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.

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.

**Particle Generations**
Antileptons
First generation		Second generation		Third generation
Name	Symbol	Name	Symbol	Name	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	Template:Subatomic particle	charm antiquark	Template:Subatomic particle	top antiquark	Template:Subatomic particle
down antiquark	Template:Subatomic particle	strange antiquark	Template:Subatomic particle	bottom antiquark	Template:Subatomic particle

Leptons

Antiquarks

Antileptons

Bosons: Massless Carriers of Fundamental Forces

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