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What Is The Standard Model Of Particle Physics

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What Is Particle Physics

The Map of Particle Physics | The Standard Model Explained
  • It is a branch of physics that studies the basic elements of matter and radiation and the interaction between them. The word particle can refer to various types of very small objects, but this branch usually investigates the irreducibly smallest detectable particles.
  • It is also called as high energy physics as many elementary particles dont come under normal circumstances in nature. But, it can be identified during the energetic collision of other particles.

The Deconstructed Standard Model Equation

The Standard Model is far more than elementary particles arranged in a table.

The Standard Model of particle physics is often visualized as a table, similar to the periodic table of elements, and used to describe particle properties, such as mass, charge and spin. The table is also organized to represent how these teeny, tiny bits of matter interact with the fundamental forces of nature.

But it didnt begin as a table. The grand theory of almost everything actually represents a collection of several mathematical models that proved to be timeless interpretations of the laws of physics.

Here is a brief tour of the topics covered in this gargantuan equation.

What Are Elementary Particles

As defined in the Standard Model of particle physics, the particles that are not composed of other constituent particles or having no measurable internal structure are called elementary particles. These particles have been discovered through experiments and the latest particle in the list of elementary particles is Higgs boson which was discovered in 2012.

Elementary particles are classified into different families and sub-families depending on their spin.

Particles which are made of elementary particles are called composite particles. Examples of composite particles include Mesons and Baryons.

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Field Content In Detail

The Standard Model has the following fields. These describe one generation of leptons and quarks, and there are three generations, so there are three copies of each fermionic field. By CPT symmetry, there is a set of fermions and antifermions with opposite parity and charges. If a left-handed fermion spans some representation its antiparticle spans the dual representation (note that 2


The value of the vacuum energy may also be treated as an additional free parameter. The renormalization scale may be identified with the Planck scale or fine-tuned to match the observed cosmological constant, however both options are problematic.

Is There Need For A New Particle Physics Model

The Standard Model of Particle Physics

High energy particle physics experiments in the recent past have brought into question certain parts of the model currently used in particle physics. The Standard Model describes how particles interact and provides a framework of conservation rules that give insight into what decays are possible. It has been relied on for decades, but it may be time for an update. Experiments involving decays of the bottom quark show transitions occurring 10% to 20% beyond the predictions of the Standard Model and decays that violate certain rules of the Standard Model. The research article entitled Importance of Loop Effects in Explaining the Accumulated Evidence for New Physics in B Decays with a Vector Leptoquark,1 uses data from former experiments and finds supporting evidence for some New Physics . This theoretical work uses some previously suggested particles, such as the leptoquark described below, to model and explain experimental results that the Standard Model cannot, and it does so very well. The researchers have since reported new results2 that support their theoretical model, from the Large Hadron Collider at CERN. The model and experimental results hint at New Physics.

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The Name Standard Model Was A Placeholder That Never Got Replaced

But in 1964, physicists Murray Gell-Mann and George Zweig theorized that many members of the particle zoo were actually composite particles made up of even smaller pieces, which we now call quarks. The list of true fundamental particles was significantly smaller, and scientists began to see new patterns. This was the beginning of the development of the Standard Model of particle physics.

The first references to a standard model appear in papers published in the 1970s. At this stage, physicists were still using standard as an adjective, not as part of a proper noun.

If you start digging through the papers, you see in lowercase, the standard model of gauge interactions and the standard description of electroweak interactions, says Richard Ruiz, a theorist at the Institute of Nuclear Physics in Krakow, Poland.

This was the era of model-building. The ideas that worked the best were considered standardbut in the traditional sense of the word. Over time, in the 80s and 90s, slowly the S and the M got capitalized.

Standard Model Of Particle Physics Facts

  • All ordinary matter, including every atom on the periodic table of elements, consists of only three types of matter particles: up and down quarks, which make up the protons and neutrons in the nucleus, and electrons that surround the nucleus.
  • The complete Standard Model took a long time to build. Physicist J.J. Thomson discovered the electron in 1897, and scientists at the Large Hadron Collider found the final piece of the puzzle, the Higgs boson, in 2012.

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Medieval European And Islamic

The Western Roman Empire fell in the fifth century, and this resulted in a decline in intellectual pursuits in the western part of Europe. By contrast, the Eastern Roman Empire resisted the attacks from the barbarians, and continued to advance various fields of learning, including physics.

In the sixth century, Isidore of Miletus created an important compilation of Archimedes’ works that are copied in the Archimedes Palimpsest.

Book of Opticscamera obscura

In sixth-century Europe John Philoponus, a Byzantine scholar, questioned Aristotle‘s teaching of physics and noted its flaws. He introduced the theory of impetus. Aristotle’s physics was not scrutinized until Philoponus appeared unlike Aristotle, who based his physics on verbal argument, Philoponus relied on observation. On Aristotle’s physics Philoponus wrote:

Philoponus’ criticism of Aristotelian principles of physics served as an inspiration for Galileo Galilei ten centuries later, during the Scientific Revolution. Galileo cited Philoponus substantially in his works when arguing that Aristotelian physics was flawed. In the 1300s Jean Buridan, a teacher in the faculty of arts at the University of Paris, developed the concept of impetus. It was a step toward the modern ideas of inertia and momentum.

Do Composite Bosons Exist

CERN: The Standard Model Of Particle Physics

Depending on the spin and statistics the hadrons, nuclei, and atoms can become composite bosons. A particle that contains an even number of fermions becomes a boson. For example, meson is a boson because it contains one quark and one antiquark.

Now, before we conclude, here is the recap of the most important topics of this article fermions and bosons.

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Theoretical Predictions Not Observed

Observation at particle colliders of all of the fundamental particles predicted by the Standard Model has been confirmed. The Higgs boson is predicted by the Standard Model’s explanation of the Higgs mechanism, which describes how the weak SU gauge symmetry is broken and how fundamental particles obtain mass it was the last particle predicted by the Standard Model to be observed. On July 4, 2012, CERN scientists using the Large Hadron Collider announced the discovery of a particle consistent with the Higgs boson, with a mass of about 126 GeV/c2. A Higgs boson was confirmed to exist on March 14, 2013, although efforts to confirm that it has all of the properties predicted by the Standard Model are ongoing.

A few hadrons whose existence is predicted by the Standard Model, which can be produced only at very high energies in very low frequencies have not yet been definitively observed, and “glueballs” have also not yet been definitively observed. Some very low frequency particle decays predicted by the Standard Model have also not yet been definitively observed because insufficient data is available to make a statistically significant observation.

  • }},}},}}} , up to vector lengths, a result due to Kohzo Nishida.

It is unclear if these empirical relationships represent any underlying physics according to Koide, they “may be an accidental coincidence”.

Is The Standard Model Really Kaput

Just last month, New Scientist reported that scientists at the Large Hadron Collider have found a deviation from the predicted rates at which particles containing the bottom quark decay into an electron and a muon. While the production of electrons and muons should be equal, it isn’t.

Other issues not explained by the Standard Model include:

  • Does the Higgs boson also give mass to neutrinos?
  • Around 95 percent of the universe is not made of ordinary matter but consists of dark energy and dark matter which do not fit into the Standard Model.
  • Gluons that convey the force of gravity have never been found.
  • Baryon asymmetry.

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Vectors Scalars And Spinors

Mathematically it may look as though all of the fields are vector-valued , since they all have several components, can be multiplied by matrices, etc., but physicists assign a more specific physical meaning to the word: a vector is something that transforms like a four-vector under Lorentz transformations, and a scalar is something that is invariant under Lorentz transformations. The B, Wj, and Ga fields are all vectors in this sense, so the corresponding particles are said to be vector bosons. The Higgs field is a scalar field.

The fermion field does transform under Lorentz transformations, but not like a vector should rotations will only turn it by half the angle a proper vector should. Therefore, these constitute a third kind of quantity, which is known as a spinor.

It is common to make use of abstract index notation for the vector fields, in which case the vector fields all come with a Lorentzian index , like so: B this may involve raising and lowering indices.

The Standard Model At 50

What Is The Standard Model of Particle Physics?

It has successfully predicted many particles, including the Higgs Boson, and has led to 55 Nobels so far, but theres plenty it still cant account for

Just over a half-century ago, the physicist Steven Weinberg published a seminal paper titled A Model of Leptons in the journal Physical Review Letters. It was just three pages long, but its contents were revolutionary: in the paper, Weinberg outlined the core of the theory now known as the Standard Model, which governs elementary particles. Hailed by many since then as the most successful theory ever conceived, the Standard Model describes the universe with a comprehensiveness that is hard to understate. All the particles it predicted to exist have been found, including most recently the Higgs boson. The masses of those particles lie within 1 percent of the theoretical value anticipated by the model. And three of the four fundamental forces of natureelectromagnetism, plus the weak and the strong nuclear forcehave all been shown to be manifestations of one underlying force as part of the Standard Model.

And one Nobel laureate, who shall go unnamed, proceeded to frame our introduction by stating I was clearly invited because I was pretty, and that I looked old enough to finish my PhD already.

The views expressed are those of the author and are not necessarily those of Scientific American.

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A Note On Particle Classification

It can be hard to keep all the names straight in particle physics, so it might be helpful to think of the animal world, where such structured naming might be more familiar and intuitive. Humans are primates, mammals, and also vertebrates. Similarly, protons are baryons, hadrons, and also fermions.

The unfortunate difference is that the terms tend to sound similar to each other. Confusing bosons and baryons, for example, is far easier than confusing primates and invertebrates. The only way to really keep these different particle groups separate is to just carefully study them and try to be careful about which name is being used.

Interaction Terms And The Path Integral Approach

The Lagrangian can also be derived without using creation and annihilation operators , by using a “path integral” approach, pioneered by Feynman building on the earlier work of Dirac. See e.g. Path integral formulation or A. Zee’s QFT in a nutshell. This is one possible way that the Feynman diagrams, which are pictorial representations of interaction terms, can be derived relatively easily. A quick derivation is indeed presented at the article on Feynman diagrams.

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Whats Wrong With The Standard Model

Experiments have shown a number of decays involving bottom quarks going into other quarks and leptons, to a very high degree of certainty in the measurements. According to the Standard Model these transitions can happen, but rarely. Experimental observations deviate from the Standard Model by 10 to 20 percent. That deviation is too much for scientists. It means either the model has to be revised or an entirely new model is needed.

The Standard Model does not allow for lepton flavor universality violation. That is, the lepton number for each kind of lepton is to be conserved in the Standard Model, but evidence, for example from the LHCb, Belle, and BaBar experiments, has consistently shown this not the case. In fact, the Standard Model deviates from experimental results by 4 standard deviations .

All measurements have uncertainty associated with them, so all experimental results are not exact values. The standard deviation is a way to describe the spread of the data points about an average value that is measured. For a theory to be good, it should not deviate much from the mean experimental results.

Elementary Particles: Standard Model Of Particle Physics

The Standard Model of Particle Physics

The behavior of all known subatomic particles can be described within a single theoretical framework called the Standard Model. This model incorporates the quarks and leptons as well as their interactions through the strong, weak and electromagnetic forces. Only gravity remains outside the Standard Model. The force-carrying particles are called gauge bosons, and they differ fundamentally from the quarks and leptons. The fundamental forces appear to behave very differently in ordinary matter, but the Standard Model indicates that they are basically very similar when matter is in a high-energy environment.

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Physics Beyond The Standard Model

Physics beyond the Standard Model refers to the theoretical developments needed to explain the deficiencies of the Standard Model, such as the inability to explain the fundamental parameters of the standard model, the strong CP problem, neutrino oscillations, matterantimatter asymmetry, and the nature of dark matter and dark energy. Another problem lies within the mathematical framework of the Standard Model itself: the Standard Model is inconsistent with that of general relativity, and one or both theories break down under certain conditions, such as spacetimesingularities like the Big Bang and black holeevent horizons.

Theories that lie beyond the Standard Model include various extensions of the standard model through supersymmetry, such as the Minimal Supersymmetric Standard Model and Next-to-Minimal Supersymmetric Standard Model , and entirely novel explanations, such as string theory, M-theory, and extra dimensions. As these theories tend to reproduce the entirety of current phenomena, the question of which theory is the right one, or at least the “best step” towards a Theory of Everything, can only be settled via experiments, and is one of the most active areas of research in both theoretical and experimental physics.

The Standard Model Is Our Best Description Of The Subatomic World Join Zme For A Stroll Through The Particle Zoo

First devised in the 1970s, the Standard Model would be used to predict a wide variety of phenomena, meet various experimental challenges, before being confirmed by the discovery of the Higgs Boson in 2012. Yet, as successful and fruitful a theory as the Standard Model is, it cant explain everything. Gravity still evades confinement within the Standard Model, and physicists have caught tantalizing glimpses of physics beyond the theorys limits.

Before these glimpses can be confirmed and a new chapter in physics is opened, lets take a trip through the particle zoo and discover the wonders of the Standard Model.

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The Fermions In Standard Model

The Fermions obey the famous Paulis exclusion principle of Quantum mechanics. In simple words, this principle states that no two fermions can be at the same place at the same time. Lets look at the macroscopic picture. Electrons, protons, neutrons, and quarks are fermions. Similarly, these fermions combine to form matter or things that are also fermions such as molecules, people, walls, etc. In the macroscopic world, a person cannot pass through a wall unless the wall is removed. Hence, two fermions- people and wall cannot be at an exact position at a particular time.

Matter & Forces: Fermions & Bosons

The Standard Model of particle physics is brilliant and ...

All elementary particles in physics are classified as either fermions or bosons. Quantum physics demonstrates the particles may have an intrinsic non-zero spin, or angular momentum, associated with them.

A fermion is a particle with a half-integer spin, while a boson is a particle with an integer spin. These spins result in different mathematical applications in certain situations, which is far beyond the scope of this article. For now, just know that the two types of particles exist.

Simple mathematics of adding integers and half-integers show the following:

  • Combining an odd number of fermions results in a fermion
  • Combining an even number of fermions results in a boson

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