1. Quantum Phenomena II: Matter Matters
2nd Handout
Second Handout
Atomic Structure
Fundamental Physics
Hydrogen atom
Quantum numbers
Electron intrinsic spin
Other atoms
More electrons!
Pauli Exclusion Principle
Periodic Table
Particle Physics
The fundamental particles
The fundamental forces
Cosmology
The big bang
The evolution of the universe
Chris Parkes
April/May 2003

2. The Structure of Matter
Quarks have most of mass
Electrons spatial extent and determine chemical properties

3. Fundamental ? 450BC Empedocles, Aristotle Democritus “Atoms & space”
4 basic elements
Similar philosophies in China / India
Democritus “Atoms & space”
1661 Boyle Elements
…Medeleyev lots of them !
C19 Dalton, elements composed of atoms
nucleus
Protons, neutrons….
Lots more started turning up!
Quarks
Standard model
"Young man, if I could remember the names of these particles, I would have been a botanist!”, Fermi

4. Looking at smaller scales
Naked Eye m
Light Microscope m
Size of Atom m
Size of Proton m
Size of quark, electron, neutrino.. 0 (so far..)
Fundamental particles
No constituents
Study using Particle Accelerators
Labs: CERN, Fermilab…
Acelerators: LEP/LHC, Tevatron
Collide particles at high energies
Look at what comes out !

5. Particle Physics Accelerators
Collisions are Fixed target or colliding beam
colliding beam uses all available energy
And accelerators:
Linacs (straight) or synchotrons (circles)
Particles are accelerated by electric fields
Bent by magnetic fields
Beams made to collide inside detectors
Can keep particles travelling round and round in circle
But lose energy, radiate photons, when travelling in a circle
CERN’s big accelerators
27 km long tunnel,100m underground
French/Swiss Border near Geneva
1989 – 2000 Large Electron Positron collider (LEP), colliding beam synchotron
2007 onwards Large Hadron Collider (LHC), proton collider

6. Fermions & Bosons
We introduced spin for electron…but general particle property
Determines particle properties
Half-integer spin particles – Fermions
Fermi-Dirac Statistics
Pauli Exclusion principle
Whole-integer spin particles – Bosons
Bose-Einstein statistics
No Exclusion principle, as many as you want in same state
Matter is made of the fundamental fermions
Forces are carried by the fundamental bosons
Standard Model is theory which contains these fundamental particles

7. Fermions: Building blocks of matter
rest mass electric charge other charges
in MeV/c2
“up” quark u /3 e colour & weak
“down” quark d /3 e colour & weak
electron e e weak
neutrino e v. small but > weak
QUARKS
LEPTONS
The first generation fermions
This is what everything around us is made of
But there are more !
Proton: uud Neutron: udd electron
Neutrino given off in Beta decay
All spin ½ particles

8. Forces of nature Forces mediated by particle exchange
Force acts on particles with that type of “charge”
e.g. electromagnetism :
photon exchange between electrically charged particles
Feynman Diagram

9. Bosons: Force Carriers
Force boson mass interaction charge relative strength range
in GeV/c2
Gravity graviton ?0? mass 
Weak W+,W-,Z /91 weak charge m
Electromagnetism Photon () 0 charge 
Strong gluon (g) 0 colour charge m
The four forces and their carriers
All particles feel gravity, graviton not discovered
All particles have weak charge feel weak force
Electric charged feel emag.
Only quarks feel strong force, confined, colour neutral
Spin 1, except graviton spin 2

10. Forces : some basic consequences
Strong
glues quarks to make protons / neutrons
Glues protons / neutrons to make nuclei
Electromagnetism
Bind electrons to nuclei
Sticks atoms together to make molecules
Gravity
Holds large lumps of matter together: stars, planets, galaxies
Weak
Radioactive decay
Cross-generational couplings….

11. Feynman Diagrams We already saw one for electron,positron annihilation
                                                                                        
We already saw one for electron,positron annihilation
Here is neutron decay
By following sets of rules, we can see if this reaction will happen
                                                         

12. Particle interactions
Some basic standard model vertices:

13. Anti-matter Each particle has an anti-particle Properties are opposite
e.g. electron / positron
Properties are opposite
Opposite charge
(and weak and colour)
same mass and spin
Electron & positron bending in magnetic field
Dirac Equation, 1930, relativistic version of Schrödinger for electrons,
but it seemed to have -ve energy electrons !
No, positive energy but anti-matter!
Anderson discovered in 1931
Some particles are their own anti-particles:
Photon, neutral pion
Dirac: “This result is too beautiful to be false; it is more important to have beauty in one's equations than to have them fit experiment.”
Bubble Chamber photo,
A very old fashioned photographic form of particle detector

14. A typical modern particle physics experiment
DELPHI LEP collider

15. E=mc2 or rather E2=(pc)2+(mc2)2
Particle and anti-particle annihilate to pure energy
m is rest mass
Add K.E. term
Basis of most modern particle physics accelerator expts
Smash highly energetic particle and anti-particle together
1st generation fermions
Bosons
Particles and their anti-particles

16. Basic Kinematics Apply what you have learnt about relativity
e.g. particle A decays into particles B & C
Work in rest frame of particle A
Reaction
momentum
Energy
Energy,momentum conservation – but energy includes rest mass
So particles go off back-to-back
and we must have enough energy to make them

17. Three generations And ONLY 3 ! LEP from number of neutrinos
Bosons: graviton, W+,W- Z0, gluon, photon
II Rabi
Muon discovered by Street & Stevenson 1937 using Wilson Cloud chamber ….
b quark was found in 1977, Fermilab
top quark MUCH heavier (40x) found in 1995, Fermilab
W/Z found at CERN 20 years ago
Still to find…
Higgs Boson
?Graviton ?
Standard Model: one extra –the Higgs boson (H), responsible for mass
No gravity
+ anti-particles. all fermions found

18. Conservation Laws Tell us which processes can happen
Short-cut for Feynman diagrams
Conserved quantities in a reaction
Same before – initial state
As after – final state
Momentum vector, p
Energy E, relativistic so due to momentum and rest mass
Baryon number B
Number of quarks remains constant
Electric Charge Q
Helpfully, most particles have charge as superscript on name
e.g. +
Lepton number, for each generation: Le,L,L

19. Fundamental Particles
Anti-particles have opposite properties
e.g. Positron e+ has
Q=+1, Le=-1
Hence, particle-antiparticle combinations have zero everything!
e.g. composite particle
made of
Baryon number is fractional, so that proton & neutron have B=1

20. Confinement Strong force very strong ! Quarks bound cannot break free
No free quarks
Lower energy to produce new particles than separate quarks
All particles observed have no net colour
Electric charge has one type +, and its opposite -
Colour charge comes in three types: red, green, blue and their opposites: anti-red,anti-green anti-blue

21. Hadrons: where quarks hide
Hadrons are the bound states of quarks we observe
Controlled by strong force, remember leptons don’t feel this
Only colourless states can be made
Coloured quark and anti- that same colour quark
This is called a Meson (integer spin, hence a boson)
Most common mesons are the pions 0 ,+ ,-
‘Mix’ three colour charges together
This is called a Baryon (½ integer spin, hence a fermion)
Most common Baryons are proton & neutron
These are the basic first generation composite states:

22. Other Hadrons These last states only contained up, down quarks
Also have strange, charm, top, bottom
Can make hadrons with these also
….hence very large number of combinations!
We will consider only the strange quark
Next lightest quark after up,down
Like a heavy version of the d quark, mass 500 MeV, Q=-1/3
Strange quark has strangeness =-1
These states are unstable decay into proton, neutron, pions
(with spin ½)
Kaon mesons are counterparts of pions with s rather than d quark
Strange Baryons
 Sigma ,  Lamda,  Xi
(with spin 0)

23. Quark Jets Don’t observe free quarks
Quarks form into composite states of two quarks (mesons) or three quarks (baryons)
in particle detectors often see showers of these particles – jets of mesons and baryons
Jet of particles seen in tracking
System of detector
Jet of mesons &
Baryons
Produced from
one initial high
Energy quark
Or anti-quark

25. Some Key Points
Forces are due to exchange of the fundamental force carrying bosons
Photon,gluon,W+,W-,Zo (and presumably graviton)
Know the fundamental particles
Three generations of quarks and leptons
Don’t observe free quarks
Confined in colourless hadrons
Added some more conservation laws
Energy, momentum, electric charge
Baryon number, lepton number
Particle interactions can be written as Feynman diagrams
Know the basic vertices, and conservation laws to see whether or not a reaction will occur.

26. Searching for a Grand Unified Theory
Electroweak theory well established in SM
Electromagnetic and weak forces are part of same theory
Unify at high energy
?? Unifies with strong force also at high energy ??
……then maybe eventually combine gravity also……

27. Particle Physics Glossary
Fermion: ½ integer spin particle
Quarks: fundamental fermions which come in six types up,down,strange,charm,top,bottom
have fractional electrical charge and colour charge
Leptons: fundamental fermions which come in six types electron, muon,tau (all with electric charge) and electron neutrino, muon neutrino, tau neutrino (all neutral)
Generations: quarks and leptons come in three generations. Each generation looks like the previous but heavier.
Boson: integer spin particle. The fundamental bosons are the force carrier particles.
Electromagnetic force: carried by photon, interacts with electrically charged particles
Strong Force: carried by gluon, interacts with colour charged particles – the quarks. Joins quarks into hadrons
Weak Force: carried by Z0,W+,W-, responsible for nuclear Beta decay
ElectroWeak Theory: Electromagnetic and Weak Forces are explained by one combined theory.
Hadron: composite particle made of quarks
Meson: type of hadron containing 2 quarks (or more precisely one quark, one anti-quark)
Pions: the most common mesons (Kaons are most common meson with s quark)
Baryon: type of hadron containing 3 quarks
Proton,neutron: the most common baryons
Anti-matter: particles have anti-matter equivalents with same mass,opposite charge these behave identically.
Standard Model: very precisely tested theory of particle physics, containing electroweak and strong forces and fundamental particles.

28. The Big Bang Evidence for the Big Bang The evolution of the universe
It is dark at night! See Olbers Paradox
Universe expanding
Cosmic microwave background
Relative abundance of elements in universe
The evolution of the universe
Stages in the formation of the universe
Big Crunch ?

29. Looking at larger scales
Man 1 m
Planet Earth 107 m
Solar System m 1 light-day
Star separation 1017 m 10 light-years
Galaxy size m 100,000 light-years
Galaxy separation 5 million light-years
in a cluster of Galaxies 50 million light-years
Large Scale Structure 1 billion light-years
Walls, voids etc.. in distribution of galaxies
Solar system seen from the outside!
Voyager 1
1977…
Picture, 1990

30. The expanding Universe
Expansion of space, not in space
Light from other galaxies is red-shifted
Doppler shift
Edwin Hubble (1929)
Whole universe is uniformly expanding
There is no centre to the universe
Hubble’s law:
H ~ 20 km/s/million light yrs
v = H x d,
Velocity Hubble const distance

31. Age of Universe Extrapolate back with Hubble’s law
Hence universe came into existence with very high density, expanded out from there
Particle and Nuclear physics determined the early stages of evolution of the universe

32. Olber’s “Paradox”: Why is the sky dark at night ?
If the observable universe is
Static (eternal)
Infinite
Approximately uniformly filled with stars
Then sky should be as bright as the surface of a star
A faraway star looks dimmer, but there are more stars further away!
Brightness falls off as 1/r2
But area at distance r in some angular region, rises as r2
Hence, these cancel and sky should be equally bright as sun.
(e.g. Snowy mountains on a sunny day, equally bright in all directions irrespective of distance)

33. Resolving Olbers “Paradox”
The universe is not infinitely old
Approx 15 billion years
The speed of light is finite
We can only see part of the universe
Sky is dark at night because
Universe is young – distant light hasn’t reached us yet
and also
Expansion causes doppler shift (red-shift) of light
So,Big Bang solves Paradox

34. Stages in the evolution of the Universe
Planck Era
GUT Era
Electroweak Era
Particle Era
Era of Nucleosynthesis
Era of Nuclei
Era of Atoms
Era of Galaxies – Now!
Book:
“The first three minutes”, by Steven Weinberg

35. (1) Planck Era: up to 10-43 seconds
Mysterious !
Universe begins at very high temperature
Maybe gravity unified with the other forces ?
General Relativity and Quantum mechanics have never been successfully combined.
We need a theory of Quantum Gravity
Characteristic Planck Time and Planck Length
Highly Speculative theories include
M-theory particles are excitations on high dimensional membranes. This has taken over from(and includes) String Theory, where particles are different vibrations of one type of string.
open string
closed string

36. (2) The GUT Era: up to 10-35 seconds
We still don’t know a great deal but have some better ideas !
Universe full of fundamental particles, antiparticles, photons, gluons…everything!
No composite particles
Maybe the electroweak and strong forces (separate in Standard Model) become united ? (GUT)
Particle physics experiments give some support for converging coupling constants
Inflation: a short period of rapid expansion in the universe.
Universe starts as a rapidly expanding quantum bubble
Analysis of cosmic background radiation of universe gives some support for this model

37. (3) The Electroweak Era: up to 10-10 seconds
Universe cooling, but still very hot, 1028K
Again, no composite particles yet.
Three forces in the universe
Gravity
Strong
Electroweak
Electromagnetism and weak force are unified in Electroweak
W+,W-,Z are massless, like the photons and gluons

38. (4) The Particle Era: up to 10-3 seconds
Temperature now dropped to ~1012K
Contains almost equal amount of particles and anti-particles
And photons, gluons…
Electroweak Force splits into Electromagnetism and Weak Interaction.
W+,W-,Z become heavy, get the Higgs boson (not found yet)
As we cool further…
Confinement starts:
Quarks, anti-quarks,gluons combine to form protons and neutrons
Antimatter disappears
Matter/anti-matter cancel out.
Small excess of matter ? Why ?
Particle physics experiments are investigating

39. (5) Era of Nucleosythensis: 0.001seconds to 3 minutes
Temperature 1012 to 109 K
The first composite particles, the protons and neutrons combine to form light nuclei:
At the End:
75% (by mass) Hydrogen nuclei p,pn,pnn
25% (by mass) Helium nuclei ppn,ppnn
~0% Lithium
Nuclei only, energy too high to bind electrons into atoms
The other nuclei come from Stars much later
75/25 % as measured, good evidence for big bang
No stable nuclei with 5 particles, so very few nuclei above He formed

40. (6) The Era of Nuclei: 3 minutes to 300,000 years
Universe is as hot as centre of sun (107K)
Plasma of light nuclei and electrons and photons

41. (7) Era of Atoms: 300,000 to 1 billion years
Universe cools so atoms can be formed (3000K)
Electrons captured by nuclei
Universe is transparent – photons can fly around freely !
No longer electrons that interact with them
This is how the microwave background was created
Most impressive evidence for big bang
Universe was once very hot!

42. Cosmic Microwave Background
Photons from when atoms formed
Universe continued to expand and cool
Expect remnant radiation with 2.7K blackbody spectrum with isotropic spectrum
Discovered Penzias,Wilson 1965
BUT not completely uniform at 10-5 K scale
COBE was first to see anisotropy, small fluctuations in temperature.
Latest results WMAP Feb. 2003
COBE satellite, 1990
Compatible with inflation model

43. (8) Era of Galaxies: 1 billion to 15 billion years (NOW)
Gravity plays its role
Neutral H and He gas attracted
Small density variations are amplified
Form gas clouds
….And eventually stars
Thermonuclear reactions in stars form heavier atoms
Helium nuclei fusion
e.g. 12C is lower energy state than 3 x 4He
Get nuclei up to Iron
Iron is most stable nuclei (binding energy per nuclei)
Higher nuclei require additional energy input
Provided in supernova explosions
So, earth is supernova debris
(but measurements on galaxy rotation show particle physics does not give enough matter! Dark matter ?)

44. The Future of the Universe ?
Gravity fights the acceleration of the universe
Expansion of universe could slow,stop, and then contract.
Big Crunch?
Amount of visible matter is not enough
But strong evidence for additional dark matter
But still not enough!
Could expand forever, but expansion slower and slower…
And if there is a cosmological constant…
An extra term that can give dark energy with negative pressure
Expansion of universe may be accelerating!

45. “I’d like to thank the Swedish Academy”: five ways you can win a Nobel prize!
Why is there more matter than anti-matter in the universe ?
Find the Higgs Boson.
Is there a Cosmological constant ?
What is dark matter ?
Develop a Theory Of Everything !