Standard Model

# Standard Model

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## Standard Model

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1. Standard Model Physicists have developed a theory called “The Standard Model” that explains what the world is and what holds it together.

2. Standard Model • It was once thought that the fundamental particles were electrons, protons, neutrons. • Now we find smaller subatomic particles – quarks & leptons that comprise matter. • Forces are carried by particles too!

3. All matter either Hadrons or Leptons. p+ & no Quarks can’t exist alone.

4. Protons, Neutrons:baryons made of only up & down quarks. • How many up & down quarks in a p+? • Charge = +1 • Baryons have 3 quarks only. • 2 up & 1 down. • u + u + d • +2/3 +2/3 – 1/3 = +1

5. How many up & down quarks in a no? • Charge = 0 • 1 up & 2 down. • u d d • +2/3 -1/3 -1/3 = 0

6. The Atom

7. Leptons • The most familiar member of this group is the electron e, but there are also heavier particles called the muon m and the tau t. • For each of those, there is a smaller “partner” called a neutrino n . • The leptons are all capable of independent existence.

8. All particles have anti-particles same mass. Antiparticles behave just like their corresponding matter particles, except they have opposite charges. A proton is electrically positive - an antiproton is negative. Gravity affects matter and antimatter the same way. When a matter & corresponding antimatter meet, they annihilate into pure energy!

9. Notation add bar: Mesons quark & antiquark.

10. A particle is composed of 2 charm, & 1 bottom quark. • Write the symbols & charges for all the particles. • Is it a meson, lepton or baryon? • c c b • +2/3 +2/3 -1/3 What is it’s charge? • +1. • Baryon.

11. A particle is composed of 1 anti-strange, & 1 down quark. • Write the symbols & charges for all the particles. • Is it a meson, lepton or baryon? • s d • +1/3 -1/3 What is it’s charge? • 0. • Meson.

12. Forces & Force Exchange Particles4 Fundamental Forces The universe exists because the fundamental particles interact. These interactions include 4 attractive & repulsive forces, decay, & annihilation. • Strong Nuclear (Nuclear) • Electromagnetic • Weak (Nuclear) • Gravity

13. Strong Force • Short Range, Attractive only – holds nuclear particles together. • Particle = gluons.

14. Electromagnetic Force • Long range. Attracts & repels charged particles (Coulomb’s Law). • Carrier particle = photon.

15. Weak Force • In the nucleus. Involved with decay of particles. Short range. The carrier particles of the weak interactions are the W+, W-, and the Z bosons.

16. Gravity • Long range weakest force. Attractive only. • The gravity force carrier particle has not been found. It, however, is predicted to exist and may someday be found: the graviton.

17. Quarks & Leptons 5:40 min.http://www.youtube.com/watch?v=aTFCKbZw8QY Hwk: Read Text 25-4 pg 917-923 Do pg 923 #1,2 Pg 928 #30 - 37

18. List 2 pieces of evidence that light is a wave. • Diffraction • Interference. List 1 piece of evidence that light is a stream of particles. • Photoelectric effect List 1 piece of evidence for the Bohr model of the atom. • Emission or Absorption spectra

19. The charge on an anti-up quark would be: • +1 • -1 • +2/3 • -2/3 Note: Antiparticles have a bar over the symbol.

20. This particle is a: • Lepton • Proton • Meson • neutron