Antiproton: A type of antimatter, antiprotons are particles that have the same mass as a proton but opposite charge.
They are created at Fermilab by colliding protons into a piece of nickel alloy;
magnets siphon off the antiprotons from the other particles produced by this reaction and
herd them into an underground storage ring much like the Tevatron.
When enough antiprotons have been accumulated,
they are injected into the Tevatron accelerator along with fresh protons, and the collisions can begin.
Baryon: A particle consisting of three quarks;
it is also a type of fermion, or "matter" particle.
Protons and neutrons are examples of baryons.
Beam pipe: The pipe through which protons and antiprotons flow around the accelerator. It runs through the center of
the CDF and DZero detectors.
Boson: Any of the “force” particles that mediate interactions between matter particles.
Examples include photons (which mediate the electromagnetic force),
gluons (which mediate the strong nuclear force that holds the components of an atomic nucleus together),
and W and Z bosons (which mediate the weak nuclear force that governs beta decay and radioactivity).
(Compare to fermions.)
Calorimeter: This section of the CDF detector measures the energy of charged and neutral particles that hit it on their way out from
the center of the detector. The calorimeter is made up of 48 wedges arranged in a circle just outside the solenoid magnet.
Each wedge consists of an electromagnetic calorimeter for catching leptons
and a hadronic calorimeter for catching hadrons,
as well as a section of muon chambers.
The layer of calorimeter wedges comes between the solenoid magnet and the steel shielding.
Central Outer Tracker (COT): This section of the CDF detector uses a drift chamber
to track charged particles passing through the detector. A passing particle ionizes the gas in the chamber, and the electrical signal is
picked up by one of the wires and carried to readout electronics. The COT is lodged between the silicon detector
and the solenoid magnet. (Read more about the Central Outer Tracker and
CDF: The Collider Detector at Fermilab, a collaboration of over 700 physicists from around the world.
The CDF detector uses Fermilab's Tevatron accelerator
to study fundamental particle physics, which includes searching for new particles and
improving our knowledge about the particles already we know about. The detector, assembly hall, and control room are housed within
a bright orange building called "B0," located just off of the Tevatron ring on the Fermilab campus.
Daughter particles are the particles created when another particle decays. Scientists can use the daughters
to determine the identity of the parent.
Drift chamber: A type of particle detector consisting of a cylindrical gas-filled tube with one or more wires stretching across it
A passing particle ionizes the gas, knocking an electron out of orbit; a difference in voltage between the wires or between a wire and the
metal container that contains it causes the electron to travel to the nearest wire, where its energy is picked up as a signal
that something passed by. Both the central outer tracker and
muon detectors are drift chambers.
(For more information about drift chambers, see ionization or visit
the Silicon Detector page.)
DZero: CDF's sister collaboration,
which uses its own detector to collect data from the Tevatron accelerator.
When one group believes it has made a discovery, the other can confirm or confute their claim.
Electromagnetic calorimeter: This section of the calorimeter is designed to stop leptons and
record their energy. It consists of alternating layers of lead and scintillator; the lead stops
the particles, and the scintillator picks up the energy they deposit. (See Calorimeters.)
Electron: A fundamental subatomic particle with a negative electric charge. Electrons are part of the lepton
family, along with muons and tau particles.
Elementary or fundamental particles are the most basic elements of nature —
the building blocks from which every other piece of matter is built. Examples include
quarks, electrons, and photons.
The goal of physicists at CDF is to study
fundamental particles to determine the nature of the universe.
Event: The collision of a proton and antiproton from the accelerator.
Event display: A schematic that shows physicists where particles have made hits in the detector.
Fermion: Any of the "matter" particles that make up physical material.
Examples are protons, neutrons, and electrons.
(Compare to bosons.)
Field wire: The thicker of the two types of wire in the central outer tracker (COT),
their job is to create a difference in voltage that will send a floating electron toward the nearest sense wire.
They also attract the positive ions whose electrons have been ripped away by a passing particle
through the process of ionization. (See sense wires.)
(Note: The positive ions do not actually move toward the field wires, but a positive ion will attract an electron from its neighbor,
and so on down the line, effectively creating a wave of ion production.)
Hadron: Any particle made up of quarks; examples include protons and neutrons.
Hadronic calorimeter: This section of the calorimeter is designed to stop hadrons
passing through it and record the energy they emit. It consists of alternating layers of steel and scintillator;
the steel stops the particles, while the scintillator catches the remaining energy and sends it off to be recorded.
Higgs boson: Said to be the holy grail of physics, this theoretical particle is thought to be responsible for
determining the masses of all the other particles we know about.
The production of a Higgs boson at CDF would be an ultra-rare process,
and it would take a large amount of data to find it categorically.
Its existence would put the final pieces of the Standard Model together.
Inner detectors: These are the silicon detector and central outer tracker,
the two innermost detectors, which detect the paths charged particles take on their journey outward from the center of the detector.
Ionization: This occurs when a subatomic particle attracts or repels the electrons in
the medium through which it is traveling, yanking them out of their atomic orbits. Atoms that have
lost electrons are called ions. At CDF, the silicon detector,
central outer tracker, and muon chambers use the process of ionization to track charged particles
through the detector.
(For a more detailed explanation of ionization, see the page on the Silicon Detector.)
Latency: The amount of time the trigger has to make its decision to accept or reject an event. (See Trigger System)
Lepton: One of two types of fundamental particles that make up matter (the other type is the quark).
Examples of leptons include electrons, muons, tau particles,
Light guide: At CDF, a tube of very clear plastic used to transmit data (in the form of light) from the
scintillators to the photomultiplier tubes, which send
the signal to the readout electronics.
The light guide carries light the way a garden hose carries water, bending it around corners and other difficult areas.
A reflective coating on the surface of the light guide keeps light inside the guide until it has reached its destination.
(Watch a video about light guides, or read about them
on the Scintillators page.)
Luminosity: The number of protons and antiprotons coursing through the accelerator per unit time.
Higher luminosity means there is a greater density of protons and antiprotons in the accelerator,
and therefore a greater chance that two of them will collide.
Magnetic fields are created from running electric current through coiled wire.
An area affected by a magnetic field will force charged particles into a circular path around the center of the field.
When a charged particle traveling in a straight line encounters a magnetic field, it will begin to corkscrew.
Momentum describes an object’s tendency to continue
moving in a certain direction at a certain speed. Momentum = mass × velocity — in other words,
the higher the particle’s mass and velocity, the greater its momentum.
(For a more detailed description of momentum, visit the Magnet page.)
Muon: A fundamental subatomic particle with a negative electric charge.
The middleweights of the lepton family, muons are heavier than
electrons and lighter than tau particles.
Muon chamber/detector: This part of the detector measures the location of and energy deposited by muons,
the only particle (with the exception of the neutrino)
that has largely escaped detection in all of the other sections of the detector.
Most of the muon chambers are located on the outskirts of the detector, behind two feet of steel shielding designed to stop
all particles except muons. An individual muon detector consists of two parts: a drift chamber
which measures the position of the muon,
and layers of scintillator to give an accurate timing for when the muon passed through.
Neutrino: An extremely light, chargeless particle that interacts with matter extremely rarely.
Of the thousands of neutrinos that pass through the Earth each second, almost none of them will interact with a single
particle of matter. Neutrinos are a member of the lepton
family, along with electrons, muons, and tau particles.
New physics describes any theory that goes beyond the Standard Model theory
of particle interactions. New physics theories include supersymmetry and String Theory.
Photon: A massless force particle, or boson, responsible for carrying electromagnetic radiation.
Light is an example of the type of radiation carried by photons.
Photomultiplier Tubes (PMTs): Cylindrical devices that turn a small signal (a few photons) into a larger signal (millions of photons),
and then convert that into an electrical signal that can be picked up by the readout electronics.
Quark: One of two types of fundamental particles that make up matter (the other type is the lepton).
Isolated quarks have not been found; they always come in groups of two or three, called hadrons.
There are six flavors of quark: up and down, charm and strange, and top and bottom.
Resistance: A property of materials that describes how difficult it is for electrical current to
travel through it. Running current through materials with a high resistance produces a lot of heat
and decreases the energy of the current.
Scintillator is a type of plastic used in the CDF detector to turn a particle "hit" into a signal that can be read out electronically.
The plastic collects energy from passing particles and converts that energy into visible light.
This light is then carried by light guides to the photomultiplier tubes, which increase the signal
and send it to the readout electronics.
Sense wire: The thinner of the two kinds of wire in the central outer tracker (COT),
their job is to pick up electrons that are released from the atoms in the gas when a particle flies past.
(See field wires.)
Shielding: Steel walls two feet thick encase the CDF detector, stopping nearly all of the particles coursing through it except for
high-energy muons and neutrinos. These do not interact with matter as often as do other types of fundamental particles;
the shielding therefore works as a sort of net that separates the muons and neutrinos from everything else.
Muons shoot straight through the steel and are detected by wire chambers on the outer edges of the machine.
Neutrinos interact with matter so rarely that they are effectively invisible to the detector.
Silicon detector: The innermost layer of detection equipment in the CDF detector. Its purpose is to give a precise
measurement of the position of each charged particle that passes through it.
Solenoid: A type of magnet that consists of a long wire tightly coiled into a cylindrical shape, like a giant slinky.
The solenoid's magnetic field is generated by running a changing current of electricity through its coils.
Solenoids are good for creating large, relatively uniform magnetic fields, as long as the length of the coil is much longer than its diameter.
CDF's solenoid creates a
magnetic field that is used to measure the momentum of particles passing through the inner detectors.
The best theory yet postulated for what the universe is composed of and how it operates.
It describes three of the four interactions between
different types of matter, and also describes all of the elementary particles
we have discovered.
At the right is an image of the Standard Model, depicted as a chart listing all the basic particles we know about.
Theories of the way the universe is structured that diverge from or go beyond the Standard Model are referred to as
Supersymmetry: A theory that postulates that every fundamental particle
we see has a counter-partner which we have not yet detected.
Supersymmetry goes beyond the Standard Model in explaining why the particles we see
have the properties they display.
Tau particle: A fundamental subatomic particle with a negative electric charge.
The tau particle is the heaviest member of the lepton family, which includes
electrons and muons.
Tevatron: Fermilab's famous particle accelerator, an underground ring four miles in circumference
that accelerates protons and antiprotons in opposite directions and then
collides them at the centers of the CDF and DZero experiments.
The goal is to use the high energies produced by the collision to recreate some of the rare processes
that occurred shortly after the Big Bang, when high energies would have made it possible for massive, short-lived particles
to be created frequently. By studying these rare particles,
scientists hope to learn about the structure of the fundamental particles that make up our universe.
Top quark: The heaviest of the six flavors of quark.
It is also the most difficult to detect,
since it requires huge amounts of energy to create and is so unstable that it decays almost immediately.
Fermilab's CDF and DZero collaborations famously discovered the top quark in 1995,
adding further support to the Standard Model theory.
Track: The path a particle takes through the detector. Tracks are reconstructed
from a series of disparate "hits" that represent places where the particle interacted with the machine through the process of
Only charged particles leave tracks in the CDF detector; neutral particles do not ionize the atoms they pass.
Trigger: A system designed to analyze incoming data quickly on a simplified level, and to discard the events that are less likely
to contain the rare processes that will teach us new things about the universe.
(Read about triggers.)
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