Elementary Particles and Particle Physics Theory
Vishesh Ramesh on elementary particles and particle theory
Short Description of Topic
History
Particle physics, and subatomic physics, has had a long history with many different and diverse scientists playing a part. The idea that matter is composed of elementary particles can be traced as far back as the 6th century B.C.E, and to scientists and philosophers of ancient Greece, India, the Middle East, and Western Europe. These early hypotheses rose from philosophical speculation and reasoning as opposed to experimentation.
John Dalton in the 19th century provided his theory of the atom, which was then believed to be the utmost fundamental particle. By the end of the 19th century, however, it was discovered that atoms were composed of yet smaller particles, when the electron and its charge was discovered via experimentation. Ernest Rutherford’s gold scattering experiment confirmed the existence of the nucleus and the proton, and further experimentation in the early 20th century led to the confirmation of the existence of the neutron.
By the middle of the 20th century, even smaller particles composing atomic nuclei were hypothesized, as the nuclear strong force was also discovered and established as a fundamental force alongside gravity and electromagnetism. Around this time, the understanding of fundamental particles also deepened, particularly with Erwin Schrödinger’s work in quantum physics and the establishment of wave-particle duality of the photon and Einstein’s work on the photoelectric effect showing photons to carry electromagnetic force.
In the mid-20th century, Marcus Fierz and Wolfgang Pauli formulated and refined the spin-statistics theorem, establishing bosons and fermions. In the time period between 1935 and 2000, positrons, muons, mesons, leptons, baryons, bosons, and neutrinos were discovered at a breathtaking and chaotic pace. The Standard Model is a theory that has its origins in this time period, born of a desire to unite these new subatomic fundamental particles and the four fundamental forces, and in the process of creating it, several more particles were hypothesized and most later discovered. The current formulation of the Standard Model was finalized in the 1970’s.
Elementary Models
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Fermions: Particles of Matter
Fermions include all fundamental particles that compose matter or antimatter.
Matter
Leptons | |||||
First generation | Second generation | Third generation | |||
Name | Symbol | Name | Symbol | Name | Symbol |
electron | Template:Subatomic particle | muon | Template:Subatomic particle | tau | Template:Subatomic particle |
electron neutrino | Template:Subatomic particle | muon neutrino | Template:Subatomic particle | tau neutrino | Template:Subatomic particle |
Quarks | |||||
First generation | Second generation | Third generation | |||
up quark | Template:Subatomic particle | charm quark | c | top quark | Template:Subatomic particle |
down quark | Template:Subatomic particle | strange quark | Template:Subatomic particle | bottom quark | Template:Subatomic particle |
Quarks
There are six types of quarks: Up, Down, Charm, Strange, Top, Bottom. All six quarks have a spin of +1/2. Up, charm, and top quarks have a charge of +2/3, while down, strange, and bottom quarks have a charge of -1/3.
Leptons
Leptons are particles with spins of 1/2,
Antimatter
Antileptons | |||||
First generation | Second generation | Third generation | |||
Name | Sign | Name | Sign | Sign | Symbol |
positron | Template:Subatomic particle | antimuon | Template:Subatomic particle | antitau | Template:Subatomic particle |
electron antineutrino | Template:Subatomic particle | muon antineutrino | Template:Subatomic particle | tau antineutrino | Template:Subatomic particle |
Antiquarks | |||||
First generation | Second generation | Third generation | |||
up antiquark | 2/3 | charm antiquark | 2/3 | top antiquark | 2/3 |
down antiquark | -1/3 | strange antiquark | -1/3 | bottom antiquark | -1/3 |
Antiquarks
Antileptons
Bosons: Massless Carriers of Fundamental Forces
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See also
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