Discovery of Subatomic Particles: About Subatomic Particle (For CBSE, ICSE, IAS, NET, NRA 2022)

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Title: Discovery of Subatomic Particles

The discovery of subatomic particles has been the base for many other discoveries and inventions

About Subatomic Particle

About Subatomic Particles
  • Subatomic particle, also called elementary particle, any of various self-contained units of matter or energy that are the fundamental constituents of all matter.
  • In the physical sciences, subatomic particles are smaller than atoms. They can be composite particles, such as the neutron and proton; or elementary particles, which according to the standard model are not made of other particles.
  • They include electrons, the negatively charged, almost massless particles that nevertheless account for most of the size of the atom, and they include the heavier building blocks of the small but very dense nucleus of the atom, the positively charged protons and the electrically neutral neutrons.
  • Particle physics and nuclear physics study these particles and how they interact.
  • A typical atom consists of three subatomic particles: protons, neutrons, and electrons (as seen in the helium atom below) .
  • Other particles exist as well, such as alpha and beta particles
  • But these basic atomic components are by no means the only known subatomic particles.
  • Protons and neutrons are themselves made up of elementary particles called quarks, and the electron is only one member of a class of elementary particles that also includes the muon and the neutrino.
  • Neutron, neutral subatomic particle that is a constituent of every atomic nucleus except ordinary hydrogen.

Quark Colors

  • The interpretation of quarks as actual physical entities initially posed two major problems.
  • Quarks had to have half-integer spin (intrinsic angular momentum) values for the model to work, but at the same time they seemed to violate the Pauli exclusion principle, which governs the behavior of all particles (called fermions) having odd half-integer spin.
  • In many of the baryon configurations constructed of quarks, sometimes two or even three identical quarks had to be set in the same quantum state — an arrangement prohibited by the exclusion principle.
  • Second, quarks appeared to defy being freed from the particles they made up.
  • Though the forces binding quarks were strong, it seemed improbable that they were powerful enough to withstand bombardment by high-energy particle beams from accelerators.

Binding Forces and “Massive” Quarks

  • The binding forces carried by the gluons tend to be weak when quarks are close together.
  • Within a proton (or other hadron) , at distances of less than 10 − 15 meter, quarks behave as though they were nearly free.
  • This condition is called asymptotic freedom.

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