Subatomic Particle

Definition: Subatomic Particle

Subatomic Particle

Noun

1. A particle that is less complex than an atom; regarded as constituents of all matter.

Domain	Definition
Aerospace	Any particle of less than atomic mass, e.g., the electron, proton, and neutron, also called atomic particle.Subatomic particles are classified by relative mass into four groups: leptons, mesons, nucleons, and hyperons, from lowest to highest masses, respectively. (references)
Source: compiled by the editor from various references; see credits.

In physics, a subatomic particle is a particle smaller than an atom. These include atomic constituents such as electrons, protons, and neutrons (protons and neutrons are actually composite particles, made up of quarks), as well as particles produced by radiative and scattering processes, such as photons, neutrinos, and muons. Many of the particles that have been discovered and studied are actually not encountered naturally; they have to be produced during scattering processes in particle accelerators. The study of subatomic particles is the most active branch of particle physics.

The electron (symbol e-) is present in all atoms; it has a mass of 1/1836 the mass of a hydrogen atom, and a negative charge. Protons (symbol p+) are also present in all atoms; a proton is about the same mass as a hydrogen atom and carries positive charge equal in magnitude but opposite in sign to electron. Neutrons (symbol n) are electrically neutral and have about the same mass as a proton.

Hadrons are particles composed of quarks. Examples include baryons and mesons. Baryons are composed of three quarks, usually of the "up" or "down" variety. They all have a large rest mass for subatomic particles. Examples of baryons are protons and neutrons.

Types of Baryons (selection)

Name Quarks Mass (GeV)

Proton uud 0.938

Neutron udd 0.940

uds 1.116

uus 1.189

uds 1.192

dds 1.197

uuu 1.232

sss 1.672

udc 2.273

Name	Quarks	Mass (GeV)
Proton	uud	0.938
Neutron	udd	0.940
	uds	1.116
	uus	1.189
	uds	1.192
	dds	1.197
	uuu	1.232
	sss	1.672
	udc	2.273

Mesons are composed of a normal quark and an antiquark, which causes the baryon number to go to zero. None of these are very stable, but have half lives on the order of nanoseconds. They have a rest mass starting with 140 MeV for the lightest mesons, the pion.

Leptons contain no quarks, but are small irreducible particles (no smaller constituent is currently known). Some have no rest mass, while others have very large rest mass. Types of leptons include electrons, muons, tauons and neutrinos.

Links

particleadventure.org: The Standard Model, Unsolved Mysteries. Beyond The Standard Model, What is the World Made of? The Naming of Quarks
particleadventure.org: Particle chart
Number 644 #1, June 30, 2003, Physics News Update: A Five-Quark State Has Been Discovered
UniSci: Anti-Proton Mass And Charge Measured For First Time Citat: "...In this case, the values agree with those of the proton (allowing for the opposite charge) to within 60 parts per billion...."
22 August, 2001, BBCNews: Physicists make 'strange' matter
21-Jan-2002 UniSci: Quantum Gravitational States Observed For First Time Citat: "...The researchers report seeing a minimum (quantum) energy of 1.4 picoelectron volts (1.4 x 10^-12 eV)..."
LHCB: Everything you ever wanted to know about CP violation and never dared to ask
BBC News 5-3-1999: 'Sensational' anti-matter discovery "...The phenomenon they think they spotted is technically called direct Charge-Parity (CP) violation. It means that particles behave differently if you swap matter for anti-matter and also swap left and right. ...The observation of direct CP violation is an exciting one for physicists as it disagrees with all the currently held theories about the nature of matter. "
Number 660 #2, November 4, 2003, Physics News Update: Acceleration Disrupts Quantum Teleportation Citat: "...While this effect is small for typical accelerations in Earthly labs the result shows an interesting relationship between the effects of space-time motion and the quantum world..."
Jose Galvez: Chapter 1 Electrodynamics (pdf)
Annotated Physics Encyclopædia: Quantum Field Theory
University of California: Particle Data Group

Synonyms: Subatomic Particle

Synonyms: elementary particle (n), fundamental particle (n). (additional references)

Crosswords: Subatomic Particle

English words defined with "subatomic particle": magneton. (references)

The following statistics estimate the number of searches per day across the major English-language search engines as identified by various trade publications. Hyperlinks lead to commercial use of the expression at Amazon.com.

Scrabble® Enable2K-Verified Anagrams
	Words within the letters "a-a-b-c-c-e-i-i-l-m-o-p-r-s-t-t-u"
	-4 letters: ectoparasitic, impracticable, misarticulate.
	-5 letters: ambulatories, articulacies, biomaterials, capitularies, malpractices, matriculates, microcapsule, particulates, plutocracies, problematics, semitropical, spectatorial, timocratical, ultracompact.
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