recreating the big bang with the large hadron collider at cern dr david evans the university of...

Recreating the Big Bang with the Large Hadron

Collider at CERN

Dr David EvansThe University of Birmingham

24th February 2009

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Somewhere in Switzerland…

Situated on the Swiss-French border, near GenevaIs the World’s largest physics laboratory

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CERN

Deep underground, we have built the World’s largest machine

Geneva

French Alps

Which will accelerate sub-atomic particles to 0.999999991 the speed of light ….

The Large Hadron Collider (LHC)

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Large Hadron Collider

…. and collide them together in four cathedral-sized caverns around the 27 km ring.

Creating sub-atomic explosions, and conditions that existed less than a billionth of a second after the Big Bang.

In 4 massive particle detectorsUp to 600 million times per second

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The LHC

Let’s start at the beginning…..

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Building Blocks of Matter

All matter around us is made of atoms. Atoms consist of a positive nucleus (containing 99.98% of the atom’s mass) and a cloud of electrons.

Nuclei consist of protons and neutrons. The protons and neutrons are made of three quarks.

in metresWe know

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Elementary Particles

Protons and neutrons are made from two types of quarks: Up (u) and Down (d).

u-quarks have electric charge +2/3 while d-quarks have charge –1/3 (electron has electric charge -1 in these units).

U+2/3

U+2/3

d-1/3

Proton

U+2/3

d-1/3

d-1/3

Neutron

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Family of Particles

So, there is a family of particles:

Up quark (u) Down quark (d) Electron (e-) Electron neutrino (e)

Mass ~ 0.003 ~ 0.006 = 0.0005 < 10-8 ?(relative to the mass of a single proton)

Everything around us (the whole Periodic Table) is made up of these four particles.

So, that’s nice and simple then!

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BUT….le

pto

ns

qu

ark

s up

down

e

e

strange

charm

bottom

top

Nature supplies us with two extra families that are very much heavier:

We don’t know why!

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Virtual Particles

The forces between fundamental particles are mediated by virtual carrier particles.

For example, the electromagnetic interaction between two charged particles (say two electrons) is understood to be due to the exchange of virtual photons.

A virtual particle is one that violates conservation of energy, but only for a short period of time (t < ħ/E) – it ‘borrows’ energy from the vacuum.

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The Forces

Force Range Mediator Rel. StrengthGravitational long graviton (massless) ?? 1Electromagnetic long photon (massless) 1035

Weak short W, Z bosons (heavy) 1033

Strong short gluons (massless) 1038

Gravity – stars, planets etc.Electromagnetic – atoms, electricity etc.

Weak force

Strong – binds quarks (residual force binds nucleons in nuclei)

Weak – beta decay, how stars generate energy

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The Standard Model

u

d s

c

b

t

e

e

quarks

leptons

}

}

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The Weak Force

u

d s

c

b

t

e

e

quarks

leptons

}

}W+

W-

Z0

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The Electromagnetic Force

u

d s

c

b

t

e

e

quarks

leptons

}

}

Photon

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The Strong Force

u

d s

c

b

t

e

e

quarks

leptons

}

}g

gluon

Gravity too weak to even consider at the atomic scale

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Antimatter

Every fundamental particle has its antiparticle. These have the same mass but opposite charge.

e- e+

u+2/3 u-2/3

electron positron

up quark up anti-quark

Etc.

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Antimatter

• If a particle and antiparticle each of mass, m collide they annihilate with the production of energy, E in the form of radiation – the total mass (2m) is converted into energy).– E = 2mc2 (using the famous equation: E = mc2)

u+2/3 u-2/3

• The opposite is also true; given enough energy, one can create matter with equal amounts of antimatter.

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Big Bang

• So far, our experiments show that equal amounts of matter and anti-matter are produced when energy is converted into matter – for every up quark created, an up anti-quark is also created etc.

• So, equal amounts of matter and anti-matter should have been created during the Big Bang.• But we live in a universe made from matter. •Where did all the anti-matter go?

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Other Questions – What is Mass?

In the mid 1960s, British physicist Peter Higgs came up with a theory on why some particles have mass.

He proposed a new heavy particle, now called the Higgs, which generates a Higgs field.

Particles who ‘feel’ this field gain mass. Light particle don’t feel this field strongly, heavy particles do.

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Higgs

• The heavier it is, the more force is needed to accelerate it.• The Higgs field makes it more difficult for particles to be accelerated thus giving them mass.• It’s a bit like walking through treacle!

Just one problem with the theory …We haven’t seen the Higgs yet.

Demonstration

• Mass is really a measure of how difficult it is to accelerate an object (F=ma).

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Dark Matter

The visible Universe (made from u, d, e, ) only accounts for about 4% of its measured mass.

What makes up the rest?

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Many More Questions …

What is mass?

4 forces?

12 matter particles?

What about gravity?

Where did all the

antimatte

r go?

Mini black holes?

How many dimensions?

What about the other 96% of the universe …..

Why no free quarks?

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How do we try to Answer these Questions?

• By colliding particles at fantastic energies and studying what comes out.

• At the LHC, the quarks (in protons) will collide with energies that existed ~ billionth of a second after the Big Bang.

Physicists at the University of Birmingham play leading roles in 2 of the 4 main LHC experiments: ALICE and ATLAS.

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Particle Accelerators

• Basic design is just like a TV– i.e. RF cavities apply accelerating

voltage– Bending magnets (dipoles) steer

the particles– Quadrupole magnets focus the

beams• A charged particle (q Coulombs)

dropping through a potential, V Volts acquires energy E=qV (1 Volt gives energy of 1eV).

• Unlike a TV (V ~ 10,000 Volts) the LHC at CERN will accelerate particles to 14 Trillion Volts.

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LHC Tunnel

Now, being commissioned

Now, being repaired!

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LHC - Facts

• 27 km circumference • Each proton goes around the 27km ring over

11,000 times a second.• Energy of proton beam in LHC > 0.3 GJ

(family car travelling at 1000 mph)• Energy stored in magnets > 1 GJ• Super-conducting magnets cooled to ~ 1.9 K

(colder than Outer Space).

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Why so Cold?

At LHC energies, we need huge magnetic fields to accelerate and steer the beams of particles – about 10,000 times that of a strong bar magnet.Not possible with conventional magnets.Need superconducting magnets.

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Back to Anti-Matter

Can you make a bomb with anti-matter?In theory, yes – ½ gram of anti-matter would produce about the same energy as the Hiroshima bomb.

The LHC will produce about 100 million anti-protons per second. Sounds a lot but 1 anti-proton only has a mass of 1.67x10-27 kg (same mass as proton). So, will take the LHC about 2 thousand million years to collect ½ gram of anti-matter. We would need to be VERY patient!

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Detecting Particles

Used Bubble Chambers in the old days

•Only 1 event / second•Photos scanned by hand•No selection on events

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Modern Detectors

ATLAS Detector(one of the four main LHC detectors)

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What Am I Working On?

It’s not all drinking coffee outside the CERN canteen!

Or standing around…Waiting for the LHC.

I’m working on understanding the Strong Force. how does it generate 98% of the mass of nuclear matter? why are there no free quarks? Etc.

And trying to unlock the secrets of the primordial state of matter, the Quark-Gluon Plasma, which would have existed up until about 10 millionths of a second after the Big Bang.

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The Quark-Gluon Plasma

Normal hadronic matter

At extreme temperatures and/or densities hadronic matter ‘melts’ into a plasma of free quarks and gluons.

This new state of matter would have existed up to about 10 millionth of a second after the Big Bang, and could be created in the core of collapsing neutron stars.

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How to Make a QGP

• Need very high energy densities

• Create sub-atomic volumes of hot, dense matter similar to conditions 10-6s after Big Bang

• Fireball must live long enough for phase transition to take place

• Collide lead ions (lead nuclei) at highest energies

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The Fireball

• Temperature of our fireball ~ 1013K i.e. > 1,000,000 times the temp of centre of Sun.

• Density ~ Great Pyramids crushed to the size of a pin-head – similar to neutron star densities (but much hotter!)

T ~ 15,000,000 K

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What Happens ?

• Energy is converted into many quarks, anti-quarks and gluons.

• QGP lasts for about 10-22 seconds

• Then thousands of particles are produced

We have to study the QGP from this!

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The ALICE Detector

ITSLow pt trackingVertexing

ITSLow pt trackingVertexing

TPCTracking, dEdxTPCTracking, dEdx

TRDElectron IDTRDElectron ID

TOFPIDTOFPID

HMPIDPID (RICH) @ high pt

HMPIDPID (RICH) @ high pt

PHOS,0 PHOS,0

MUON -pairs MUON -pairs

PMD multiplicityPMD multiplicity

52 feet (16 metres) high, 85 feet (26 metres) long, and weighs about 10,000 tons

ALICE in December 07 – photo by Simon Hadley, Birmingham Post

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Data & Computing Challenges

• Write data to tape ~ 1.2 Gbytes/sec (2 CDs/sec)

• Equivalent to writing the Encyclopaedia Britannica every two seconds

• ~ 2 Pbytes / year (3.3 million CDs worth – that’s a stack of CDs 3 miles high - >12 miles high for all LHC experiments)

• Computing requirements: ~ 50,000 PCs (3 GHz) x 3.3 million

Concorde(15 Km)

Balloon(30 Km)

CD stack with1 year LHC data!(~ 20 Km)

Mt. Blanc(4.8 Km)

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Summary

Particle physics has discovered much about how the Universe works

Still many outstanding questionsThe World’s largest machine (LHC) will add to

this knowledgeHuge challenges aheadBut LHC will find new & exciting physicsWe will learn more about the very early UniverseBirmingham will play an important role in this.Thank you for listening.

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Particle Physics Spin-offs

Medical Imaging Education

TechnologyComputing

Research

For every £10 spent on NHS, only 1p is spent on particle physics. No, PET scanners, no MRS scans, no cancer killing particle beams etc. without particle physics