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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)


Probing Inner Space

• 3 basic ways

Look at it Heat it Smash it

Wavelength Temperature T Energy E

hc/ = kT E=


Remarkable comment

All three the same fundamental physics!

Uses ‘light’ Uses ‘heat’ T Uses ‘probe’ E

hc/ = kT E=

Photons Photons ‘Photons’


Scattered electronScattered lepton

Constituents

Particle Hammers

proton

electron

{Proton fragments

Scattered ‘parton’

PhotonPhoton, W, Z


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


The Particle Physicist’s “Periodic Table”

u

ud

d

du

Proton Neutron

The Chemist’s Periodic Table


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!


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


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?


CERN from Space


Arial view of the CERN site

© CERN


… and what is beneath the surface

© CERN


ALEPHA detector for LEP Physics

© CERN & PPARC


Some events

Ze+e- Z+-

Z+ -Zqq


More (complicated) events

Z+- Zqqg

Z4 ‘jets’

e+e-

W+W-


The Large Hadron Collider

ATLAS

CMS


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!


… but look what we have done to ‘empty space’

• It is filled with these ‘fields’


Origin of Mass ?

m=0, v = speed of light

No Higgs field

00

00H

H

H

H

V < c, m > 0

With Higgs field


From microscopes to telescopes …


The biggest challenge

… the Creation of the Universe!

TheBig

Bang


From the Big Bang to today

© CERN


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


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


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


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


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)


Dark Matter

Prof. Richard Pogge

Huge structures in ‘Empty Space’Rotation Curves for Galaxies


Dark Energy – more properties of the vacuum


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


… 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


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


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!

Documents

[email protected] Particle Physics and the structure of Space, Time and Matter Tuesday 20 th March Prof