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+
15© John Parkinson
Space
Time
Electron Capture
p
w+
enep
w+
e-
n ve
16© John Parkinson
Space
Time
Neutrino - Neutron Collision
n
w+
epn e
w+
ve
pe-
17© John Parkinson
Space
Time
Antineutrino - Proton Collision
p
w+
enp e
w+
n e+
e
18© John Parkinson
Space
Time
Electron - Proton Collision
p
w-
enep
w-
n ve
e-
19© John Parkinson
THREE GENERATIONS OF MATTER
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