Antiproton Decelerator
Encyclopedia
The Antiproton Decelerator (AD) is a storage ring
at the CERN
laboratory in Geneva
. It was built as a successor to the Low Energy Antiproton Ring
(LEAR) and started operation in the year 2000. The decelerated antiprotons are ejected to one of several connected experiments.
research project that took place at the Antiproton Decelerator. In August 2002, it was the first experiment to produce 50,000 low-energy antihydrogen
atoms, as reported in Nature
. In 2005, ATHENA was disbanded and many of the former members worked on the subsequent ALPHA experiment.
to be created, antiproton
s and positron
s (also called antielectrons) must first be prepared. The antiprotons are provided by the Antiproton Decelerator, while positrons are obtained from a positron accumulator. Both are then led into a recombination trap, where they bind together
and form an antihydrogen atom. After preparation, a high-resolution detector confirms that antihydrogen was created. It then looks at the antihydrogen spectrum in order to compare it against "normal" hydrogen spectrum.
developed out of TRAP, a collaboration whose members pioneered cold antiproton
s, cold positron
s, and first made the ingredients of cold antihydrogen
to interact. ATRAP members also pioneered accurate hydrogen
spectroscopy
and first observed hot antihydrogen atoms.
and microwave spectroscopy of the hyperfine structure
of antihydrogen
. It also measures atomic and nuclear cross sections
of antiprotons on various targets at extremely low energies. The spokesperson for the experiment is Ryugo S. Hayano from the University of Tokyo
. It was originally proposed in 1997.
The ALPHA experiment is designed to trap neutral antihydrogen
in a magnetic trap
, and conduct experiments on them. The ultimate goal of this endeavour is to test CPT symmetry
through comparison of the atomic spectra of hydrogen
and antihydrogen (see hydrogen spectral series
). The ALPHA collaboration consists of some former members of the ATHENA collaboration (the first group to produce cold antihydrogen, in 2002), as well as a number of new members.
s – are notoriously weak; only atoms with kinetic energies equivalent to less than one kelvin
may be trapped. The cold antihydrogen created first in 2002 by the ATHENA and the ATRAP collaborations was produced by merging cold plasmas
of positron
s (also called antielectrons) and antiproton
s. While this method has been quite successful, it creates antiatoms with kinetic energies too large to be trapped. Furthermore, to do laser spectroscopy on these anti-atoms, it is important that they are in their ground state
, something which does not seem to be the case for the majority of the anti-atoms created thus far.
Antiprotons are received by the Antiproton Decelerator and are 'mixed' with positrons from a specially-designed positron accumulator in a versatile Penning trap
. The central region where the mixing and thus antihydrogen formation takes place is surrounded by a superconducting octupole magnet and two axially separated short solenoids "mirror-coils" to form a "minimum-B" magnetic trap. Once trapped antihydrogen
can be subjected to detailed study and be compared to hydrogen
.
In order to detect trapped antihydrogen
atoms ALPHA also comprises a silicon vertex detector. This cylindrically shaped detector consists of three layers of silicon panels (strips). Each panel acts as a position sensitive detector for charged particles passing through. By recording how the panels are excited ALPHA can reconstruct the tracks of charged particles traveling through their detector. When an antiproton annihilates (disintegrates) the process typically results in the emission of 3-4 charged pion
s. These can be observed by the ALPHA detector and by reconstructing their tracks through the detector their origin, and thus the location of the annihilation, can be determined. These tracks are quite distinct from the tracks of cosmic rays which are also detected but are of high energy and pass straight through the detector. By carefully analyzing the tracks ALPHA distinguishes between cosmic rays and antiproton annihilations.
To detect successful trapping the ALPHA trap magnet that created the minimum B-field was designed to allow it to be quickly and repeatedly de-energized. The currents' decay during de-energization has a characteristic time of 9 ms, orders of magnitude faster than similar systems. This fast turn-off and the ability to suppress false signal from cosmic rays should allow ALPHA to detect the release of even a single trapped antihydrogen atom during de-energization of the trap.
In order to make antihydrogen cold enough to be trapped the ALPHA collaboration has implemented a novel technique, well known from atomic physics, called evaporative cooling. The motivation for this is that one of the main challenges of trapping antihydrogen is to make it cold enough. State-of-the art minimum-B traps like the one ALPHA comprises have depths in temperature units of order one Kelvin. As no readily available techniques exist to cool antihydrogen, the constituents must be cold and kept cold for the formation. Antiprotons and positrons are not easily cooled to cryogenic temperatures and the implementation of evaporative cooling is thus an important step towards antihydrogen trapping.
in the same way it affects matter
by testing its effect on an antihydrogen
beam. By sending a stream of antihydrogen through a series of diffraction grating
s, the pattern of light and dark patterns would allegedly enable the position of the beam to be pinpointed with up to 1% accuracy. It was originally proposed in 2007.
Storage ring
A 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 the CERN
CERN
The European Organization for Nuclear Research , known as CERN , is an international organization whose purpose is to operate the world's largest particle physics laboratory, which is situated in the northwest suburbs of Geneva on the Franco–Swiss border...
laboratory in Geneva
Geneva
Geneva In the national languages of Switzerland the city is known as Genf , Ginevra and Genevra is the second-most-populous city in Switzerland and is the most populous city of Romandie, the French-speaking part of Switzerland...
. It was built as a successor to the Low Energy Antiproton Ring
Low Energy Antiproton Ring
The Low Energy Anti-Proton Ring was an experiment at CERN designed to decelerate and store antimatter, to study the properties of antimatter and to create atoms of antihydrogen. The experiment was constructed in 1982 and operated until 1996, when it was converted into the Low Energy Ion Ring,...
(LEAR) and started operation in the year 2000. The decelerated antiprotons are ejected to one of several connected experiments.
AD experiments
| Experiment |
Codename |
Spokesperson |
Title |
Proposed |
Approved |
Began |
Completed |
Link |
Website |
|---|---|---|---|---|---|---|---|---|---|
| AD1 | ATHENA | Alberto Rotondi | Antihydrogen production and precision experiments | ?? | 12 Jun 1997 | ?? | 16 Nov 2004 | SPIRES Grey Book |
Website |
| AD2 | ATRAP | Gerald Gabrielse Gerald Gabrielse Gerald Gabrielse is an American physicist and the George Vasmer Leverett Professor of Physics at Harvard University. In 2007, he was elected a member of the National Academy of Sciences.- Education :... |
Cold antihydrogen for precise laser spectroscopy | ?? | 12 Jun 1997 | ?? | Running | SPIRES Grey Book |
Website |
| AD3 | ASACUSA | Ryugo Hayano | Atomic spectroscopy and collisions using slow antiprotons | 7 Oct 1997 | 20 Nov 1997 | ?? | Running | SPIRES Grey Book |
Website |
| AD4 | ACE | Michael Holzscheiter | Relative biological effectiveness and peripheral damage of antiproton annihilation | ?? | 6 Feb 2003 | ?? | Running | Grey Book | Website |
| AD5 | ALPHA | Jeffrey Hangst | Antihydrogen laser physics apparatus | ?? | 2 Jun 2005 | ?? | Running | Grey Book | Website |
| AD6 | AEGIS | Gemma Testera | Antihydrogen experiment gravity interferometry spectroscopy | 8 Jun 2007 | 5 Dec 2008 | Not yet | N/A | Grey Book | Website |
ATHENA
ATHENA was an antimatterAntimatter
In 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...
research project that took place at the Antiproton Decelerator. In August 2002, it was the first experiment to produce 50,000 low-energy antihydrogen
Antihydrogen
Antihydrogen is the antimatter counterpart of hydrogen. Whereas the common hydrogen atom is composed of an electron and proton, the antihydrogen atom is made up of a positron and antiproton...
atoms, as reported in Nature
Nature (journal)
Nature, first published on 4 November 1869, is ranked the world's most cited interdisciplinary scientific journal by the Science Edition of the 2010 Journal Citation Reports...
. In 2005, ATHENA was disbanded and many of the former members worked on the subsequent ALPHA experiment.
ATHENA physics
For antihydrogenAntihydrogen
Antihydrogen is the antimatter counterpart of hydrogen. Whereas the common hydrogen atom is composed of an electron and proton, the antihydrogen atom is made up of a positron and antiproton...
to be created, antiproton
Antiproton
The antiproton is the antiparticle of the proton. Antiprotons are stable, but they are typically short-lived since any collision with a proton will cause both particles to be annihilated in a burst of energy....
s and positron
Positron
The 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 (also called antielectrons) must first be prepared. The antiprotons are provided by the Antiproton Decelerator, while positrons are obtained from a positron accumulator. Both are then led into a recombination trap, where they bind together
Bound state
In physics, a bound state describes a system where a particle is subject to a potential such that the particle has a tendency to remain localised in one or more regions of space...
and form an antihydrogen atom. After preparation, a high-resolution detector confirms that antihydrogen was created. It then looks at the antihydrogen spectrum in order to compare it against "normal" hydrogen spectrum.
ATHENA collaboration
The ATHENA collaboration comprised the following institutions:ATRAP
The ATRAP collaboration at CERNCERN
The European Organization for Nuclear Research , known as CERN , is an international organization whose purpose is to operate the world's largest particle physics laboratory, which is situated in the northwest suburbs of Geneva on the Franco–Swiss border...
developed out of TRAP, a collaboration whose members pioneered cold antiproton
Antiproton
The antiproton is the antiparticle of the proton. Antiprotons are stable, but they are typically short-lived since any collision with a proton will cause both particles to be annihilated in a burst of energy....
s, cold positron
Positron
The 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, and first made the ingredients of cold antihydrogen
Antihydrogen
Antihydrogen is the antimatter counterpart of hydrogen. Whereas the common hydrogen atom is composed of an electron and proton, the antihydrogen atom is made up of a positron and antiproton...
to interact. ATRAP members also pioneered accurate hydrogen
Hydrogen
Hydrogen is the chemical element with atomic number 1. It is represented by the symbol H. With an average atomic weight of , hydrogen is the lightest and most abundant chemical element, constituting roughly 75% of the Universe's chemical elemental mass. Stars in the main sequence are mainly...
spectroscopy
Spectroscopy
Spectroscopy is the study of the interaction between matter and radiated energy. Historically, spectroscopy originated through the study of visible light dispersed according to its wavelength, e.g., by a prism. Later the concept was expanded greatly to comprise any interaction with radiative...
and first observed hot antihydrogen atoms.
ATRAP physics
ATRAP is a collaboration between physicists around the world with the goal of creating and experimenting with antihydrogen. ATRAP accumulates positrons with using a radioactive sodium-22 source. These positrons are trapped in a Penning trap and then combined with antiprotons to create antihydrogen. The long-term goal is to trap antihydrogen in a Ioffe trap and collect enough antihydrogen to perform accurate laser spectroscopy on it.ATRAP collaboration
The ATRAP collaboration comprises the following institutions:ASACUSA
ASACUSA (Atomic Spectroscopy And Collisions Using Slow Antiprotons) is an experiment testing for CPT-symmetry by laser spectroscopy of antiprotonic heliumAntiprotonic helium
Antiprotonic helium is a three-body atom composed of an antiproton and an electron orbiting around a helium nucleus. It is thus made partly of matter, and partly of antimatter. The atom is electrically neutral, since both electrons and antiprotons have a charge of -1, whereas helium nuclei have a...
and microwave spectroscopy of the hyperfine structure
Hyperfine structure
The term hyperfine structure refers to a collection of different effects leading to small shifts and splittings in the energy levels of atoms, molecules and ions. The name is a reference to the fine structure which results from the interaction between the magnetic moments associated with electron...
of antihydrogen
Antihydrogen
Antihydrogen is the antimatter counterpart of hydrogen. Whereas the common hydrogen atom is composed of an electron and proton, the antihydrogen atom is made up of a positron and antiproton...
. It also measures atomic and nuclear cross sections
Cross section (physics)
A cross section is the effective area which governs the probability of some scattering or absorption event. Together with particle density and path length, it can be used to predict the total scattering probability via the Beer-Lambert law....
of antiprotons on various targets at extremely low energies. The spokesperson for the experiment is Ryugo S. Hayano from the University of Tokyo
University of Tokyo
, abbreviated as , is a major research university located in Tokyo, Japan. The University has 10 faculties with a total of around 30,000 students, 2,100 of whom are foreign. Its five campuses are in Hongō, Komaba, Kashiwa, Shirokane and Nakano. It is considered to be the most prestigious university...
. It was originally proposed in 1997.
ALPHA
Antihydrogen
Antihydrogen is the antimatter counterpart of hydrogen. Whereas the common hydrogen atom is composed of an electron and proton, the antihydrogen atom is made up of a positron and antiproton...
in a magnetic trap
Magnetic trap (atoms)
A magnetic trap uses a magnetic gradient to trap neutral particles with a magnetic moment. Although such traps have been employed for many purposes in physics research, they are best known as the last stage in cooling atoms to achieve Bose-Einstein condensation...
, and conduct experiments on them. The ultimate goal of this endeavour is to test CPT symmetry
CPT symmetry
CPT symmetry is a fundamental symmetry of physical laws under transformations that involve the inversions of charge, parity, and time simultaneously.-History:...
through comparison of the atomic spectra of hydrogen
Hydrogen
Hydrogen is the chemical element with atomic number 1. It is represented by the symbol H. With an average atomic weight of , hydrogen is the lightest and most abundant chemical element, constituting roughly 75% of the Universe's chemical elemental mass. Stars in the main sequence are mainly...
and antihydrogen (see hydrogen spectral series
Hydrogen spectral series
The emission spectrum of atomic hydrogen is divided into a number of spectral series, with wavelengths given by the Rydberg formula. These observed spectral lines are due to electrons moving between energy levels in the atom. The spectral series are important in astronomy for detecting the presence...
). The ALPHA collaboration consists of some former members of the ATHENA collaboration (the first group to produce cold antihydrogen, in 2002), as well as a number of new members.
ALPHA physics
ALPHA faces several challenges. Magnetic traps – wherein neutral atoms are trapped using their magnetic momentMagnetic moment
The magnetic moment of a magnet is a quantity that determines the force that the magnet can exert on electric currents and the torque that a magnetic field will exert on it...
s – are notoriously weak; only atoms with kinetic energies equivalent to less than one kelvin
Kelvin
The kelvin is a unit of measurement for temperature. It is one of the seven base units in the International System of Units and is assigned the unit symbol K. The Kelvin scale is an absolute, thermodynamic temperature scale using as its null point absolute zero, the temperature at which all...
may be trapped. The cold antihydrogen created first in 2002 by the ATHENA and the ATRAP collaborations was produced by merging cold plasmas
Plasma (physics)
In physics and chemistry, plasma is a state of matter similar to gas in which a certain portion of the particles are ionized. Heating a gas may ionize its molecules or atoms , thus turning it into a plasma, which contains charged particles: positive ions and negative electrons or ions...
of positron
Positron
The 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 (also called antielectrons) and antiproton
Antiproton
The antiproton is the antiparticle of the proton. Antiprotons are stable, but they are typically short-lived since any collision with a proton will cause both particles to be annihilated in a burst of energy....
s. While this method has been quite successful, it creates antiatoms with kinetic energies too large to be trapped. Furthermore, to do laser spectroscopy on these anti-atoms, it is important that they are in their ground state
Ground state
The ground state of a quantum mechanical system is its lowest-energy state; the energy of the ground state is known as the zero-point energy of the system. An excited state is any state with energy greater than the ground state...
, something which does not seem to be the case for the majority of the anti-atoms created thus far.
Antiprotons are received by the Antiproton Decelerator and are 'mixed' with positrons from a specially-designed positron accumulator in a versatile Penning trap
Penning trap
Penning traps are devices for the storage of charged particles using a homogeneous static magnetic field and a spatially inhomogeneous static electric field. This kind of trap is particularly well suited to precision measurements of properties of ions and stable subatomic particles which have...
. The central region where the mixing and thus antihydrogen formation takes place is surrounded by a superconducting octupole magnet and two axially separated short solenoids "mirror-coils" to form a "minimum-B" magnetic trap. Once trapped antihydrogen
Antihydrogen
Antihydrogen is the antimatter counterpart of hydrogen. Whereas the common hydrogen atom is composed of an electron and proton, the antihydrogen atom is made up of a positron and antiproton...
can be subjected to detailed study and be compared to hydrogen
Hydrogen
Hydrogen is the chemical element with atomic number 1. It is represented by the symbol H. With an average atomic weight of , hydrogen is the lightest and most abundant chemical element, constituting roughly 75% of the Universe's chemical elemental mass. Stars in the main sequence are mainly...
.
In order to detect trapped antihydrogen
Antihydrogen
Antihydrogen is the antimatter counterpart of hydrogen. Whereas the common hydrogen atom is composed of an electron and proton, the antihydrogen atom is made up of a positron and antiproton...
atoms ALPHA also comprises a silicon vertex detector. This cylindrically shaped detector consists of three layers of silicon panels (strips). Each panel acts as a position sensitive detector for charged particles passing through. By recording how the panels are excited ALPHA can reconstruct the tracks of charged particles traveling through their detector. When an antiproton annihilates (disintegrates) the process typically results in the emission of 3-4 charged pion
Pion
In 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. These can be observed by the ALPHA detector and by reconstructing their tracks through the detector their origin, and thus the location of the annihilation, can be determined. These tracks are quite distinct from the tracks of cosmic rays which are also detected but are of high energy and pass straight through the detector. By carefully analyzing the tracks ALPHA distinguishes between cosmic rays and antiproton annihilations.
To detect successful trapping the ALPHA trap magnet that created the minimum B-field was designed to allow it to be quickly and repeatedly de-energized. The currents' decay during de-energization has a characteristic time of 9 ms, orders of magnitude faster than similar systems. This fast turn-off and the ability to suppress false signal from cosmic rays should allow ALPHA to detect the release of even a single trapped antihydrogen atom during de-energization of the trap.
In order to make antihydrogen cold enough to be trapped the ALPHA collaboration has implemented a novel technique, well known from atomic physics, called evaporative cooling. The motivation for this is that one of the main challenges of trapping antihydrogen is to make it cold enough. State-of-the art minimum-B traps like the one ALPHA comprises have depths in temperature units of order one Kelvin. As no readily available techniques exist to cool antihydrogen, the constituents must be cold and kept cold for the formation. Antiprotons and positrons are not easily cooled to cryogenic temperatures and the implementation of evaporative cooling is thus an important step towards antihydrogen trapping.
ALPHA collaboration
The ALPHA collaboration comprises the following institutions:AEGIS
AEGIS (Antimatter experiment: Gravity, interferometry, spectroscopy), is a proposed experiment to be set up at the Antiproton Decelerator.AEGIS physics
AEGIS would attempt to determine if gravity affects antimatterAntimatter
In 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...
in the same way it affects matter
Matter
Matter 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...
by testing its effect on an antihydrogen
Antihydrogen
Antihydrogen is the antimatter counterpart of hydrogen. Whereas the common hydrogen atom is composed of an electron and proton, the antihydrogen atom is made up of a positron and antiproton...
beam. By sending a stream of antihydrogen through a series of diffraction grating
Diffraction grating
In optics, a diffraction grating is an optical component with a periodic structure, which splits and diffracts light into several beams travelling in different directions. The directions of these beams depend on the spacing of the grating and the wavelength of the light so that the grating acts as...
s, the pattern of light and dark patterns would allegedly enable the position of the beam to be pinpointed with up to 1% accuracy. It was originally proposed in 2007.