Particle physics

Particle physics . Branch of physics that studies the elemental components of matter and the interactions between them.

The fundamental particles are subdivided into Bosons (integer spin particles such as 0, 1, 2 …), which are responsible for transmitting the fundamental forces of nature, and Fermiones ( Semientero spin particles such as 1 / 2 or 3/2).

This branch is also known as high-energy physics because many of the particles can be seen only in large collisions caused by particle accelerators.

Summary

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  • 1 History
  • 2 elementary particles
    • 1 Bosons
    • 2 Fermions
  • 3 Composite Particles
    • 1 baryons
    • 2 Mesons
  • 4 hypothetical particles
    • 1 Supersymmetry
    • 2 Others
    • 3 Classification by speed
  • 5 Quasiparticles
  • 6 Main research centers
  • 7 See also
  • 8 Source

History

Man since ancient times has imagined that the Universe in which he lives is composed of several elements; for example, Empedocles in the 5th century before our era postulated that everything that exists could be obtained from the mixture of water, earth, fire and air. We could mention Democritus as the first to indicate the existence of atoms, as a kind of indivisible elements.

Scientific advancements from the early 20th century by Max Planck , Albert Einstein , Niels Bohr, and others led to the birth of quantum mechanics. The photoelectric effect showed the quantum nature of light to explain its interaction with matter, the photon being the “quantum” of light. Three other particles that interact with matter are now known, called Bosons .

To understand the structure of matter, different atomic models appeared, being, around 1930 , electrons, protons and neutrons the basic constituents of matter. By 1960 , thanks to Murray Gell-Mann , more elemental constituents for protons and neutrons, the Quarks , are predicted , so that the basic constituent elements of matter become quarks, electrons, and neutrinos .

Elementary particles

Particle physicists have struggled from the start to classify known particles and to describe all matter and its interactions. Throughout the history of physics, there have been many particles that have once been defined as indivisible, such as protons and neutrons, which have later been shown not to be. After different atomic and nuclear theories, the so-called standard model is now used to describe the matter that makes up the universe and its interactions.

According to the standard model, there are six types of quarks, six types of leptons and four types of bosons. These particles are divided into two main categories by the Pauli exclusion principle: those that are not subject to this principle are the bosons and those that are are called Fermions .

Bosons

Name and electric charge of the components of the matter.

Bosons are particles that do not meet the Pauli exclusion principle, so two particles can occupy the same quantum state. At very low temperatures they tend to occupy the lowest energy level, with all particles occupying the same quantum state. In 1924 , Satyendra Nath Bose and Albert Einstein postulated a statistical model, now known as the Bose-Einstein statistic, for molecules at temperatures very close to absolute zero; This same statistic turns out that it can also be applied to this type of particle.

According to the standard model, there are four bosons:

Particle Symbol Mass (in GeV / c 2 ) Electric charge Spin Interaction
Photon gamma 0 0 one electromagnetic
Boson W ± 80.4 ± 1 one weak
Boson Z 0 91,187 0 one weak
Gluon g 0 0 one strong

The mathematical theories that study the phenomena of these particles are in the case of strong interaction, of gluons, quantum chromodynamics, and in the case of electroweak interaction , of photons and bosons W and Z, quantum electrodynamics .

Fermions

The fermions are particles with spin, or angular moment intrinsic, fractionally and who are subject to the Pauli exclusion principle, namely that two particles can not be in the same quantum state at the same time. Its distribution is governed by the Fermi-Dirac statistic , hence its name.

Fermions are basically particles of matter, but unlike bosons, not all fermions are elementary particles. The clearest case is that of protons and neutrons; These particles are fermions but are made up of quarks that, at our current level of knowledge, are considered elemental.

Fermions are divided into two groups: quarks and leptons. This difference applies because leptons can exist in isolation, unlike quarks that are always in the presence of other quarks. The groups of quarks cannot have a color charge because the gluons that unite them have a color charge. The basic properties of these particles are found here:

Fermion type Name Symbol charge
electromagnetic
Weak charge *
Color Loading
Mass
Lepton
Electron -one -1/2 0 0.511 MeV / C ²
Muon mu  -one -1/2 0 105.6 MeV / C ²
Tauon tau  -one -1/2 0 1,784 GeV / C ²
Electronic neutrino nu e 0 +1/2 0 <50 EV / C ²
Muonic neutrino nu mu 0 +1/2 0 <0.5 MeV / C ²
Tauonic neutrino nu tau 0 +1/2 0 <70 MeV / C ²
Quark
up or +2/3 +1/2 R / G / B ~ 5 MeV / C ²
charm c +2/3 +1/2 R / G / B ~ 1.5 GeV / C ²
top t +2/3 +1/2 R / G / B > 30 GeV / C ²
down d -1/3 -1/2 R / G / B ~ 10 MeV / C ²
strange s -1/3 -1/2 R / G / B ~ 100 MeV / C ²
bottom b -1/3 -1/2 R / G / B ~ 4.7 GeV / C ²

The particles in the table are only weakly charged if they are left-handed or, for antiparticles, if they are left-handed.

The particles are grouped into generations . There are three generations: the first is made up of the electron, its neutrino, and the up and down quarks. Ordinary matter is made up of particles from this first generation. The particles of other generations disintegrate into particles of the lower generations.

Composite particles

Particle physicists refer to hadrons as particles that are made up of more elementary ones. Hadrons are made up of quarks, antiquarks, and gluons. The electric charge of the hadrons is an integer, so the sum of the charge of the quarks that compose them must be an integer.

The strong interaction is the one that predominates in Hadrons , although the electromagnetic and weak interaction are also manifested. Color-charged particles interact through gluons; quarks and gluons having color charge are confined to remain united in a neutral color charged particle.

The theoretical formulation of these particles was carried out simultaneously and independently by Murray Gell-Mann and George Zweig in 1964 in the so-called quark model. This model has received numerous experimental confirmations since then.

Hadrons are subdivided into two classes of particles, baryons and mesons.

Baryons

Baryons are particles that contain three quarks, some gluons, and some antiquarks. The best known baryons are nucleons, that is, protons and neutrons, in addition to other more massive particles known as hyperons.

Within baryons there is an intense interaction between quarks through gluons, which carries the strong interaction.

As Gluons have a color charge, in baryons the particles that contain it change color charge rapidly, but the baryon as a whole remains with a neutral color charge.

Baryons are also fermions so the spin value is 1/2, 3/2 …. Like all particles, baryons have their antimatter particle called an antibarion that is formed by the union of three antiquarks. Excluding nucleons, most baryons are unstable.

Mesons

Mesons are particles made up of a quark, an antiquark and the particle that unites them, gluon. All the inns are unstable; Despite this, they can be isolated because the color charges of the quark and the antiquark are opposite, obtaining a meson with a neutral color charge.

The mesons are also Bosons since the sum of the spins, of their quark-antiquark plus the contribution of the movement of these particles, is an integer. The meson is also known to have strong, weak, and electromagnetic interactions.

This group includes the pion, the kaon, the J / ψ, and many others. Exotic mesons may also exist although there is no experimental evidence for them.

Hypothetical particles

Among the main particles theoretically conjectured and that have not yet been confirmed by any experiment until 2008 , are:

Higgs figs is the only standard particle model not observed. In the formulation of the electroweak model, the particle that could explain the mass difference of the W and Z bosons and the photon; it is postulated that in order to spontaneously break the symmetry of a Yang-Mills field, you need a particle, now known as the Fig Boson .

This particle in a Higgs field would give the answers to this question. Scientists hope to discover the Higgs boson in the Large Hadron Collider (LHC), a particle accelerator expected to go live in the fall of 2009 at CERN.

The graviton is the hypothetical boson for the gravitational interaction that has been proposed in the theories of quantum gravity. It is not usually part of the standard model because it has not been found experimentally. It is theorized that it would interact with Leptons and quarks and that it would have no mass.

Supersymmetry

The supersymmetry theory raises the existence of superpartner particles of the current existing particles, thus among the most outstanding we have:

The Neutralino is the best candidate in the standard model for dark matter particle. In supersymmetry theory, neutralino is a neutral, stable and super light particle, which does not have a symmetrical pair in ordinary particles.

Sleptons and squarks are the supersymmetric partners of standard model fermions. The fotito , the wino , the [zino]], the gravitino and gluino are superpartners particles bosons.

Others

A WIMP (from English: massive particle that interacts weakly) is one of many particles proposed to explain dark matter (such as neutralino or axion). The Pomerón , used in Regge theory to explain the phenomenon of elastic dispersion of hadrons and the position of Regge’s poles . The Skirmión , a topological Soliton for the pion field that is used to model the low energy properties of the nucleon.

E Goldstone boson is a massless excitation of a field whose symmetry has been spontaneously rotated. The Piones are almost Goldstone bosons by breaking the symmetry of isospin of chirality in QCD (it is not because it has mass). The Goldstino (fermion) is then produced by the spontaneous breakdown of supersymmetry by the goldstone boson. The instanton is a field configuration that is a local minimum of a Euclidean action. They are used in non-disturbing calculations of the tunnel effect.

 

Speed ​​classification

According to their mass and achievable speed range, hypothetical (and real) particles can be classified as:

A Tardion travels slower than light and has a non-zero resting mass. All particles with mass belong to this category. A Luzon travels exactly at the speed of light, and has no mass. All massless bosonic particles belong to this category, it is usually accepted that neutrinos also belong to this category. A tachyon is a hypothetical particle that travels faster than light, and whose mass must be imaginary. No examples of this type of particle have been detected.

Quasiparticles

The field equations of condensed matter physics are very similar to those of particle physics. For this reason, much of the theory of particle physics can be applied to the physics of condensed matter, assigning to each field or excitation of the same a model that includes ” Quasiparticles “. Are included:

The Fonons , vibratory modes in a crystalline structure. Excitons, which are the superposition of an electron and a hole. The plasmons , set of coherent excitations of a plasma. The polaritons are the mixture of one photon and one of the quasiparticles from this list. Polarons, which are moving charged quasiparticles that are surrounded by ions in a material. Magnons are coherent excitations of the spins of electrons in a material.

Main research centers

In particle physics, the main international laboratories are:

CERN , located between the Franco-Swiss border near the Swiss city of Geneva . Its main current project is the Large Hadron Collider or LHC, finished construction and operational. This will be the largest particle collider in the world. At CERN we can also find the LEP, electron positron collider, and the synchrotron Superproton .

Fermilab , located near Chicago in the United States , has the Tevatron that can collide protons and antiprotons and is the second most energetic particle accelerator in the world after the LHC.

Brookhaven National Laboratory , located on Long Island (United States), has a relativistic heavy ion accelerator that can collide heavy ions such as gold and polarized protons. It was the first heavy ion accelerator and is the only one that can accelerate polarized protons.

DESY , located in Hamburg ( Germany ), has the HERA that can accelerate electrons, positrons and protons.

KEK , located in Tsukuba ( Japan ), is the Japanese high-energy research organization. Many interesting experiments have taken place here such as the neutrino oscillation experiment and the experiment to measure CP symmetry violation in meson B.

SLAC , located in Palo Alto ( United States ), has PEP-II that can collide electrons and positrons.

These are the main laboratories but there are many more.

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