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The Future of Particle Physics. S F King Southampton, March 22, 2004. universe.exe. Cosmic microwave background. Our Universe is filled with photons from the time of atom formation (380,000 yrs). They were produced during the BIG BANG.

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slide1

The Future of Particle Physics

S F King

Southampton, March 22, 2004

universe.exe

slide5

Cosmic microwave background

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.

Microwave

Anisotropy

Probe

slide6

Temperature Maps

Earth

Universe

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.

slide10

Answer: only 84 times!

A single atom

A nucleus with orbiting electrons

nanometre

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

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?

slide11

Matter

Antimatter

Matter

The electrical attraction is caused by photon exchange

-

slide12

The quarks are stuck together by gluons

The nucleus of the atom is positively charged

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

The protons and neutrons are made of charged quarks

The quarks also carry a new “colour charge”

slide14

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

Nothing lasts for ever

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

slide15

Photo of Sun taken underground using neutrinos

Neutrinos 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

slide16

Electroweak theory predicted a heavy version of the photon called the which was discovered in 1983

W particles – the left-handed alchemists

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

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

This shatters mirror symmetry!

slide20

Mass

t

u

d

c

e

s

b

What is the origin of the particle masses?

slide21

The Higgs Boson

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

slide22

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

1 TeV

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

slide23

The CERN Large Hadron Collider c.2007

Atlas

particle_event_full_ns.mov

slide24

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

slide26

.

.

Neutrino Oscillations

(only possible if neutrinos have mass)

slide29

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

Neutrino 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)

So neutrino mass implies new physics beyond the Standard Model!

slide30

1. 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

SFK 98-

A theoretical interpretation

2. Neutrinos mix strongly with one another

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).

slide34

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.”

slide35

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

What is Supersymmetry ?

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

slide36

SPIN ½ FERMIONS

SPIN 0 BOSONS

Squarks

Quarks

Sleptons

SUSY

Leptons

The Generations of Smatter

The Generations of Matter

slide37

BOSONS

SUSY

Photino

FERMIONS

Gluino

Gravitino

slide38

Higgs Boson

Higgs Boson

Higgsino

Higgsino

SUSY

SUSY

SUSY

What about the Higgs Boson?

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

slide40

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

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

What has SUSY ever done for us?

slide41

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!

slide42

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)

slide43

Standard Model

SUSY

Strong

Weak

Electromagnetic

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

slide44

t

u

c

d

b

s

GUT

e

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

colour

slide45

string1.avi

Strings live in 11 dimensions

slide49

Both! – nutcracker approach

Top-down or bottom-up?

Energy

1 trillion trillion Volts

1 trillion Volts

slide50

The Next Standard Model

The Future of Particle Physics:

Neutrino Physics

SUSY

Cosmology

Strings