Announcements Please fill out ECAFE online evaluations !!! https://www.hawaii.edu/ecafe/ Today is Werner Heisenberg’s birthday (born in 1901) Will cover particle physics in the remaining classes. Some clicker questions but no more quizzes !! One missing clicker registration->name mapping (A024A622). Please contact me.

Goals for Chapter 44 To learn the key varieties of fundamental particles To see how accelerators and detectors are used to investigate subatomic particles To learn how subatomic particles interact with each other To understand how quarks explain the structure of many subatomic particles To learn how we probe the standard model of particles and interactions To investigate the Big Bang and the expansion of the universe

Particle Physics and Cosmology The physics on the microscopic scale is essential to understand the universe on its largest scale. (Particle physics and cosmology are closely related.) How much of the universe is composed of “normal” matter? Fundamental known elementary particles ?

What is the most famous equation in modern physics ?

Wrong ! Paul Dirac, a strange and introverted genius who played a critical role in the development in modern physics. These negative energy solutions come from requiring consistency of quantum mechanics with special relativity. or Dirac: The negative energy solutions have a physical meaning !

Some history of fundamental particles Figure 44.1 (right) shows the first known positron track. Figure 44.2 (below) deals with Dirac’s prediction of the positron.

The positron is the antiparticle of the electron. Pair production The positron is the antiparticle of the electron. Figure 44.3 (right) shows pair production of electron-positron pairs.

Discovery of the anti-proton Berkeley, California 1955 (before the internet) Emilio Segre Life before internet. A key ingredient was the construction of a new particle accelerator (“atom smasher”) called the Bevatron, which could operate just above the energy threshold for production of anti-protons. This was 6.1-6.3 Billion Electron Volts (Bev). Owen Chamberlain

Fundamental Physics/Application of anti-matter in medicine

Antimatter can be used for PET (Positron Emission Tomography) Scans For example, Queen’s Hospital in Honolulu has a PET scanner operated in cooperation with Hamamatsu Photonics. Also a cyclotron to make radioactive isotopes for PET scans.

Particles as force mediators Figure 44.4 (right) shows an analogy for how particles act as force mediators. Figure 44.5 (below) shows the Yukawa potential-energy function. Concept of “Virtual Particles”

27 year old Hideki Yukawa makes a breakthrough Photo after WWII

How Yukawa came up with the pion. He thought there might be a propagator particle for the strong interaction. The range of the strong interaction is 1.5 x 10-15m=1.5 fm, the typical lifetime of the particle should be

Particle accelerators and detectors The figure below shows the layout and operation of a cyclotron. Acceleration each time they cross the gap

Fixed target vs colliding beams Question: Which is most effective for producing new particles ? (Use energy and momentum in special relativity) Question: what is the result for colliding beams, energy Em ?

Fixed target vs colliding beams For example, collide an 800 GeV beam of protons on protons in a fixed target, What about colliding beams of 800 GeV ? Ea=1600 GeV

Clicker question on particle accelerators What is the advantage of using colliding beams in particle physics experiments? A. The available energy is larger. B. The reaction products are always produced at rest, so they can be studied at leisure. C. There are fewer problems with the apparatus becoming radioactive. D. both A. and B. E. all of A., B., and C. Answer: A

A44.2 What is the advantage of using colliding beams in particle physics experiments? A. The available energy is larger. B. The reaction products are always produced at rest, so they can be studied at leisure. C. There are fewer problems with the apparatus becoming radioactive. D. both A. and B. E. all of A., B., and C.

Particles and interactions The four fundamental interactions (forces) are: the strong interaction the electromagnetic interaction the weak interaction the gravitational interaction.

Particles and interactions The four fundamental interactions (forces) are: the strong interaction the electromagnetic interaction the weak interaction the gravitational interaction.

Clicker question on Fundamental interactions The strong nuclear force has a short range compared to the electromagnetic force. Why is this? A. The particles that mediate the strong force are charged, while those that mediate the electromagnetic force are neutral. B. The particles that mediate the strong force are massive, while those that mediate the electromagnetic force are massless. C. The particles that mediate the strong force have spin 0, while those that mediate the electromagnetic force have spin 1. D. all of A., B., and C. E. none of A., B., or C. Answer: B

A44.1 The strong nuclear force has a short range compared to the electromagnetic force. Why is this? A. The particles that mediate the strong force are charged, while those that mediate the electromagnetic force are neutral. B. The particles that mediate the strong force are massive, while those that mediate the electromagnetic force are massless. C. The particles that mediate the strong force have spin 0, while those that mediate the electromagnetic force have spin 1. D. all of A., B., and C. E. none of A., B., or C.