# Presentation: 662372

## What’s the Matter With Antimatter?

***What’s the Matter With Antimatter?***

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

**Notes:**
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.

## The Prediction of Antimatter

**1900 - 1920’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 **

**Notes:**
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

## The Discovery of Antimatter

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

**Notes:**
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 

## What is a Fundamental Particle?

**Greeks:  Earth, Air, Fire, Water**

**1897:  Thomson discovers the electron**
**1911:  Rutherford discovers the nucleus**
**1919:  Rutherford discovers the proton**
**1932: Chadwick discovers the neutron**

**1800’s:  Periodic table of the elements**

**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)**

**Notes:**
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 1967...

## Slide 5

## 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**

- 
- 
- 
- 

**Increasing Mass ******

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

**Do all particles have antimatter partners?**

**Notes:**
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.

## 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

**Notes:**
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.

## The Mirror Universe

**The Mirror Universe**

**All fundamental particles                                                     have anti-matter partners**
**The neutrino********may be its own        anti-particle**
**Quark and anti-quarks form bound **
**states called mesons **
**************ud       ****K****0************ds**
**B****0**** ********bd       ****B****0**** ********bd**

**The “Standard Model” particles **

**Notes:**
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

## Matter and Energy

**Matter and Energy**

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

**Notes:**
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.

## 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****+ ****+ ******
**pn + p => ****3****He + ******
**3****He + ****3****He => ****4****He + 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)**

## 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**

**Notes:**
nuclear annihilation produces photons redshifted into gamma rays today
observed gamma ray spectrum rules out domains smaller than 1000 Mpc
Cohen, duRujula, Glashow 1998

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## Energy budget of Universe

***Dark***
***Energy:***
***~70%***

***Dark***
***Matter:***
***~25%***

*Energy budget of Universe*

**Antimatter:      0%**

- ~25%

- ~70%

## 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 ***

****

**Notes:**
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.

## 1957 Discovery of Parity Violation

**1957 Discovery of Parity Violation**

**The Universe knows its right hand from its left!**

**C.S. WU**

- Co60

- B field

**e-**

******e**

**n -> p e****-**** ******** **

- Beta Decay of Co60

**Notes:**
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.

## Another way to look at CP Violation

- Bob Cahn

- Left-handed particle => Right-handed anti-particle

## An Unexpected Discovery In 1964

- 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 -> 
- 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

**1980 NOBEL PRIZE**

**J.Cronin**

**V. Fitch**

**Notes:**
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!  

## CP Violation => T Violationunless CPT is also violated!

- Antiproton Decelerator at CERN

- ATHENA experiment

- Anti-hydrogen annihilation
- near walls of trap

## 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?

- 1975 Nobel Peace Prize

- All of these ingredients were present
- in the early Universe!

## 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.**

**quark doublets**

**e**
******e**

****
********

****
********

**lepton doublets**

- Standard Model Particles

## An Asymmetric B Factory to Study CP Violation

**CP violation in K****0**** (******** sd) meson decays was exhaustively studied for over three decades **
**the effects are very small, and hard to interpret theoretically**
**In B****0**** (******** 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**

**Notes:**
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.  

## Slide 22

## 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.

**Notes:**
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.

## The BaBar Collaboration: 

**The BaBar Collaboration: **
** ****~600 physicists from 73 **
**institutions and 9 countries**

**  ****The BaBar Detector**

**Notes:**
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.

## How the BaBar Detector Works

**Notes:**
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.

## Measuring CP Violation with B0s

**Measuring CP Violation with B****0****s**

**Not equal –**
**CP Violation!**

## B0B0 Mixing

**Matter-antimatter oscillations occur in neutral K****0**** and B****0**** 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**

*B*0

*b*

*d*

*   **t*

-    *t*

*W***

*W***

- the mixing “box” diagram

- first  - third
- generation
- coupling

## The Asymmetric B Factory Concept

- 9 GeV e-

- 3 GeV e+

**Notes:**
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

## Golden Mode for CP Violation in B decay

** ****B****0**** ************J/********K****s**** is the best decay mode to measure the CP violating angle ********, the phase due to the mixing diagram**
**B****0**** ************J/********K****s ****also has a relatively large branching ratio (1 per million) and is “easy” to reconstruct**

**Golden Mode for CP Violation in B decay**

*b*

*d*

*c*

*c*

*s*

*d*

- W+

*Ks*

*J/***

## 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, t
- Compare t distributions for                                                      B0   and B0  tagged events;                                                            the difference measures                                                              CP violation, the difference                                                            between matter and                                                                      antimatter

**B tagged**
**   **

**B tagged**
**     **

- t (ps)

**Notes:**
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.

## 270 Million BB pairs produced since 1999 and recorded by the BaBar detector

- Year

## 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 by~10,000 PMTs**

## 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.

**Notes:**
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.  

## Tracking Charged Particles in the SVT

**Tracking Charged Particles in the SVT**

**Notes:**
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.

## Latest results from BaBar on 

- difference of matter and antimatter:

- Sin2

## What does this result mean?

**sin2********=0.72±0.04**

**Maximum asymmetry => sin2********1**
**Zero asymmetry => ****sin2********0**
**Much larger asymmetry than in K****0**** 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!**

## 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...**

**Notes:**
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.

## sin 2in a different mode

**sin2********measured in final states with charm agrees with the Standard Model predictions**
**sin2********can also be measured in other “penguin” decays and should agree within a few percent **
**New physics could enter in loops!**

- 

*b*

*d*

*c*

*c*

*s*

*d*

- W+

*Ks*

*J/***

- tree diagram

- penguin diagram

## World average for sin2 in “penguins” compared to J/Ks

**World average for sin2******** in “penguins” compared to J/********K****s**

- ... hint of new physics, or a statistical  fluctuation?

## 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 **

## Summary

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

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

**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**

## The Anti-Hydrogen Economy?

**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!**

## What really happens in beta decay?

- neutron

- d u + W-

- proton + W boson

- W- e- + 

- proton + electron + anti-neutrino

## 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!**

**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.**

- 

- 

- 

- 

- P

- C P

## The Force Carriers

**Quarks and leptons interact via four different types of forces, each with its own force “carrier”**
**electromagnetism - the photon,  ******
**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**

**Notes:**
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.   

## 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****?**

## v 0.56 c

**E(e****-****) = 9.0 GeV,   E(e****+****) = 3.1 GeV**

**v******** 0.56 c**

_**Design      Achieved**_

**Luminosity (cm****-2**** s****-1****)     3 x 10****33****   4.5 x 10****33**
**Int. Lum / day (pb****-1****)       135          303**
**Int. Lum / month (fb****-1****)    3.3           6.3**

**2****nd**** PRL (30 fb****-1****)**

**The PEP-II asymmetric e****+****e******** storage ring**

**1****st**** PRL (20 fb****-1****)**

**This result**
**(56 fb****-1****)**

**Run1**

**Run2a**

**Run2b**

## First Observation of CP Violation in  B Decays - Announced July 6, 2001

**First Observation of CP Violation in  B Decays - Announced July 6, 2001**

- t in  trillionths of a second

- 

**CP Asymmetry Measuurement:  sin2********=0.59±0.14**

- NYT:  “Tiny Discovery May Answer a Question About the Big Bang”

## Latest result:

- Sin2