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LHC – the greatest experiment

Dr. K.P.Satheesh

& the origin of mass

Principal, GCB

on Earth

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The Large Hadron

Collider will

collide the nuclei

of atoms with 10times higher

energy than has

previously been

achieved (14 TeV)

1232, 35 ton,

superconducting dipole

magnets accelerate ions andfocus them into bunches for

collision

36,000 tons of coolant below

2K!

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Proton-Proton collisions (hydrogen atom nuclei)

100 billion protons per bunch

20 collisions per crossing

1 crossing every 25ns

600 million collisions per second

14 TeV centre of mass energy

To store all collision data would involve storing 10 Petabytes of

data a year ie a 20km high stack of CDs… more than can be made

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Why the LHC...Why the LHC...LHC Is constructed to helpLHC Is constructed to help

scientists in general and particlescientists in general and particlephysicists in particular to answerphysicists in particular to answer

certain key unresolved questionscertain key unresolved questions

in Particle Physics. Thein Particle Physics. Theunprecedented energy it offersunprecedented energy it offers

has already started revealinghas already started revealing

some unexpected results that nosome unexpected results that noone has ever thought of.one has ever thought of.

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During the steady growth of During the steady growth of

Particle Physics in the lastParticle Physics in the last

century physicists have beencentury physicists have been

able to describe withable to describe with

increasing detail theincreasing detail thefundamental particles thatfundamental particles that

make up the universe and themake up the universe and the

interaction between them.interaction between them. The Standard Model. The Standard Model.

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Even though the standardEven though the standard

model is highly successful itmodel is highly successful itcontains several gaps andcontains several gaps and

cannot tell us the whole story.cannot tell us the whole story.

To complete the story To complete the story

experimental data at the teraexperimental data at the tera

scale is required. LHCscale is required. LHCpromises this data.promises this data.

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What is the Large HadronWhat is the Large Hadron

Collider (LHC)?Collider (LHC)? The LHC is a very large The LHC is a very large

particle accelerator,particle accelerator,roughly 17 miles long androughly 17 miles long and

finished on September 10finished on September 10thth

,,2008.2008.

Its primary function is toIts primary function is touse electric fields to forceuse electric fields to forcecharged particles to movecharged particles to move

at very high speeds andat very high speeds andstill keep them understill keep them undercontrol.control.

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What is it made out of?What is it made out of?

The Large Hadron Collider The Large Hadron Collidercontains:contains:

2 adjacent parallel beams2 adjacent parallel beams 1232 dipole magnets1232 dipole magnets 392 quadrupole magnets392 quadrupole magnets 1,600 superconducting1,600 superconducting

magnetsmagnets 96 tons of liquid helium for96 tons of liquid helium for

temperature maintenancetemperature maintenancepurposespurposes

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How does it work?How does it work?

I don’t know the answer to this one…I don’t know the answer to this one…

…just kidding

In simplest terms, the LHC works by forcing two beams of

atomic particles to travel in opposite directions

surrounding the physical LHC itself. Once these beams

reach their maximum speed, the LHC forces them tocollide in four places on their path. These collisions create

new particles and energy, allowing physicists to use the

detectors in the LHC to observe much about the basic

structure of our world.

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What went wrong with it?What went wrong with it?

The reason behind the The reason behind theinability of the LHC to beinability of the LHC to beappropriately followedappropriately followedthrough with as anticipatedthrough with as anticipated

on September 19th was anon September 19th was anelectrical fault between twoelectrical fault between twomagnets which caused an arc,magnets which caused an arc,making the helium leak. Oncemaking the helium leak. Oncethe outer layer of the heliumthe outer layer of the heliumbroke, it flooded the area,broke, it flooded the area,breaking 10-ton magnets andbreaking 10-ton magnets and

covering the tubes of protoncovering the tubes of protonwith soot.with soot.

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WHAT DO PARTICLE PHYSICISTS DO?WHAT DO PARTICLE PHYSICISTS DO?

Some unanswered questionsSome unanswered questions

Why do we observe matter and almost no antimatter if weWhy do we observe matter and almost no antimatter if webelieve there is a symmetry between the two in thebelieve there is a symmetry between the two in theuniverse?universe?

What is this "dark matter" that we can't see that has visibleWhat is this "dark matter" that we can't see that has visible

gravitational effects in the cosmos?gravitational effects in the cosmos? Why can't the Standard Model predict a particle's mass?Why can't the Standard Model predict a particle's mass?

Are quarks and leptons actually fundamental, or made upAre quarks and leptons actually fundamental, or made upof even more fundamental particles?of even more fundamental particles?

Why are there exactly three generations of quarks andWhy are there exactly three generations of quarks and

leptons?leptons? How does gravity fit into all of this?How does gravity fit into all of this?

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The Particles and their Properties.The Particles and their Properties.

There are two types of particles that are thought to be fundamental. Thatis, they cannot be broken down into any smaller constituent particles.

These two types of particles are the leptons and the quarks.

However, these can, under the right conditions, be converted into energy, or

be formed from bundles of energy. Also, the heavier ones can decay intolighter ones, with the release of some of their energy.

As the regions of the universe near us are now in a much lower-energy

state than they were shortly after the big bang, only the lightest particles in

each family are now very commonly observed.

Others can be re-created by high-energy collisions, such as those

produced in particle accelerators.

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The most familiar member of this group is the electron, but there arealso similar, heavier (and hence more energetic) particles called the

muon and the tau.

The Leptons The Leptons

For each one of these, there is a smaller “partner” called a neutrino – theelectron neutrino, the muon neutrino and the tau neutrino.

Each of these 6 also has an antiparticle, for example, the anti-electron or

positron.

The leptons are all capable of independent existence.

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Properties of the LeptonsProperties of the Leptons

The electron, muon and tau all have mass.The neutrinos have no mass, according to

the Standard Model. However, there is

some evidence that neutrinos do have an

actual, very small mass.

The electron, muon and tau all have

electric charges of –1, and their anti-

particles have electric charges of +1.

The neutrinos have no electric charge.

All of the leptons have another

property called “spin”. Their spins

can be +½ or -½.

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The Quarks The Quarks

The quarks are not capable of independentexistence, and are found only as groups, making

up larger particles (called “bound states”).

The quarks have mass and electric charge. The

electric charges are either + or - for⅔ ⅓

quarks, and - or + for the matching anti-⅔ ⅓

quarks.

There are 6 quarks, called up, down, charm, strange,

bottom and top. The “everyday” quarks are the up and

down quarks. For each quark there is an anti-quark.

They also have spin of ±½. There is also another

property called “colour” charge, which comes in 3

varieties, red, green and blue. The anti-quarks

have anti-colours: anti-red, anti-green and anti-

blue.

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Rules The Particles FollowRules The Particles Follow

There are also other rules, for example about spin,

which must also be obeyed.

This relates particularly to the grouping together of quarks.

The “bound states” must be colour-neutral.

This means that only two types of groupings are

possible; 3 quarks (or 3 anti-quarks), or a quark-

antiquark pair. The particles of the first type are

called baryons, and the most familiar examples

are the proton and the neutron. The second type is

the mesons. Together they are called hadrons.

As a consequence of this, the bound states can only

have integral charges (0, ±1, ±2).

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3 Some Familiar Particles3 Some Familiar Particles

Example: The proton has a charge of +1. It

is a baryon, so it is made up of 3 quarks.

Since the up quark has a charge of + and the⅔down quark has a charge of - , the only way to⅓

make up a proton is uud. ( +⅔

- = 1).⅔ ⅓

The quarks will be one each of rgb, makingthe proton colour-neutral, and all the rules

are satisfied.

u

+

⅔

u

+

⅔

d -

⅓

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The History of Standard Model

1. The Nobel Prize winner

1979 Nobel Prize-- GLASHOW, SALAM and WEINBERG

the theory of the unified weak and electromagneticinteraction.

1984 Nobel Prize-- RUBBIA and VAN DER MEER

the discovery of the field particles W and Z, communicators of weak

interaction.

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Ancient times People think that earth, air, fire, and water are the fundamental elements.

1802 Dalton’s Atomic theory began forming.

1897 J. J. Thompson discovered the electron.

1911 Rutherford discovered positive nucleus.

1930 Pauli invented the neutrino particle.

1932 James Chadwick discovered the neutron.

1937 The muon was discovered by J. C. Street and E. C. Stevenson.

1956 First discovery of the neutrino by an experiment: the electron neutrino.

1962 Discovery of an other type of neutrino: the muon neutrino.

1969 Friedman, Kendall, and Taylor found the first evidence of quarks.

1974 The charmed quark was observed.

1976 The tau lepton was discovered at SPEAR.

1977 Experimenters found proof of the bottom quark.

1983 Carlo Rubbia and Simon Van der Meer discovered the W and Z bosons.

1991 LEP experiments show that there are only three light neutrinos.

1995 The top quark was found at Fermilab.

1998 Neutrino oscillations may have been seen in LSND and Super-Kamiokande.

2000 The tau neutrino was observed at Fermilab.

2003 A Five-Quark State has been discovered.

A short summary of events

http://www.jlab.org/news/articles/2003/5quark.html

http://c/Documents%20and%20Settings/xjin/Desktop/Lessons1-History/preview/index.htm

http://c/Documents%20and%20Settings/xjin/Desktop/Lessons1-History/preview/index.htm

http://www.jlab.org/news/articles/2003/5quark.html

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2. Question: What is Standard Model?

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4. Physicists are human beings

1898 Joseph Thompson : “plum-pudding”model of the atom

1911 Ernest Rutherford: “planetary” model of the atom

It took 10 years to realize the muon wasn’t Yukawa’s pion.

At the beginning, the “quark” model was not accepted widely.

……

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The Story So Far

Electrons and their electromagnetic

interactions are responsible for

chemistry and day to day forces

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Dirac’s LegacyElectrons can absorb photons

But in Relativity, rotatingthis in space-time gives…

The electron travelling back in time is a hole or anti-

particle

Every particle has a twin of the same mass butprecisely opposite charges – particles and anti-

particles annihilate into photons.

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Gauge Theory - QED

How do you know which to callparticle and which anti-particle?

Nature has the same problem – it may

make a different choice in causallydisconnected bits of space

Nature has invented an interaction so

that two charged particles can probe

the choice each other made – that

force is electro-magnetism.

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Understanding Mass - The Quantum Vacuum

E t > h

The vacuum can borrow energy for short periods

E = mc2

The borrowed energy can be used to create particles

The quantum vacuum is a seething mass of particles appearing and

disappearing constantly….

(You can’t just create an electron because of chargeconservation - but can create electron positron pair)

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How Can You Tell?

The effective charge

seen in two electron

scattering depends on

the separation of the

electrons.

The “virtual” particle

pairs interfere in

electron scattering

processes.

g-2 is tested to 13 sigfigs!

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The Strong Nuclear Force

The strong nuclear force is

described by a gauge theory

… except that the 8 gaugefields, gluons, carry colour

charge…..This difference changes the

way in which the vacuum is

polarized so that…

Quarks come in 3 colours!

“asymptotic freedom”

Gross, Politzer, Wilczek

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Confinement

You can never pull hard enough to

liberate a quark from a proton…

The Quantum Vacuum

Every so often quantum effects create a quark anti-quark pair.

The attractive force is so strong that

binding energy >> mass energy

The vacuum has lower energy if it fills itself with quark anti-

quark pairs!

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The vacuum is really full of quark anti-quark pairs with a density

like that of an atomic nucleus (10 grams/cm ) !!15

The Proton Mass

The quark pairs are responsible for the proton’s mass

Interactionenergy provides

proton mass

3

Strongly coupled QCD is a

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QCD & StringsStrongly coupled QCD is a

tough maths problem – how

do we compute beyond

perturbation theory?

String theory gets meson properties

right because a q anti-q pair look likea string

BUT relativistic strings like t

live in 10 dimensions!

String theory contains

quantum gravity

A string is a one dimensional

object with tension

G G it D lit

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Gauge Gravity Duality

Maldacena

In recent years we have realized that strings in 10d

are in fact the QCD string… a weird and wonderful

alternative description of quarks and glue…

The extra

dimensions areholographic

creations.

EG a quark is a string with an

up label on one end and a

colour label on the other

If the space-time stretches it

the quark becomes massive

Classical General Relativity

computations solve strongly

coupled quantum problems!

Is real gravity a hologram??

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Quarks in a Dense QCD Plasma

Computations of gravity wave propagation tell

us about transport properties of a quark gluonplasma

Larry Yaffe’s calculations of the shock wave produced by a moving quark

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The ALICE ConnectionA lead-lead collider at LHC

In heavy ion collisions we squeeze

quarks together testing asymptoticfreedom.

At LHC energies the quark gluon

plasma is a strongly coupled liquid

Gauge gravity duality is currently our best tool to describe this

mayhem!

What else have we found?

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What else have we found?

Why do otherwiseidentical particleshave differentmasses?

Massive gauge

bosons for the

weak nuclear

force!

Th O i i f M

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The Origin of MassThe strong nuclear force cannot explain the mass of the electron

though…

The Higgs BosonWe suspect the vacuum is full of another sort of matter that is

responsible – the higgs…. a new sort of matter – a scalar?

Or very heavy quarks top mass = 175 proton mass

To explain the W mass the higgs vacuum must be 100 times

denser than nuclear matter!!

It must be weak charged but not electrically charged

Th S h f h Hi

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The Search for the Higgs

EG look for Higgs

decay to two

photons

There are variants….

Is the Higgs some new

quark anti-quark pair

bound by a new ultra

strong force?

Should we embrace a new

symmetry that requires a

scalar for every fermion

Supersymmetry…

No Loose

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No Loose

What if our theories are wrong and there is no higgs?

Without the higgs our theory of

WW interactions predicts

scattering cross sections greaterthan one… there must be

something there…

What could it be? – extra space-time dimensions

- a bigger gauge symmetry SU(2)xSU(2)x…

- something new…

2 Question: What is Standard Model?

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2. Question: What is Standard Model?

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