The
BaBar experiment, or simply
BaBar, is an international collaboration of more than 500 physicists and engineers studying the subatomic world at energies of approximately ten times the rest mass of a proton (~10
GeVIn physics, the electron volt is a unit of energy equal to approximately joule . By definition, it is equal to the amount of kinetic energy gained by a single unbound electron when it accelerates through an electric potential difference of one volt...
). Its design was motivated by the investigation of CP violation. BaBar is located at the SLAC National Accelerator Laboratory, which is operated by
Stanford UniversityThe Leland Stanford Junior University, commonly referred to as Stanford University or Stanford, is a private research university on an campus located near Palo Alto, California. It is situated in the northwestern Santa Clara Valley on the San Francisco Peninsula, approximately northwest of San...
for the
Department of EnergyThe United States Department of Energy is a Cabinet-level department of the United States government concerned with the United States' policies regarding energy and safety in handling nuclear material...
in
CaliforniaCalifornia is a state located on the West Coast of the United States. It is by far the most populous U.S. state, and the third-largest by land area...
.
Physics
BaBar was set up to understand the
disparityThe baryon asymmetry problem in physics refers to the apparent fact that there is an imbalance in baryonic matter and antibaryonic matter in the universe. Neither the standard model of particle physics, nor the theory of general relativity provide an obvious explanation for why this should be so;...
between the
matterMatter is a general term for the substance of which all physical objects consist. Typically, matter includes atoms and other particles which have mass. A common way of defining matter is as anything that has mass and occupies volume...
and
antimatterIn particle physics, antimatter is the extension of the concept of the antiparticle to matter, where antimatter is composed of antiparticles in the same way that normal matter is composed of particles...
content of the universe by measuring
CP violationIn particle physics, CP violation is a violation of the postulated CP-symmetry: the combination of C-symmetry and P-symmetry . CP-symmetry states that the laws of physics should be the same if a particle were interchanged with its antiparticle , and left and right were swapped...
. CP symmetry is a combination of
Charge-conjugation symmetry (C symmetry) and
Parity symmetry (P symmetry), each of which are conserved separately except in
weak interactionWeak interaction , is one of the four fundamental forces of nature, alongside the strong nuclear force, electromagnetism, and gravity. It is responsible for the radioactive decay of subatomic particles and initiates the process known as hydrogen fusion in stars...
s. BaBar focuses on the study of CP violation in the
B mesonB mesons are mesons composed of a bottom quark or bottom antiquark and either an up , down , strange or charm quark . The combination of a bottom antiquark and a top quark is not thought to be possible because of the top quark's short lifetime...
system. The name of the experiment is derived from the nomenclature for the B meson (symbol
) and its
antiparticleCorresponding to most kinds of particles, there is an associated antiparticle with the same mass and opposite electric charge. For example, the antiparticle of the electron is the positively charged antielectron, or positron, which is produced naturally in certain types of radioactive decay.The...
(symbol
, pronounced
B bar). The experiment's
mascotThe term mascot – defined as a term for any person, animal, or object thought to bring luck – colloquially includes anything used to represent a group with a common public identity, such as a school, professional sports team, society, military unit, or brand name...
was accordingly chosen to be
Babar the ElephantBabar the Elephant is a French children's fictional character who first appeared in Histoire de Babar by Jean de Brunhoff in 1931 and enjoyed immediate success. An English language version, entitled The Story of Babar, appeared in 1933 in Britain and also in the United States. The book is based on...
.
If CP symmetry holds, the decay rate of B mesons and their
antiparticleCorresponding to most kinds of particles, there is an associated antiparticle with the same mass and opposite electric charge. For example, the antiparticle of the electron is the positively charged antielectron, or positron, which is produced naturally in certain types of radioactive decay.The...
s should be equal. Analysis of secondary particles produced in the BaBar detector showed this was not the case – in the summer of 2002, definitive results were published based on the analysis of 87 million / meson-pair events, clearly showing the decay rates were not equal. Consistent results were found by the
Belle experimentThe Belle experiment is a particle physics experiment conducted by the Belle Collaboration, an international collaboration of more than 400 physicists and engineers investigating CP-violation effects at the High Energy Accelerator Research Organisation in Tsukuba, Ibaraki Prefecture, Japan.The...
at the KEK laboratory in Japan.
CP violation was already predicted by the
Standard 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 physicsParticle physics is a branch of physics that studies the existence and interactions of particles that are the constituents of what is usually referred to as matter or radiation. In current understanding, particles are excitations of quantum fields and interact following their dynamics...
, and well established in the neutral kaon system (/ meson pairs). The BaBar experiment has increased the accuracy to which this effect has been experimentally measured. Currently, results are consistent with the standard model, but further investigation of a greater variety of decay modes may reveal discrepancies in the future.
The BaBar detector is a multilayer
particle detectorIn 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...
. Its large
solid angleThe solid angle, Ω, is the two-dimensional angle in three-dimensional space that an object subtends at a point. It is a measure of how large that object appears to an observer looking from that point...
coverage (near
hermeticIn particle physics, a hermetic detector is a particle detector designed to observe all possible decay products of an interaction between subatomic particles in a collider by covering as large an area around the interaction point as possible and incorporating multiple types of sub-detectors...
), vertex location with precision on the order of 10
μmA micrometer , sometimes known as a micrometer screw gauge, is a device incorporating a calibrated screw used widely for precise measurement of small distances in mechanical engineering and machining as well as most mechanical trades, along with other metrological instruments such as dial, vernier,...
(provided by a silicon vertex detector), good
pionIn particle physics, a pion is any of three subatomic particles: , , and . Pions are the lightest mesons and they play an important role in explaining the low-energy properties of the strong nuclear force....
–
kaonIn particle physics, a kaon is any one of a group of four mesons distinguished by the fact that they carry a quantum number called strangeness...
separation at multi-
GeVGEV or GeV may stand for:*GeV or gigaelectronvolt, a unit of energy equal to billion electron volts*GEV or Grid Enabled Vehicle that is fully or partially powered by the electric grid, see plug-in electric vehicle...
momenta (provided by a novel Cherenkov detector), and few-percent precision electromagnetic calorimetry (CsI(Tl) scintillating crystals) allow a list of other scientific searches apart from CP violation in the B meson system. Studies of rare decays and searches for exotic particles and precision measurements of phenomena associated with mesons containing
bottomThe 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...
s and
charm quarkThe charm quark or c quark is the third most massive of all quarks, a type of elementary particle. Charm quarks are found in hadrons, which are subatomic particles made of quarks...
s, as well as phenomena associated with
tau leptonThe tau , also called the tau lepton, tau particle or tauon, is an elementary particle similar to the electron, with negative electric charge and a spin of . Together with the electron, the muon, and the three neutrinos, it is classified as a lepton...
s are possible.
The BaBar detector ceased operation on 7 April 2008, but data analysis is ongoing.
Detector description
The BaBar detector is cylindrical with the interaction region at the center. In the interaction region, 9
GeVGEV or GeV may stand for:*GeV or gigaelectronvolt, a unit of energy equal to billion electron volts*GEV or Grid Enabled Vehicle that is fully or partially powered by the electric grid, see plug-in electric vehicle...
electrons collide with 3.1 GeV antielectrons (sometimes called positrons) to produce a
center-of-massIn physics, the center of mass or barycenter of a system is the average location of all of its mass. In the case of a rigid body, the position of the center of mass is fixed in relation to the body...
collision energy of 10.58 GeV, corresponding to the
The
BaBar experiment, or simply
BaBar, is an international collaboration of more than 500 physicists and engineers studying the subatomic world at energies of approximately ten times the rest mass of a proton (~10
GeVIn physics, the electron volt is a unit of energy equal to approximately joule . By definition, it is equal to the amount of kinetic energy gained by a single unbound electron when it accelerates through an electric potential difference of one volt...
). Its design was motivated by the investigation of CP violation. BaBar is located at the SLAC National Accelerator Laboratory, which is operated by
Stanford UniversityThe Leland Stanford Junior University, commonly referred to as Stanford University or Stanford, is a private research university on an campus located near Palo Alto, California. It is situated in the northwestern Santa Clara Valley on the San Francisco Peninsula, approximately northwest of San...
for the
Department of EnergyThe United States Department of Energy is a Cabinet-level department of the United States government concerned with the United States' policies regarding energy and safety in handling nuclear material...
in
CaliforniaCalifornia is a state located on the West Coast of the United States. It is by far the most populous U.S. state, and the third-largest by land area...
.
Physics
BaBar was set up to understand the
disparityThe baryon asymmetry problem in physics refers to the apparent fact that there is an imbalance in baryonic matter and antibaryonic matter in the universe. Neither the standard model of particle physics, nor the theory of general relativity provide an obvious explanation for why this should be so;...
between the
matterMatter is a general term for the substance of which all physical objects consist. Typically, matter includes atoms and other particles which have mass. A common way of defining matter is as anything that has mass and occupies volume...
and
antimatterIn particle physics, antimatter is the extension of the concept of the antiparticle to matter, where antimatter is composed of antiparticles in the same way that normal matter is composed of particles...
content of the universe by measuring
CP violationIn particle physics, CP violation is a violation of the postulated CP-symmetry: the combination of C-symmetry and P-symmetry . CP-symmetry states that the laws of physics should be the same if a particle were interchanged with its antiparticle , and left and right were swapped...
. CP symmetry is a combination of
Charge-conjugation symmetry (C symmetry) and
Parity symmetry (P symmetry), each of which are conserved separately except in
weak interactionWeak interaction , is one of the four fundamental forces of nature, alongside the strong nuclear force, electromagnetism, and gravity. It is responsible for the radioactive decay of subatomic particles and initiates the process known as hydrogen fusion in stars...
s. BaBar focuses on the study of CP violation in the
B mesonB mesons are mesons composed of a bottom quark or bottom antiquark and either an up , down , strange or charm quark . The combination of a bottom antiquark and a top quark is not thought to be possible because of the top quark's short lifetime...
system. The name of the experiment is derived from the nomenclature for the B meson (symbol
{{SubatomicParticle|B}}) and its
antiparticleCorresponding to most kinds of particles, there is an associated antiparticle with the same mass and opposite electric charge. For example, the antiparticle of the electron is the positively charged antielectron, or positron, which is produced naturally in certain types of radioactive decay.The...
(symbol
{{SubatomicParticle|AntiB}}, pronounced
B bar). The experiment's
mascotThe term mascot – defined as a term for any person, animal, or object thought to bring luck – colloquially includes anything used to represent a group with a common public identity, such as a school, professional sports team, society, military unit, or brand name...
was accordingly chosen to be
Babar the ElephantBabar the Elephant is a French children's fictional character who first appeared in Histoire de Babar by Jean de Brunhoff in 1931 and enjoyed immediate success. An English language version, entitled The Story of Babar, appeared in 1933 in Britain and also in the United States. The book is based on...
.
If CP symmetry holds, the decay rate of B mesons and their
antiparticleCorresponding to most kinds of particles, there is an associated antiparticle with the same mass and opposite electric charge. For example, the antiparticle of the electron is the positively charged antielectron, or positron, which is produced naturally in certain types of radioactive decay.The...
s should be equal. Analysis of secondary particles produced in the BaBar detector showed this was not the case – in the summer of 2002, definitive results were published based on the analysis of 87 million {{SubatomicParticle|B}}/{{SubatomicParticle|AntiB}} meson-pair events, clearly showing the decay rates were not equal. Consistent results were found by the
Belle experimentThe Belle experiment is a particle physics experiment conducted by the Belle Collaboration, an international collaboration of more than 400 physicists and engineers investigating CP-violation effects at the High Energy Accelerator Research Organisation in Tsukuba, Ibaraki Prefecture, Japan.The...
at the KEK laboratory in Japan.
CP violation was already predicted by the
Standard 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 physicsParticle physics is a branch of physics that studies the existence and interactions of particles that are the constituents of what is usually referred to as matter or radiation. In current understanding, particles are excitations of quantum fields and interact following their dynamics...
, and well established in the neutral kaon system ({{SubatomicParticle|link=yes|Kaon}}/{{SubatomicParticle|link=yes|Antikaon}} meson pairs). The BaBar experiment has increased the accuracy to which this effect has been experimentally measured. Currently, results are consistent with the standard model, but further investigation of a greater variety of decay modes may reveal discrepancies in the future.
The BaBar detector is a multilayer
particle detectorIn 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...
. Its large
solid angleThe solid angle, Ω, is the two-dimensional angle in three-dimensional space that an object subtends at a point. It is a measure of how large that object appears to an observer looking from that point...
coverage (near
hermeticIn particle physics, a hermetic detector is a particle detector designed to observe all possible decay products of an interaction between subatomic particles in a collider by covering as large an area around the interaction point as possible and incorporating multiple types of sub-detectors...
), vertex location with precision on the order of 10
μmA micrometer , sometimes known as a micrometer screw gauge, is a device incorporating a calibrated screw used widely for precise measurement of small distances in mechanical engineering and machining as well as most mechanical trades, along with other metrological instruments such as dial, vernier,...
(provided by a silicon vertex detector), good
pionIn particle physics, a pion is any of three subatomic particles: , , and . Pions are the lightest mesons and they play an important role in explaining the low-energy properties of the strong nuclear force....
–
kaonIn particle physics, a kaon is any one of a group of four mesons distinguished by the fact that they carry a quantum number called strangeness...
separation at multi-
GeVGEV or GeV may stand for:*GeV or gigaelectronvolt, a unit of energy equal to billion electron volts*GEV or Grid Enabled Vehicle that is fully or partially powered by the electric grid, see plug-in electric vehicle...
momenta (provided by a novel Cherenkov detector), and few-percent precision electromagnetic calorimetry (CsI(Tl) scintillating crystals) allow a list of other scientific searches apart from CP violation in the B meson system. Studies of rare decays and searches for exotic particles and precision measurements of phenomena associated with mesons containing
bottomThe 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...
s and
charm quarkThe charm quark or c quark is the third most massive of all quarks, a type of elementary particle. Charm quarks are found in hadrons, which are subatomic particles made of quarks...
s, as well as phenomena associated with
tau leptonThe tau , also called the tau lepton, tau particle or tauon, is an elementary particle similar to the electron, with negative electric charge and a spin of . Together with the electron, the muon, and the three neutrinos, it is classified as a lepton...
s are possible.
The BaBar detector ceased operation on 7 April 2008, but data analysis is ongoing.
Detector description
The BaBar detector is cylindrical with the interaction region at the center. In the interaction region, 9
GeVGEV or GeV may stand for:*GeV or gigaelectronvolt, a unit of energy equal to billion electron volts*GEV or Grid Enabled Vehicle that is fully or partially powered by the electric grid, see plug-in electric vehicle...
electrons collide with 3.1 GeV antielectrons (sometimes called positrons) to produce a
center-of-massIn physics, the center of mass or barycenter of a system is the average location of all of its mass. In the case of a rigid body, the position of the center of mass is fixed in relation to the body...
collision energy of 10.58 GeV, corresponding to the
The
BaBar experiment, or simply
BaBar, is an international collaboration of more than 500 physicists and engineers studying the subatomic world at energies of approximately ten times the rest mass of a proton (~10
GeVIn physics, the electron volt is a unit of energy equal to approximately joule . By definition, it is equal to the amount of kinetic energy gained by a single unbound electron when it accelerates through an electric potential difference of one volt...
). Its design was motivated by the investigation of CP violation. BaBar is located at the SLAC National Accelerator Laboratory, which is operated by
Stanford UniversityThe Leland Stanford Junior University, commonly referred to as Stanford University or Stanford, is a private research university on an campus located near Palo Alto, California. It is situated in the northwestern Santa Clara Valley on the San Francisco Peninsula, approximately northwest of San...
for the
Department of EnergyThe United States Department of Energy is a Cabinet-level department of the United States government concerned with the United States' policies regarding energy and safety in handling nuclear material...
in
CaliforniaCalifornia is a state located on the West Coast of the United States. It is by far the most populous U.S. state, and the third-largest by land area...
.
Physics
BaBar was set up to understand the
disparityThe baryon asymmetry problem in physics refers to the apparent fact that there is an imbalance in baryonic matter and antibaryonic matter in the universe. Neither the standard model of particle physics, nor the theory of general relativity provide an obvious explanation for why this should be so;...
between the
matterMatter is a general term for the substance of which all physical objects consist. Typically, matter includes atoms and other particles which have mass. A common way of defining matter is as anything that has mass and occupies volume...
and
antimatterIn particle physics, antimatter is the extension of the concept of the antiparticle to matter, where antimatter is composed of antiparticles in the same way that normal matter is composed of particles...
content of the universe by measuring
CP violationIn particle physics, CP violation is a violation of the postulated CP-symmetry: the combination of C-symmetry and P-symmetry . CP-symmetry states that the laws of physics should be the same if a particle were interchanged with its antiparticle , and left and right were swapped...
. CP symmetry is a combination of
Charge-conjugation symmetry (C symmetry) and
Parity symmetry (P symmetry), each of which are conserved separately except in
weak interactionWeak interaction , is one of the four fundamental forces of nature, alongside the strong nuclear force, electromagnetism, and gravity. It is responsible for the radioactive decay of subatomic particles and initiates the process known as hydrogen fusion in stars...
s. BaBar focuses on the study of CP violation in the
B mesonB mesons are mesons composed of a bottom quark or bottom antiquark and either an up , down , strange or charm quark . The combination of a bottom antiquark and a top quark is not thought to be possible because of the top quark's short lifetime...
system. The name of the experiment is derived from the nomenclature for the B meson (symbol
{{SubatomicParticle|B}}) and its
antiparticleCorresponding to most kinds of particles, there is an associated antiparticle with the same mass and opposite electric charge. For example, the antiparticle of the electron is the positively charged antielectron, or positron, which is produced naturally in certain types of radioactive decay.The...
(symbol
{{SubatomicParticle|AntiB}}, pronounced
B bar). The experiment's
mascotThe term mascot – defined as a term for any person, animal, or object thought to bring luck – colloquially includes anything used to represent a group with a common public identity, such as a school, professional sports team, society, military unit, or brand name...
was accordingly chosen to be
Babar the ElephantBabar the Elephant is a French children's fictional character who first appeared in Histoire de Babar by Jean de Brunhoff in 1931 and enjoyed immediate success. An English language version, entitled The Story of Babar, appeared in 1933 in Britain and also in the United States. The book is based on...
.
If CP symmetry holds, the decay rate of B mesons and their
antiparticleCorresponding to most kinds of particles, there is an associated antiparticle with the same mass and opposite electric charge. For example, the antiparticle of the electron is the positively charged antielectron, or positron, which is produced naturally in certain types of radioactive decay.The...
s should be equal. Analysis of secondary particles produced in the BaBar detector showed this was not the case – in the summer of 2002, definitive results were published based on the analysis of 87 million {{SubatomicParticle|B}}/{{SubatomicParticle|AntiB}} meson-pair events, clearly showing the decay rates were not equal. Consistent results were found by the
Belle experimentThe Belle experiment is a particle physics experiment conducted by the Belle Collaboration, an international collaboration of more than 400 physicists and engineers investigating CP-violation effects at the High Energy Accelerator Research Organisation in Tsukuba, Ibaraki Prefecture, Japan.The...
at the KEK laboratory in Japan.
CP violation was already predicted by the
Standard 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 physicsParticle physics is a branch of physics that studies the existence and interactions of particles that are the constituents of what is usually referred to as matter or radiation. In current understanding, particles are excitations of quantum fields and interact following their dynamics...
, and well established in the neutral kaon system ({{SubatomicParticle|link=yes|Kaon}}/{{SubatomicParticle|link=yes|Antikaon}} meson pairs). The BaBar experiment has increased the accuracy to which this effect has been experimentally measured. Currently, results are consistent with the standard model, but further investigation of a greater variety of decay modes may reveal discrepancies in the future.
The BaBar detector is a multilayer
particle detectorIn 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...
. Its large
solid angleThe solid angle, Ω, is the two-dimensional angle in three-dimensional space that an object subtends at a point. It is a measure of how large that object appears to an observer looking from that point...
coverage (near
hermeticIn particle physics, a hermetic detector is a particle detector designed to observe all possible decay products of an interaction between subatomic particles in a collider by covering as large an area around the interaction point as possible and incorporating multiple types of sub-detectors...
), vertex location with precision on the order of 10
μmA micrometer , sometimes known as a micrometer screw gauge, is a device incorporating a calibrated screw used widely for precise measurement of small distances in mechanical engineering and machining as well as most mechanical trades, along with other metrological instruments such as dial, vernier,...
(provided by a silicon vertex detector), good
pionIn particle physics, a pion is any of three subatomic particles: , , and . Pions are the lightest mesons and they play an important role in explaining the low-energy properties of the strong nuclear force....
–
kaonIn particle physics, a kaon is any one of a group of four mesons distinguished by the fact that they carry a quantum number called strangeness...
separation at multi-
GeVGEV or GeV may stand for:*GeV or gigaelectronvolt, a unit of energy equal to billion electron volts*GEV or Grid Enabled Vehicle that is fully or partially powered by the electric grid, see plug-in electric vehicle...
momenta (provided by a novel Cherenkov detector), and few-percent precision electromagnetic calorimetry (CsI(Tl) scintillating crystals) allow a list of other scientific searches apart from CP violation in the B meson system. Studies of rare decays and searches for exotic particles and precision measurements of phenomena associated with mesons containing
bottomThe 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...
s and
charm quarkThe charm quark or c quark is the third most massive of all quarks, a type of elementary particle. Charm quarks are found in hadrons, which are subatomic particles made of quarks...
s, as well as phenomena associated with
tau leptonThe tau , also called the tau lepton, tau particle or tauon, is an elementary particle similar to the electron, with negative electric charge and a spin of . Together with the electron, the muon, and the three neutrinos, it is classified as a lepton...
s are possible.
The BaBar detector ceased operation on 7 April 2008, but data analysis is ongoing.
Detector description
The BaBar detector is cylindrical with the interaction region at the center. In the interaction region, 9
GeVGEV or GeV may stand for:*GeV or gigaelectronvolt, a unit of energy equal to billion electron volts*GEV or Grid Enabled Vehicle that is fully or partially powered by the electric grid, see plug-in electric vehicle...
electrons collide with 3.1 GeV antielectrons (sometimes called positrons) to produce a
center-of-massIn physics, the center of mass or barycenter of a system is the average location of all of its mass. In the case of a rigid body, the position of the center of mass is fixed in relation to the body...
collision energy of 10.58 GeV, corresponding to the {{SubatomicParticle resonance. The {{SubatomicParticle|Upsilon}}(4S) decays immediately into a pair of B mesons – half the time {{SubatomicParticle|B+}}{{SubatomicParticle|B-}} and half the time {{SubatomicParticle|B0}}{{SubatomicParticle|AntiB0}}. To detect the particles there are a series of subsystems arranged cylindrically around the interaction region. These subsystems are as follows, in order from inside to outside:
- Silicon Vertex Tracker (SVT)
- Made from 5 layers of double-sided silicon strips, the SVT records charged particle tracks very close to the interaction region inside BaBar.
- Less expensive than silicon, the 40 layers of wires in this gas chamber detect charged particle tracks out to a much larger radius, providing a measurement of their momenta. In addition, the DCH also measures the energy loss of the particles as they pass through matter. See Bethe-Bloch formula.
- Detector of Internally Reflected Cherenkov Light (DIRC)
- The DIRC is composed of 144 quartz
Quartz is the second-most-abundant mineral in the Earth's continental crust, after feldspar. It is made up of a continuous framework of SiO4 silicon–oxygen tetrahedra, with each oxygen being shared between two tetrahedra, giving an overall formula SiO2. There are many different varieties of quartz,...
bars which radiate and focus Cherenkov radiationCherenkov radiation is electromagnetic radiation emitted when a charged particle passes through a dielectric medium at a speed greater than the phase velocity of light in that medium...
to differentiate between kaonIn particle physics, a kaon is any one of a group of four mesons distinguished by the fact that they carry a quantum number called strangeness...
s and pionIn particle physics, a pion is any of three subatomic particles: , , and . Pions are the lightest mesons and they play an important role in explaining the low-energy properties of the strong nuclear force....
s.
- Electromagnetic Calorimeter
In particle physics, a calorimeter is an experimental apparatus that measures the energy of particles. Most particles enter the calorimeter and initiate a particle shower and the particles' energy is deposited in the calorimeter, collected, and measured. The energy may be measured in its...
(EMC)
- Made from 6580 CsI
Caesium iodide is an ionic compound often used as the input phosphor of an x-ray image intensifier tube found in fluoroscopy equipment....
crystals, the EMC identifies electrons and antielectrons, which allows for the reconstruction of the particle tracks of photons (and thus of neutral pions ({{SubatomicParticle|Pion0}})) and of "long Kaons" ({{SubatomicParticle|K-long}}), which are also electrically neutral.
- Magnet
A magnet is a material or object that produces a magnetic field. This magnetic field is invisible but is responsible for the most notable property of a magnet: a force that pulls on other ferromagnetic materials, such as iron, and attracts or repels other magnets.A permanent magnet is an object...
- The Magnet produces a 1.5 T
The tesla is the SI derived unit of magnetic field B . One tesla is equal to one weber per square meter, and it was defined in 1960 in honour of the inventor, physicist, and electrical engineer Nikola Tesla...
field inside the detector, which bends the tracks of charged particles allowing deduction of their momentum.
- Instrumented Flux Return (IFR)
- The IFR is designed to return the flux of the 1.5 T
The tesla is the SI derived unit of magnetic field B . One tesla is equal to one weber per square meter, and it was defined in 1960 in honour of the inventor, physicist, and electrical engineer Nikola Tesla...
magnet, so it is mostly iron but there is also instrumentation to detect muonThe muon |mu]] used to represent it) is an elementary particle similar to the electron, with a unitary negative electric charge and a spin of ½. Together with the electron, the tau, and the three neutrinos, it is classified as a lepton...
s and long kaons. The IFR is broken into 6 sextants and two endcaps. Each of the sextants has empty spaces which held the 19 layers of Resistive Plate Chambers (RPC), which were replaced in 2004 and 2006 with Limited Streamer Tubes (LST) interleaved with brass. The brass is there to add mass for the interaction length since the LST modules are so much less massive than the RPCs. The LST system is designed to measure all three cylindrical coordinates of a track: which individual tube was hit gives the φ coordinate, which layer the hit was in gives the ρ coordinate, and finally the z-planes atop the LSTs measure the z coordinate.
Notable events
On 9 October 2005, BaBar recorded a record
luminosityLuminosity is a measurement of brightness.-In photometry and color imaging:In photometry, luminosity is sometimes incorrectly used to refer to luminance, which is the density of luminous intensity in a given direction. The SI unit for luminance is candela per square metre.The luminosity function...
just over {{nowrap|1 × 10
34 cm
−2s
−1}} delivered by the PEP-II
positron-electron colliderA 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...
. This represents 330% of the luminosity that PEP-II was designed to deliver, and was produced along with a world record for stored current in an
electronThe electron is a subatomic particle with a negative elementary electric charge. It has no known components or substructure; in other words, it is generally thought to be an elementary particle. An electron has a mass that is approximately 1/1836 that of the proton...
storage ringA storage ring is a type of circular particle accelerator in which a continuous or pulsed particle beam may be kept circulating for a long period of time, up to many hours. Storage of a particular particle depends upon the mass, energy and usually charge of the particle being stored...
at 1,732 mA, paired with a record 2,940 mA of
positronThe positron or antielectron is the antiparticle or the antimatter counterpart of the electron. The positron has an electric charge of +1e, a spin of ½, and has the same mass as an electron...
s. "For the BaBar experiment, higher luminosity means generating more collisions per second, which translates into more accurate results and the ability to find physics effects they otherwise couldn’t see."
In 2008, BaBar physicists detected the lowest energy particle in the bottomonium quark family. Spokesman
Hassan JawaheryHassan Jawahery is an Iranian-American physicist and former spokesperson for the BaBar Collaboration. He received his B.S. in Physics from Tehran University in Iran and his Ph.D. in Physics from Tufts University...
said: "These results were highly sought after for over 30 years and will have an important impact on our understanding of the strong interactions."
Data record
| Run | Period | Total integrated luminosity
(fbA barn is a unit of area. Originally used in nuclear physics for expressing the cross sectional area of nuclei and nuclear reactions, today it is used in all fields of high energy physics to express the cross sections of any scattering process, and is best understood as a measure of the...
−1) |
| 1 |
22 October 1999 - 28 October 2000 |
23.62 |
| 2 |
2 February 2001 - 30 June 2002 |
70.30 |
| 3 |
8 December 2002 - 27 June 2003 |
35.79 |
| 4 |
17 September 2003 - 31 July 2004 |
111.97 |
| 5 |
16 April 2005 - 17 August 2006 |
148.57 |
| 6 |
25 January 2007 - 4 September 2007 |
86.57 |
| 7 |
13 December 2007 - 7 April 2008 |
54.00 |
| Total |
22 October 1999 - 7 April 2008 |
530.82 |
External links