1. Quarks
Remember the family of ordinary matter consists of only 4 particles, (not counting their antiparticles)
quark u d
lepton
(electron) e
Lepton
(electron neutrino)
Of these all of matter is made only of the first three. Neutrino’s exist in plenty but are not found confined in atoms

2. No naked quarks
The strong force holding quarks together in a hadron ( a proton or neutron) does not weaken with increasing distance.
It actually becomes larger as the interquark distance increases: q q
The (gamma) energy that we have to put is so high that it results in pair production before the quarks can be separated.
We never see a “naked” quark.

3. Quark Confinement Baryon and Meson
Trying to split up the baryon results in a form of pair production where a quark and antiquark pair are produced from the energy of the incident photon.
A quark and antiquark pair form a meson

4. Strong Decay Baryon and Meson
Heavy baryons produced in high energy collisions have lots of spare energy already and this is how they break up so quickly to form a more stable baryon ( eventually if not immediately a proton) and a meson.
This is decay due to the strong force and takes about 10-23s
e.g.

5. A new model for beta decay
A neutron has the quark structure udd
The neutron becomes a proton with the quark structure uud
The only change in the baryon is that a single down quark has changed into an up quark.

6. The change from u to d changes the overall charge
Total charge
u + d + d
Total charge
u + u + d

7. A new model for beta decayu
A down quark
Becomes an up quark
So normal (negative) beta decay can be represented by the equation below:
Write a corresponding equation for positron emission

8. A new model for beta decay
positron emission can be represented by the equation
An up quark
Becomes an down quark

9. Quarks and Forces
Quarks are the only fundamental particles which get involved with all of the four fundamental forces.
They have mass and are therefore affected by the gravitational force.
They have electrical charge and are therefore subject to the electromagnetic force
They get involved in beta decay and are therefore affected by the weak force.
They make up baryons and mesons and therefore are involved in the strong force

10. Forces and Exchange Particles
A Japanese scientist Yukawa tried to explain forces He suggested that:
an exchange of particles can be responsible both for attraction and repulsion.
Yukawa based his ideas on the fact that two nuclei can be held together by the exchange of an electron in a molecule

11. Two proton are held together by an electron in this H+ ion.

12. We extended this idea to show how the electromagnetic force can account for the repulsion of charged particles by the exchange of a photon.
This is how all fundamental particles which respond to the electromagnetic force interact.
electron
electron
Like charges repel each other by exchanging photons
Opposite charges attract each other by exchanging photons.
The photons transfer momentum from one particle to the other.
These photons of exchange are known as virtual photons.

13. The electromagnetic force
The electromagnetic force only applies to particles with charge.
When charged particles interact electromagnetically, they exchange photons

14. Electromagnetic Attraction
When a proton attracts an electron it is as a result of the exchange of photons
Exchange photons of this kind are called virtual photons

15. The Feynman diagram for the electromagnetic force.
time e- e-
space
The angles in the diagram mean nothing e- e-

16. Exchange particles of the Weak Interaction
The weak interaction is slightly more complex. Photons are not the particles of exchange.
The weak force is mediated by two new particles:
These particles have mass and electronic charge
They are the W- and W+ particles

17. beta decay and the weak force
electron W-
antineutrino
down quark flips to become up quark
It emits a W- particle
The W- particle immediately decays to become the electron and antineutrino.

18. The Feynman diagram for the beta.
time u νe
space
The angles in the diagram mean nothing W- d