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Ashraf A

on 15 January 2014

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Particles are grouped into famlies
Smallest family is the photon, which consists of just the photon itself. It interacts with charged particles only and is its own anti-particle
Other families are Lepton and Hadron, which is the largest family
Hadrons were thought to be made up of three quarks and their anti-quarks
Mesons had two quarks and baryons had three quarks, named up (u), down (d) and strange (s)
quarks have fractional charges of + 2/3 e, -1/3 e and -1/3 e respectively, and anti-quarks have the same size but opposite charges
Neutrinos and positrons
Neutrinos are extremely tiny and neutral particles that have almost no interaction with matter
It is suggested that Neutrinos have mass, and if they do have mass, we can figure out how the nuclear reactions occur in the sun
Positrons are anti-electrons, when positrons and electrons interact, they destroy each other and transform into two gamma rays
More discoveries
Many more particles found in the 1930's and 40's
Physicists also discovered that every elementary particle has an anti particle
S.H. Neddermeyer and C. D. Anderson discovered positive and negative muons (μ+ and μ-) that have a mass about 207 times that of an electron.
Muons only exist for about 2.2 × 10−6 s and decay.
These discoveries also lead to finding muon neutrinos and muon antineutrinos (Vμ)
μ+ --> e- + Vμ + Ve
μ- --> e+ + Vμ + Ve
History of Elementary Particles
Proton, Neutron and Electron don't make up all of matter
Missing energy and momentum in beta decay and Pauli's proposal of the neutrinos and positrons were the first hint of other particles
In 1935, another particle was suggested that had a mass between that of a proton and electron and holds the nuclei together
In 1947, this particle was discovered to have nothing to do with holding the nuclei, but they exist, named pi meson or pion
Started a revolution in physics and new particle discovery

Collision and formation
Electric and magnetic fields are used to accelerate particles close to the speed of light
When these particles collide, they form new particles for a very short amount of time and then decay into gamma rays
For example, when a high energy proton collides with another high energy proton, a particle called a neutral pion forms for about 0.8 x 10^-6 s, then decays into gamma rays
Physicists started discovering more particles
Physicists started categorizing depending on the types of force through which they interact with other particles
For example, protons and neutrons interact through the strong nuclear force, whereas electrons do not experience the strong nuclear force
Particles are usually affected by one or more of the four fundamental forces: gravitational, electromagnetic, strong nuclear, and weak nuclear forces
Cloud Chamber
Physicists use a machine known as a "Cloud Chamber" to study these fast decaying particles
"Cloud Chambers" contain a cold, supersaturated gas and when any form of ionizing radiation passes through, the ions formed in the path of the particle form condensation nuclei and the cold gas liquefies, creating a visible droplet.
If a magnetic field is placed, the charged particles follow a curved path
Physicists analyze these "tracks" to determine the size and speed of the particle
Lepton Family
The lepton family of particles interact through the weak nuclear force
Leptons can interact through the gravitational and electromagnetic forces, but are immune to strong nuclear force
Electrons and electron neutrinos are leptons, muons and their neutrinos are also leptons
Recently discovered particle, the tau particle and its neutrino, also fit into the lepton family
The antiparticles always have the same mass but opposite charge of the particles. If the particle is neutral, the antiparticle is also neutral
Leptons and their antiparticles are thought to be true elementary particles as there is nor proof that they consist of more fundamental particles
Hadron Family
Particles of the Hadron family interact through both the strong and weak nuclear forces, gravitational force and electromagnetic force (if charged)
Hadron is the largest family and is divided into smaller groups of Mesons and Baryons
and neutrons and their antiparticles are baryons, and pions are mesons
With larger and faster accelerators, more Hadrons are being discovered
Physicists theorize Hadrons may not be elementary particles
Quarks and Anti-Quarks
This model of quarks was accepted until 1974, when more hadrons were discovered and three more quarks were added to the list
The three new quarks were named charmed (c), top (t) (aka truth) and bottom (b) (aka beauty)
Quarks have more properties than just a charge, other properties such as the one called "colour" explain other characteristics of quarks
Standard model refers to the currently accepted mechanisms of the strong, weak and electromagnetic forces
Physicists are trying but cant bring gravitational force into the model
Physicists have found particles that are exchanged by the elementary particles that account for the interactions between them.
When charged particles interact through the electromagnetic force, they exchange a photon, because photons have no mass and travel at the speed of light, the range of the force is unlimited.
The weak nuclear force is mediated by bosons that have a large mass and such a short lifetime that the range of the interaction is extremely short.
The exchange of gluons holds quarks together in hadrons. The theory is that when quarks exchange gluons, they change colour.
By: Ashraf A & Purtha S
That was a brief summary of elementary particles
Everyday, physicists are discovering more and more new particles
We have yet to figure out many more particles that exist in our universe
The discovery of elemental particles is one of the most active research fields in physics
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