2. What is particle physics?

3. Why do we build the machine?

4. Why do we build these big machines, big smashers?
CERN

6. Detector

7. USA Fermi Lab
Why do we build these big machines?

9. What is the world made of? What holds it together?
Fundamental Constituent Structure
Of the material nature

11. 到了西元前五世紀，Leucippus 和Democritus 提倡所有物質都是由微小而永恆不可分割的粒子組成，他們叫這粒子Atom─原子.
“在這世界上，可以看到顏色，可以聞到氣味，可以嘗到甜味，可是真實存在的只有原子和空間。”

12. To see the details, you need to get closer.
Why do we need high energy collider to study the fundamental structure?
1st reason
To see the details, you need to get closer.

13. To get closer, you need higher energy, faster particles.

14. Energy can transfer into mass and generate new heavier particles.
2nd reason
Energy can transfer into mass and generate new heavier particles.

15. But ????
SR allows these new particles to be produced E→M,
but also allow these particles to decay M→E.
Heavier particles usually don’t exist in nature. They decay.

16. Only four stable particles in nature
Neutron
Proton
Electron
Photon

17. They made up the world. Nucleus Atom Solids Molecule
Why stirs trouble by producing heavy new particles?

18. Particles get partners-Antiparticles
1st reason

21. 2nd reason We need invisible particles to describe visible interaction!!!!
Force at a distance
Mediating field

22. Virtual Particles
Mediate an interaction
Virtual particles only exist for a short time, but can be responsible what happens in real life, just we don’t see it directly.
So heavy particles (they could be virtual) do matter.

23. Electromagnetic interaction
Photon

24. Feynman’s Diagram

25. Attraction is harder to visualize
Attraction is harder to visualize. Let’s say, a cloud of mediating particles traps the two ………

27. Weak Interaction
β Decay

28. p e ν n p W n
Weak interaction is weak because the mediation particle W and Z are too heavy.

30. Weak Interaction through Z particle