What

1
Whats the Matter With Antimatter?Or, The
Leftover Universe

• Dr. Natalie A. Roe
• Lawrence Berkeley National Laboratory

2
Outline

• What is Antimatter? (What is Matter? )
• What is the Matter with Antimatter
• New Result on CP Violation from the Asymmetric B
  Factory
• Why Does it Matter?

3
What is Matter?

• What are the fundamental constituents?

• Greeks Earth, Air, Fire, Water

• 1800s Periodic table of the elements

• 1897 Thomson discovers the electron
• 1919 Rutherford discovers the proton
• 1932 Chadwick discovers the neutron

• 1967 Kendall, Friedman and Taylor discover
  quarks in electron-nucleon scattering experiments
  at SLAC.

• Quarks
• are fractionally charged
• always occur in pairs or triplets, never singly
• come in 6 different kinds, arranged in 3
  generations

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Why Three Generations?

• Only the first generation of particles is needed
  to make our world
• proton (uud) and neutron (udd)
• protons and neutrons form nuclei, electrons to
  form neutral atoms
• 3 fundamental particles to make all of the
  Universe!

Charge
2/3 -1/3 0 -1

• Nature has 2 additional generations of heavier,
  unstable particles
• Why?
• What determines the quark and lepton masses?
• Central questions for particle physicists

Increasing Mass --gt
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The Prediction of Antimatter

• Nature is full of symmetries mathematics is the
  language we use to describe symmetry
• Diracs equation for motion of a relativistic
  electron (1928) had two solutions
• one was the electron
• the other was an electron with
  negative energy

• Dirac originally attributed this
  solution to the proton (only known
  positively charged particle in
  1928!)

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Matter and Energy

• Einstein first realized the equivalence of matter
  and energy
• When matter and antimatter meet, they annihilate
  into energy
• Energy can also materialize as particle-antipartic
  le pairs

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The Discovery of Antimatter

• The positron was discovered in 1932 in cosmic
  rays by Carl Anderson at Caltech
• The photograph shows how positrons were first
  identified in cosmic rays using a cloud chamber,
  magnetic field and lead plate

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More About Antimatter

• All charged leptons and quarks have
  anti-matter
  partners
• n may be its own anti-particle
• Anti-proton was discovered
  in 1955 at Berkeley
  
• billions are now produced
  every year
  at accelerator labs
• Quark-antiquark combinations
  called mesons also exist
• p ud K0 ds
• B0 bd B0 bd

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Imaging With Antimatter

• PET scans use positrons created in radioactive
  beta decay, by detecting the photons created in
  the subsequent e e- annihilation

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How to create and store anti-particles
1. create p p pairs separate out the p
2. store p with magnetic fields accelerate with
RF cavities
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Colliding protons and anti-protons

• At Fermilab, located near Chicago, protons and
  antiprotons collide with the highest energy
  available in the world

• The discovery of the top quark was made in 1995
  at the Tevatron Collider

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Colliding electrons and positrons
Stanford Linear Accelerator Center, Stanford,
California

• At Stanford, electron-positron collisions have
  been used to discover the charm quark, the tau
  lepton - and to study the matter-antimatter
  asymmetry.

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What is the Matter with Antimatter?

• In the Big Bang particle-antiparticle pairs
  were created from pure energy in a spontaneous
  explosion
• Today we cannot detect significant amounts of
  antimatter in the universe - why not?
• Matter and antimatter then annihilated into
  photons but a small amount of matter survived -
  but how?

• In 1967, Sakharov stated
  three conditions necessary
  to
  create an excess of
  matter in the early
  
  Universe - one of which
  is CP Violation in
  particle
  interactions.

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What is CP Violation?

• C Charge conjugation particle
  ?antiparticle P Parity (mirror
  reflection) x ? -x
  
• C and P together change matter to antimatter. If
  the world were CP symmetric, an antimatter world
  would be indistinguishable from our world. Any
  difference between matter and antimatter is
  evidence for CP Violation.Until 1964, most
  physicists assumed that CP symmetry was obeyed in
  all particle interactions.

CP Mirror
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CP Violation Was Discovered In 1964
1980 NOBEL PRIZE
V. Fitch
J.Cronin
Cronin and Fitch discovered the violation of CP
in the decay of the long-lived, CP-odd neutral K
meson into a CP-even final state Br(KL -gt
pp- ) 0.2 There is a difference between
matter and antimatter! We are hopeful that at
some epoch, perhaps distant, this cryptic message
from nature will be deciphered. J. Cronin
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The Motivation for Asymmetric B Factories

• CP violation in K0 ( sd) meson decays has been
  exhaustively studied, but the effect is small and
  theoretical uncertainties are large.
• In B0 ( bd) meson decays, the Standard Model
  predictions for CP violation are theoretically
  clean.
• Large asymmetries between B and anti-B meson
  decay rates into special CP eigenstates are
  expected (10- 50), but the decay rates are small
  gt need a B meson factory
• To observe the CP asymmetry between B and anti-B
  mesons, a special type of ee- collider is
  required with unequal beam energies - the
  Asymmetric B Factory, proposed by Pier Oddone of
  Berkeley Lab in 1987

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Measuring CP Violation with B0s
Not equal CP Violation!
CP violation occurs in the interference between
mixing and decay to a CP eigenstate,
eg B0 -gt p p -
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PEP-II
Stanford Linear Accelerator Center, Stanford,
California
Approved as a Presidential Initiative in 1993
completed in 1999. Reached full
design luminosity in 2000. Japanese B Factory
has also been built with similar design.
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The Asymmetric B Factory Concept
3 GeV e
9 GeV e-
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The BaBar Detector
The BaBar Collaboration 500 physicists from
73 institutions and 9 countries
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How the BaBar Detector Works
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Silicon Vertex Tracker (SVT)
Uses five layers of silicon microstrip
detectors to measure B decay vertices to better
than 0.1 mm
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Tracking Charged Particles in the SVT
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Recipe for Measuring CP Violation in B Meson
Decays

• Produce many B0 B0 pairs (several 10s of
  millions)
• Reconstruct one B in a special decay called a CP
  eigenstate
• Tag the other B0 to make the matter/antimatter
  distinction
• Determine the time between the two B0 decays, Dt,
  using SVT
• Compare Dt distributions for
  B0 and B0
  tagged events
  the difference measures
  
  CP violation, the difference
  
  between matter and
  antimatter

B tagged
B tagged
Dt (ps)
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The PEP-II asymmetric ee? storage ring
E(e-) 9.0 GeV, E(e) 3.1 GeV
This result (56 fb-1)
v?? 0.56 c
Design Achieved
Run2b
Luminosity (cm-2 s-1) 3 x 1033 4.5 x
1033 Int. Lum / day (pb-1) 135
303 Int. Lum / month (fb-1) 3.3 6.3
2nd PRL (30 fb-1)
Run2a
1st PRL (20 fb-1)
Run1
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First Observation of CP Violation in B Decays -
Announced July 6, 2001
NYT Tiny Discovery May Answer a Question About
the Big Bang
-6 -5 -4-3 -2-1 0 1 2 3 4 5 6 7
Dt in trillionths of a second
CP Asymmetry Measuurement sin2b0.590.14
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Latest result Sin2???????????????
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What does this result mean?
sin2b0.750.10

• Maximum asymmetry gt sin2b 1
• Zero asymmetry gt sin2b 0
• Much larger CP asymmetry than in K0 decays
  (75 vs 0.2) and very small theoretical error
• Error is 1/7 of the central value gt very
  unlikely to be a statistical fluctuation
• The result is consistent with the prediction of
  the Standard Model, our best current particle
  theory

• But Standard Model calculations of early
  Universe do not produce a large enough
  matter/antimatter asymmetry!

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Why Does it Matter?

• We believe there must be some new physics beyond
  the Standard Model - this is only one of several
  clues
• As we collect more data, we will measure CP
  violation more precisely, and compare different
  types of asymmetries
• These precision tests of the Standard Model may
  show us an inconsistency which will point the way
  to new physics
• This approach is complementary to the searches
  for new particles at the energy frontier
  accelerators, such as the Fermilab Tevatron and
  the CERN Large Hadron Collider

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Summary

• Antimatter exists and can be created at
  accelerators but there is very little antimatter
  naturally occurring in our Universe

• CP violation is required in any theory starting
  from the Big Bang to explain the dominance of
  matter over antimatter

• CP symmetry between matter and antimatter is
  violated at the quark level
• recent measurement of CP violation in B mesons by
  the BaBar experiment

• We need more CP violation to produce our Universe
  - our theory is not complete!

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Could Antiprotons Be Useful?

• Antimatter engines on Starship Enterprise were
  powered by p p annihilation...
• Creating, storing antiprotons requires a lot of
  energy, and trapping them is also very
  inefficient
• All the antiprotons created in one year at
  Fermilab would only power a 100 watt bulb for 30
  minutes, even with 100 trapping and conversion
  efficiency!

Penning Trap
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Creating Anti-hydrogen
Anti-protrons are created and stored, then passed
through cold xenon gas. An ee- pair is created
as the antiproton passes by the heavy xenon
nucleus. The antiproton and the positron will
occasionally form a stable bound state - an atom
of anti-hydrogen!
Detecting Anti-hydrogen
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The Force Carriers

• Quarks and leptons interact via four different
  types of forces, each with its own force
  carrier
• electromagnetism - the photon, g
• strong force - the gluon, g
• weak force - the W and Z bosons
• gravitational force - the graviton?

• One more particle completes
  the minimal Standard
  Model-
  the Higgs particle
• prime target at Fermilabs
  Tevatron Collider
• CERNs Large Hadron Collider
  will continue search in
  2006

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1957 Discovery of Parity Violation
ne
Co60
n -gt p e- n
B field
e-
Beta Decay of Co60
C.S. WU
The Universe knows its right hand from its left!
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What really happens in beta decay?
proton W boson
neutron
d -gt u W-
proton electron anti-neutrino
W- -gt e- n
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CP was still OK!!
Because P reverses the handedness of a particle,
a left-handed neutrino turns into a right-handed
neutrino in the P-mirror but right-handed
neutrinos do not exist in Nature!
n
n
P
Now if we reflect in the C-mirror and P-mirror
combined, a left-handed neutrino turns into a
right-handed anti-neutrino, which does exist.
n
n
C P