Recap Elementary Particles

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Recap Elementary Particles

• Define the following particles baryons, mesons,
  hadrons, leptons, fermions, bosons.
• What are in todays science the basic bricks of
  matter ?
• Describe the Standard Model of bricks and force
  carriers.
• How do experimentalists look for a certain new
  particle ?
• How can experimentalists see the Universe at a
  very small scale (say 10-16 cm) ?
• What are the components of a high-energy physics
  experiment ? What are the two types of
  experiments in high-energy physics ?
• How deep can we see today ?
• Why todays standard model cannot be the final
  answer ?

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The Standard Clasification
Leptons Anti-leptons
Quarks
Anti-quarks
Mesons Anti-mesons
Baryons
Anti-baryons
Bricks
Hadrons and Anti-hadrons
Force
Acts on
Force Carriers
foton electromagnetic
all charged particles weakon
weak all particles gluon
colour
quarks graviton gravitational all
particles
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The Second Unification

• 1st unification was electromagnetism in the 19th
  century.
• 2nd unification involved electromagnetism and the
  weak force
• No similarities between electromagnetism
  (electrical wires, the compass) and the weak
  nuclear force (the disintegration of nuclei or of
  heavy leptons).
• No similarities between their carriers the
  photon is neutral and with zero mass, the weakon
  is usually electrically charged and has a large
  mass (about 50GeV)
• But in spite of all these differences the two
  forces were proven to be closely related.

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The carrier of the weak nuclear force (II)
Each weakon changes its composition depending on
circumstances. This magic behaviour (justifies
the name universal alchemist) allows the weak
force to act on all the particles. The Zo diagram
shows that this weakon can have the same
composition as the photon, the carrier of the
electromagnetic force.
W
e
ud
ud
e
e
ud
W-
du
du
e
du
e
Zo
dd
ss
ee
cc
uu
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The Electro-Weak Force

• 1968 S.Weinberg and A.Salam unified the gauge
  field theories corresponding to electromagnetism
  and weak force. They used a theory which employed
  zero mass carriers.
• J.Goldstone and P.Higgs have shown since 1960
  that when nature breaks symmetry it creates some
  heavy bosons called the Higgs bosons.
• Higgs bosons, like the weakons, rotate only to
  the left and can be attached to weakons.
• The fact that photons rotate both to the left and
  right ensure that only weakons will couple with
  the Higgs bosons and will become heavy.
• The Higgs bosons were discovered experimentally
  only in 2000.

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Spontaneous Symmetry Breaking

• The structure of salt (NaCl)
• At high level one sees the straight lines in
  the crystalline structure.
• At the 10-8 cm level the spherical symmetry of
  the Na and Cl- ions is evident.
• Electro-weak force
• the change of symmetry is at about 10-16 cm.
• Below 10-16 cm the electromagnetic force and the
  weak nuclear force look the same, except that
  weakons rotate only to the left.

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Observing Heavy Light

• Theory
• Theoretical mass predictions were W about 74
  GeV, Z about 86 GeV.
• Until 1980 the heaviest particle observed was
  Upsilon with 9.4 GeV.
• Experiment
• 1980 CERN accomplished the building of the first
  proton-antiproton supercollider with an effective
  energy of 540 GeV.
• 1983 two experiments (UA1 and UA5) reported the
  first findings of the W bosons. Out of about 1
  million collisions which were sufficiently
  violent for the weakons to form the two
  experiments found only 10 which were associated
  with the W particles.
• 1984 UA1 obtained 14 events corresponding to Z
  and about 100 events corresponding to W and their
  masses were in 3 agreement with the theory.

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The Standard Model Re-Written

• Todays Standard Model is based on the
  electro-weak theory and on quantum
  chromodynamics.
• This theoretical model explains well the
  experimental results.
• But the Standard Model is not a final unified
  theory.
• A final unified theory would probably have a new
  symmetry which incorporates all the known
  particles.
• This theory should explain many numbers that the
  physicists were not able to explain (for instance
  the masses of all fermions).
• The total number of parameters in the Standard
  Model is no less than 27 and it is hard to
  believe that they are all as fundamental as the
  speed of light.

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Limitations of the The Standard Model

• Not a true unification of all 4 forces
• Too many parameters
• The mystery of the 3 generations
• The model of a generation
• No explanation for the fact that the differences
  between the electric charges of various fermions
  must be integers, while the electric charges can
  be fractions.
• No explanation for the fact that the charge of an
  electron is rigorously equal to that of a proton.
• No explanation for the fact that colored fermions
  have fractions of electric charges, while white
  fermions have integer charges.

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Theoretical Alternatives

• The most successful are
• Grand Unification Theories (GUTs)
• Compounds Models such as the Pati-Salam preons.
• Super-symmetry (SUSY) Models
• Superstring Theories
• How to choose between them ?
• Theoretical Consistency
• Experimental verification (predictions)

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The Pati-Salam Model (I)

• Basic idea
• Each quark contains two pre-quarks (or preons),
  one corresponding to the type (u,d,s,c) and the
  other to its colour (red, green, blue).
• Leptons were part of the same model, being built
  with a type preon and a violet preon.
• The number of bricks was reduced from 16(4x34)
  to 8. (see next diagram)
• Implications
• Integer charges for quarks
• Disintegration of quarks into leptons.

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The Pati-Salam Model (II)
Preons
d
u
s
c
red
blue
green
violet
Muonic Neutrino or
Neutrino or
ured
cred
Same for blue and green
uviolet
cviolet
dred
sred
Muon or
Electron or
dviolet
sviolet
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The Life of a Proton

• Will an isolated proton live for ever ?
• Pati-Salams model showed that even proton has a
  finite lifetime 1031 years.
• Statistical meaning
• Proton decays through the weak force into a
  positron and a few neutrinos.
• In the Pati-Salam model the lifetime of a quark
  is 10-9 but the chance of all 3 disintegrating in
  the same time is extremely small.
• Experiments have tried to see decaying protons
  but few were successful
• 1977 in a South African gold mine an experiment
  established a lifetime of 1029 years
• 1983 in the Mont Blanc tunnel a 150 tons detector
  obtained data corresponding to 1031 years
• Experiments at the bottom of the Pacific failed
  to obtain and positive results.

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GUTs

• Put together tables of quarks and leptons
  together with the carriers of forces in their
  interaction
• Use Group Theories (with basic sets,
  representations and classes) to incorporate all
  known particles
• 1973 S.Glashow and H.Georgi propose SU(5), the
  simplest GUT (shown next)
• All GUTs allow quarks to desintegrate into
  leptons through the hyperweak force (X bosons)

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SU(5) Basic Set
photon anti-neutrino
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Another Change of Symmetry

• 1974 - H.Quinn and collab. calculated that the
  SU(5) symmetry can be seen at distances below
  10-29 cm.
• Using SU(5) one can describe the structure of
  matter with the following diagram
• SU(5) colourelectroweak
  colour, weak, elmg.
• 10-29 cm
  10-16 cm
• Higgs bosons could be created through the change
  to the SU(5) symmetry and they are responsible
  for the mass of the X bosons.

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SU(5) and Experiments

• Although we cannot see the world at the 10-29
  cm level (we would need 1015 GeV projectiles !),
  we can test SU(5) through the verifications of
  its predictions.
• 1977 a CERN experiment showed that the ratio
  between the masses of the quark b and the tau
  lepton is larger than 2.5, while SU(5) predicts
  3.
• 1983 the Mont Blanc protons disintegration
  experiment obtains results which suggest 1031
  years as protons lifetime but SU(5) predicts
  1029 years.
• Other, more complex GUTs predict values closer
  to 1031 years.

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Super-Symmetry (SUSY)

• SUSY for each fermion there is a boson with the
  same properties except the spin and the other way
  round.
• All the these particles are organized in
  symmetric super-multiplets.
• As no experiment has seen these new particles,
  SUSY has no real support.
• SUGRASUSY GUTs gravitation. It introduced
  many useful ideas
• It deals with all universal forces
• It introduces the need to work in many dimensions
  (11 dimensions)

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More than 4 Dimensions ?

• Michio Kakus Hyperspace for a history
• Visualizing hyperspace a Sphere in Flatland.

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Supergravity in 11 Dimensions

• Kaluza-Klein model was applied successfully in 11
  dimensions to account for all the particles of
  SUGRA(8). The metric tensor of this model is
  shown below.

Einsteins Gravity
Maxwells Light
Gauge Theory Bosons
Matter quarks and leptons
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Superstrings (I)

• Superstrings correspond to resonances
• The basic idea is that particles correspond to
  resonances that correspond to distinct
  frequencies of vibration of some strings.
• Superstrings are extremely small
• They are 1020 times smaller than a proton, or
  10-36 cm.
• Complicated motions
• No infinities if calculated in 10 dimensions.

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Superstrings (II)

• Recently there were 5 competing 10-dimensional
  superstrings theories
• E.Witten proved the 5 theories to be equivalent
  and related to an 11-dimensional M-Theory
• The M-theory has similarities with supergravity
• Contemporary experiments performed with the most
  powerful supercolliders will try to produce the
  sparticles predicted by the M-theory
• The M-theory has not only superstrings, but also
  2,3.. etc -dimensional branes (multidimensional
  vibrations)