a short journey to the infinitely small fundamentals of particle physics stefania ricciardi ral,...
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A short journey to the infinitely small
Fundamentals of Particle Physics
Stefania Ricciardi
RAL, March 2008
• 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
Z0
Gluon hold quarks together as they move further apart until the gluon connection
snaps and other quark-antiquark pairs are created out of the energy released
Force Particles (summary)Particles interact and/or decay thanks to forcesForces are also responsible of binding particles together
Strong: gluonsOnly quarks
can feel it 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?
matter Anti-matterPuff
Good thing for us that there is no antimatter around!
The development of the Universe containing matter and no antimatter requires that matter and antimatter behave differently
This phenomenon is due to CP violation..
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 full!Installation of major structures is complete
Muon detector
Calorimeters
RICH-2
Magnet
OT
VELO
RICH-1
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 Monika will tell you all about the Higgs, the LHC, and much more!
NOT