1. What’s the Matter With Antimatter?
Thank you for the introduction.
This evening my topic is “What’s the Matter with Antimatter”, and my title slide is an artist’s impression of matter meeting antimatter, and as they shake hands they annihilate. Obviously antimatter is not something that we are used to dealing with in our every day life, for if it were we would surely find a safer way to greet strangers than shaking hands and risking annihilation!
This evening I will introduce you to the world of antimatter and try to explain that it is not so different, after all, and that the real puzzle is why there is any matter in the Universe at all.
Dr. Natalie A. Roe
Lawrence Berkeley National Laboratory

2. The Prediction of Antimatter
’s: Development of relativity, quantum mechanics
1928: Paul Dirac’s 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
1933 Nobel Prize in Physics
Hubble used 100m telescope on Mt Wilson to observe
first galaxies outside of our own and realized they are
almost all moving away from us with velocity proportional
to their distance - Hubble’s law, implying that the universe
is not static and famously causing Einstein to regret
the insertion of the cosmological constant into the
equations of general relativity to offset gravity and make
the universe static. How surprised would he be if he knew
that the cosmological constant has made a come back as
one theory for dark energy.
Physics: in addition to relativity the revolution of QM
Dirac tried to unify new fields of relativity and QM by
writing down relativistic equation of motion for the e-,
found 2 solutions and realized the 2nd solution was
not a negative energy e- but an anti-electron or
positron with positive energy. Prediction of antimatter
soon confirmed by in cosmic ray experiments by
Anderson at Caltech, and both Dirac and Anderson
received nobel prizes.
Concept of antimatter combined with Einstein’s
equation relating matter and energy meant that
matter could be created out of energy in particle
antiparticle pairs and in his Nobel lecture Dirac
speculated that there must be antimatter worlds
out there in the universe
Precision data has since shown us a wide variety
of new particles and their anti-matter counterparts,
and Alan Guth’s theory of inflation explailned how
the universe starting in a Big Bang could have become
so flat and so uniform
However the symthesis of all these theories and
this precision data is still lacking and there are
many open questions. We are still waiting for the
21st century Newton

3. The Discovery of Antimatter
The positron was discovered in 1932 in cosmic rays by Carl Anderson
1936 Nobel Prize in Physics
Antimatter started as a figment of Dirac’s imagination, but amazingly enough he was correct and the experimental evidence for antimatter was found just 4 years after he wrote down his famous equation.
Cosmic rays are particles that enter our atmosphere from outer space, often very energetic particles that may have originated far away in some cataclysmic event. For example if an energetic proton enters our atmosphere and collides with a molecule of air, it will produce what we call a shower of particles, growing in number as they diminish in energy. Particle antiparticle pairs are created in these showers. By observing cosmic rays with a bubble chamber, Carl Anderson found evidence for positively charged particles

4. What is a Fundamental Particle?
Greeks: Earth, Air, Fire, Water
1800’s: 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.
Definition of fundamental - like lego blocks
Greeks - Democritus had a competing theory, that everything was made of atoms - Greek for uncuttable. But Socrates favored the theory of 4 elements as being more elegant, and the atomic theory languished for thousands of years.
In the 1800’s the concept of the atom came back as chemistry advanced and many elements were identified and organized into the Periodic Table according to atomic weight, ~ 100 elements
A series of discoveries beginning in 1897 with JJ Thomson’s measurement of the electron’s charge/mass ratio led to our modern view of the atom - a nucleus consisting of protons and neutrons, surrounded by a cloud of much lighter electrons. Only 3 fundamental particles needed - very elegant.
But this tidy picture was changed forever in
Quarks
are fractionally charged
occur in pairs or in triplets, never singly
are point-like objects (to the limit of our ability to measure)

6. 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 -1
2 additional generations of particles have been discovered
Why 3 generations?
What determines their masses?
What determines their decays?
uud = proton, udd = neutron - explain charge
Greek letter nu stands for Neutrinos - fascinating particles, almost massless, neutral and able to pass through the earth without interacting.
All the complexity of the periodic table, over 100 elements, can be explained in terms of 3 fundamental particles. A theory with an elegance Socrates would appreciate.
The additional generations are heavier and short-lived, decaying down into the first generation in fractions of a second. Particle physicists have discovered 4 additional quarks, called the charm, strange, top and bottom quarks. In addition we have discovered cousins of the electron that are very similar except for the fact that they are much heavier and unstable. Greek letters mu for muon and tau.
Increasing Mass -->
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
Lawrence and McMillan set Bevatron energy at 6 GeV in order to have sufficient energy to produce p p-bar pairs.
Anti-protons were produced by colliding protons into a target, then selecting negatively charged particles with the momentum expected for anti-protons. Velocity was determined using both time of flight and Cerenkov counters. p = mv, so determining both p and v allowed determination of m which should be equal to the proton mass.
1939 Nobel Prize in Physics
1959 Nobel Prize in Physics

8. The Mirror Universe p+ = ud K0 = ds B0 = bd B0 = bd
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
Antimatter sounds lke something only in Star Trek but
it is science fact and a very normal part of the SM of particle physics
explain baryons and anti-baryons
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
Energy can also materialize as particle-antiparticle pairs
This is what happened in the “Big Bang” g e- e+ e- e+ g
Feynman diagram
total energy of universe can stil be zero because energy in
the mass of the particle antiparticle pairs is offset by the
negative energy in the gravitational field
So universe could be a quantum fluctuation, created literally
out of nothing.

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 => pn (deuterium) + e+ + n
pn + p => 3He + g
3He + 3He => 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)
Gamma Ray emission
from Solar flare on
July 23, 2003
Blue = MeV
Purple = MeV
Red = 2.2 MeV

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
nuclear annihilation produces photons redshifted into gamma rays today
observed gamma ray spectrum rules out domains smaller than 1000 Mpc
Cohen, duRujula, Glashow 1998
The AMS experiment will search for primordial antimatter from its orbit on the International Space Station

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13. Energy budget of Universe
Dark
Energy:
~70%
Dark
Matter:
~25%
Antimatter: %
~25%
~70%

14. 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!!! + e- - e+
CP Mirror
C alone is not enough because of a property called spin that particles have; parity reverses the spin, just like changing a right-handed screw to a left-handed screw. Anti-particles not only have opposite charge but they also have opposite spin. g e- e+ g e- e+ 

15. 1957 Discovery of Parity Violationne
Co60
n -> p e- n
B field e-
The experiment performed by Wu in 1957 involved C060 atoms that were polarized in a magnetic field . Wu measured the direction of the electrons that were emitted when Co60 underwent beta decay, a weak interaction in which a neutron decays to a proton, emitting an electron and an anti-neutrino which goes undetected. Wu found electrons were emitted only in the direction opposite to that of the applied magnetic field, and never in the opposite direction.This total violation of parity symmetry was profoundly shocking because it was the first evidence that Instead of being perfectly symmetric a the subatomic level, Nature knew its left hand from its right hand.
Beta Decay of Co60
C.S. WU
The Universe knows its right hand from its left!

16. Another way to look at CP Violation
Left-handed particle => Right-handed anti-particle
Bob Cahn

17. 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 -> p+p- ) ~ 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
This tiny asymmetry means that if we were to communicate with intelligent life in a distant part of the galaxy, we could ask their particle physicists to tell us the results of their experiments with K mesons and determine whether they lived in a matter world or an antimatter world!

18. CP Violation => T Violation unless CPT is also violated!
Prototype for a next generation experiment to trap anti-hydrogen and characterize with laser spectorscopy J. Fajans, J. Wurtele et al
Discovery of CPT violation would be revolutionary!
Alpha Test Trap and Superconducting
Magnet Prototype built at LBNL
Antiproton Decelerator at CERN
Anti-hydrogen annihilation
near walls of trap
ATHENA experiment

19. Sakharov’s 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!
(nB - nB )/ ng= 6.1 x 10-10
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. u d
c s t b 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 => 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 e+e- collider is required with unequal beam energies - the Asymmetric B Factory
It wasn’t enough just to observe CP violation as a tiny effect in K meson decays - we want to understand where it comes from. Is it a peculiarity that is somehow confined only to K mesons? Or is it a generic feature? To answer these questions, raised by Cronin in his Nobel prize speech, we need to study CP violation in another system that will allow us to get answers with fewer theoretical uncertainties.

22. 1999: Pier Oddone and Jonathan Dorfan in the PEP-II tunnel

23. Stanford Linear Accelerator Center,
PEP-II
Stanford Linear Accelerator Center,
Stanford, California
Approved as a Presidential
Initiative in 1993; completed
in Reached full design
luminosity in 2000.
Japanese B Factory has also
been built with similar design.
Collide electrons and positrons to create B anti-B meson pairs, hence name of detector - BaBar.
Japanese B Factory located in Tsukuba was completed at about the same time and has similar performance, so we are in a race with them.

24. The BaBar Collaboration: ~600 physicists from 73
The BaBar Detector
The BaBar detectors is a huge enormously complicated instrument. It weighs 1200 tons, has hundreds of thousands of readout channels and involves cutting edge technology in electronics, instrumentation and computing. It took 500 physicists about 5 years to build it at a rough cost of $100M. About half of the physicists come from countries outside the US, and they contributed about half the cost as well.
The BaBar Collaboration:
~600 physicists from 73
institutions and 9 countries

25. How the BaBar Detector Works
The Babar detector consists of layers of detectors, beginning with the precise silicon vertex detectors close to the interaction point to measure the B decay vertices, followed by drift chambers to track charged particles inside a magnetic field, particle identificaiton devices, calorimetry to measure photons and electrons, and muon detectors located in the iron yoke of the magnet.

26. Measuring CP Violation with B0s
B0(t)
fCP B0
Not equal –
CP Violation!
CP violation occurs in the interference between mixing and decay to a CP eigenstate, eg B0 -> p+ p -

27. B0B0 Mixing the mixing “box” diagram
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 b d B0 B0 W- W- d b t
first - third
generation
coupling
the mixing “box” diagram

28. The Asymmetric B Factory Concept
e+ e-->U(4S) ->BB
decay of B “tag”
B ->CP eigenstate
3 GeV e+
9 GeV e-
Dt µ Dz
The asymmetric B factory concept is illustrated here.
Imagine this is the beampipe, and the e- beamcomes this way and collides with lower energy e+ beam here, producing the Upsilon (4S) resonance…
Mention tagging

29. 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

30. 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
Here is the recipe that we must follow to measure CP violation in B decays.
The end result is a histogram such as you see here.
We are looking for a difference between the red curve and the blue curve. The area under each curve is the same, which means there are just as many B0 events as B0-bar events. We have to see the time separation between their vertices in order to detect the asymmetry - this is the reason for the unequal beam energies.
B tagged
Dt (ps)

31. 270 Million BB pairs produced since 1999 and recorded by the BaBar detector
Year

32. How to “tag” a B or anti-B meson: The DIRC DetectorK+
p - n
B0 -> D* e n
Angle of Cherenkov light is related to particle velocity
Transmitted by internal reflection
Detected by~10,000 PMTs
Particle
Quartz bar
Cherenkov light
Active Detector Surface

33. How to measure the decay times: The 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.
You might be wondering what is is like to work with 500 other physicists, and how we ever got organized enough to build such a complicated detector. The answer is that the BaBar detector is divided into several different sub-detectors, and smaller groups were organized to build each of these. I led a group of 6 US and 6 Italian institutions that built the silicon vertex tracker, or SVT. This device uses precision silicon microstrip detectors with an accuracy of about 1/100th of a mm, allowing us to point back to where the B meson decayed with an accuracy of 1/10th of a mm.

34. Tracking Charged Particles in the SVT
This shows an end view of the SVT and how the charged tracks bend in the magnetic field. Each blue line is a detector that registers a hit wherever a track crosses it.

35. Latest results from BaBar on
difference of matter and antimatter:
Sin2220400.023

36. What does this result mean?
sin2b=0.72±0.04
Maximum asymmetry => sin2b = 1
Zero asymmetry => 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!

37. What is the Matter with Antimatter?
How can a parameter between 0 and 1 provide the missing 10 orders of magnitude?
It can’t
New particles can provide the required CP violation
The effects of new particles may be observable in B decays…
I’ve tried to show that antimatter is very similar to matter at the particle level. However, when we look around our Universe there is noticeable problem: everything is made of matter and there is very little antimatter.
In the Big Bang...
If there were regions of antimatter in our Universe, we would expect to detect the characteristic photons created when matter and antimatter annihilated at the interface. Experiments have searched for this signature and found nothing.
Andrei Sakharov, the dissident Russian physicist who was awarded the Nobel Peace Prize, made a remarkable observation back in 1967.

38. 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 => 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?
Antimatter engines on Starship Enterprise were powered by p + p annihilation!
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!
Penn State Univ
Penning Trap
Penning Trap

43. What really happens in beta decay?
neutron
d -> u + W-
proton + W boson
proton + electron + anti-neutrino
W- -> 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

45. 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 Fermilab’s Tevatron Collider
CERN’s Large Hadron Collider will continue search in 2006
To complete our picture of matter, we have to describe how the fundamental particles interact.
We have identified just 4 forces, each with its own associated carrier particle which transmit the force between particles.
Higgs - another lecture topic. An elusive particle that is responsible for giving mass to all particles.

46. What’s 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?

47. The PEP-II asymmetric e+e 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) x x 1033
Int. Lum / day (pb-1)
Int. Lum / month (fb-1)
2nd PRL (30 fb-1)
1st PRL (20 fb-1)
Run2a
This result: 56 fb-1 on-resonance.
62 million BB events.
Run1

48. First Observation of CP Violation in B Decays - Announced July 6, 2001
NYT: “Tiny Discovery May Answer a Question About the Big Bang”
Dt Distributions for B0
and B0 - tagged events
Difference between B0
and B0 tagged events vs
time between decays
Dt in trillionths of a second
CP Asymmetry Measuurement: sin2b=0.59±0.14

49. Latest result:
Sin2