What

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Whats the Matter with Antimatter

• What happened to all the Antimatter in the
  Universe?

2
In 2008 a new space-shuttle mission will be
launched carrying an instrument to look for
antimatter in outer space

• What is antimatter?
• How is antimatter made?
• Why search for it in outer space?
• Why should we care?

3
What is Antimatter?

• Every fundamental particle has an associated
  antiparticle
• Antiparticles have the same mass, lifetime, and
  intrinsic angular momentum (spin)
• Charges, electric and color, are opposite

4
Discovery of Antimatter

• Antimatter was first predicted by Dirac in 1928
  as a consequence of his famous equation combining
  Quantum Mechanics and Special Relativity

• The anti-electron, or positron, was discovered by
  Anderson at Caltech in 1932.
• Antiproton discovered in 1955.
• Antineutron discovered in 1956.
• Antihydrogen in 1997.

5
How do you make Antimatter?

• Need lots of concentrated energy E gt 2mc2
• Particles and antiparticles are always produced
  together

• This is routinely done at particle accelerators
• Total made 1016 antiprotons (10-8 g) 1017
  positrons (10-10 g)

6
How do you detect antimatter?

• Not possible if isolated antimatter behaves
  just like matter
• An anti-atom will have exactly the same spectrum
  as an atom and its chemistry will be identical
  photon is its own antiparticle
• Best way to detect antimatter is to have it
  annihilate with its antimatter partner and detect
  the resulting high-energy products

7
Detecting antimatter by annihilation could be
dangerous!
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What use is Antimatter?

• Imaging PET scan
• Research pp and ee- colliders

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What use is Antimatter?

• Antimatter is the ultimate energy source 50
  of rest mass goes into useable energy
• The energy from
• 1 kg of antimatter
• 1 kg matter
• This is equivalent to
• 1,500,000 kg of natural Uranium
• 30,000,000,000 kg of coal
• NASA investigating its use for space flight
• Two big problems
• how to make it efficiently
• e 1/10,000,000 65 trillion/g!
• how to store it safely

10
What use is Antimatter?
11
Why do Matter and Antimatter Behave Similarly?

• The reason that matter and antimatter behave in
  the same manner is related to fundamental
  symmetries of nature.
• To a physicist a symmetry is an invariance with
  respect to some transformation.
• A picture is symmetric if it is invariant under
  reflection, or Parity, that is, if it can be
  superimposed on its mirror image.

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Snowflakes are Symmetric (Invariant) under
Reflection and Rotations
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Parity is Sometimes Called Mirror Reflection
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Angels and Demons Mirror Symmetric?
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Many Things are not Mirror Symmetric

• Screws are asymmetric and hence not superposable
  on their mirror images
• Such asymmetric molecules are called
  stereoisomers, or left-handed (sinistral) and
  right-handed (dextral) molecules, or enantiomers.

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Why are Symmetries Important in Physics?

• Often problems that would be intractable
  otherwise, can be solved easily by invoking
  symmetry constraints.
• Possible new theories severely constrained by
  known symmetries of nature we would not
  construct a new theory that is not invariant
  under Lorentz transformations, for example.
• Deep relationship between symmetries and the
  great conservation laws of nature.

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The Great Conservation Laws of Physics are all
Related to Symmetries of Space and Time
Discrete
Continuous
Space translation invariance ? Conservation of
Momentum Space rotation invariance ? Conservation
of Angular Momentum Time translation
invariance ? Conservation of Energy
Reflection of space ? Conservation of Parity,
P Reflection of charge ? Conservation of Charge
Parity, C Reflection of time ? Conservation of
Time Parity, T
This profound connection between symmetries of
nature and conservation laws was first
elucidated by (the mathematician) Emmy Noether
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The basic laws of nature are indifferent as to
the direction of time. There is no more
distinction between past and future then between
left and right. Arthur Stanley Eddington, 1927
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Despite Natures Apparent Desire for Symmetry,
it is often Broken
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One Doesnt Have to Go Far to Find Symmetry
Violations in Nature

• Molluscs
• shells come in right- and left-handed varieties
• Some species are always right-handed, some always
  left, and some come in both varieties
• Most are right handed
• Fiddler crabs are asymmetric, but equal amounts
  of both varieties are seen

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Plants too Exhibit Symmetry Violations
Honeysuckle
Bindweed
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Humans are symmetric on the outside, asymmetric
on the inside

• 1/10,000 have their organs reversed situs
  inversus

23
Most Humans are Right Handed
Right-handers tend to see the lower face as
happier, whereas the opposite is true for
left-handers
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Toads are Too!
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At the microscopic level we find further evidence
of asymmetry
DNA Left Right
Amino Acids Left Right

• This asymmetry is not found in inorganic
  substances

Life as manifested to us is a function of the
asymmetry of the universe and the consequences of
this fact Louis Pasteur
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There is More to these Asymmetries than what
Meets the Eye

• Two forms of limonene one smells of orange and
  the other of lemon
• Table sugar, or sucrose, is right-handed. The
  left-handed form (levo-sugar) tastes the same but
  cannot be digested

• Thalidomide
• Right-handed form accounts for sedative
  properties
• Left-handed form caused horrible birth defects
• Has recently been reintroduced

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Mystery

• The fundamental laws of physics appear to be
  perfectly symmetric.
• Life, however, exhibits all sorts of asymmetries.
• How did these asymmetries come about?

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Producing an Asymmetry
the single most important finding since chemists
discovered the chiral carbon atom itself
It was just too good to be true.

• No one has yet succeeded in doing so without
  seeding the bath
• Successes are occasionally reported, but never
  verified.

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Spontaneous Symmetry Breaking
30
Spontaneous Symmetry Breaking
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Spontaneous Symmetry Breaking
32
Fall of Symmetry Conservation in Fundamental
Interactions
Parity First

• First discovered in 1928 (Cox, McIlwraith, and
  Kurelmeyer, Proc. Nat. Acad. Science, 4, 544
  (1928)
• Predicted by Lee and Yang in 1956 (Nobel prize
  1957)
• Rediscovered by Wu et al., Lederman et al., and
  others in 1957
• Only seen in the weak interaction

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CPT Theorem Requires that Either C or T is also
Violated

• CPT theorem based on very fundamental
  assumptions it had better be true!
• Consequences of CPT theorem
• Particles and antiparticles have equal mass and
  lifetimes
• Either C or T is also violated

34
Charge conjugation invariance was also found to
be violated right-handed neutrinos and
left-handed antineutrinos dont exist.
To go from matter to antimatter C is not enough
CP is needed.
35
Matter-Antimatter (CP) Invariance was soon Found
Violated

• Kaons, particles composed of a down quark and an
  anti-strange quark, oscillate back and forth into
  anti-Kaons, 5 billion times per second.
• Matter-antimatter symmetry (CP symmetry) requires
  equal numbers of K0 and anti-K0 decays.
• In 1964 Cronin, Fitch et al., found a 0.23
  difference!
• Only seen in weak interaction.
• Because of CPT, T violated!

is preferred over by 0.23
36
Matter-Antimatter Asymmetry

• Unlike Parity Violation, which lead to a great
  leap forward in our understanding of particle
  physics, the origin of CP violation remains a
  mystery.
• Unlike Parity Violation, which is maximal, CP
  violation is a frustratingly small effect.
• CP violation gives us a convention-independent
  way of distinguishing matter from antimatter we
  can communicate this to other beings on other
  planets.

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• Do these microscopic asymmetries we observe in
  the fundamental laws of physics - Parity
  Violation and/or CP Violation - account for the
  asymmetries we see in Nature?

• Many attempts have been made to link the two, so
  far without success
• One possible exception the greatest asymmetry
  of them all the asymmetry between matter and
  antimatter in the Universe

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Theory of a Symmetric Universe

• We know that the universe started about 13.7
  billion years ago with a big bang

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Symmetric Universe

• The very early universe was composed of equal
  amounts of matter and antimatter.
• After 10-6 s (T1013K) baryons (neutrons and
  protons, and their antipartners) formed as the
  universe cooled.
• The universe was sufficiently dense that by 10-3
  s (T1012K) all the baryons and antibaryons
  annihilated, leaving only photons the
  annihilation catastrophe.

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What Actually Happened

• What we actually observe is quite different
• There is no compelling evidence for any
  antimatter in the Universe
• The observed ratio of baryons to photons is nine
  orders of magnitude too large!

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The Annihilation Catastrophe Almost Happened

• For every 10 billion antibaryons, 10 billion and
  one baryons were produced.
• The one extra baryon is what you and me and the
  rest of the observable Universe is made out of.

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Evidence for Antimatter in the Universe

• Earth there is a trickle of antimatter at
  exotic places such as Fermilab, CERN, SLAC, etc
• Two types of searches
• Direct cosmic rays
• Some antiprotons and positrons seen
• No antinucleus has ever been observed
• Indirect decay products
• Planets weve put things on planets without
  them blowing up.

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Evidence for Antimatter in the Universe

• Sun solar wind is matter.

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Evidence for Antimatter in the Universe

• Clusters of galaxies no g-ray excess from
  intracluster gas

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Antimatter Seen in Crab Nebula?

• Crab remnant of supernova in 1054
• Pulsar is accelerating particles producing matter
  and antimatter
• Chandra X-ray telescope has probably detected
  X-rays from annihilation

46
Antimatter Seen in Crab Nebula?
Chandra X-Ray observatory claims to have seen
evidence of positrons.
47
Antimatter Seen in Galactic Center
Integral
Not much and almost certainly not primordial
antimatter!
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What Caused this Asymmetry?

• For some reason the Universe just started out
  with more matter than antimatter.
• Ugly! Why? Inflation wipes it out anyway.
• Statistical fluctuations caused the difference.
• Cant come close!
• Matter and antimatter exist in widely separated
  regions of the Universe.
• Akin to an explosion where all the Carbon atoms
  ended up in one place, and the Nitrogen atoms in
  another.
• Some dynamical reason caused matter to dominate
  over antimatter.
• Remember by dominate, we mean a preponderance of
  one part in ten billion.

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How to Get an Asymmetry

• Sakharov in 1967 first elucidated the three
  needed ingredients
• Baryon number must be violated. Need a way to
  get rid of matter (or antimatter) that doesnt
  involve annihilation. Grand Unified Theories
  (GUTs) do this.
• Violation of both C and CP. This produces
  different decay rates for particles and
  antiparticles.
• A departure from thermal equilibrium when the
  antimatter was turning into matter. Otherwise,
  if in thermal equilibrium the reverse processes
  occur with an equal rate.

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Theory must Produce the Universe we See!
51
Baryon Number Nonconservation

• Never seen p lifetime gt 1033 years
• Electroweak nonconservation possible through
  quantum tunneling phenomenon sufficiently
  violent?

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Baryon Number Nonconservation Leptogenesis

• Recent discovery of neutrino mass has given this
  idea much impetus to this idea.
• A lepton asymmetry is formed and then
  transformed to a baryon asymmetry
• Lepton electron, muon, neutrinos
• Baryon particles made of quarks

53
CP Violation

• Problems
• the asymmetry seen in 1964 did not involve decays
  but only Kaon mixing
• matter-antimatter asymmetry only seen in the Kaon
  system
• Leptogenesis CP violation never seen in leptons

54
CP Violation Problems Fixed?

1. after a 35 year search an asymmetry in Kaon
   decays was found in 2000
2. in 2001 matter-antimatter asymmetry also seen in
   particles called beauty mesons.
3. searches are beginning to search for CP violation
   in leptons (neutrinos)

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CP Violation

• Problem the CP violation seen so far is too
  weak to cause the asymmetry between baryons and
  antibaryons in the Universe
• we see 10-20 effect, need 10-10
• Solution most beyond-the-standard-model
  theories, such as supersymmetry, predict
  additional, perhaps larger, sources of CP
  violation
• There has been a world-wide search for other
  manifestations of matter-antimatter asymmetry

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HyperCP Search for New Sources of Matter
Antimatter Asymmetries

• Search for a difference in Lambda and anti-Lambda
  hyperon decays
• Hyperon decays are particularly sensitive to new
  sources of CP violation

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HyperCP

• Experiment proposed and largely constructed by
  the UVa group.
• To achieve great sensitivity took more data than
  any other experiment
• 231 billion events
• 120 Terabytes
• 29,401 tapes
• How much is that?
• Encyclopedia Britanica 1 Gbyte
• WWW as of 9/11/02 5 Tbytes
• Video store 8 Tbytes
• Unfortunately no evidence for exotic sources of
  CP violation were found.

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Conclusions

• The copious amounts of matter and antimatter
  created at the very earliest stages of the
  Universe have largely disappeared.
• Matter 1/10,000,000,000 of what was made
  remains.
• Antimatter disappeared almost entirely.
• This large-scale asymmetry between matter and
  antimatter is almost certainly related to the
  microscopic asymmetries in the laws of physics
  that have been discovered in recent years.
• We think we have all the right ingredients needed
  to cause an asymmetry between the matter and
  antimatter in the universe, but the right mix
  remains to be worked out.
• Stay tuned progress is being made.

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Conclusions