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 ionizing elementary particle, particles, such as t ...

s a detection of internally reflected Cherenkov light (DIRC) detector measures the

velocity Velocity is a measurement of speed in a certain direction of motion. It is a fundamental concept in kinematics, the branch of classical mechanics that describes the motion of physical objects. Velocity is a vector (geometry), vector Physical q ...

charged particle In physics, a charged particle is a particle with an electric charge. For example, some elementary particles, like the electron or quarks are charged. Some composite particles like protons are charged particles. An ion, such as a molecule or atom ...

s and is used for

particle identification Particle identification is the process of using information left by a particle passing through a particle detector to identify the type of particle. Particle identification reduces backgrounds and improves measurement resolutions, and is essentia ...

. It is a design of a

ring imaging Cherenkov detector The ring-imaging Cherenkov, or RICH, detector is a device for identifying the type of an electrically charged subatomic particle of known momentum, that traverses a transparency and translucency, transparent refractive medium, by measurement of the ...

where Cherenkov light that is contained by

total internal reflection In physics, total internal reflection (TIR) is the phenomenon in which waves arriving at the interface (boundary) from one medium to another (e.g., from water to air) are not refracted into the second ("external") medium, but completely refl ...

inside the solid radiator has its angular information preserved until it reaches the light sensors at the detector perimeter. DIRC Schema01 2009-08-13

A charged particle travelling through a material (for instance

fused silica Fused quartz, fused silica or quartz glass is a glass consisting of almost pure silica (silicon dioxide, SiO2) in amorphous (non-crystalline) form. This differs from all other commercial glasses, such as soda-lime glass, lead glass, or borosil ...

) with a speed greater than c/n (n

refractive index In optics, the refractive index (or refraction index) of an optical medium is the ratio of the apparent speed of light in the air or vacuum to the speed in the medium. The refractive index determines how much the path of light is bent, or refrac ...

, c vacuum speed of light) emits Cherenkov radiation. If the light angle on the surface is sufficiently shallow, this radiation is contained inside and transmitted through internal reflections to an expansion volume, coupled to

photomultiplier A photomultiplier is a device that converts incident photons into an electrical signal. Kinds of photomultiplier include: * Photomultiplier tube, a vacuum tube converting incident photons into an electric signal. Photomultiplier tubes (PMTs for sh ...

s (or other types of photon detectors), to measure the angle. Preserving the angle requires a precise planar and rectangular cross section of the radiator. Knowledge of the angle at which the radiation was produced, combined with the track angle and the particle's momentum (measured in a tracking detector like a

drift chamber A wire chamber or multi-wire proportional chamber is a type of proportional counter that detects charged particles and photons and can give positional information on their trajectory, by tracking the trails of gaseous ionization. was located via ...

) may be used to calculate the particle's mass. A DIRC was first proposed by

Blair Ratcliff Blair is a Scots-English-language name of Scottish Gaelic origin. The surname is derived from any of the numerous places in Scotland called ''Blair'', derived from the Scottish Gaelic ''blàr'', meaning "plain", "meadow" or "field", frequently ...

as a tool for particle identification at a B-Factory, and the design was first used by the

BaBar Babar (), also variously spelled as Baber, Babur, and Babor is a male given name of Persian language, Persian origin, and a popular male given name in Pakistan. It is generally taken in reference to the Persian language, Persian ''babr'' (Persian ...

collaboration at

SLAC SLAC National Accelerator Laboratory, originally named the Stanford Linear Accelerator Center, is a federally funded research and development center in Menlo Park, California, United States. Founded in 1962, the laboratory is now sponsored ...

. Since the successful operation in the BaBar experiment next-generation DIRC-type detectors have been designed for several new particle physics experiments, including Belle-II,

PANDA The giant panda (''Ailuropoda melanoleuca''), also known as the panda bear or simply panda, is a bear species endemic to China. It is characterised by its white coat with black patches around the eyes, ears, legs and shoulders. Its body is ...

, and

GlueX GlueX is a particle physics experiment located at the Thomas Jefferson National Accelerator Facility (JLab) accelerator in Newport News, Virginia. Its primary purpose is to better understand the nature of confinement in quantum chromodynamics (Q ...

. The DIRC differs from earlier

RICH Rich may refer to: Common uses * Rich, an entity possessing wealth * Rich, an intense taste, flavor, color, sound, texture, or feeling **Rich (wine), a descriptor in wine tasting Places United States * Rich, Mississippi, an unincorporated c ...

and CRID Cherenkov light detectors in that the quartz bars used as radiators also transmit the light.

See also