Dark Matter and Dark Energy

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Matter-Antimatter Asymmetry

• Sridhara Dasu
• University of Wisconsin

Some portions adapted from H. Maruyama,
UC-Berkeley
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Outline

• What is anti-matter?
• What led us to it?
• But, why is it so rare?
• The Standard Model
• Flavor
• Mixing
• Fundamental asymmetry between matter-antimatter
• Experimental Program
• Meson decay asymmetries
• Quark mixing parameters

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The smallness of the electron

• At the end of 19th century
• Physicists pondered about the electron
• Electron is point-like
• At least smaller than 10-17 cm
• Like charges repel
• Hard to keep electric charge in a small pack
• Need a lot of energy to keep it small!

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Ehn, Emc2

• Need LOTS of energy to pack electric charge
  tightly inside the electron
• But the observed energy of the electron is only
  0.5 MeV
• Breakdown of theory of electromagnetism

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Uncertainty Principle

• Energy-Time Uncertainty Principle
• You can violate energy conservation but only for
  a short time

Werner Heisenberg
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Relativistic Quantum world

• Dirac formulated Relativistic Quantum Mechanics
• Schrodinger equation
• Not relativistic (space2 but time1)
• Predicted antimatter
• Anderson discovered positron
• Vacuum is full of quantum bubbles!

Paul Adrian Maurice Dirac
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Anti-Matter Helps

• Electron creates a force to repel itself
• Vacuum bubble of matter anti-matter
  creation/annihilation
• Electron annihilates the positron in the bubble
• ? Size of the electron is no longer a relevant
  parameter - the closer you probe, the more you
  see the structure of vacuum matter and
  antimatter pairs

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Anti-Matter Helps

• Anti-matter attraction cancels Like-charge
  repulsion
• It does not cost too much energy to tightly pack
  the electric charge inside the electron
• Needed anti-matter double particles
• Theory of electromagnetism (QED) now works at
  very short distances (12 digits accuracy!)

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Matter-Antimatter

• All elementary particles come in matter-
  antimatter pairs
• Opposite electric charge
• Identical in almost all other respects
• Electron-Positron
• Proton-Antiproton
• Neutron-Antineutron
• Up quark - Anti up quark
• Energy conservation can be violated for short
  periods of time to generate any of these or other
  particle-antiparticle pairs in vacuum
• Relativistic Quantum Mechanics

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Elementary particles
Heavier elementary particles decay - only the
first generation (e,u,d), photons (g) and
neutrinos (n) are stable.
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Flavor Changing Interactions

• Charged W particles (like photons but massive -
  80 GeV) change flavor of quarks
• For short period energy conservation can be
  violated to create virtual heavy W particles
• Heavier quarks, leptons decay to lighter
  generations (u, d, electron, neutrinos)
• Cross generational coupling exists
• b quark decays to c quark X
• The down-type quarks mix together
• Quantum mechanical superposition of states

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Quark Mixing Matrix
Matter reactions are transposed to antimatter
reactions using CP transformation - i.e., CP
asymmetry is allowed.
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Mesons and Baryons
Free quarks cannot exist - they always occur in
meson or baryon clusters.
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Mesons

• Many types
• Decays
• Detection
• Interactions with matter
• Calculating combined masses using detected
  particles

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Matter-Antimatter AsymmetryEarly Universe
10,000,000,001
10,000,000,000
They basically have all annihilated away except a
tiny difference between them
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Baryon AsymmetryCurrent Universe
us
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They basically have all annihilated away except a
tiny difference between them
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Sakharovs Conditions

• Necessary requirements for genesis of our
  universe
• CP violation
• Baryon, Lepton number violation
• protons ? anti-protons
• electrons ? positrons
• Consequences
• CP violation
• Proton decay, etc.

CP violation is experimentally observed in meson
systems. However, all particle reactions observed
in nature so far conserve total Baryon and Lepton
numbers!
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CP Violation Strange Mesons

• Discovered in kaon system (Cronin and Fitch)
• Theoretically difficult (confinement effect for
  light quarks in mesons is difficult to compute -
  relativistic quantum mechanics calculations)

Pursuing studies in more theoretically
accessible heavy B meson system
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Detector
Particle physicists can reconstruct the events
that occur when high energy matter-antimatter are
annihilated. Allows one to probe what happened in
the early universe when these particles were
abundant!
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Upsilon Meson BaBar Events
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CP Violation B meson system
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Summary

• Matter Antimatter Asymmetry
• Is necessary for the very existence of our
  universe
• Requires CP violation and Baryon/Lepton number
  violation
• CP Violation
• Observed in K meson system 1964, 1998
• Observed in B meson system
• Detailed measurements in progress
• Baryon/Lepton number violation
• Proton decay not observed yet
• Many theoretical models
• Avenues for exploration abound
• Both laboratory and astrophysical searches
  underway/planned