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

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!

We and all things around us are made of atoms

Human Hair ~ 50 m = 50 10-6 m = 0.000050 m

Atom ~ 10-10 m = 0.0000000001 m

Magritte

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

electron

proton

neutron

Protons, neutrons are made up of quarks

The electron was thefirst elementaryparticle to be discovered(JJ Thomson 1897)

From the atom to the quark

Atoms and sub-atomic particles are much smaller than visible light wave-length Therefore, we cannot really “see” them (all graphics are artist’s 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

<10-18 m

<10-1 8

m

Wave-particle duality of NatureCentral concept of quantum mechanics:all particles present wave-like properties

De Broglie showed that moving particles have anequivalent wavelength

p

1 So high momentum gives us

short wavelengths so we can make out small details

Example: electron microscope

Not only light has a dual nature

Electron Microscope ImageGold atoms(0.2 nm apart)

Copyright © FEI

1911Rutherford found a nucleus in the atom by firing alpha particles at gold and observing them bounce back

Rutherford: atoms are not elementary particles!

Precursor of modern scattering experiments at accelerator

Quarks detected within protons

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

2 miles long accelerator

End Station Aexperimental area

Freeway 280

Protons and neutrons in the quark model

proton (charge +1) neutron (charge 0)

uu dddd

uu uudd

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

Is the whole Universe made only of quarks and electrons?

No! There are also neutrinos!

Electron, proton and neutrons are rarities! For each of them in the Universe there is 1 billion neutrinos

Neutrinos are the most abundant matter-particles in the Universe!

1 cm Within each cm3 of space: ~300 neutrinos from Big Bang

Neutrinos are everywhere!in the outer space, on Earth, in our bodies..

1 cm

Neutrinos get under your skin!

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

No worries! Neutrinos do not harm us.

Our bodies are transparent to neutrinos

14 neutrinos per second from Sun

are zipping through you

Every cm2 of Earth surface is crossed every second by more than 10 billion (1010) neutrinos produced in the Sun

The particles of ordinary matter

ee

ee--

uu

dd-1/3

+2/30

-1

charge

All stable matter around uscan be described using

electrons, neutrinos, u and d “quarks”

Quarks:u = upd = down

Leptons:neutrinoe = electron

3 Families (or Generations)

--

cc

ss

--

tt

bbOrdinary 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

ee

ee--

uu

dd-1/3

+2/3

We believe these to be the fundamental building blocks of matter

-1 -1 -1

0 00

Quark masses

020406080

100120140160180

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

Anti-matter• For every fundamental particle of matter there is an anti-particle

with same mass and properties but opposite charge

ee

ee--

uu

dd-1/3

+2/3

ee

ee++

uu

dd+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 top to indicateanti-particle

Matter-antimatter pair creation

•Electron-positron pair created out of photons hitting the bubble-chamber liquid

•Example of conversion of photon energy into matter and anti-matter

•Matter and anti-matter spiral in opposite directions in the magnetic field due to the opposite charge

•Energy and momentum is conserved

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

uu dd+2/3 -1/3uuuu ddddup 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

uuuu

pion

pp

Strong forces “glue” quarks together in bound states

Building more particles

bb bb

J/

cc cc

Y

bb uuB-

uu bbB+

bb ddB0

dd bbB0

B mesons (bq)

Many more mesons and baryons…

The Particle Physicist’s Bible: Particle Data Bookhttps://pdg.lbl.gov

"Young man, if I could remember

the names of these particles,

I would have been a botanist!“

E.Fermi to his student

L. Lederman (both Nobel laureates)

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

THE WEAK FORCEBeta Decay

n p

Antineutrino

Electron

Neutron -decay

A (free) neutron decays after 15 min

uu dddd

nn uu uudd

pp ee--

d→ u e- e

ee

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!

The 4 forces of NatureWeak• Beta-decay• pp fusion

Strong• Quark binding

Electromagnetic•TV, PCs • Magnets

• e- e+ creation

GravityResponsible ofKeeping us well-planted on earth

Electric charge

mass

weak charge

strongcharge

Electromagnetic force

e- e-

Photon

The repulsive force that two approaching electrons “feel”

Photon is the particle associated to the electromagnetic force“smallest bundle” of force

Photon exchangeFeynman Diagram

e- e-

e-e-

Weak force: W-,W+,Z0

decayn→pee

Electric chargeconserved at eachvertex

W-

Strong force: gluons

Gluons interact with quarks Gluons interact with other gluons

Quark confinement • There are no free quarks, quarks and antiquarks are “confined” in colourless doublet (mesons) or triplets (baryons) by the exchange of gluons

The new quarks boundto the old quarks and form new mesons

until the gluon connection snaps, and other quark-antiquark pairs are created out of the energy released

Gluon hold quarks together as they move further apart

Z0

Decay

® S.Ward

Force Particles (summary)

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

Strong: gluonsOnly quarks

(because of their

colour charge)

Weak: W+, W-, Z0

Leptons and quarks (only force for neutrinos)

Electromagnetic:Quarks and charged leptons (no neutrinos)

Gravity: graviton?Still to be discovered

Negligible effects on particles

The Standard Model

Matter• 6 quarks• 6 leptonsGrouped in three generations

Forces• Electroweak:

(photon) - Z0, W±

• Strong - g (gluon)

Very successful to describe all observed phenomena in the subatomic world so far. But there ought to be more..

Framework which includes:

Not gravity! No quantum field theory of gravity yet..H= the missing ingredient: the Higgs Boson

Beyond the Standard Model:Unification of forces

WEAK

STRONG GRAVITY

ELECTRO-MAGNETIC

UNIFIEDFORCE?

Looking for a simple elegant unified theory

Open question:Why is the Universe made of

matter and not equally of 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 of large amount of antimatter in the Universe..

Why has all the anti-matter gone?

Anti-matter

The development of the Universe containing matter and no antimatter requires that matter and antimatter behave differently

This phenomenon is due to CP violation..

matter Puff

Good thing for us that there is no antimatter around!

CP Violation

• CP = Charge Conjugation (reverse charge) x Parity (reverse spatial coordinates as in a mirror)

CPCP

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)

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

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

The CPV quest will go on at LHCThe CPV quest will go on at LHC

CMS ALICE

CERN

LHCb experiment:LHCb experiment:700700 physicistsphysicists5050 institutes institutes 1515 countriescountries

LHCb cavernLHCb cavern

LHCb

ATLAS

Recent view of the LHCb cavern

It’s complete!

RICH-1

The experiment is fully installed and ready for first collisions

RICH2 RICH1

Muon detector

Calorimeters OT Magnet

VELO

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 don’t really know …– Perhaps partially composed of neutrinos, or possibly neutralinos particles predicted by

super-symmetric theories beyond the Standard Model?

Dark MatterVisible Matter

False-color imagesThe brightness of clumps corresponds to the density of mass.

Looking for Dark Matter at the Boulby Underground Laboratory

Neutrinos do matter to us:Neutrinos do matter to us:If there were no neutrinos If there were no neutrinos the sun would not shine!the 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 Universe bringing information from the origin of space and time

Puzzling neutrinos

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

30 years (1969-1999)

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

R. DavisSolar neutrinos pioneer

Neutrino oscillationsIf you let the neutrino travel enough,

it can change its flavour!

e

a huge neutrino detectorin the right place exists!

A detector here does not see any

Kamioka Observatory, ICRR (Institute for Cosmic Ray Research), The University of Tokyo

a huge neutrino detector exists!

A detector here sees all

in the Kamioka mine in Japan SuperKamiokande is measuring neutrinos born in the atmosphereabove the detector..

flux from below only ½ of flux from above!

..and below the detector (on the other side of the Earth!!)Total neutrino flux from below = total flux from above _

Discovery of neutrino oscillation Super-Kamiokande (1998)

Half of the are lost! Oscillated to undetected

2002 Nobel PrizeKoshiba (superK Spokesman)shared with Davis

Up-going Down-going

What have we learnt?

• A number of surprising things:– A limited number of forces and matter particles

describe all the Universe we know about;– A theory of the interactions of matter with forces

called the Standard Model describes successfully the phenomena of the subatomic world;

– There are evidences that there is lot more that we do not know about and our research should find: such as the missing anti-matter, dark matter, puzzling neutrino properties, but also the Standard Model key-vault ..the Higgs!

Looking into the future

• The Higgs should be found at the LHC…please be patient for a few more hours….and you will learn about the Higgs, the LHC, and much more!

NOT