1. Stefania Ricciardi RAL, March 2009
A short journey to the infinitely small Fundamentals of Particle Physics
Building blocks: particles and forces
Current areas of research
Stefania Ricciardi
RAL, March 2009

2. Warning Stay awake and keep an open mind!
This journey may change your vision of the Universe.
What you will hear may alter your perception of reality.
Stay awake and keep an open mind!
We are entering a Quantum World..

3. We and all things around us are made of atoms
Human Hair
~ 50 mm = m
= m
Atom ~ m
= m
Magritte

4. Atoms Atoms are all similarly made of:
- protons and neutrons in the nucleus
- electrons orbiting around
proton
The electron was the
first elementary
particle to be
discovered
(JJ Thomson 1897)
Protons, neutrons are made up of quarks
electron
neutron

5. From the atom to the quark
How small are the smallest constituents of matter?
<10-18 m
< m
~ m
~ m
~ m
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

6. Wave-particle duality of Nature
Central concept of quantum mechanics:
all particles present wave-like properties l
Not only light has a dual nature
De Broglie showed that moving particles have an
equivalent wavelength l
Electron Microscope Image
Gold atoms
(0.2 nm apart)
So high momentum gives us
short wavelengths so we can
make out small details
Example: electron microscope
Copyright © FEI

7. Rutherford: atoms are not elementary particles!
1911
Rutherford found a nucleus in the atom by firing alpha particles at gold and observing them bounce back
Precursor of modern scattering experiments at accelerator

8. Quarks detected within protons
Freeway 280
End Station A
experimental area
2 miles long accelerator
Stanford (SLAC), California, late 1960s
Fire electrons at proton: big deflections seen!

9. Protons and neutrons in the quark model
Quarks have fractional electric charge!
u electric charge + 2/3
d electric charge -1/3
proton (charge +1)
neutron (charge 0) u u u d
So we know now that protons and neutrons are made of quarks. d d

10. 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!
n n n n n nnnnnnnn
nn n n nn n nnnnnnn
n nn nn nn n n n n n
nn n n nn n nnnnnn
n nn nn nn nnnnnnn
nn nn n nnn nnnnnnn
Within each cm3 of
space: ~300 neutrinos
from Big Bang
1 cm
1 cm
Neutrinos are everywhere!
in the outer space, on Earth, in our bodies..

11. Neutrinos get under your skin!
per second from Sun
are zipping through you n
Every cm2 of Earth surface is crossed every second by more than 10 billion (1010) neutrinos produced in the Sun
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

12. The particles of ordinary matterne e- u d
-1/3
+2/3
charge
Leptons:
n = neutrino
e = electron
Quarks:
u = up
d = down -1
All stable matter around us
can be described using
electrons, neutrinos, u and d “quarks”

13. 3 Families (or Generations)
1st generation
2nd generation
3rd generation ne e- u d
-1/3
+2/3
+2/3
+2/3 nm m- c s nt t- t b -1 -1
-1/3 -1
-1/3
Ordinary matter
Cosmic rays
Accelerators
3 generations in everything similar but the mass
We believe these to be the fundamental
building blocks of matter

14. Quark masses 175 GeV Top (discovered 1995)
E= mc2
1 proton mass ~ 1GeV (10-27 Kg)
0.003
0.006
4.5
0.095
1.2
The mass grows larger in each successive family

15. Anti-matter
For every fundamental particle of matter there is an anti-particle with same mass and properties but opposite charge
Matter
Anti-Matter ne e- u d
-1/3
+2/3 e+
+1/3
-2/3 +1 -1
Bar on top
to indicate
anti-particle
positron
Correspondent anti-particles exist for all three families
Anti-matter can be produced using accelerators

16. 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

17. Quarks and colour
All quark flavours come in 3 versions, called “colours” u d
+2/3
-1/3 up
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
Strong forces “glue” quarks together in bound states
proton p u
pion u p

18. Building more particles
B mesons (bq) c c
J/y b b Y
Many more mesons and baryons…

19. The Particle Physicist’s Bible: Particle Data Book https://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)
The Particle Physicist’s Bible: Particle Data Book
Most particles are not stable and can decay to lighter particles..

20. THE WEAK FORCE Beta Decayn p
Antineutrino
Electron

21. A (free) neutron decays after 15 min
Neutron b-decay
At quark level:
d→ u e- ne u d p u d n
15 min e- ne
A (free) neutron decays after 15 min
Long life time (15min is an eternity in particle physics!)  “weak”
without such weak interactions the Sun would shut down!

22. The 4 forces of Nature Weak Electromagnetic weak charge Electric
Beta-decay
pp fusion
Electromagnetic
TV, PCs
Magnets
e- e+ creation
weak
charge
Electric
charge
Strong
Quark binding
Gravity
Responsible of
Keeping us
well-planted on earth
strong
charge
mass

23. Electromagnetic force
The repulsive force that two approaching electrons “feel” e- e-
Photon is the particle
associated to the electromagnetic force
“smallest bundle” of force
Photon

24. Photon exchange Feynman Diagram

25. Weak force: W-,W+,Z0 b-decay n→pene W- Electric charge
conserved at each
vertex

26. Strong force: gluons Gluons interact with quarks
Gluons interact with other gluons

27. Quark confinement
There are no free quarks, quarks and antiquarks are “confined”
in colourless doublet (mesons) or triplets (baryons) by the exchange of gluons
Decay 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
The new quarks bound
to the old quarks
and form new mesons
® S.Ward

28. Force Particles (summary)
Particles interact and/or decay thanks to forces
Forces are also responsible of binding particles together
Strong: gluons
Only quarks
(because of their
colour charge)
Weak: W+, W-, Z0
Leptons and quarks (only force for neutrinos)
Electromagnetic:g
Quarks and charged leptons (no neutrinos)
Gravity: graviton?
Still to be discovered
Negligible effects on particles

29. The Standard Model Framework which includes: Not gravity! No quantum
Matter
6 quarks
6 leptons
Grouped in three generations
Forces
Electroweak:
g (photon)
Z0, W±
Strong
g (gluon)
Not gravity! No quantum
field theory of gravity yet..
H= the missing ingredient: the Higgs Boson
Very successful to describe all observed phenomena in the
subatomic world so far. But there ought to be more..

30. Beyond the Standard Model:Unification of forces
ELECTRO-
MAGNETIC
UNIFIED
FORCE?
GRAVITY
STRONG
WEAK
Looking for a simple elegant unified theory

31. 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..

32. Why has all the anti-matter gone?
Puff
matter
Anti-matter
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..

33. CP Violation
CP = Charge Conjugation (reverse charge) x Parity (reverse spatial coordinates as in a mirror)
“Nobody
is perfect” CP
beauty
anti-beauty B0 B0
CP-Violation: B0 and B0 do not behave exactly in the same way
(their decay pattern as a function of time is different)

34. 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

35. The CPV quest will go on at LHC
LHCb experiment:
700 physicists
50 institutes
15 countries
LHCb cavern
LHCb
CERN
ATLAS
CMS
ALICE

36. Recent view of the LHCb cavern
RICH-1
Muon
detector OT
Magnet
Calorimeters
VELO
It’s complete!
RICH2
RICH1
The experiment is fully installed and ready for first collisions

37. 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?
Visible Matter
Dark Matter
False-color images
The brightness of clumps
corresponds to the
density of mass.

38. Looking for Dark Matter at the Boulby Underground Laboratory

39. Puzzling neutrinos
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
Neutrinos do matter to us: If there were no neutrinos the sun would not shine!

40. R. Davis: measuring the solar neutrino flux in a gold mine in South Dakota for 30 years (1969-1999)
Solar neutrinos
pioneer
…and observing only 1/3 of the expected flux!! Why?

41. Neutrino oscillationsnm nt
If you let the neutrino travel enough,
it can change its flavour! m
Kamioka Observatory, ICRR (Institute for
Cosmic Ray Research),
The University of Tokyo
a huge neutrino detector
exists! t
a huge neutrino detector
in the right place exists!
A detector here
does not see any nm
A detector here
sees all nm

42. nm flux from below only ½ of flux from above!
in the Kamioka mine in Japan
SuperKamiokande is measuring neutrinos born in the atmosphere
above the detector..
nm 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 _

43. Discovery of neutrino oscillation Super-Kamiokande (1998)
2002 Nobel Prize
Koshiba
(superK Spokesman)
shared with Davis
Up-going
Down-going
Half of the nm are lost!
Oscillated to undetected nt

44. 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!

45. 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