Fundamentals of Particle Physics

7/31/2019 Fundamentals of Particle Physics

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A short journey to the infinitely small

Fundamentals of

Particle Physics

Stefania Ricciardi

RAL, March 2009

Building blocks: particles and forces Current areas of research


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Warning

This journey may change your vision of the Universe.

What you will hear may alter your perception of reality.

We are entering a Quantum World..

Stay awake and keep an open mind!


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We and all things around us aremade of atoms

Human Hair~ 50 m = 50 10-6 m

= 0.000050 m

Atom ~ 10-10 m= 0.0000000001 m

Magritte


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Atoms

Atoms are all similarly made of:- protons and neutrons in the nucleus- electrons orbiting around

electron

proton

neutron

Protons,neutrons are

made up ofquarks

The electron was thefirst elementary

particle to bediscovered(JJ Thomson 1897)


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From the atom to the quark

Atoms and sub-atomic particles are much smaller than visible light wave-lengthTherefore, we cannot really see them (all graphics are artists impressions)To learn about the sub-atomic structure we need particle accelerators

How small are the smallest constituents of matter?

~ 10-10 m~ 10-14 m

~ 10-15 m


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Wave-particle duality of Nature

Central concept of quantum mechanics:all particles present wave-like properties

De Broglie showed that moving particles have anequivalent wavelength l

p

1

lSo high momentum gives usshort wavelengths so we canmake out small details

Example: electron microscope

Not only light has a dual nature

Electron Microscope Image

Gold atoms(0.2 nm apart)

Copyright FEI


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1911Rutherford found a nucleus in theatom by firing alpha particles at gold

and observing them bounce back

Rutherford: atoms are notelementary particles!

Precursor of modern scattering experiments at accelerator


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Quarks detected within protons

Stanford (SLAC), California, late 1960sFire electrons at proton: big deflections seen!

2 miles long accelerator

End Station Aexperimental area

Freeway 280


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Protons and neutronsin the quark model

proton (charge +1) neutron (charge 0)

u d

d

u u

d

Quarks have fractional electric charge!u electric charge + 2/3d electric charge -1/3

13

1

3

2

3

2

-

pduu 0

3

1

3

1

3

2nddu

-

-


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Neutrinos get under your skin!

Within your body at any instant:roughly 30 million neutrinos fromthe Big Bang

No worries!Neutrinos do not harm us.

Our bodies are transparent to neutrinos

14 neutrinosper second from Sun

are zipping through you

n

Every cm2

of Earth surface iscrossed every second by morethan 10 billion (1010) neutrinosproduced in the Sun


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The particles of ordinary matter

ne

e-

u

d-1/3

+2/30

-1

charge

All stable matter around uscan be described using

electrons, neutrinos, u and d quarks

Quarks:u = up

d = down

Leptons:neutrino

e = electron


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3 Families (or Generations)

nm

m-

c

s

nt

t-

t

b

Ordinary matter Cosmic rays Accelerators

1st generation 2nd generation 3rd generation

3 generations in everything similar but the mass

-1/3-1/3

+2/3 +2/3

ne

e-

u

d-1/3

+2/3

We believe these to be the fundamentalbuilding blocks of matter

-1 -1 -1

0 00


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Quark masses

0

20

40

60

80

100

120

140

160180

Mass

(GeV)

Quarks

Up Down Strange Charm Bottom Top

0.003 0.006 0.095 1.2 4.5

Top(discovered 1995)

175 GeV

E= mc2

1 proton mass ~ 1GeV (10-27 Kg)

The mass grows larger in each successive family


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Anti-matter

For every fundamental particle of matter there is an anti-particlewith same mass and properties but opposite charge

ne

e-

u

d

-1/3

+2/3

ne

e+

u

d

+1/3

-2/3

+1

0

-1

0

positron

Correspondent anti-particles exist for all three families Anti-matter can be produced using accelerators

Matter Anti-Matter

Bar on topto indicateanti-particle


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Matter-antimatter pair creation

Electron-positron pair created out ofphotons hitting the bubble-chamberliquid

Example of conversion of photonenergy into matter and anti-matter

Matter and anti-matter spiral in oppositedirections in the magnetic field due tothe opposite charge

Energy and momentum is conserved


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Quarks and colourAll quark flavours come in 3 versions, called colours

u d+2/3 -1/3uu ddup down

Quarks combine together to form colourless particles

-Baryons(three quarks: red+ green + blue = white)

-Mesons(quark-antiquark pair)such as red+anti-red u-ubar state

proton

uu

pion

p

Strong forcesglue quarks

together inbound states


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Building more particles

b b

J/y

c c

Y

b u

B-

u b

B+

b d

B0

d b

B0

B mesons (bq)

Many more mesons and baryons


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The Particle Physicists Bible:

Particle Data Book

https://pdg.lbl.gov

"Young man, if I could rememberthe names of these particles,

I would have been a botanist!

E.Fermi to his student

L. Lederman (both Nobellaureates)

Most particles are not stable and can decay to lighter particles..


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THE WEAK FORCEBeta Decay

n p

Antineutrino

Electron


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Neutron b-decay

A (free) neutron decays after 15 min

u d

d

n u ud

p e-

d u e-

ne

ne

15 min

At quark level:

Long life time (15min is an eternity in particle physics!) weak

without such weak interactions the Sun would shut down!


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The 4 forces of Nature

Weak Beta-decay pp fusion

StrongQuark binding

ElectromagneticTV, PCs Magnets

e- e+ creation

GravityResponsible of

Keeping uswell-planted on earth

Electriccharge

mass

weak

charge

strongcharge


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Electromagnetic force

e- e-

Photon

The repulsive force that two approaching electrons feel

Photon is the particleassociated to the electromagnetic forcesmallest bundle of force


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Weak force: W-,W+,Z0

b-decaynpene

Electric chargeconserved at each

vertex

W-


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Strong force: gluons

Gluons interact with quarks Gluons interact with other gluons


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Quark confinementThere are no free quarks, quarks and antiquarks are confined

in colourless doublet (mesons) or triplets (baryons) by the exchangeof gluons

The new quarks boundto the old quarksand form new mesons

until the gluon connectionsnaps, and other quark-antiquarkpairs are created out of theenergy released

Gluon hold quarkstogether as they movefurther apart

Z0

Decay

S.Ward

Force Particles (summary)


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Force Particles (summary)

Particles interact and/or decay thanks to forcesForces are also responsible of binding particles together

Strong: gluons

Only quarks

(because of their

colour charge)

Weak: W+, W-, Z0

Leptons and quarks (onlyforce for neutrinos)

Electromagnetic:gQuarks and charged leptons(no neutrinos)

Gravity: graviton?Still to be discovered

Negligible effects onparticles


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O ti :


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Open question:

Why is the Universe made of

matter and not equallyof anti-matter?

We have seen that for every fundamental

particle there is a corresponding antiparticle.

Where are these anti-particles?

Large amount of matter but no evidence oflarge amount of antimatter in the Universe..


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Why has all the anti-matter gone?

Anti-matter

The development of the Universe containing

matter and no antimatter requires thatmatter and antimatter behave differently

This phenomenon is due to CP violation..

matter Puff

Good thing for us that there is no antimatter around!


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CP Violation

CP = Charge Conjugation (reverse charge) x Parity (reverse spatialcoordinates as in a mirror)

CP

beauty anti-beauty

B0 B0

Nobody

is perfect

CP-Violation: B0 and B0 do not behave exactly in the same way

(their decay pattern as a function of time is different)


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Discovery of CP violation in theB-meson system at Babar (SLAC, 2001)

A visible difference is detected, but tiny, not enoughto explain the matter-antimatter asymmetry in the Universe


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The CPV quest will go on at LHC

CMS ALICE

CERN

LHCb experiment:700physicists

50institutes15countries

LHCb cavern

LHCb

ATLAS


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Recent view of the LHCb cavern

Its complete!

RICH-1

The experiment is fully installed and ready for first collisions

RICH2 RICH1

Muondetector

Calorimeters OT Magnet

VELO


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Another open question:What is the Dark Matter?

Astronomical observations have shown that observable mass

represent less than 4% of the Universe!

What is dark matter? We dont really know

Perhaps partially composed of neutrinos, or possibly neutralinos particlespredicted by super-symmetric theories beyond the Standard Model?

Dark MatterVisible Matter

False-color imagesThe brightness ofclumpscorresponds to thedensity of mass.
http://imagine.gsfc.nasa.gov/docs/dict_ad.htmlhttp://imagine.gsfc.nasa.gov/docs/dict_ad.html


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Looking for Dark Matter at theBoulby Underground Laboratory


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Neutrinos do matter to us:If there were no neutrinosthe sun would not shine!

Almost no interactions (only weak)

Can cross light-years of material without being affected Can travel from the most remote corners of the Universebringing information from the origin of space and time

Puzzling neutrinos


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R. Davis: measuring the solar neutrinoflux in a gold mine in South Dakota for

30 years (1969-1999)

and observing only 1/3 of the expected flux!! Why?

R. DavisSolar neutrinospioneer


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Neutrino oscillationsIf you let the neutrino travel enough,

it can change its flavour!nm

nt

ent

a huge neutrino detectorin the right place exists!

A detector heredoes not see any nm

Kamioka Observatory, ICRR (Institute for

Cosmic Ray Research),The University of Tokyo

a huge neutrino detectorexists!

A detector heresees all nm


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in the Kamioka mine in JapanSuperKamiokande is measuring neutrinos born in the atmospherabove the detector..

flux from below only of flux from above!

..and below the detector (on the other side of the Earth!!)

Total neutrino flux from below = total flux from above _


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Discovery of neutrino oscillationSuper-Kamiokande (1998)

Half of the nm are lost!

Oscillated to undetected nt

2002 Nobel PrizeKoshiba

(superK Spokesman)shared with Davis

Up-going Down-going


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What have we learnt?

A number of surprising things:

A limited number of forces and matter particlesdescribe all the Universe we know about;

A theory of the interactions of matter with forcescalled the Standard Model describes successfully thephenomena of the subatomic world;

There are evidences that there is lot more that we donot know about and our research should find: such asthe missing anti-matter, dark matter, puzzling neutrinoproperties, but also the Standard Model key-vault..the Higgs!


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Looking into the future

The Higgs should be found at theLHCplease be patient for a few more

hours.and you will learn about the

Higgs, the LHC, and much more!

NOT

Fundamentals of Particle Physics

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