© john parkinson 1 e+e+ e-e- annihilation © john parkinson 2 atom 1x10 -10 m + + + n n n n nucleus...

1© John Parkinson

e+ e-ANNIHILATION

2© John Parkinson

Atom 1x10-10 m

+

++ n

nn

n Nucleus 1x10-15 m

U Quarks 1x10-18 mU

D

? ? ?

3© John Parkinson

GREEK (leptos) =

CLASSIFICATIONCLASSIFICATION

ALL PARTICLE, EXCEPT FOR THE GAUGE BOSONS, ARE EITHER :

LIGHTLIGHT

OR

GREEK (hadros) =ROBUSTROBUST

ORORHEAVYHEAVY

Gauge BosonsGauge Bosons are the exchange particles which mediate the four types of interactions or forces

4© John Parkinson

LEPTONS HADRONS

GAUGE

BOSONSElectron e

electron neutrino e

Muon

muon neutrino

Tau particle Tau neutrino

Baryons Mesons 3

Quarks

QQQ

2 Quarks

Q antiQProton

p

Neutron n

Pions ,,0

Kaons KKK ,,0

All leptons and hadrons have a corresponding antimatter particle

virtual photons

Electromagnetic force

W+ W- Z0

The weak force

gluons

The strong force

gravitons

Gravity

(fundamental)(not fundamental)

5© John Parkinson

Matter and Antimatter annihilate each other

e.g. a collision between an electron and a positron

can produce two gamma rays

6© John Parkinson

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 = mc2], equivalent to E = 2 me c2, where 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: 2mec2 = 2hf

7© John Parkinson

MATTER AND ANTIMATTERCorresponding 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

8© John Parkinson

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 = 2mec2 + EK

9© John Parkinson

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.

10© John Parkinson

11© John Parkinson

Range

Infinite

10-18 m

Force Particles it affects

Exchange particle

Electro-magneticanything with

chargevirtual photon

Weakall

fundamental particles

W+, W-,Z0

Strong nuclear force

quarks gluon

Gravityanything with

massgraviton

10-15 m

Infinite

Relativestrength

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.

12© John Parkinson

FEYNMAN DIAGRAMSFEYNMAN DIAGRAMSTHESE ARE DIAGRAMS IN SPACE AND TIME USED

TO REPRESENT VARIOUS INTERACTIONS

Space

Time

-e e -

e - e -

In the interaction below 2 electrons come together, throw virtual photons at one another,

thus repelling each other.

13© John Parkinson

Space

Time

Beta Minus Emission

n

p

e-

e

w -

eepn

w -

14© John Parkinson

Space

Time

Beta PLUS Emission

p

n

w+

eenp

e+

νew+

20© John Parkinson

UU

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

UD

D

U

AD

proton neutron π+ meson

21© John Parkinson

CLASSIFICATION BY SPIN

FERMIONS BOSONSHave odd half integer spin

usually sometimes2

1

2

5,

2

3Have 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

© john parkinson 1 e+e+ e-e- annihilation © john parkinson 2 atom 1x10 -10 m + + + n n n n nucleus...

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