Explain the Elementary Particles and Particle AcceleratorsMore than 100 particles smaller than the proton, electron and neutron have been discovered and are referred to as elementary particles. Most of these are now believed to be composed of a small number of quarks, whose charge is believed to be 1/3 that of an electron. A proton and an electron are believed to contain three quarks each. Mesons have a mass between that of the electron and that of the proton. Neutral mesons as well as positive and negative mesons have been found. The negative pi-meson has a mass about 270 times that of the electron. Mesons are unstable. When the pi-meson decays, a lighter particle known as a muon is produced. Particles heavier than the neutron, such as the upsilon particle which has a mass 10 times that of a proton, have also been found. Antiparticles have the same mass but opposite charge to the corresponding particle. The positron is the antiparticle of the electron. The neutrino is a neutral particle of practically zero rest mass introduced by Pauli in 1931 and detected experimentally in 1956. The photon is usually classified as an elementary particle that travels at the speed of light. It has zero rest mass and an amount of energy dependent on its frequency. The muon has an associated neutrino. The tau particle, which is heavier than the muon, also has an associated neutrino. All have antiparticles. Particle Accelerators are the main tools used to examine the nucleus. The greater the energy of the particles used to “smash” the nucleus, the more detail about its structure and particles is available. The bombarding particles are usually described as possessing energy in millions of electron volts (MeV) or billions of electron volts (GeV). Electrons or protons can be used to bombard nuclei. These particles, since they are charged, can be accelerated by being placed in an electric field. A linear accelerator or cyclotron, which is able to circulate the particles up to 100 times to increase the particles' energy by millions of eV, is used to accelerate electrons or protons. At these high energies, subatomic particles can start showing relativistic effects. As particles move at an appreciable percentage of the speed of light, the mass of the particle increases and the lengths traveled decrease from rest values. Stanford University operates a linear accelerator, SLAC, and several laboratories operate synchrotrons, the largest being run by Fermilab in Batavia, Illinois.