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http://www.adams-institute.ac.uk [email protected]
Particle Physics and
the structure of Space, Time and Matter
Tuesday 20th MarchProf. Ken Peach
University of Oxford &
Royal Holloway University of London
Ken Peach John Adams Institute 20 March 2007 2
What is ‘Particle Physics’?
• The Particle Physics (or ‘High Energy Physics’) ‘Mission’ – identify the fundamental constituents of matter– describe the interactions (forces) between them
• A long and honourable history– Constituents
• ‘Earth, Fire, Air and Water’ of the Greeks• ‘Atoms’ of Democretus and Lucretius
– Forces• Gravity (Newton)• Electricity (Coulomb)
• A significant achievement of the 20th century– The electron (JJ Thomson, 1897)– The top quark (CDF & D0, 1995)– QED, QCD, electro-weak (gravity)
Ken Peach John Adams Institute 20 March 2007 3
Probing Inner Space
• 3 basic ways
Look at it Heat it Smash it
Wavelength Temperature T Energy E
hc/ = kT E=
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Remarkable comment
All three the same fundamental physics!
Uses ‘light’ Uses ‘heat’ T Uses ‘probe’ E
hc/ = kT E=
Photons Photons ‘Photons’
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Scattered electronScattered lepton
Constituents
Particle Hammers
proton
electron
{Proton fragments
Scattered ‘parton’
PhotonPhoton, W, Z
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HiggsHiggsBosonBosonHiggsHiggsBoson?Boson?
For
ceF
o rce
Car
rier
sC
arr i
ers
ZZ boson
WW boson
photon
ggluon
Generations of Generations of matter matter
tau
-neutrino
bbottom
ttop
III III
muon
-neutrino
sstrange
ccharm
II II
eelectron
ee-neutrino
ddown
upu
I I
Lep
tons
L
epto
ns
Qua
rks
Qua
rks
Particles and their Interactions
Each with its own
‘antiparticle’
© Brian Foster
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The Particle Physicist’s “Periodic Table”
u
ud
d
du
Proton Neutron
The Chemist’s Periodic Table
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The Standard Model
The ParametersThe Parameters• 6 quark masses
– mu , mc, mt
– md, ms, mb
• 3 lepton masses– me, m, m
• 2 vector boson masses– Mw, MZ
• (m, mg=0)
• 1 Higgs mass– Mh
• 3 coupling constants– GF, , s
• 3 quark mixing angles– 12, 23, 13
• 1 quark phase–
Neutrino masses set to 0!
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What still remains to be done?
• The origin of mass– “Hunting the Higgs”
• The origin of the forces– Strong, electro-weak & gravity, or just one fundamental force
• The origin of “Dark Matter” (& Dark Energy)– Accounting for most of the mass of the universe
• The origin of cosmological matter-antimatter asymmetry– Why does the universe today consist only of matter, not equal
amounts of matter and antimatter
Fundamental questions in particle physics that are equally fundamental questions in cosmology
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How do we know all this?
© CERN
Matter & antimatter annihilate into energy
• Go to the highest energy• See what happens
Energy (MeV)
0.000001
0.1
100,000
10,000
1,000
100
10
1
e
u,d
s
cb
W Zt
leptonsquarksWeak Bosons
Higgs?
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More (complicated) events
Z+- Zqqg
Z4 ‘jets’
e+e-
W+W-
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The problem of mass
• The Standard Model relies on– Relativity+ Quantum mechanics
• Relativistic Quantum Field Theory– Each particle has an associated all-pervasive ‘field’ (x,t)
– Symmetry• There is no ‘special place’ in the Universe• There are no ‘preferred directions’ in space-time• There is ‘local autonomy’ for the particle fields
– Produces a beautiful theory– … with all particles massless!
• Adding mass violates the beautiful symmetries
• The Higgs Mechanism– Fill space-time with another (Higgs) field (x,t)
• A new type of force with special properties– … that give mass to the particles
…and leaves a signature behind …– the Higgs Boson!
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… but look what we have done to ‘empty space’
• It is filled with these ‘fields’
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Origin of Mass ?
m=0, v = speed of light
No Higgs field
00
00H
H
H
H
V < c, m > 0
With Higgs field
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The biggest challenge
… the Creation of the Universe!
TheBig
Bang
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Galaxy formation
The state of the Universe
10-15 10-12 10-9 10-6 10-3 1 103 106 109 1012 1015 1018
Time (sec)
1
104
108
1012
1016
1020
Temperature (oK)
The Big Bang
Biology
Solar System forms
Atoms form
Chemistry begins
To
day
3 x 1018s
3oK
Neutron lifetimenucleosynthesis
Protons, neutrons & nuclei form
W & Z
production
Particle
physics
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Particle Physics and Cosmology
The Higgs potential …
Primordial ripples
Fundamental mode
Geometry
Potential wells
m
compression
baryons
Rarefaction… etc
WMAP Data, Verde, LP03
the particle spectrum …
and the unknown …
Illustrations from Muryama, LP03
should explain
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What is the Vacuum?
Dictionary Definitions:
An entirely (or very nearly) empty spaceChambers 20th Century
1. Emptiness of space; space unoccupied by matter
2. (a) A space entirely empty of matter
(b) A space empty of air, esp. one from which the air has been artificially withdrawn
3. An empty space; a portion of space (left) unoccupied or unfilled with the usual or natural contents
OED
My definition:
That which remains when everything else is taken away
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New physics scale
Note: The vacuum ‘knows’ about particles already found
… and all of the particles still to be found!
30
60
50
40
20
10
0
i-1
Log 10 [Energy Scale (GeV)]3 5 7 9 11 13 15 17
No Grand Unification
Unification !
“e/m”
“weak”
“strong”
Supersymmetry?
Evolution of the strength of the interactions with increasing energy
3-1
2-1
1-1
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The Cosmic Recipe
1. The Hubble Constant [H0]
• expansion rate of the Universe (~7.510-9y-1)• The Age of the Universe [t0] (12-18 109y)
2. The Temperature [ T0]
• temperature of the cosmic microwave background today (~2.7oK)
3. The Critical Density [c]
• just prevents eventual collapse (3H02/8GN~10-29g/cc)
• The actual density relative to c[] (0.751.25)
4. The relative energy density of free space []
• [aka the Cosmological Constant] (0.60.8)
____________… two related numbers________________
a) The relative total matter density [m]• [all forms of gravitational matter] (0.150.45)
b) The relative visible matter density [B]• [normal ‘baryonic’ matter] (0.0050.012)
____________… and two more numbers______________
I. The ratio of the electron to proton mass [me/mp] (1/1896)
II. The fine structure constant [] (1/137)
___________________… and …_____________________
• The number of dimensions of space-time [d] (=3+1)
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Dark Matter
Prof. Richard Pogge
Huge structures in ‘Empty Space’Rotation Curves for Galaxies
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The Cosmological Budget -
• From the ‘flatness’ of space
1• From the observed galaxies & nucleosynthesis
B 0.01
• From rotation curves of galaxies & large scale structure
Matter 0.34• Rate of expansion
Space 0.65
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… but …
• The matter-antimatter asymmetry in particle physics so far discovered is too small (by 10 orders of magnitude)– although physics beyond the Standard Model has more
sources of matter-antimatter asymmetry
• … but the vacuum knows that there should be such an asymmetry!– Without this, matter, galaxies, the Sun, the Earth cannot
be• And neither can we!
The Big Bang
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The vacuum …
1. ‘knows’ about all particles that exist… and that can exist
2. ‘knows’ about all forces that exist… and that can exist
3. has more energy (x 10) than all normal matter in the universe
… we are cosmologically less significant than ‘empty space’
4. created the Universe … as we know it today
5. made more matter than antimatter… and so created the conditions that allow us to exist!
Remember
The vacuum is the most complicated thing in the Universe
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Summary
• We have a wonderful “model” to describe the particle world– but it is not a theory
• it describes but does not explain
– and has “missing links”• What about gravity?• Why 3 forces?• Why 3 generations?• How does the matter-antimatter asymmetry
arise?• Why 3 space and 1 time dimension?• Are there more dimensions?• …
• (fortunately) still a lot to learn!