Where has all of the antimatter gone
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Where has all of the Antimatter Gone?. Kevin Pitts University of Illinois September 26, 2001. Outline. Why do we think the antimatter is missing? Quarks, gluons and all that the early universe The Fermilab Tevatron The CDF Detector

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Where has all of the antimatter gone

Where has all of the Antimatter Gone?

Kevin Pitts

University of Illinois

September 26, 2001



  • Why do we think the antimatter is missing?

    • Quarks, gluons and all that

    • the early universe

  • The Fermilab Tevatron

  • The CDF Detector

  • What it’s like to collaborate with 500 others

  • What the future holds

I. Physics

II. Technology

III. Sociology

The standard model

The Standard Model

  • 6 quarks

    • quarks combine to make hadrons

    • p=uud, +=ud

  • 6 leptons

    • “free particles”

    • electron, electron neutrino

  • Bosons carry force

    • W,Z,,g




  • Masses are heirerarchical

    • strange “heavier” than down

    • bottom “heavier” than strange

  • More massive particles more difficult to produce in accelerators

    • converting energy to matter

    • more energy = more difficult

  • Aside: in Standard Model, neutrinos are massless.

    • Experimental evidence indicates that neutrinos do have mass

Mass energy


  • Einstein was right:

    • the speed of light, c, is a constant

    • therefore, we have an equivalence between mass and energy

  • Implications:

    • the kinetic energy of the collisions can be converted to mass!

      • Example: pp  tt + X

      • kinetic energy of proton/antiproton gets converted into top quark mass

    • Massive particles can decay to products with less mass

      • Example: t  b 

      • m(top) >> m(b) + m() + m()

      • the remaining mass/energy of the top goes into kinetic energy of the b, , and 

E = mc2

Universal evolution

Universal Evolution

  • The early universe (t<1sec) was quite hot…so hot that there was a “soup” of quarks, photons and gluons

    • reaction:   qq proceeded in both directions

      • photons creating matter/antimatter (need high-energy photons)

      • matter/antimatter annihilation (can be low energy quarks)

    • these types of reactions are quite frequent in particle accelerators and are well measured

  • The universe cooled  lower energy 

    • cool universe: qq   and not the opposite direction!

  • Produce equal amounts of matter and antimatter. Annihilation requires equal amounts of matter and antimatter….

    • Q: Why isn’t the universe full of photons?

    • Q: Why aren’t there equal amounts of matter and antimatter left?



  • First experiment:

    • do you know of anyone or anything that has annihilated?

  • Locally, we are quite sure that there is virtually no antimatter

    • exception: small amounts of antimatter are produced when cosmic rays interact in the atmosphere

  • Non-locally, astronomers see no evidence for annihilating stars or galaxies

    • if there is antimatter, then it has to be isolated

    • unlikely, because there would have to have been a segregation in the early universe.

  • Actually, our universe is full of photons:

    • N/Nbaryon ~ 109

    • after annihilations: 100000001 quark for every 1000000000 antiquark

Sakarhov s conditions

Sakarhov’s Conditions

Soviet physicist Andrei Sakarhov put forth three conditions required for a matter/antimatter asymmetry in the universe:

  • Baryon number violation

    • example: proton decay (not seen)

  • CP violation

    • some force of nature treats matter and antimatter differently!

  • Phase transition

    • at some point, a phase transition “froze out” this asymmetry

Cp violation

CP Violation

CP violation is jargon for a force that doesn’t treat matter and antimatter the same.

In the 1960’s, everybody thought CP was conserved (not violated)

Then in 1964, CP violation was (unexpectedly) observed in the decays of mesons containing strange quarks.

More than 35 years later, we still don’t really understand this phenomena,

but now we have a new system to study CP violation

the strange quark has a heavy brother: bottom

Why study b s

Why Study B’s

1964:CP violation was (unexpectedly) observed in the decays of mesons containing strange quarks.

Since the bottom quark is a heavy version of a strange quark, should see CP violation in B decays, too.

Also, the bottom is quite interesting (unique) for other reasons:

1. It wants to decay to top, but can’t.

2. It has a long lifetime. (It lives on average .45mm)

3. It can “mix” with it’s anti-partner (B /B mixing)

How to measure b decays

Need an accelerator

particle is massive

mB = 5mp

doesn’t occur “naturally”

at least in a detectable way

accelerator produce it via high energy collisions

Need a detector

must measure the collisions

B’s are more rare than most things, less rare than others (like top, W/Z, Higgs?)

Need lots of readout electronics and data acquisition

high rates

require fast processing

Need lots of computing power and storage

data sizes in PetaByte range


lots of cpu cycles to process large data samples

Need lots of people!

To make it all happen

How to Measure B Decays

The fermilab tevatron

The Fermilab Tevatron

  • Collides proton-antiprotons

  • Energy

    • 2.0 TeV = 2000 mp

    • highest energy in the world

  • Rate

    • collisions occur every 396ns

    • 2.5M collisions/second!

    • ~1000 B’s /second!

  • Technology

    • superconducting magnets

  • Size

    • 4 miles in circumference

Fermi national accelerator laboratory fermilab

Fermi National Accelerator Laboratory (Fermilab)

Wilson Hall and accelerator complex

Aerial view of the laboratory

Accelerator components

Accelerator Components

Linear accelerator


Tevatron tunnel

Antiproton ring



  • Antiprotons are indeed “antimatter”

  • We use part of the accelerator chain to produce and “store” antiprotons

  • Antiprotons constantly cycled through another ring

Antiproton source

The cdf detector

The CDF Detector

  • Specifically designed to measure Tevatron collisions

  • Size

    • 4 stories tall

    • 5000 tons

  • Sensitivity

    • 1 million channels

      • each channel: 1 piece of info

  • Detector is cylindrical in shape

    • need to cover entire interaction region

The cdf detector1

The CDF Detector

Central + Endplug detectors

Detector rolling off of the beamline

Detector strategy

Precise measurements close-in

track trajectories, vertices

Coarse measurements further out

calorimeters measure total energy

Muon detectors last

muons penetrate deeply

High speed DAQ and trigger electronics

Detector Strategy

CDF II Detector cross section

Assembly of vertex detector

Assembly of Vertex Detector

Silicon strips surround the


Provide VERY precise measurements (~50m) at

at distance of 2-10 cm from the beam line.

Schematic of cdf detector

Schematic of CDF Detector

Measures trajectory

of charged particles

Stringing the cot

Stringing the COT

COT = Central Outer Tracker

70,000 wires strung between


Measures trajectory of charged tracks as the pass through the chamber.

A high energy collision

A High Energy Collision

A high energy collision as seen by the previous version of the CDF detector

Lines represent reconstructed trajectories

Charged particles bend in magnetic field

big bendlow momentum

Triggering and readout

Need to reduce rate:

2.5M collisions per second

can write data from 50-100 collisions per second

must decide which 2.4999M events to discard each second in real time !

What if the B decays aren’t part of the 100?

“Trigger” is the fast logic used to make these decisions

Response time is too short to use standard computers

We build dedicated electronics for these purposes

“hardware” computers

utilize memory, processors, fast logic

not arbitrarily programmable

Triggering and Readout

Illinois xtrp trigger system

Illinois XTRP Trigger System

  • Dedicated system to combine info from other system:

    • tracks

    • energy clusters

    • muons

  • The XTRP system brings this info together

  • Pipelined system

    • new data every 33ns

    • 4 events in the boards at a time

XTRP test stand

Computing and data rates

Computing and Data Rates


  • Each event about 250kB

  • Write ~100 events/secdisk

    • 25MB of data every second

  • Acquire data at a higher rate

    • 250MB/sec sustained rate

    • burst rates higher

  • Incoming data processed by a farm of PCs running Linux (~300 dual-processor machines)

Tape robot in computing center

Uiuc students at work

UIUC Students at Work

Graduate students

Raeghan Byrne and

Trevor Vickey

hard at work on the

CDF muon systems


The cdf collaboration

The CDF Collaboration

  • 500 physicists

    • students, postdocs, faculty

  • 35 institutions

    • US, Italy, Japan, Korea, Great Britain, France

  • many support personnel

    • engineers

    • technicians

    • support staff



  • Although the experiments are big, the work gets done in small groups (2-4 people).

  • It’s also a great environment and opportunity to be constantly interacting with physicists from around the world.

  • I like the variety, too. In addition to physics, we dabble in things like

    • computing, mechanical engineering, electrical engineering

    • budgets, conflict management

Other experiments

Other Experiments

  • e+e bb

  • Different accelerators/ environment

  • Many techniques are similar

  • Three accelerators:

    • Cornell

    • Stanford (SLAC)

    • Japan (KEK)

Experimental status

Experimental Status

CDF made one of the first measurements

Now, BaBar and Belle have made more precise measurements

Ultimate goal: make very precise measurements of CP violation in many different ways. We then can test the theory for

1. Results

2. Self-consistency

Standard model Higgs branching ratio versus mass

Summary final thoughts

Summary--Final Thoughts

  • This is an exciting time for particle physics

  • There are many other interesting subjects and measurements that we perform

    • CDF has published well over 100 papers on a variety of topics, such as:

      • top quark physics

      • Quantum Chromodynamics (QCD)

      • Electroweak phenomena (W/Z production and decay)

      • bottom quark physics

      • searches for new phenomena (supersymmetry, technicolor, quantum gravity)

      • …the list goes on

Top 10 great things about particle physics

1. You straight can use the words, “squarks”, “gluinos”, “WIMPs” and “technirho” with a face.

2. For exercise, you can run around your experiment.

3. Collaborate with institutions like Harvard and Yale and then ask them about their sports teams.

4. 4500 Amps of current and 1000 cubic meters of flammable gas.

5. Two words: “beam dump.”

6. Create more W bosons before 9am than most people do in a whole day.

7. Seven truckloads of LN2 per day.

8. Al Gore didn’t invent the internet….we did!

9. Find out if irradiated objects really glow!

10. Actually have to worry about the speed of light.

Top 10 Great Things About Particle Physics

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