2. © John Parkinson 1 e+e+ e-e- ANNIHILATION

3. © John Parkinson 2 Atom 1x10 -10 m + + + n n n n Nucleus 1x10 -15 m U Quarks 1x10 -18 m U D ? ? ?

4. © John Parkinson 3 GREEK  (leptos) = CLASSIFICATION ALL PARTICLE, EXCEPT FOR THE GAUGE BOSONS, ARE EITHER : LIGHT OR GREEK  (hadros) = ROBUSTORHEAVY Gauge Bosons Gauge Bosons are the exchange particles which mediate the four types of interactions or forces

5. © John Parkinson 4 LEPTONSHADRONSGAUGE BOSONS Electron electron neutrino Muon muon neutrino Tau particle Tau neutrino Baryons Mesons 3 Quarks QQQ 2 Quarks Q antiQ Proton p Neutron n Pions Kaons All leptons and hadrons have a corresponding antimatter particle virtual photons Electromagnetic force W + W - Z 0 The weak force gluons The strong force gravitons Gravity (fundamental) (not fundamental)

6. © John Parkinson 5 Matter and Antimatter annihilate each other e.g. a collision between an electron and a positron can produce two gamma rays

7. © John Parkinson 6 e+e+ e-e- ANNIHILATION The two gamma rays have to travel in opposite directions so that momentum is conserved The amount of energy released is, in line with Einstein's theory of Special Relativity [E = mc 2 ], equivalent to E = 2 me me c 2, where me me is the mass of the electron [and the positron] The energy of a photon of frequency,f, is given by E = hf, where h is Planck’s constant. Hence the frequency of the gamma rays is found by equating: 2m e c 2 = 2hf

8. © John Parkinson 7 MATTER AND ANTIMATTER Corresponding Matter and Antimatter Particles have : the same mass opposite charges, if they are charged opposite spin One particle is like the MIRROR IMAGE of the other The antimatter particle behaves as though it has negative energy and is travelling backwards in time, when it is compared with its matter equivalent

9. © John Parkinson 8 PAIR PRODUCTION IN THE PRESENCE OF A MASSIVE NUCLEUS, A PHOTON CAN PRODUCE AN ELECTRON POSITRON PAIR NUCLEUS If there is a magnetic field acting inwards, which is the positron? + - hf = 2m e c 2 + E K

10. © John Parkinson 9 We currently think of four main forces of nature: electromagnetism weak force strong nuclear force gravity Physicists think that all forces are caused by the exchange of particles. Imagine two jugglers playing on a frozen lake. When they start throwing their batons at each other, they will be pushed apart. The batons carry momentum from one juggler to the other. This momentum pushes each juggler away from the other across the slippery ice.

11. © John Parkinson 10

12. © John Parkinson 11 Range Infinite 10 -18 m ForceParticles it affects Exchange particle Electro-magnetic anything with charge virtual photon Weak all fundamental particles W +, W -, Z 0 Strong nuclear force quarks gluon Gravity anything with mass graviton 10 -15 m Infinite Relative strength 10 -5 1 10 -39 10 -2 The Higgs particle or field is a kind of stuff in the vacuum causing originally zero mass particles to gain mass. In the electro-weak theory the photon (and the gluon in the quark theory) remain massless.

13. © John Parkinson 12 FEYNMAN DIAGRAMS THESE ARE DIAGRAMS IN SPACE AND TIME USED TO REPRESENT VARIOUS INTERACTIONS Space Time In the interaction below 2 electrons come together, throw virtual photons at one another, thus repelling each other.

14. © John Parkinson 13 Space Time Beta Minus Emission n p e-e- w -

15. © John Parkinson 14 Space Time Beta PLUS Emission p n w+w+ e+e+ νeνe w+w+

16. © John Parkinson 15 Space Time Electron Capture p w+w+ w+w+ e-e- n veve

17. © John Parkinson 16 Space Time Neutrino - Neutron Collision n w+w+ w+w+ veve p e-e-

18. © John Parkinson 17 Space Time Antineutrino - Proton Collision p w+w+ w+w+ n e+e+

19. © John Parkinson 18 Space Time Electron - Proton Collision p w-w- w-w- n veve e-e-

20. © John Parkinson 19 THREE GENERATIONS OF MATTER

21. © John Parkinson 20 U U D Quarks also have another property called “COLOUR CHARGE” [ usually referred to as just “colour” ] The three possible colours are red, blue and green. Red blue and green together make white and quarks particles can only exist where the quarks altogether produce a colourless mix U D D U AD protonneutron π + meson

22. © John Parkinson 21 CLASSIFICATION BY SPIN FERMIONSBOSONS Have odd half integer spin usually sometimes Have integer spin Leptons Quarks Baryons Gauge Bosons [Force carriers] Mesons An atomic nucleus is either a fermion or boson depending on whether the total number nucleons is odd or even, respectively. This accounts for superconductivity and the superfluidity of Helium [ a boson ] at low temperatures