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The Future of Particle PhysicsThe Future of Particle Physics

Steve King, University of Southampton, Masterclass, 24th March, 2009

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The Milky Way Spiral Galaxy You are here

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The Milky Way Local Group: satellites

You are here

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The Milky Way Local Group: including Andromeda galaxy

N.B. Large galaxies separated by about 1,000,000 pc = 1 Mpc

You are here

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The Virgo Supercluster: containing Virgo Cluster and our Local Group

Each dot is a bright galaxy. Milky Way is dot in the exact centre.

You are here

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Our Neighbouring Superclusters: Virgo Supercluster at the centre

Note the presence of filaments and voids in an irregular cellular pattern.

50Mpc

You are here

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On the largest distance scales the Universe appears smooth, with no further structures

You are here

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To understand the origin of the Universe we need to understand high energy particle physics

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1. The resolving power of a microscope is limited by the wavelength of the light.

L

Why “High Energy”? There are three reasons:

e.g. bats use high frequency sonar with wavelength less than or about same the size of an insect.

LL

So, like bats, to see small things we need light with small wavelength and high frequency – hence high energy photons since E hf

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2E mc 2. Einstein taught us that

So high energy is equivalent to large mass. With high energies we are able to produce very heavy particles.

The basic unit of energy is the “electron Volt” which is the energy that a single electron receives when it passes from the negative terminal to the positive terminal of a 1 Volt battery.

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3. Boltzmann taught us that so high energy means high temperature where is Boltzmann’s constant. In the early Universe, just after the big bang, the universe was very small and very hot. So high energy physics teaches us about the early Universe.

E kTkT

E

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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?

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-

The electrical attraction is caused by photon exchange

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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

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I think I finally understand atoms

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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

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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

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Neutrino Oscillations Neutrino Oscillations

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

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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

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The four forces of Nature The four forces of Nature

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Quarks and Leptons Quarks and Leptons

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

t

bc

s

ude

e

Mass

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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.

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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)

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The CERN Large Hadron Collider c.2007

Atlas

particle_event_full_ns.mov

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2008 Run…

But 200 nOhm of resistance set in between two magnets… an arc… punctured the He containers…

Safety issues… so start up September 2009 with running upgrades…probably 10 TeV but running over Winter…

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What about Super- symmetry?

What will the LHC discover?

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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

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u

ebd

tc

e

Lep

tons

Qua

rks

The Generations of Matter

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SPIN ½ FERMIONS

u

ebdtc

e

Sle

pton

sS

quar

ks The Generations of Smatter

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SPIN 0 BOSONS

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BOSONS

Gravitino0W W Z Photino GluinoFERMIONS

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What about the Higgs Boson?

Higgs Boson Higgsino

Higgs Boson Higgsino

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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

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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!

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Strong

Weak

Electromagnetic

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

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string1.avi

Strings live in 11 dimensions

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Why wouldn’t we notice extra dimensions?

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Top-down or bottom-up?

Both! – nutcracker approachEnergy

1 trillion Volts

1 trillion trillion Volts

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Neutrino Physics

SUSY

Cosmology

The Future of Particle Physics?:

Strings