ANNIHILATION
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ANNIHILATION. PARTICLE PHYSICS. PARTICLE PHYSICS. e +. e -. Atom 1x10 -10 m. Nucleus 1x10 -15 m. +. n. n. +. n. n. +. U. U. Quarks 1x10 -18 m. D. ?. ?. ?. CLASSIFICATION. ALL PARTICLE, EXCEPT FOR THE GAUGE BOSONS, ARE EITHER :. LEPTONS. GREEK leptos ( leptos) =.

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E

ANNIHILATION

PARTICLE

PHYSICS

PARTICLE

PHYSICS

e+

e-


E

Atom 1x10-10 m

Nucleus 1x10-15 m

+

n

n

+

n

n

+

U

U

Quarks 1x10-18 m

D

?

?

?


E

CLASSIFICATION

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

LEPTONS

GREEK leptos (leptos) =

LIGHT

OR

ROBUST

OR

HEAVY

HADRONS

GREEK hadros (hadros) =

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


E

LEPTONS

HADRONS

GAUGE

BOSONS

Electron

Baryons

Mesons

virtual photons

electron neutrino

muon neutrino

Electromagnetic force

Muon

W+ W- Z0

The weak force

gluons

Tau particle

The strong force

Tau neutrino

(not fundamental)

(fundamental)

3 Quarks

QQQ

2 Quarks

Q antiQ

Proton p

Pions

Neutron n

Kaons

gravitons

Gravity

All leptons and hadrons have a corresponding antimatter particle


E

Matter and Antimatter annihilate each other

e.g. a collision between an electron and a positron can produce two gamma rays


E

ANNIHILATION

The two gamma rays have to travel in opposite directions so that

momentum is conserved

e+

e-

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


E

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


E

PAIR PRODUCTION

+

-

IN THE PRESENCE OF A MASSIVE NUCLEUS,

A PHOTON CAN PRODUCE AN ELECTRON POSITRON PAIR

If there is a magnetic field acting inwards, which is the positron?

NUCLEUS

hf= 2mec2 + EK


E

  • 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.


E

Force

Particles it affects

Exchange particle

Electro-magnetic

anything with charge

virtual photon

Range

Relative

strength

Weak

all fundamental particles

W+, W-,Z0

Strong nuclear force

quarks

gluon

Gravity

anything with mass

graviton

Infinite

10-2

10-18 m

10-5

10-15 m

1

Infinite

10-39

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.


E

FEYNMAN DIAGRAMS

Time

Space

THESE ARE DIAGRAMS IN SPACE AND TIME USED TO REPRESENT VARIOUS INTERACTIONS

In the interaction below 2 electrons come together, throw virtual photons at one another, thus repelling each other.


E

e-

p

Time

n

Space

Beta Minus Emission

w -

w -


E

e+

n

νe

Time

p

Space

Beta PLUS Emission

w+

w+


E

ve

n

Time

p

e-

Space

Electron Capture

w+

w+


E

p

e-

Time

n

ve

Space

Neutrino - Neutron Collision

w+

w+


E

e+

n

Time

p

Space

Antineutrino - Proton Collision

w+

w+


E

ve

n

Time

p

e-

Space

Electron - Proton Collision

w-

w-


E

THREE GENERATIONS OF MATTER


E

Quarks also have another property called “COLOUR CHARGE”

[ usually referred to as just “colour” ]

D

D

U

U

U

D

AD

U

The three possible colours arered,blueandgreen. Red blue and green together make white and quarks particles can only exist where the quarks altogether produce a colourless mix

proton

neutron

π+ meson


E

Have odd half integer spin

usually sometimes

CLASSIFICATION BY SPIN

FERMIONS

BOSONS

Have integer spin

Gauge Bosons [Force carriers]

Mesons

Leptons

Quarks

Baryons

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


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