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Particle Physics & Cosmology

Physics 50602

Colin [email protected]

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Course Information

Website: http://www.nd.edu/~cjessop/teaching/phys50602

Office Hours: Monday after class (3.30-4.30pm in my office)but also I am available most afternoonsemail or call me to make an appointment

Makeup class day/time: Necessary because I have to make one or two tripsto visit research funding agencies. I will send a doodle poll.(Friday 2.00-3.15pm ?)

Schedule

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First 9 weeks: Particle Physics – The Standard Model of Particle Physics

Last 5 weeks: Cosmology - The Standard Model of Cosmology

(You need to know particle physics to understand parts of cosmologybut not vice versa)

I will give you a full picture of the subject but necessarily I mustmake some simplifications that preserve the physical principles butavoid some detailed math.

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Course TextsNo course text because no one text book covers allmaterial. Notes will be largely self contained withreferences for further reading. (Lecture notes areon reserve in Chem/Phys library after lecture)

Background Reading:

1. General descriptive account“The Ideas of Particle Physics” - Caughlan and Dodd. On reserve: QC 793.2 D6 ( Also available from amazon.com $28 )

2. The History of the Subject (original papers)“The experimental Foundations of Particle Physics” Cahn and Goldhaber On reserve: QC 793.2 C34

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References

Quarks and Leptons – Halzen and MartinOn Reserve: QC 793.3.Q2522 H34Standard Graduate Text

Quantum Field Theory - Mandl and ShawOn Reserve: QC 174.45 M32A good introduction to underlying theory of particle interactions

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PrerequisitesMath: Matrices,vectors,calculus,vector calculus

(grad,div,curl)

Physics: Introductory Special Relativity, Intro Quantum Mechanics, Electromagnetism(Maxwells equations).

I will revise relevent special relativity (lecture 2),Quantum Mechanics (handout) and EM (lecture5) but a basic familiarity is assumed.

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Outline of Course

1. Introduction – Overview of the Standard Model2. Relativistic Quantum Mechanics3 Quantum Electrodynamics - Interactions of electrons and photons4 Particle Accelerators & Detectors5 Symmetries in Particle Physics6 Quantum Chromodynamics - Strong interactions of quarks7 Weak Interactions - Radioactive Decay8 Symmetry Breaking and the Higgs Boson9 Neutrinos

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What is Particle PhysicsThe ultimate reductionism - the breaking down ofa problem into its smallest components.

In our case the problem is to elucidate the mostelemental structure of all matter and the interactions between those elements

We hope to find an underlying simplicity. A unifyingset of principles that explains everything in the Universe. Our current state of knowledge is expressedin

The Standard Model of Particle Physics

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Atoms and the Nucleus

pp nn

e

Helium AtomAll atoms are made ofelectrons,protons andneutrons.

Are electrons protonsand neutrons made ofsomething smaller ?

What stops coulomb repulsion from destroying the nucleus ?

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Quarks and Leptons

pp nn

e

Electrons are elemental. They arepart of a family of particles calledleptons

n

p

Nucleons are made of Quarks“up” quark charge=+2/3

“down” quark charge=-1/3

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Discovery of Quarks

Quarks discovered here

High Energy (2 miles of acceleration) Electron Beam used for this experiment

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High Energy to see Quarks20 GeV electrons

m -16 10 x »D

GeV 20 p »D

p2h xp ³DD

Observed by high energy “Rutherford Scattering”Need momentum transfer of Dp to resolve structureat Dx scales. Particle physics also called high energyphysics for this reason.

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Particle Accelerators

20 GeV = 2 x 109 eV

Like 100,000 TV’s back to back 2 miles

electron

EMF wave14

Particle Experiments

20 GeV Electrons

targetDetector

Detector is a set of different devices that measurethe momentum, energy,charge and mass of the resultantparticles

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Particle InteractionsRelativistic Quantum Field Theory describes particleinteractions.

Incoming electron Outgoing electron

Outgoing quarkIncoming quark

time

space

Photon

The electron and quark interact electromagneticallyby the exchange of a photon

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Particle InteractionsA particle is a quantum excitation of a field



Photon

At the “vertices” the incoming electron/quark is annihilated, the photon created/annihilated, and the outgoing electron/quark is created. The photon “propagates” the force.

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Particle InteractionsThese are called “Feynman Diagrams”



Photon

They are mathematical mneumonics. Each vertex andline represents a term in the expression to calculatethe kinematics of the interaction

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Particle InteractionsA goal of the course is that you be able to understandthese diagrams and be able to calculate a simple one



Photon

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Quarks and LeptonsMatter is made of fermions (spin 1/2) (quarks and leptons (e.g electron)) which interact by exchange of gauge bosons (spin 1) (e.g photons).



Photon

This is the electromagnetic interaction but there areother types of interaction

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The Four ForcesForce Boson Lepton Quark Strength*

Strong Gluon No Yes 1

Electromagnetic

Photon Yes Yes 10-2

Weak W+,W-Z0 Yes Yes 10-7

Gravity Graviton? Yes Yes 10-39

*Strength of force is normalized to strong interaction at 1 fm seperation The graviton is predicted but not yet observed

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The Electromagnetic ForceThe theory of the electromagnetic force is called Quantum Electrodynamics.(QED)



Photon

a

2/3a

The photon “couples” to charge with strength a=e/4p. I.e the force isproportional to charge. It also smaller as the electron and quark get further apart

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The Strong Force.

Incoming quarkOutgoing quark


Gluon

The gluon couples to “color charge” with strength as. However there arethree types of charge red,blue and green. Also the force gets stronger asthe quarks get further apart ! . It is the strong forcewhich holds the nucleus together.

The theory of the strong interaction is called Quantum Chromo Dynamics (QCD)

as

as

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The Weak Neutral ForceQuarks and leptons can couple “weakly” through the neutral Z boson



aw

aw

The Z boson couples to quarks and leptons with strength aw=e.f(sin qw). Thefunction f is different for quarks and leptons. The Z boson has a massof 90 GeV (90 times proton !) which accounts for the weakness of theforce. The weak force is closely related to the electromagnetic force.

Z0

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The Weak Charged ForceQuarks and leptons can couple “weakly” through the charged W+ and W- bosons

aw

aw

W-

d uu ud dneutron proton

electron

Anti-neutrino

The weak charged force can turn a down quark into an up quark. It isresponsible for radioactive decay (eg beta decay as above). Like theweak charged force it is closely related to the electromagnetic force

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The Neutrino The neutrino only couples “weakly”. In the charged weak decaysit is associated with the electron

The neutrino is a neutral lepton with spin 1/2. Until recently itwas believed to be massless. In 2000 it was discovered that ithad a very small mass - a significant result with profound implications

Because of its weak interaction it is very difficult to detect directly

÷÷ø

öççè

æ

ene

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AntimatterThe combination of special relativity and QuantumMechanics leads to a new entity - antimatter

+electron Anti-electron

“Positron”

S=-1/2

Anti-electron/quark has opposite charge and spin to electron/quark but the same mass.

-

-1/3 +1/3

S=+1/2

S=+1/2 S=+1/2

quark antiquark

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AntiMatterIncoming electron Outg

oing l

epton

/qua

rk

Outgoing anti-lepton/quark

Incom

ing po

sitron

Photon

Matter and antimatter is created/annihilated in pairs

We can collide matter with antimatter to make othermatter/antimatter pairs 28

Matter-Antimatter Collisions

electrons positrons

Can Collide electrons and positrons in storage rings . Example of a collider experiment

SPEAR at SLAC

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Matter-AntiMatter CollisionsThe Universe evolved from the Big Bang

Creating a packet of pure energy replicates the conditions at 10-9-10-12 s aftercreation (we are now at 1018 s). Understanding these particle physics atthese high energies helps understand how the universe evolved from theseearly times

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3 Generations of Leptons

÷÷ø

öççè

æ

ene

÷÷ø

öççè

æ

µnµ

÷÷ø

öççè

æ

tnt

electron muon tau

The second and third generations couple exactly the same as first (electron). The mass of the neutrinosis a current research topic of great interest

Mass(GeV) 0.00051 .105 1.777

Mass(GeV) ? ? ?

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The MuonIn nature a flux of muons is produced by the interaction of cosmicrays with the atmosphere

Earth

muons

Cosmic Rays

Flux = 1 cm-2 s-1 at surface

During this lecture 200,000 havepassed through your hand

Muons can interact to cause alterations in geneticmaterial - source of mutations

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The Tau

tpppppt v+-+-++ ®

tt vve e-- ®

Discovered in e+e- collisions

The tau can decay weakly toleptons and quarks

W

t nt

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3 Generations of Quarks

÷÷ø

öççè

ædownup

÷÷ø

öççè

æstrangecharm

÷÷ø

öççè

æbeautytruth

The second and third generations couple exactly the same as first. The third generation is the subjectof great interest right now.

Mass(GeV) 0.0025 1.2 176

Mass(GeV) 0.0050 0.135 5.3

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HadronsQuarks only exist in “color neutral” combinations

u

d

Baryons eg. Proton Mesons (eg. p )

Red-green-blue

Blue - antibluegreen - antigreenred - antired

uu

u

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HadronsThere are hundreds of baryons and mesons. See theonline “Particle Data Book” for the full list

http://www.pdg-lbl.gov

cb

b

c

Charmonium (charm-anticharm) Upisilon (beauty-antibeauty)

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The charm quarkDiscovered in e+e- collisions

c

c

electron positron

The charm-anticharm mesondecays shortly after production

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The beauty quarkDiscovered in 1977 at Fermilab. Shown below is the beauty-quark “factory”Where we produced a billion of them to study rare decays

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u

Matter-Antimatter Collisions

u u

d d

u

Proton Anti-Proton

It is possible to accelerate protons and antiprotons to much greater energies than electrons and positrons. This effectively makes a quark-antiquark collider

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Proton - AntiProton Collisions

Fermilab ( Chicago)

The worlds highest energyCollider from 1988-2010

900 GeV Protons +900 GeV Antiprotons

4 miles circumference

The CDF detector

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Discovery of the Top Quark 1994Top Quark Event

quark antiquark(proton) (antiproton)

Top

Anti-top

(My PhD thesis ) 42

The Large Hadron ColliderThe LHC at CERN, Switzerland. 16 Miles Circumferenceextends across France-Switzerland Border. 14000 GeV

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The CMS Detector

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The Higgs Boson

The LHC was designed to search for and discover the Higgs Boson

This is a particle that couples to all matter and is ultimately responsiblefor all particles having mass

It was discovered in 2012 at the LHC. My research group at Notre Dameare members of the discovery team.

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A Higgs Boson Decaying to two photons in the CMS detector

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Summary - The Standard Model

+ anti quarks anti leptons

+ Higgs

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