Ring imaging Cherenkov detector
Encyclopedia
A Ring Imaging Cherenkov detector (RICH detector) is a particle detector
that can determine the velocity,
, of a charged particle. This is done by an indirect measurement of the Cherenkov angle, 
, i.e. the angle between the emitted Čerenkov radiation and the particle path. This is related to the velocity by 
, where 
is the speed of light and 
is the refractive index of the medium.
The technique of this detector has been proposed by T. Ypsilantis and J. Séguinot, working in Max Ferro-Luzzi's group. The first large-scale application was for the DELPHI experiment at LEP (Large Electron-Positron Collider
) at CERN
.
A cone of Cherenkov light is produced when a high speed particle traverses a suitable medium, often called radiator, with a velocity greater than the speed of light in that medium (
, 
being the refractive index
of the medium). In a RICH detector this light cone is detected on a position sensitive planar photon detector, which allows reconstructing a ring or disc, the radius of which is a measure for the Cherenkov emission angle. Both focusing and proximity-focusing detectors are in use. In a focusing RICH detector the photons are collected by a spherical mirror with focal length
and focused onto the photon detector placed at the focal plane. The result is a circle with a radius 
, independent of the emission point along the particle track. This scheme is suitable for low refractive index radiators, i.e. gases, with their larger radiator length needed to create enough photons.
In the more compact proximity-focusing design a thin radiator volume emits a cone of Cherenkov light which traverses a small distance - the proximity gap - and is detected on the photon detector plane. The image is a ring of light the radius of which is defined by the Cherenkov emission angle and the proximity gap. The ring thickness is mainly determined by the thickness of the radiator. An example of a proximity gap RICH detector is the High Momentum Particle Identification (HMPID), a detector currently under construction for ALICE (A Large Ion Collider Experiment
), one of the five experiments at the LHC (Large Hadron Collider
) at CERN
.
In a DIRC (Detection of Internally Reflected Cherenkov light), another design of a RICH detector, light that is captured by total internal reflection inside the solid radiator reaches the light sensors at the detector perimeter, the precise rectangular cross section of the radiator preserving the angular information of the Cherenkov light cone. One example is the DIRC of the BaBar
experiment at SLAC.
The LHCb
experiment on the Large Hadron Collider uses two RICH detectors for differentiating between pions
and kaons
. The first (RICH-1) is located immediately after the Vertex Locator (VELO) around the interaction point and is optimised for low-momentum tracks and the second (RICH-2) is located after the magnet
and tracker layers and optimised for higher-momentum tracks.
The Alpha Magnetic Spectrometer
device AMS-02, recently mounted on the International Space Station
uses a RICH detector in combination with other devices to analyze cosmic rays.
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...
that can determine the velocity,
, of a charged particle. This is done by an indirect measurement of the Cherenkov angle, , i.e. the angle between the emitted Čerenkov radiation and the particle path. This is related to the velocity by , where is the speed of light and is the refractive index of the medium.The technique of this detector has been proposed by T. Ypsilantis and J. Séguinot, working in Max Ferro-Luzzi's group. The first large-scale application was for the DELPHI experiment at LEP (Large Electron-Positron Collider
Large Electron-Positron Collider
The Large Electron–Positron Collider was one of the largest particle accelerators ever constructed.It was built at CERN, a multi-national centre for research in nuclear and particle physics near Geneva, Switzerland. LEP was a circular collider with a circumference of 27 kilometres built in a...
) at 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...
.
A cone of Cherenkov light is produced when a high speed particle traverses a suitable medium, often called radiator, with a velocity greater than the speed of light in that medium (
, being the refractive indexRefractive index
In optics the refractive index or index of refraction of a substance or medium is a measure of the speed of light in that medium. It is expressed as a ratio of the speed of light in vacuum relative to that in the considered medium....
of the medium). In a RICH detector this light cone is detected on a position sensitive planar photon detector, which allows reconstructing a ring or disc, the radius of which is a measure for the Cherenkov emission angle. Both focusing and proximity-focusing detectors are in use. In a focusing RICH detector the photons are collected by a spherical mirror with focal length
and focused onto the photon detector placed at the focal plane. The result is a circle with a radius , independent of the emission point along the particle track. This scheme is suitable for low refractive index radiators, i.e. gases, with their larger radiator length needed to create enough photons.In the more compact proximity-focusing design a thin radiator volume emits a cone of Cherenkov light which traverses a small distance - the proximity gap - and is detected on the photon detector plane. The image is a ring of light the radius of which is defined by the Cherenkov emission angle and the proximity gap. The ring thickness is mainly determined by the thickness of the radiator. An example of a proximity gap RICH detector is the High Momentum Particle Identification (HMPID), a detector currently under construction for ALICE (A Large Ion Collider Experiment
A Large Ion Collider Experiment
ALICE is one of the six detector experiments at the Large Hadron Collider at CERN. The other five are: ATLAS, CMS, TOTEM, LHCb, and LHCf. ALICE is optimized to study heavy ion collisions. Pb-Pb nuclei collisions will be studied at a centre of mass energy of 2.76 TeV per nucleon...
), one of the five experiments at the LHC (Large Hadron Collider
Large Hadron Collider
The Large Hadron Collider is the world's largest and highest-energy particle accelerator. It is expected to address some of the most fundamental questions of physics, advancing the understanding of the deepest laws of nature....
) at 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...
.
In a DIRC (Detection of Internally Reflected Cherenkov light), another design of a RICH detector, light that is captured by total internal reflection inside the solid radiator reaches the light sensors at the detector perimeter, the precise rectangular cross section of the radiator preserving the angular information of the Cherenkov light cone. One example is the DIRC of the BaBar
Babar
Babar means Lion. Babar may refer to:Names* Babur , 16th-century ruler of Indian subcontinent and founder of the Mughal Empire* Babar Luck, musician from England...
experiment at SLAC.
The LHCb
LHCb
LHCb is one of six particle physics detector experiments collecting data at the Large Hadron Collider accelerator at CERN. LHCb is a specialized b-physics experiment, that is measuring the parameters of CP violation in the interactions of b-hadrons...
experiment on the Large Hadron Collider uses two RICH detectors for differentiating between pions
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....
and kaons
Kaon
In 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...
. The first (RICH-1) is located immediately after the Vertex Locator (VELO) around the interaction point and is optimised for low-momentum tracks and the second (RICH-2) is located after the magnet
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...
and tracker layers and optimised for higher-momentum tracks.
Alpha Magnetic Spectrometer
The Alpha Magnetic Spectrometer, also designated AMS-02, is a particle physics experiment module that is mounted on the International Space Station. It is designed to search for various types of unusual matter by measuring cosmic rays. Its experiments will help researchers study the formation of...
device AMS-02, recently mounted on the International Space Station
International Space Station
The International Space Station is a habitable, artificial satellite in low Earth orbit. The ISS follows the Salyut, Almaz, Cosmos, Skylab, and Mir space stations, as the 11th space station launched, not including the Genesis I and II prototypes...
uses a RICH detector in combination with other devices to analyze cosmic rays.