Collider Detector at Fermilab
Encyclopedia
The Collider Detector
at Fermilab
(CDF) experimental collaboration studies high energy particle collisions at the Tevatron
,the world's former highest-energy particle accelerator
. The goal is to discover the identity and properties of the particle
s that make up the universe and to understand the force
s and interactions between those particles.
CDF is an international collaboration of about 600 physicist
s (from about 30 American
universities and National laboratories and about 30 groups from universities and national laboratories from Italy
, Japan
, UK
, Canada
, Germany
, Spain
, Russia
, Finland
, France
, Taiwan
, Korea
, and Switzerland
). The CDF detector itself weighs 5000 ton
s , is about 12 meters in all three dimensions. The goal of the experiment is to measure exceptional events
out of the billions of collisions
in order to:
The Tevatron
collides protons and antiprotons at a center-of-mass energy
of about 2 TeV. The very high energy available for these collisions makes it possible to produce heavy particles such as the Top quark
and the W and Z bosons
, which weigh much more than a proton
(or antiproton). These heavier particles are identified through their characteristic decays. The CDF apparatus records the trajectories and energies of electrons, photons and light hadrons. Neutrinos do not register in the apparatus leading to an apparent missing energy. Other hypothetical particles might leave a missing energy signature, and some searches for new phenomena are based on that.
There is another experiment similar to CDF called D0
located at another point on the Tevatron ring.
CDF can be divided into layers as follows:
Understanding the different components of the detector is important because the detector determines what data will look like and what signal one can expect to see for each of your particles. It is important to remember that a detector is basically a set of obstacles used to force particles to interact, allowing physicists to “see” the presence of a certain particle. If a charged quark is passing through the detector, the evidence of this quark will be a curved trajectory in the silicon detector and COT deposited energy in the calorimeter. If a neutral particle, such as a neutron, passes through the detector, there will be no track in the COT and silicon detector but deposited energy in the hadronic calorimeter. Muons may appear in the COT and silicon detector and as deposited energy in the muon detectors. Likewise, a neutrino, which rarely if ever interacts, will express itself only in the form of missing energy.
Particle detector
In experimental and applied particle physics, nuclear physics, and nuclear engineering, a particle detector, also known as a radiation detector, is a device used to detect, track, and/or identify high-energy particles, such as those produced by nuclear decay, cosmic radiation, or reactions in a...
at Fermilab
Fermilab
Fermi National Accelerator Laboratory , located just outside Batavia, Illinois, near Chicago, is a US Department of Energy national laboratory specializing in high-energy particle physics...
(CDF) experimental collaboration studies high energy particle collisions at the Tevatron
Tevatron
The Tevatron is a circular particle accelerator in the United States, at the Fermi National Accelerator Laboratory , just east of Batavia, Illinois, and is the second highest energy particle collider in the world after the Large Hadron Collider...
,the world's former highest-energy particle accelerator
Particle accelerator
A particle accelerator is a device that uses electromagnetic fields to propel charged particles to high speeds and to contain them in well-defined beams. An ordinary CRT television set is a simple form of accelerator. There are two basic types: electrostatic and oscillating field accelerators.In...
. The goal is to discover the identity and properties of the particle
Elementary particle
In particle physics, an elementary particle or fundamental particle is a particle not known to have substructure; that is, it is not known to be made up of smaller particles. If an elementary particle truly has no substructure, then it is one of the basic building blocks of the universe from which...
s that make up the universe and to understand the force
Force
In physics, a force is any influence that causes an object to undergo a change in speed, a change in direction, or a change in shape. In other words, a force is that which can cause an object with mass to change its velocity , i.e., to accelerate, or which can cause a flexible object to deform...
s and interactions between those particles.
CDF is an international collaboration of about 600 physicist
Physicist
A physicist is a scientist who studies or practices physics. Physicists study a wide range of physical phenomena in many branches of physics spanning all length scales: from sub-atomic particles of which all ordinary matter is made to the behavior of the material Universe as a whole...
s (from about 30 American
United States
The United States of America is a federal constitutional republic comprising fifty states and a federal district...
universities and National laboratories and about 30 groups from universities and national laboratories from Italy
Italy
Italy , officially the Italian Republic languages]] under the European Charter for Regional or Minority Languages. In each of these, Italy's official name is as follows:;;;;;;;;), is a unitary parliamentary republic in South-Central Europe. To the north it borders France, Switzerland, Austria and...
, Japan
Japan
Japan is an island nation in East Asia. Located in the Pacific Ocean, it lies to the east of the Sea of Japan, China, North Korea, South Korea and Russia, stretching from the Sea of Okhotsk in the north to the East China Sea and Taiwan in the south...
, UK
United Kingdom
The United Kingdom of Great Britain and Northern IrelandIn the United Kingdom and Dependencies, other languages have been officially recognised as legitimate autochthonous languages under the European Charter for Regional or Minority Languages...
, Canada
Canada
Canada is a North American country consisting of ten provinces and three territories. Located in the northern part of the continent, it extends from the Atlantic Ocean in the east to the Pacific Ocean in the west, and northward into the Arctic Ocean...
, Germany
Germany
Germany , officially the Federal Republic of Germany , is a federal parliamentary republic in Europe. The country consists of 16 states while the capital and largest city is Berlin. Germany covers an area of 357,021 km2 and has a largely temperate seasonal climate...
, Spain
Spain
Spain , officially the Kingdom of Spain languages]] under the European Charter for Regional or Minority Languages. In each of these, Spain's official name is as follows:;;;;;;), is a country and member state of the European Union located in southwestern Europe on the Iberian Peninsula...
, Russia
Russia
Russia or , officially known as both Russia and the Russian Federation , is a country in northern Eurasia. It is a federal semi-presidential republic, comprising 83 federal subjects...
, Finland
Finland
Finland , officially the Republic of Finland, is a Nordic country situated in the Fennoscandian region of Northern Europe. It is bordered by Sweden in the west, Norway in the north and Russia in the east, while Estonia lies to its south across the Gulf of Finland.Around 5.4 million people reside...
, France
France
The French Republic , The French Republic , The French Republic , (commonly known as France , is a unitary semi-presidential republic in Western Europe with several overseas territories and islands located on other continents and in the Indian, Pacific, and Atlantic oceans. Metropolitan France...
, Taiwan
Taiwan
Taiwan , also known, especially in the past, as Formosa , is the largest island of the same-named island group of East Asia in the western Pacific Ocean and located off the southeastern coast of mainland China. The island forms over 99% of the current territory of the Republic of China following...
, Korea
Korea
Korea ) is an East Asian geographic region that is currently divided into two separate sovereign states — North Korea and South Korea. Located on the Korean Peninsula, Korea is bordered by the People's Republic of China to the northwest, Russia to the northeast, and is separated from Japan to the...
, and Switzerland
Switzerland
Switzerland name of one of the Swiss cantons. ; ; ; or ), in its full name the Swiss Confederation , is a federal republic consisting of 26 cantons, with Bern as the seat of the federal authorities. The country is situated in Western Europe,Or Central Europe depending on the definition....
). The CDF detector itself weighs 5000 ton
Ton
The ton is a unit of measure. It has a long history and has acquired a number of meanings and uses over the years. It is used principally as a unit of weight, and as a unit of volume. It can also be used as a measure of energy, for truck classification, or as a colloquial term.It is derived from...
s , is about 12 meters in all three dimensions. The goal of the experiment is to measure exceptional events
Event (particle physics)
An event in particle physics describes one set of particle interactions occurring in a brief span of time, typically recorded together. At modern particle accelerators this refers to the interactions that occur as a result of one beam crossing inside a detector....
out of the billions of collisions
Beam crossing
A beam crossing in a particle collider occurs when two packets of particles, going in opposite directions, reach the same point in space. Most of the particles in each packet cross each other, but a few may collide, producing other particles that may be observed in a particle detector...
in order to:
- Look for evidence for phenomena beyond the Standard ModelStandard ModelThe Standard Model of particle physics is a theory concerning the electromagnetic, weak, and strong nuclear interactions, which mediate the dynamics of the known subatomic particles. Developed throughout the mid to late 20th century, the current formulation was finalized in the mid 1970s upon...
of particle physics - Measure and study the production and decay of heavy particles such as the TopTop quarkThe top quark, also known as the t quark or truth quark, is an elementary particle and a fundamental constituent of matter. Like all quarks, the top quark is an elementary fermion with spin-, and experiences all four fundamental interactions: gravitation, electromagnetism, weak interactions, and...
and Bottom QuarksBottom quarkThe bottom quark, also known as the beauty quark, is a third-generation quark with a charge of − e. Although all quarks are described in a similar way by the quantum chromodynamics, the bottom quark's large bare mass , combined with low values of the CKM matrix elements Vub and Vcb, gives it a...
, and the W and Z bosonsW and Z bosonsThe W and Z bosons are the elementary particles that mediate the weak interaction; their symbols are , and . The W bosons have a positive and negative electric charge of 1 elementary charge respectively and are each other's antiparticle. The Z boson is electrically neutral and its own... - Measure and study the production of high-energy particle jets and photons
- Study other phenomena such as diffractionDiffractionDiffraction refers to various phenomena which occur when a wave encounters an obstacle. Italian scientist Francesco Maria Grimaldi coined the word "diffraction" and was the first to record accurate observations of the phenomenon in 1665...
The Tevatron
Tevatron
The Tevatron is a circular particle accelerator in the United States, at the Fermi National Accelerator Laboratory , just east of Batavia, Illinois, and is the second highest energy particle collider in the world after the Large Hadron Collider...
collides protons and antiprotons at a center-of-mass energy
Energy
In physics, energy is an indirectly observed quantity. It is often understood as the ability a physical system has to do work on other physical systems...
of about 2 TeV. The very high energy available for these collisions makes it possible to produce heavy particles such as the Top quark
Top quark
The top quark, also known as the t quark or truth quark, is an elementary particle and a fundamental constituent of matter. Like all quarks, the top quark is an elementary fermion with spin-, and experiences all four fundamental interactions: gravitation, electromagnetism, weak interactions, and...
and the W and Z bosons
W and Z bosons
The W and Z bosons are the elementary particles that mediate the weak interaction; their symbols are , and . The W bosons have a positive and negative electric charge of 1 elementary charge respectively and are each other's antiparticle. The Z boson is electrically neutral and its own...
, which weigh much more than a proton
Proton
The proton is a subatomic particle with the symbol or and a positive electric charge of 1 elementary charge. One or more protons are present in the nucleus of each atom, along with neutrons. The number of protons in each atom is its atomic number....
(or antiproton). These heavier particles are identified through their characteristic decays. The CDF apparatus records the trajectories and energies of electrons, photons and light hadrons. Neutrinos do not register in the apparatus leading to an apparent missing energy. Other hypothetical particles might leave a missing energy signature, and some searches for new phenomena are based on that.
There is another experiment similar to CDF called D0
D0 experiment
The DØ experiment consists of a worldwide collaboration of scientists conducting research on the fundamental nature of matter...
located at another point on the Tevatron ring.
History of CDF
There are currently two particle detectors located on the Tevatron at Fermilab: CDF and D0. CDF predates D0 as the first detector on the Tevatron. Construction of CDF began in 1982 under the leadership of John Peoples. The Tevatron was completed in 1983 and CDF began to take data in 1985. Over the years, two major updates have been made to CDF. The first upgrade began in 1989 and the second upgrade began in 2001. Each upgrade is considered a "run." Run 0 was the run before any upgrades, Run I was after the first upgrade and Run II was after the second upgrade. Run II includes upgrades on the central tracking system, preshower detectors and extension on muon coverage.Discovery of the Top Quark
One of CDF's most famous observations is the observation of the top quark in February 1995. The existence of the top quark was hypothesized after the observation of the Upsilon in 1977, which was found to consist of a bottom quark and an anti-bottom quark. The Standard Model, which today is the most widely accepted theory describing the particles and interactions, predicted the existence of three generations of quarks. The first generation quarks are the up and down quarks, second generation quarks are strange and charm, and third generation are top and bottom. The existence of the bottom quark solidified physicists’ conviction that the top quark existed. The top quark was the very last quark to be observed, mostly due to its comparatively high mass. Whereas, the masses of the other quarks range from .005 GeV (up quark) to 4.7GeV (bottom quark), the top quark has a mass of 175 GeV. Only Fermilab’s Tevatron had the energy capability to produce and detect top anti-top pairs. The large mass of the top quark caused the top quark to decay almost instantaneously, within the order of 10−25 seconds, making it extremely difficult to observe. The Standard Model predicts that the top quark may decay leptonically into a bottom quark and a W boson. This W boson may then decay into a lepton and neutrino (t→Wb→ѵlb). Therefore, CDF worked to reconstruct top events, looking specifically for evidence of bottom quarks, W bosons neutrinos. Finally in February 1995, CDF had enough evidence to say that they had "discovered" the top quark.How CDF Works
In order for physicists to understand the data corresponding to each event, they must understand the components of the CDF detector and how the detector works. Each component affects what the data will look like. Today, the 5000-ton detector sits in B0 and analyzes millions of beam collisions per second. The detector is designed in many different layers. Each of these layers work simultaneously with the other components of the detector in an effort to interact with the different particles, thereby giving physicists the opportunity to "see" and study the individual particles.CDF can be divided into layers as follows:
- Layer 1: Beam Pipe
- Layer 2: Silicon Detector
- Layer 3: Central Outer Tracker
- Layer 4: Solenoid Magnet
- Layer 5: Electromagnetic Calorimeters
- Layer 6: Hadronic Calorimeters
- Layer 7: Muon Detectors
Layer 1: The Beam Pipe
The beam pipe is the innermost layer of CDF. The beam pipe is where the protons and anti-protons, traveling at approximately .99996c, collide head on. Each of the protons is moving extremely close to the speed of light with extremely high energies. Therefore, in a collision, much of the energy is converted into mass. This allows proton- anti-proton annihilation to produce daughter particles, such as top quarks with a mass of 175 GeV, much heavier than the original protons.Layer 2: Silicon Detector
Surrounding the beam pipe is the silicon detector. This detector is used to track the path of charged particles as they travel through the detector. The silicon detector begins at a radius of r = 1.5 cm from the beam line and extends to a radius of r = 28 cm from the beam line. The silicon detector is composed of seven layers of silicon arranged in a barrel shape around the beam pipe. Silicon is often used in charged particle detectors because of its high sensitivity, allowing for high-resolution vertex and tracking. The first layer of silicon, known as Layer 00, is a single sided detector designed to separate signal from background even under extreme radiation. The remaining layers are double sided and radiation-hard, meaning that the layers are protected from damage from radioactivity. The silicon works to track the paths of charged particles as they pass through the detector by ionizing the silicon. The density of the silicon, coupled with the low ionization energy of silicon, allow ionization signals to travel quickly. As the silicon detector is located within a magnetic field, the curvature of the path of the silicon allows physicists to calculate the momentum of the particle. More curvature means less momentum and vice versa. As a particle travels through the silicon, its position will be recorded in 3 dimensions. The silicon detector has a track hit resolution of 10 um, and impact parameter resolution of 30 um. Physicists can look at this trail of ions and determine the path that the particle took.Layer 3: Central Outer Tracker (COT)
Outside of the silicon detector, the central outer tracker works in much the manner as the silicon detector as it is also used to track the paths of charged particles and is also located within a magnetic field. The COT, however, is not made of silicon. Silicon is tremendously expensive and is not practical to purchase in extreme quantities. COT is a gas chamber filled with tens of thousands of gold wires arranged in layers and argon gas. Two types of wires are used in the COT: sense wires and field wires. Sense wires are thinner and attract the electrons that are released by the argon gas as it is ionized. The field wires are thicker than the sense wires and attract the positive ions formed from the release of electrons. There are 96 layers of wire and each wire is placed approximately 3.86mm apart from one another. As in the silicon detector, when a charged particle passes through the chamber it ionizes the gas. This signal is then carried to a nearby wire, which is then carried to the computers for read-out. The COT is approximately 3.1 m long and extends from r = 40 cm to r = 137 cm. Although the COT is not nearly as precise as the silicon detector, the COT has a hit position resolution of 140μm and a momentum resolution of 0.0015 (GeV/c)−1.Layer 4: Solenoid Magnet
The solenoid magnet surrounds both the COT and the silicon detector. The purpose of the solenoid is to bend the trajectory of charged particles in the COT and silicon detector by creating a magnetic field parallel to the beam. The solenoid has a radius of r=1.5 m and is 4.8m in length. The curvature of the trajectory of the particles in the magnet field allows physicists to calculate the momentum of each of the particles. The higher the curvature, the lower the momentum and vice versa. Because the particles have such a high energy, a very strong magnet is needed to bend the paths of the particles. The solenoid is a superconducting magnet cooled by liquid helium. The helium lowers the temperature of the magnet to 4.7K or -268.45°C which reduces the resistance to almost zero, allowing the magnet to conduct high currents with minimal heating and very high efficiency, and creating a powerful magnetic field.Layers 5 and 6: Electromagnetic and Hadronic Calorimeters
Calorimeters quantify the total energy of the particles by converting the energy of particles to visible light though polystyrene scintillators. CDF uses two types of calorimeters: electromagnetic calorimeters and hadronic calorimeters. The electromagnetic calorimeter measures the energy of light particles and the hadronic calorimeter measures the energy of hadrons. The central electromagnetic calorimeter uses alternating sheets of lead and scintillator. Each layer of lead is approximately 3/4in wide. The lead is used to stop the particles as they pass through the calorimeter and the scintillator is used to quantify the energy of the particles. The hadronic calorimeter works in much the same way except the hadronic calorimeter uses steel in place of lead. Each calorimeter forms a wedge, which consists of both an electromagnetic calorimeter and a hadronic calorimeter. These wedges are about 8 feet in length and are arranged around the solenoid.Layer 7: Muon Detectors
The final "layer" of the detector consists of the muon detectors. Muons are charged particles that may be produced when heavy particles decay. These high-energy particles hardly interact so the muon detectors are strategically placed at the farthest layer from the beam pipe behind large walls of steel. The steel ensures that only extremely high-energy particles, such as neutrinos and muons, pass through to the muon chambers. There are two aspects of the muon detectors: the planar drift chambers and scintillators. There are four layers of planar drift chambers, each with the capability of detecting muons with a transverse momentum PT>1.4GeV/c. These drift chambers work in the same way as the COT. They are filled with gas and wire. The charged muons ionize the gas and the signal is carried to readout by the wires.Understanding the different components of the detector is important because the detector determines what data will look like and what signal one can expect to see for each of your particles. It is important to remember that a detector is basically a set of obstacles used to force particles to interact, allowing physicists to “see” the presence of a certain particle. If a charged quark is passing through the detector, the evidence of this quark will be a curved trajectory in the silicon detector and COT deposited energy in the calorimeter. If a neutral particle, such as a neutron, passes through the detector, there will be no track in the COT and silicon detector but deposited energy in the hadronic calorimeter. Muons may appear in the COT and silicon detector and as deposited energy in the muon detectors. Likewise, a neutrino, which rarely if ever interacts, will express itself only in the form of missing energy.