What

1
Whats the Matter With Antimatter?

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

2
The Prediction of Antimatter

• 1900 - 1920s Development of relativity,
  quantum mechanics
• 1928 Paul Diracs relativisitic equation of
  motion for the electron
• Predicted the positron, antimatter partner of the
  electron
• Predicted that negative protons must also exist
• Speculated that half the stars may be made of
  antimatter

3
The Discovery of Antimatter

• The positron was discovered in 1932 in cosmic
  rays by Carl Anderson

4
What is a Fundamental Particle?

• Greeks Earth, Air, Fire, Water

• 1800s Periodic table of the elements

• 1897 Thomson discovers the electron
• 1911 Rutherford discovers the nucleus
• 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
• occur in pairs or in triplets, never singly
• are point-like objects (to the limit of our
  ability to measure)

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Quirks of quarks

• Two types of quarks are needed to make our world,
  up and down
• proton (uud) and neutron (udd)
• protons and neutrons form nuclei
• add electrons to form neutral atoms
• neutrinos are emitted in nuclear processes that
  power the sun
• 4 fundamental particles are building blocks of
  our world

Charge
2/3 -1/3 0 -1

• 2 additional generations of particles have been
  discovered
• Why 3 generations?
• What determines their masses?
• What determines their decays?

Increasing Mass --gt

• Do all particles have antimatter partners?

7
Discovery of the Anti-proton at Berkeley Lab in
1955
Surrounding Edward Lofgren (center), head of the
Bevatron, are discoverers of the antiproton,
(left to right) E.Segre, C.Wiegand, O.
Chamberlain and T.Ypsilantis.
E.O. Lawrence, inventor of the cyclotron and
founder of Berkeley Lab
1939 Nobel Prize in Physics
1959 Nobel Prize in Physics
8
The Mirror Universe

• All fundamental particles
  have anti-matter
  partners
• The neutrino ( n ) may be its own
  anti-particle
• Quark and anti-quarks form bound
• states called mesons
• p ud K0 ds
• B0 bd B0 bd

The Standard Model particles
9
Matter and Energy

• Einstein first realized the equivalence of matter
  and energy
• When matter and antimatter meet,
• they annihilate into energy

10
Antimatter Production in the Sun

• Every second, thermonuclear reactions in the sun
  convert 600 million tons of hydrogen into 595
  million tons of helium, and 5 million tons of
  mass is converted to energy
• p p gt pn (deuterium) e n
• pn p gt 3He g
• 3He 3He gt 4He p p
• Solar flares accelerate particles, producing
  electron-positron pairs.
• 0.5 kg antimatter produced in large flare!
• Image of flare by RHESSI satellite
  (PI Bob Lin of UC
  Berkeley/SSL)

11
Where is all the Antimatter?

• No antimatter within our galactic cluster
• Can Universe be a quilt of matter antimatter
  domains?
• Gamma ray spectrum in space rules out antimatter
  domains smaller than 1000 Mpc
• No evidence yet for antimatter in primordial
  cosmic rays

• The AMS experiment will search for primordial
  antimatter from its orbit on the International
  Space Station

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     Results 1 - 10 of about 589,000 for
antimatter definition. (0.10 seconds)       Anti
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13
Energy budget of Universe
Dark Energy 70
Dark Matter 25
Antimatter 0
25
70
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Symmetries of Matter C, P and T

• C Charge conjugation particle
  ?antiparticle P Parity (mirror
  reflection) x ? -x
  
• C and P together change matter to antimatter
• T Time reversal t ? -t
• The product CPT always invariant!!!

CP Mirror
?
15
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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Another way to look at CP Violation
Left-handed particle gt Right-handed anti-particle
Bob Cahn
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An Unexpected Discovery In 1964
1980 NOBEL PRIZE
V. Fitch
J.Cronin
Cronin and Fitch discovered CP violation 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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CP Violation gt T Violationunless CPT is also
violated!
Antiproton Decelerator at CERN
Anti-hydrogen annihilation near walls of trap
ATHENA experiment
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Sakharovs Recipe for BAU (1967)(Baryon
Asymmetry of the Universe)

• Necessary ingredients are
• Baryon number violation
• Thermal non-equilibrium
• C and CP violation
• Do we understand the cause of CP violation in
  particle interactions?
• Can we calculate the BAU from first principles?

All of these ingredients were present in the
early Universe!
1975 Nobel Peace Prize
20
An Astounding Connection

• In 1973, M. Kobayashi and T. Maskawa predicted
  CP violation ? third generation of quarks!
• Subsequent discoveries confirmed the prediction
  
• b quark was discovered in 1977 at Fermilab by
  Lederman et al
• t quark was discovered in 1994 at Fermilab by
  CDF and D0
• The three-generation Standard Model naturally
  includes CP violation in certain particle decays.

e ?e
? ??
? ??
quark doublets
lepton doublets
Standard Model Particles
21
An Asymmetric B Factory to Study CP Violation

• CP violation in K0 ( sd) meson decays was
  exhaustively studied for over three decades
• the effects are very small, and hard to interpret
  theoretically
• In B0 ( bd) meson decays, the Kobayishi- Maskawa
  theory predicts large CP violation effects
• besides being large, the effects are
  theoretically clean
• But - the decay rates are small gt need to
  produce millions of B mesons in a B 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

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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 BaBar Detector
The BaBar Collaboration 600 physicists from
73 institutions and 9 countries
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How the BaBar Detector Works
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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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B0B0 Mixing

• Matter-antimatter oscillations occur in neutral
  K0 and B0 mesons
• Mixing adds CP violating couplings, with time
  dependence
• Observation of the time dependence requires the
  use of asymmetric energy beams
• this boosts the B mesons so they travel a
  measurable distance before decaying
• measuring the B decay vertices establishes when
  the B decayed

t
B0
W-
W-
d
b
t
first - third generation coupling
the mixing box diagram
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The Asymmetric B Factory Concept
3 GeV e
9 GeV e-
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Golden Mode for CP Violation in B decay

• B0 ? J/Y Ks is the best decay mode to measure
  the CP violating angle b , the phase due to the
  mixing diagram
• B0 ? J/Y Ks also has a relatively large branching
  ratio (1 per million) and is easy to reconstruct

b
c
J/Y
c
W
s
Ks
d
d
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Recipe for Measuring CP Violation in B Meson
Decays

• Produce many B0 B0 pairs (hundreds 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
• 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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270 Million BB pairs produced since 1999 and
recorded by the BaBar detector
Year
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How to tag a B or anti-B meson The DIRC
Detector

• Angle of Cherenkov light is related to particle
  velocity
• Transmitted by internal reflection
• Detected by10,000 PMTs

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How to measure the decay timesThe Silicon
Vertex Tracker (SVT)
Uses five layers of silicon microstrip
detectors to measure B decay vertices to better
than 0.1 mm and determine the time between the
two B meson decays.
34
Tracking Charged Particles in the SVT
35
Latest results from BaBar on difference of
matter and antimatter
Sin2???????22?????040?0.023
36
What does this result mean?
sin2b0.720.04

• Maximum asymmetry gt sin2b 1
• Zero asymmetry gt sin2b 0
• Much larger asymmetry than in K0 decays
  (72 vs 0.2) combined experimental plus
  theoretical error is small
• The result is consistent with the prediction of
  the three-generation Standard Model

• But our best calculations of early Universe do
  not produce enough excess matter - off by 10
  orders of magnitude!

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What is the Matter with Antimatter?

• How can a parameter between 0 and 1 provide the
  missing 10 orders of magnitude?
• It cant
• New particles can provide the required CP
  violation
• The effects of new particles may be observable in
  B decays

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sin 2b in a different mode

• sin2b measured in final states with charm agrees
  with the Standard Model predictions
• sin2b can also be measured in other penguin
  decays and should agree within a few percent
• New physics could enter in loops!

, f
b
c
J/Y
c
W
s
Ks
d
d
tree diagram
penguin diagram
39
World average for sin2b in penguins compared to
J/Y Ks
hint of new physics, or a statistical
fluctuation?
40
Future Prospects for BaBar

• The BaBar experiment has published 150 papers
  so far in refereed journals on a wide variety of
  topics
• Expect to collect 4x more data over next 3-4
  years gt statistical errors will decrease by x2
• In a race with the Japanese B Factory
• behind right now in total luminosity
• advantage in the ability to confirm any
  unexpected results
• The Large Hadron Collider at CERN will turn on in
  2007, data taking by 2008
• could directly produce new particles

41
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, as measured by BaBar
  - but not enough !

• More detailed measurements may give clues to new
  physics beyond the Standard Model

42
The Anti-Hydrogen Economy?

• Distinguish between energy source and method to
  store and transport energy -
• 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!
• Cost 62.5 trillion per gram!

43
What really happens in beta decay?
proton W boson
neutron
d -gt u W-
proton electron anti-neutrino
W- -gt e- n
44
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
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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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Whats the Matter with Antimatter?

• Our present view of matter - the Standard Model
  of particle physics
• The amazing prediction and discovery of
  antimatter
• Is antimatter useful, Dr. Spock?
• Colliding matter and antimatter
• What happened to all the antimatter ? - the
  search for CP Violation
• Why does it matter?

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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???????????????