object of Nature, may find himself in varied energy states. The Higgs field thus could pass into a lower energy state. The Higgs field moreover, according to the recentest studies, is lying nowadays into a state of 'metastability', which means it is neither stable in a low nor unstable in a hight. It is extra-stable in a intermediate state. That explains why the Universe exists since 13 billion years. Through the 'tunnel effect,' which is a usual quantum phenomenon allowing a object or a field to cross the 'walls' which edge it, the Higgs field might, one day, tip over into void and the field would thicken as any particle would aquire a too strong mass, and the electrons, for example, would wall unto atoms' nucleus. According to physicists however, the Higgs field's metastability should last 10100 years (dozens of billion of billion years). Quantum physics being per se, unforeseeable, such a move could also occur without notice. Another flat to the theory is that energies implied would be a hundred million times more powerful than those obtained by the LHC and the Standard Model might not be true anymore at such levels. At 126 billion electron volts the mass of the Higgs boson is about 126 times the one of the proton. That value is just what is needed to make the Universe fundamentally unstable. That could either be a coincidence, or it could be that some physics is causing that
Another question is the question of very weak forces which might be involved into very long duration decays like the decay of the proton (1032 years) or be responsible for the mass of the neutrinos. Two main other centers of interest for physicists are the idea of unification of the strong, weak and electromagnetic forces into one "Grand Unified Theory" (GUT) -mathematical theories for these different forces are somehow similar, and the famous attempt of the String Theory to unify the four forces -strong, weak, electromagnetic and gravity- although gravity rests on a different mathematical theory and that there is no quantum theory of gravity. If all this proves to be real and based, it is likely that, in the same way that the Standard Model included its predecessors -the atom and the newtonian models- any further model for physics will embed the Standard Model, Relativity, and quantum physics. Understanding the Standard Model of physics if of importance for astronomy: Big Bang is seen as the moment when unified forces were progressively splitted and when elementary particles were progressively created and linked together. The latest discovery about the Standard Model is a new particle, called "theta". This particle was found at Brookhaven RHIC and is strangely composed of four quarks and an antiquark as usual baryons and mesons are formed by three quarks (or antiquarks) or one quark and one antiquark only. Some other advances in the particules science should be provided by the next 'Large Hadron Collider Particle Accelerator' being built by the European Organization for Nuclear Research (CERN) at the French-Swiss border near Geneva. Also, collisions between particles and their antimatter counterparts often include so-called B-bar mesons, which are made of a bottom-flavoured quark and its antiquark. Looking for a particular decay process where B-bar mesons decay into a D meson (a quark and a antiquark, one of which is 'charm' flavored), a antineutrino and a tau lepton, U.S. physicists found that the process happens more often than the Standard Model predicts. Six years' worth of LHC data have failed to produce a definitive detection of anything unexpected in the Standard Model, and yet, as a description of the Universe, its is uncomplete like unable to explain antimatter, dark matter or dark energy. Current research in physics, by 2018, are towards a better understanding of the electron or neutrons and atoms that could reveal a violation of one of nature’s symmetries, or the decay of the B-mesons which hold the bottom or beauty, b quark
The Standard Model, generally, is not valid beyond temperatures and pressions at which it has been deviced and at which is it proven to work. That entails that the Standard Model itself is not apt to entirely explain the first moments of the Universe when temperatures and pressions were higher still
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