1

The Future of Particle Physics

The Future of Particle Physics

S F King Southampton, March 22, 2004

S F King Southampton, March 22, 2004

universe.exe

2

3

4

5

Our Universe is filled with photons from the time of atom formation (380,000 yrs). They were produced during the BIG BANG.Their temperature distribution gives information about the age and composition of the universe.

Cosmic microwave background

MicrowaveAnisotropyProbe

6

Relic radiation from the big bang fireball began its journey as visible light 13 billion years ago. During its long journey the Universe has expanded and its wavelength has been stretched to microwave wavelengths of a few cm. Picture above shows hot and cold fluctuations which seeded clusters of galaxies. The sound you hear is the (frequency shifted) “sound of the big bang” during the first 700,000 years, based on BOOMERANG data.

Temperature Maps

Earth

Universe

7

1

…means the Universe is flat

8

The Energy Budget of the Universe

9

10

What have we learned from High Energy Physics? - Matter is made of particles (“particle physics”)

Answer: only 84 times! A single atom

nanometre

A nucleus with orbiting electrons

To understand this, take an apple and a knife, and cut the apple in half once. Then cut one half in half again. Then continue the process. After some number of cuts you will arrive at a single atom.

Question: how many cuts are required?

11

-

The electrical attraction is caused by photon exchange

12

It is made of protons (p) and neutrons (n)

The nucleus of the atom is positively charged

The protons and neutrons are made of charged quarks

The quarks also carry a new “colour charge”

The quarks are stuck together by gluons

13

I think I finally understand atoms

14

This decay process is very weak (15 minutes is an eternity!) Without such weak interactions the Sun would shut down!

The (free) neutron is radioactive and decays after 15 minutes into proton, electron and “neutrino” (electron-like neutral particle)

Nothing lasts for everNothing lasts for ever

15

Neutrinos from the SunNeutrinos from the Sun

Question: How many neutrinos from the Sun are passing through your fingernail in one second?

Answer: 40 billion! – day and night since neutrinos can pass right through the Earth without interacting

Photo of Sun taken underground using neutrinos

16

W particles – the left-handed alchemistsW particles – the left-handed alchemists

WW

Electroweak theory predicted a heavy version of the photon called the which was discovered in 19830Z

W WThe quarks and leptons can only see W particles if they spin to the left!

This shatters mirror symmetry!

Just like rifle bullets, quarks and leptons spin as they whizz along

17

The four forces of Nature The four forces of Nature

18

Quarks and Leptons Quarks and Leptons

19

20

What is the origin of the particle masses?What is the origin of the particle masses?

t

bc

s

ude

e

Mass

21

The Higgs BosonThe Higgs Boson

What is the Higgs boson? In 1993, the then UK Science Minister, William Waldegrave, issued a challenge to physicists to answer the questions 'What is the Higgs boson, and why do we want to find it?' on one side of a single sheet of paper. This cartoon is based on David Millar’s winning entry.

In the “Standard Model” the origin of mass is addressed using a mechanism named after the British physicist Peter Higgs. This predicts a new particle: the Higgs boson.

22

2E mc

With such high energy it is hoped to produce the Higgs boson via .

p p

H

1 TeV

The CERN Large Hadron Collider (LHC) will collide protons on protons at energy of 14 trillion electron Volts (14 TeV)

23

The CERN Large Hadron Collider c.2007

Atlas

particle_event_full_ns.mov

24

Isn’t all this too expen$ive?

The practical benefits of Particle Physics - discovery of electrons gave us electronics - discovery of positron gave us positron emission tomography - discovery of the Internet at a particle physics lab CERN

The intellectual benefits of Particle Physics - the greatest adventure of all is the voyage of scientific discovery - like building a cathedral over generations - same reason as Chinese went into space - “(doing particle physics) will do nothing to defend our country except to make our country worth defending” Robert Wilson

25

26

e

.

.

Neutrino Oscillations Neutrino Oscillations

(only possible if neutrinos have mass) (only possible if neutrinos have mass)

27

Atmospheric oscillations have been seen

28

Solar oscillations have also been seen e

29

Neutrino MassNeutrino Mass

The discovery of neutrino oscillations and hence mass is the greatest discovery in particle physics in the past 20 years (since W and Z)

In the Standard Model the neutrinos spin only to the left and so travel straight through the Higgs field without acquiring mass

So neutrino mass implies new physics beyond the Standard Model!

30

2. Neutrinos mix strongly with one another

1

10,000,000 e

m

m1. Neutrinos must have a very small mass

The single right-handed neutrino then couples equally to and causing them to have one small mass, and mix strongly

R R

SFK 98-

These two facts can be explained by introducing one new heavy neutrino into the Standard Model which spins to the right (plus some other less important right-handed neutrinos).

A theoretical interpretationA theoretical interpretation

31

Thanks to David King

This is based on the see-saw mechanismThis is based on the see-saw mechanism

32

This is based on the see-saw mechanismThis is based on the see-saw mechanism

Thanks to David King

33

What about Super- symmetry?

34

Quote from Ed Witten in preface of Gordon Kane’s book “Supersymmetry”Quote from Ed Witten in preface of Gordon Kane’s book “Supersymmetry”

“Supersymmetry, if it holds in nature, is part of the quantum structure of space and time… Discovery of supersymmetry would be one of the real milestones in physics… Indeed, supersymmetry is one of the basic requirements of string theory… Discovery of supersymmetry would surely give string theory an enormous boost… The search for supersymmetry is one of the great dramas in present day physics.”

35

What is Supersymmetry ?

There are two types of particles in nature: fermions and bosons.

Fermions have half units of spin, and tend to shy away from each other, like people who always stay in single rooms at the fermion motel.

Bosons have zero or integer units of spin, and like to be with each other, like people who stay in shared dormitories at the boson inn.

Supersymmetry says that for every fermion in Nature there must be a boson and vice-versa. Supersymmetric particles have not been observed (yet) so they must be heavier - SUSY must be broken by some mechanism

36

u

ebd

tc

e

Lep

tons

Qua

rks

The Generations of Matter

s

SPIN ½ FERMIONS

u

ebdtc

e

Sle

pton

sS

quar

ks The Generations of Smatter

s

SPIN 0 BOSONS

37

BOSONS

Gravitino0W W Z Photino GluinoFERMIONS

38

What about the Higgs Boson?

Higgs Boson

A further non-interacting “singlet” Higgs and Higgsino can even explain the origin of Higgs mass itself (Elliott, SFK, White 93-95)

Higgsino

Higgs Boson Higgsino

39

40

What has SUSY ever done for us?What has SUSY ever done for us?

The Standard Model requires fine-tuning to one part in a trillion trillion to work! - it is rather like fine-tuning the knobs on an old fashioned radio

The SUSY Standard Model acts like a Digital radio that eliminates nearly all the fine-tuning – however a few % tuning remains (SFK, Kane 98)

41

So what else has SUSY ever done for us?So what else has SUSY ever done for us?

SUSY provides an excellent candidate for dark matter: the spin ½ partner to the photon which is the lightest SUSY particle and is cosmologically stable called the photino!

42

But what else has SUSY ever done for us?But what else has SUSY ever done for us?

SUSY provides the basis for cosmological theories in which the Universe naturally inflates to its present size, and explain how the microwave background radiation appears isotropic

For example a SUSY version of the Standard Model with extra Higgs singlets has been constructed that explains inflation, large scale structure, the origin of Higgs mass, and the origin of right-handed neutrino mass (Bastero-Gi,SFK, Di Clemente)

43

Strong

Weak

Electromagnetic

OK, but what else has SUSY ever done for us?OK, but what else has SUSY ever done for us?

44

b

t

cs

ud

ee

The pattern of quark and lepton masses is explained by assigning each SUSY generation a new charge (SFK, G.Ross 01,03)

45

string1.avi

Strings live in 11 dimensions

46

47

Why wouldn’t we notice extra dimensions?

48

Brane New Worlds

49

Top-down or bottom-up?

Both! – nutcracker approachEnergy

1 trillion Volts

1 trillion trillion Volts

50

Neutrino Physics

SUSY

Cosmology

The Future of Particle Physics:

Strings