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What is the Standard Model of Particle Physics?
A theory explaining the relationships between known fundamental interactions between elementary particles that make up all matter is the standard model of particle physics. It is a quantum field theory that is consistent with quantum mechanics and special relativity that was developed between 1970 and 1973. Nearly all experimental tests of the three forces defined by the standard model are in line with their predictions to date.
The Standard Model in a Nutshell
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However, the standard model does not become a complete theory of fundamental interactions because it does not include gravity, the fourth known fundamental interaction, and also because of the high number of numerical parameters (such as masses and constants that come together) that must be put together in theory (rather than derived from first principles).
Currently, in Physics, the dynamics of matter and energy in nature are best understood in terms of kinematics and fundamental particle interactions. To date, science has managed to reduce laws that seem to govern the behaviour and interaction of all types of matter and energy we know, to a small set of fundamental laws and theories. An important goal of physics is to find the common basis that would unite all of these in a theory of the whole, in which all the other laws we know would be special cases, and from which the behaviour of all matter and energy can be derived (ideally from first principles).
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Within this, the standard model brings together three important theories –quantum chromodynamics – which provides an internally consistent theory that describes the interactions between all experimentally observed particles. Technically, the mathematical basis for the standard model is given by quantum field theory. In terms of a mathematical field, the standard model defines each sort of particle.
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The standard model can be divided into three sections, which are matter particles, force-mediating particles, and the Higgs boson, for ease of description.
Matter Particles
Matter particles made of the standard model all known matter are made up of particles that have an intrinsic property called spin whose value is 1/2.All matter particles are fermions, in terms of the standard model. For this reason, according to the spin’s statistics theorem, they obey Pauli’s exclusion principle, and it is what causes its quality of matter. Apart from its associated anti-particles, the standard model explains a total of twelve different types of matter particles. The Rose Six of these are classified as quarks (up, down, strange, charm, top, and bottom), and the other six as leptons (electron, muon, tau, and their corresponding neutrinos).
Particles of matter also carry loads that make them susceptible to fundamental forces, as described in the next section.
- Each quark can carry three loads of color – red, green, or blue, allowing them to participate in strong interactions.
- Up, top, or charm quarks carry an electrical charge of +2/3, and the down, strange, and bottom type carry an electrical charge of -1/3, allowing both types to participate in electromagnetic interactions.
- Leptons do not carry any color charges – they are neutral in this regard, avoiding that they participate in strong interactions.
- Down leptons (the electron, muon, and lepton tau) carry an electrical charge of -1, allowing them to participate in electromagnetic interactions.
- Up leptons (neutrinos) do not carry any electrical charges, avoiding that they participate in electromagnetic interactions.
- Quarks and leptons carry various loads of flavor, including weak isospin, allowing all of them to interact with each other via weak nuclear interaction.
Pairs of each group (a quark type up, a quark type down, a lepton type down, and its corresponding neutrino) form the families. The corresponding particles between each family are identical to each other, except for their mass and a characteristic known as their taste.
Means of Forces
Forces in physics are the way particles interact with each other and influence each other. At the macroscopic level, for example, electromagnetic force allows particles to interact with and through magnetic fields, and the force of gravitation allows two mass particles to attract each other according to Newton’s law of gravitation.
When a force mediating particle is exchanged, the effect is equivalent to a force influencing both at the macroscopic level, and it is said that the particle mediated (i.e., was the agent of) that force. The reason for the forces and interactions between the particles observed in the laboratory and in the universe is thought to be force-mediating particles.
The force mediating particles defined by the Particle Physics standard model also have spin (like particles of matter), but the spin value is 1, if appropriate, meaning that all force mediating particles are bosons. Consequently, they do not obey Pauli ‘s principle of exclusion. The different kinds of particles that mediate force are described below.
- Photons mediate electromagnetic force between electrically charged particles. The photon has no mass and is described by the theory of quantum electrodynamics.
- Gauge bosons W, W+–, and Z0 weak nuclear interactions between particles of various flavours (all quarks and leptons). They’re massive, with the Z0 more massive than the. Weak interactions involving acting exclusively on left-handed particles and not on left-handed antiparticles. In addition, he carries an electrical charge of +1 and -1 and participates in electromagnetic interactions. Both left-handed particles and anti-particles interact with the electrically neutral Z0 boson. Along with the photons, these three gauge bosons are grouped together and the electro-weak interactions are collectively measured.
- The eight gluons mediate strong nuclear interactions between coloured-charged particles (quarks). Gluons have no mass. The multiplicity of gluons is labelled by combinations of colour and an anti colour load (i.e., Red-anti-Green). Since gluon has an efficient colour load, they are able to communicate with each other. The theory of quantum chromodynamics explains gluons and their interactions.
The interactions between all particles described by the standard model are summarized in the following illustration.
Interactions described by the Standard Model along with the gauge groups and bosons associated with each of them. The column on the left represents the fundamental constants that indicate the relative force of each interaction.
Higgs Boson
A hypothetical huge scalar elemental particle predicted by the standard model is the Higgs particle, and the only fundamental particle predicted by that model that has not been fully observed until now. This is partly because it requires an exceptionally large amount of energy to create and observe it under laboratory circumstances. It has spin S-0, so it is a boson.
In the standard Particle Physics Model, the Higgs boson plays a special, and dominant role in explaining the origins of the mass of other elementary particles, particularly the difference between the massless photon and the heavy bosons W and Z. In certain aspects of the structure of microscopic (and thus macroscopic) matter, the masses of elementary particles and the differences between electromagnetism (caused by the photon) and the weak force (caused by the W and Z bosons) are critical; so, if it is found to exist, the Higgs boson would have a major influence on the world around us.
To date, no experiment has observed the presence of the Higgs boson directly, but some indirect evidence of it is available. CERN’s hadron collider is expected to bring experimental evidence to confirm its existence.
Limitations of Standard Model of Particle Physics
There is still no experimental indication of the existence of the Higgs boson, although it is expected to be detected by the Large Hadron Collider (LHC) when it is repaired after a first failed attempt and enters full operation in 2010. [1] Even when the Standard Model of particle Physics has been very successful in explaining experimental results, it has certain important flaws:
1.The problem of the number of fundamental physical constants. There are 19 free parameters in the model, such as particle masses, which must be experimentally determined (in addition to 10 for neutrino masses). It is not possible to independently measure these parameters.
2.Quantum gravitational force. The model does not describe the gravitational force, nor the current candidates to build a quantum theory of gravity, resemble the standard model.
3.Antimatter. Within it, matter and antimatter are symmetrical. The preponderance of matter in the universe could be explained by saying that the universe began with other initial conditions, but most physicists think this explanation is not elegant.
There are alternatives to the Standard Model of Particle Physics that attempt to address these “deficiencies”, such as string theory.
In particle physics, supersymmetry is a proposed hypothetical symmetry that would relate the properties of bosons and fermions. Although supersymmetry has not yet been experimentally verified as a symmetry of nature, it is a fundamental part of many theoretical models, including super-remember theory. Supersymmetry is also known by the English acronym SUSY.
According to the standard model of particle physics (SM), the matter is made up of fermions (in turn divided into quarks and leptons), while the particles that transmit the two fundamental interactions of nature (strong interaction and electrodelic nuclear interaction) are bosons.
Supersymmetry extends the number of PARTICLEs in the MS so that each particle has a supersymmetric companion called a super companion. Thus, each boson has a super fermion companion and vice versa.
The super companions of fermions are bosons and receive names that begin with the letter s; thus, the electron has as a super companion the electron, and the quarks, the squarks. The super companions of the bosons are fermions with names ending in -ino, so that of the photon is the fotin and that of the graviton (if gravity is included in the model), gravitino.
MSSM (Minimal Supersymmetric Standard Model) is defined as the minimum extension of the standard model of particle physics that involves supersymmetry.
However, because these supersymmetric companions have not yet been able to be created in the laboratory, their masses must be much larger than those of the original particles. This implies that supersymmetry, if true, is broken by some mechanism. Specifying such a mechanism results in various simplifications of the MSSM.
Some supersymmetric particles, such as neutral, could explain the problem of dark matter in the universe.
Thanks to the great potential of being able to explain many questions of Particle Physics and Astrophysics, the theory of supersymmetry has a great popularity, mainly in Theoretical Physics. The most popular scientific theories, the Theory of Great Unification and Super-Remember Theory, are supersymmetric. However, despite encouraging theoretical arguments, so far, it has not been experimentally demonstrated that supersymmetry actually exists in nature.
The first model in particle physics was presented in 1973 by Julius Wess and Bruno Zumino. This model, known as Model Wess-Zumino, is not a real model of nature, but rather a minimal supersymmetric model with only one Fermion and his super companion Boson.
Although the Wess-Zumino model does not represent a real physical model, it serves for its simplicity of example model to show certain aspects of supersymmetric physical models. The first supersymmetric model compatible with the standard model of particle physics called the Minimum Standard Supersymmetric Model (MSSM), was enunciated in 1981 by Howard Georgi and Savas Dimopoulos.
According to the MSSM, the masses of the super companions can be observed in the region between 100 GeV to 1 TeV using the particle accelerator known as the “large hadron collider” (LHC), completed in 2008 on the Franco-Swiss border. Scientists hope to demonstrate through the LHC the existence of the super companions of the elementary particles already known.
Recommended Books
1. Particle Physics Brick by Brick: Atomic and Subatomic Physics Explained
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2. Modern Particle Physics
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