Particle physics
Standard Model of particle physics |
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Particle physics or high-energy physics is the study of
The fundamental particles in the universe are classified in the Standard Model as fermions (matter particles) and bosons (force-carrying particles). There are three generations of fermions, although ordinary matter is made only from the first fermion generation. The first generation consists of up and down quarks which form protons and neutrons, and electrons and electron neutrinos. The three fundamental interactions known to be mediated by bosons are electromagnetism, the weak interaction, and the strong interaction.
Quarks cannot exist on their own but form hadrons. Hadrons that contain an odd number of quarks are called baryons and those that contain an even number are called mesons. Two baryons, the proton and the neutron, make up most of the mass of ordinary matter. Mesons are unstable and the longest-lived last for only a few hundredths of a microsecond. They occur after collisions between particles made of quarks, such as fast-moving protons and neutrons in cosmic rays. Mesons are also produced in cyclotrons or other particle accelerators.
Particles have corresponding antiparticles with the same mass but with opposite electric charges. For example, the antiparticle of the electron is the positron. The electron has a negative electric charge, the positron has a positive charge. These antiparticles can theoretically form a corresponding form of matter called antimatter. Some particles, such as the photon, are their own antiparticle.
These elementary particles are excitations of the quantum fields that also govern their interactions. The dominant theory explaining these fundamental particles and fields, along with their dynamics, is called the Standard Model. The reconciliation of gravity to the current particle physics theory is not solved; many theories have addressed this problem, such as loop quantum gravity, string theory and supersymmetry theory.
Practical particle physics is the study of these particles in radioactive processes and in particle accelerators such as the Large Hadron Collider. Theoretical particle physics is the study of these particles in the context of cosmology and quantum theory. The two are closely interrelated: the Higgs boson was postulated by theoretical particle physicists and its presence confirmed by practical experiments.
History
The idea that all
Throughout the 1950s and 1960s, a bewildering variety of particles was found in collisions of particles from beams of increasingly high energy. It was referred to informally as the "
Standard Model
The current state of the classification of all elementary particles is explained by the
The Standard Model, as currently formulated, has 61 elementary particles.
Subatomic particles
Types | Generations | Antiparticle | Colours | Total | |
---|---|---|---|---|---|
Quarks | 2 | 3 | Pair | 3 | 36 |
Leptons | Pair | None | 12 | ||
Gluons | 1 | None | Own | 8 | 8 |
Photon | Own | None | 1 | ||
Z Boson | Own | 1 | |||
W Boson | Pair | 2 | |||
Higgs | Own | 1 | |||
Total number of (known) elementary particles: | 61 |
Modern particle physics research is focused on
Dynamics of particles are also governed by quantum mechanics; they exhibit wave–particle duality, displaying particle-like behaviour under certain experimental conditions and wave-like behaviour in others. In more technical terms, they are described by quantum state vectors in a Hilbert space, which is also treated in quantum field theory. Following the convention of particle physicists, the term elementary particles is applied to those particles that are, according to current understanding, presumed to be indivisible and not composed of other particles.[9]
Quarks and leptons
Ordinary
There are three known generations of quarks (up and down, strange and charm, top and bottom) and leptons (electron and its neutrino, muon and its neutrino, tau and its neutrino), with strong indirect evidence that the fourth generation of fermions does not exist.[17]
Bosons
Bosons are the mediators or carriers of fundamental interactions, such as electromagnetism, the weak interaction, and the strong interaction.[18] Electromagnetism is mediated by the photon, the quanta of light.[19]: 29–30 The weak interaction is mediated by the W and Z bosons.[20] The strong interaction is mediated by the gluon, which can link quarks together to form composite particles.[21] Due to the aforementioned color confinement, gluons are never observed independently.[22] The Higgs boson gives mass to the W and Z bosons via the Higgs mechanism[23] – the gluon and photon are expected to be massless.[22] All bosons have an integer quantum spin (0 and 1) and can have the same quantum state.[18]
Antiparticles and color charge
Most aforementioned particles have corresponding
e−
and
e+
.[25] When a particle and an antiparticle interact with each other, they are annihilated and convert to other particles.[26] Some particles, such as the photon or gluon, have no antiparticles.[citation needed
Quarks and gluons additionally have color charges, which influences the strong interaction. Quark's color charges are called red, green and blue (though the particle itself have no physical color), and in antiquarks are called antired, antigreen and antiblue.
Composite
The neutrons and protons in the atomic nuclei are baryons – the neutron is composed of two down quarks and one up quark, and the proton is composed of two up quarks and one down quark.[28] A baryon is composed of three quarks, and a meson is composed of two quarks (one normal, one anti). Baryons and mesons are collectively called hadrons. Quarks inside hadrons are governed by the strong interaction, thus are subjected to quantum chromodynamics (color charges). The bounded quarks must have their color charge to be neutral, or "white" for analogy with mixing the primary colors.[29] More exotic hadrons can have other types, arrangement or number of quarks (tetraquark, pentaquark).[30]
A normal atom is made from protons, neutrons and electrons.[
Hypothetical
The graviton is a hypothetical particle that can mediate the gravitational interaction, but it has not been detected or completely reconciled with current theories.[33]
Experimental laboratories
The world's major particle physics laboratories are:
- Budker Institute of Nuclear Physics (Novosibirsk, Russia). Its main projects are now the electron-positron colliders VEPP-2000,[36] operated since 2006, and VEPP-4,[37] started experiments in 1994. Earlier facilities include the first electron–electron beam–beam collider VEP-1, which conducted experiments from 1964 to 1968; the electron-positron colliders VEPP-2, operated from 1965 to 1974; and, its successor VEPP-2M,[38] performed experiments from 1974 to 2000.[39]
- CERN (European Organization for Nuclear Research) (Franco-Swiss border, near Geneva). Its main project is now the Large Hadron Collider (LHC), which had its first beam circulation on 10 September 2008, and is now the world's most energetic collider of protons. It also became the most energetic collider of heavy ions after it began colliding lead ions. Earlier facilities include the Large Electron–Positron Collider (LEP), which was stopped on 2 November 2000 and then dismantled to give way for LHC; and the Super Proton Synchrotron, which is being reused as a pre-accelerator for the LHC and for fixed-target experiments.[40]
- PETRA III, FLASH and the European XFEL.
- Fermi National Accelerator Laboratory (Fermilab) (Batavia, United States). Its main facility until 2011 was the Tevatron, which collided protons and antiprotons and was the highest-energy particle collider on earth until the Large Hadron Collider surpassed it on 29 November 2009.[42]
- Institute of High Energy Physics (IHEP) (Beijing, China). IHEP manages a number of China's major particle physics facilities, including the Beijing Electron–Positron Collider II(BEPC II), the Beijing Spectrometer (BES), the Beijing Synchrotron Radiation Facility (BSRF), the International Cosmic-Ray Observatory at Yangbajing in Tibet, the Daya Bay Reactor Neutrino Experiment, the China Spallation Neutron Source, the Hard X-ray Modulation Telescope (HXMT), and the Accelerator-driven Sub-critical System (ADS) as well as the Jiangmen Underground Neutrino Observatory (JUNO).[43]
- Tsukuba, Japan). It is the home of a number of experiments such as the K2K experiment, a neutrino oscillation experiment and Belle II, an experiment measuring the CP violation of B mesons.[44]
- Linac Coherent Light Source X-ray laser as well as advanced accelerator design research. SLAC staff continue to participate in developing and building many particle detectors around the world.[45]
Theory
Quantum field theory |
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History |
Theoretical particle physics attempts to develop the models, theoretical framework, and mathematical tools to understand current experiments and make predictions for future experiments (see also theoretical physics). There are several major interrelated efforts being made in theoretical particle physics today.
One important branch attempts to better understand the
Another major effort is in model building where model builders develop ideas for what physics may lie
A third major effort in theoretical particle physics is
There are also other areas of work in theoretical particle physics ranging from particle cosmology to loop quantum gravity.[citation needed]
Practical applications
In principle, all physics (and practical applications developed therefrom) can be derived from the study of fundamental particles. In practice, even if "particle physics" is taken to mean only "high-energy atom smashers", many technologies have been developed during these pioneering investigations that later find wide uses in society. Particle accelerators are used to produce
Future
Major efforts to look for physics beyond the Standard Model include the Future Circular Collider proposed for CERN[50] and the Particle Physics Project Prioritization Panel (P5) in the US that will update the 2014 P5 study that recommended the Deep Underground Neutrino Experiment, among other experiments.
See also
- Particle physics and representation theory
- Atomic physics
- Astronomy
- High pressure
- International Conference on High Energy Physics
- Introduction to quantum mechanics
- List of accelerators in particle physics
- List of particles
- Magnetic monopole
- Micro black hole
- Number theory
- Resonance (particle physics)
- Self-consistency principle in high energy physics
- Non-extensive self-consistent thermodynamical theory
- Standard Model (mathematical formulation)
- Stanford Physics Information Retrieval System
- Timeline of particle physics
- Unparticle physics
- Tetraquark
- Track significance
- International Conference on Photonic, Electronic and Atomic Collisions
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