Transcript Van_May97_ABW

Kevin Pitts February 1, 2001
UIUC Physics Society
Where has all of the
Antimatter Gone?
Kevin Pitts
University of Illinois
September 26, 2001
#1
Kevin Pitts February 1, 2001
UIUC Physics Society
#2
Outline

Why do we think the antimatter is missing?
Quarks, gluons and all that
the early universe

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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
Kevin Pitts February 1, 2001
UIUC Physics Society
The Standard Model

6 quarks
 quarks combine to make
hadrons
 p=uud, +=ud

6 leptons
baryons
 “free particles”
 electron, electron neutrino

Bosons carry force
 W,Z,,g
#3
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Masses
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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
#4
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UIUC Physics Society
#5
Mass/Energy

Einstein was right:
E = mc2
 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 
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UIUC Physics Society
#6
Universal Evolution
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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?
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UIUC Physics Society
#7
Today
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First experiment:
 do you know of anyone or anything that has annihilated?
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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
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UIUC Physics Society
#8
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)
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CP violation
 some force of nature treats matter and antimatter differently!
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Phase transition
 at some point, a phase transition “froze out” this asymmetry
Kevin Pitts February 1, 2001
UIUC Physics Society
#9
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
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UIUC Physics Society
# 10
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)
Kevin Pitts February 1, 2001
UIUC Physics Society
# 11
How to Measure B Decays
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Need an accelerator
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 particle is massive
-
mB = 5mp
 doesn’t occur “naturally”
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 high rates
 require fast processing
at least in a detectable way
 accelerator produce it via high
energy collisions
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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
Need lots of computing
power and storage
 data sizes in PetaByte range
-
kB,MB,GB,TB,PB
 lots of cpu cycles to process
large data samples
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Need lots of people!
 To make it all happen
Kevin Pitts February 1, 2001
UIUC Physics Society
# 12
The Fermilab Tevatron
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Collides proton-antiprotons
Energy
 2.0 TeV = 2000 mp
 highest energy in the world
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Rate
 collisions occur every 396ns
 2.5M collisions/second!
 ~1000 B’s /second!
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Technology
 superconducting magnets
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Size
 4 miles in circumference
Kevin Pitts February 1, 2001
Fermi National Accelerator
Laboratory (Fermilab)
UIUC Physics Society
Wilson Hall and accelerator complex
Aerial view of the laboratory
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UIUC Physics Society
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Accelerator Components
Linear accelerator
(LINAC)
Tevatron tunnel
Antiproton ring
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UIUC Physics Society
# 15
Antimatter
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Antiprotons are indeed
“antimatter”
We use part of the
accelerator chain to produce
and “store” antiprotons
Antiproton source
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Antiprotons constantly
cycled through another ring
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UIUC Physics Society
# 16
The CDF Detector
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Specifically designed to
measure Tevatron collisions
Size
 4 stories tall
 5000 tons
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Sensitivity
 1 million channels
-

each channel: 1 piece of info
Detector is cylindrical in
shape
 need to cover entire
interaction region
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UIUC Physics Society
# 17
The CDF Detector
Central + Endplug detectors
Detector rolling off of the beamline
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Detector Strategy
CDF II Detector cross section
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Precise measurements
close-in
 track trajectories, vertices
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Coarse measurements
further out
 calorimeters measure total
energy
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Muon detectors last
 muons penetrate deeply
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High speed DAQ and
trigger electronics
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UIUC Physics Society
# 19
Assembly of Vertex Detector
Silicon strips surround the
beampipe.
Provide VERY precise
measurements (~50m) at
at distance of 2-10 cm from
the beam line.
Kevin Pitts February 1, 2001
UIUC Physics Society
Schematic of CDF Detector
Measures trajectory
of charged particles
# 20
Kevin Pitts February 1, 2001
UIUC Physics Society
Stringing the COT
COT = Central Outer Tracker
70,000 wires strung between
endplates.
Measures trajectory of
charged tracks as the pass
through the chamber.
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UIUC Physics Society
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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
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UIUC Physics Society
# 23
Triggering and Readout
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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?
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“Trigger” is the fast logic
used to make these
decisions
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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
Kevin Pitts February 1, 2001
UIUC Physics Society
# 24
Illinois XTRP Trigger System
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Dedicated system to
combine info from other
system:
 tracks
 energy clusters
 muons
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XTRP test stand
The XTRP system brings
this info together
Pipelined system
 new data every 33ns
 4 events in the boards at a
time
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UIUC Physics Society
# 25
Computing and Data Rates
Rates:
 Each event about 250kB
 Write ~100 events/secdisk
 25MB of data every second
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Acquire data at a higher rate
 250MB/sec sustained rate
 burst rates higher
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Incoming data processed by
a farm of PCs running Linux
(~300 dual-processor
machines)
Tape robot in computing center
Kevin Pitts February 1, 2001
UIUC Physics Society
# 26
UIUC Students at Work
Graduate students
Raeghan Byrne and
Trevor Vickey
hard at work on the
CDF muon systems
H=40feet
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UIUC Physics Society
# 27
The CDF Collaboration

500 physicists
 students, postdocs, faculty
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35 institutions
 US, Italy, Japan, Korea,
Great Britain, France
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many support personnel
 engineers
 technicians
 support staff
Kevin Pitts February 1, 2001
UIUC Physics Society
# 28
Sociology
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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
Kevin Pitts February 1, 2001
UIUC Physics Society
Other Experiments
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e+e  b b
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Different accelerators/
environment
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Many techniques are
similar
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Three accelerators:
 Cornell
 Stanford (SLAC)
 Japan (KEK)
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UIUC Physics Society
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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
Kevin Pitts February 1, 2001
UIUC Physics Society
# 31
Summary--Final Thoughts
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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
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gravity)
…the list goes on
Kevin Pitts February 1, 2001
Top 10 Great Things
About Particle Physics
UIUC Physics Society
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.
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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.