33.1 The Yukawa Particle and the Heisenberg Uncertainty Principle Revisited

33.1 The Yukawa Particle and the Heisenberg Uncertainty Principle Revisited

• The story is not complete because quarks and electrons may have smaller structures.

• The basics of particle physics are covered in this chapter.
• Particle physics is evolving with an amazing convergence of topics.
• Nature on the smallest scale may have the greatest influence on the large-scale character of the universe.
• It is an adventure that surpasses the best science fiction because it is real.

• Hideki Yukawa came up with the idea of particle physics in 1935.
• The concept of fields, such as electric and magnetic fields, was very useful to physicists who had long been concerned with how forces are transmitted.
• The force of the object through space is carried by a field.
• Yukawa was interested in the strong nuclear force and was able to explain it in an ingenious way.
• His idea is a blend of forces, particles, and quantum mechanics.
• The force is transmitted by the exchange of particles.

• The particles are in the field.

• The creation and exchange of a pion is how the strong nuclear force is transmitted.
• The pion is created through a violation of mass-energy and travels from the protons to the neutrons.
• It's called a virtual particle because it's not directly observable.
• The Heisenberg uncertainty principle limits the range of force because the pion can only exist for a short time.
• The larger the mass of the carrier particle, Yukawa used the finite range of the strong nuclear force to estimate it.

• The pion can only be created by violating mass-energy.
• The Heisenberg uncertainty principle allows this if it occurs for a short period of time.

• For a period of time, no process can detect a violation of mass-energy.
• The temporary creation of a particle of mass can be done.
• The shorter the time it can exist, the bigger the mass.
• The force can only travel a limited distance in a finite amount of time.

• The pion cannot be directly observed because it would amount to a permanent violation of mass-energy-conservation.
• Yukawa used the range of the strong nuclear force to estimate the mass of the pion.

• Taking the range of the strong nuclear force to be about 1 fermi, calculate the approximate mass of the pion carrying the force, assuming it moves at nearly the speed of light.

• The calculation is approximate because of the assumptions made about the force and speed of the pion, but also because a more accurate calculation would require the sophisticated mathematics of quantum mechanics.
• The Heisenberg uncertainty principle is used to calculate the time that the pion exists, given that the distance it travels is about 1 fermi.
• The mass of the pion can be determined from the Heisenberg uncertainty principle.
• Since we are often considering converting mass to energy and vice versa, we will use the units of mass.

• It's about 200 times the mass of an electron and one-tenth the mass of a nucleon.
• There were no known particles when Yukawa made his proposal.

• The method of force transfer proposed by Yukawa is intriguing.
• It would be possible to free the pion from the nucleus if enough energy was present.
• Energy greater than 100 MeV is required to conserve both energy and momentum.
• In 1947, pions were observed in cosmic-ray experiments, which were designed to supply a small amount of high-energy protons.
• The pions were created in the laboratory under controlled conditions.
• Three pions were discovered, two with charge and one neutral, and given the symbols.

• The pions, or -mesons as they are also called, have mass close to those predicted and feel a strong nuclear force.
• The idea of implosion for plutonium bombs was originated by one of the discoverers of the muon.
• The particle predicted by Yukawa was thought to be the mass of a muon.
• The muons do not feel the strong nuclear force and could not be Yukawa's particle.