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 particles, such as those produced by ...

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

velocity Velocity is the directional speed of an object in motion as an indication of its rate of change in position as observed from a particular frame of reference and as measured by a particular standard of time (e.g. northbound). Velocity i ...

of charged particles 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 essenti ...

. It is a design of a ring imaging Cherenkov detector where Cherenkov light that is contained by

total internal reflection Total internal reflection (TIR) is the optical 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 reflecte ...

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) with a speed greater than c/n (n

refractive index In optics, the refractive index (or refraction index) of an optical medium is a dimensionless number that gives the indication of the light bending ability of that medium. The refractive index determines how much the path of light is bent, o ...

, 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 s ...

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

Blair Ratcliff Blair is an English-language English is a West Germanic language of the Indo-European language family, with its earliest forms spoken by the inhabitants of early medieval England. It is named after the Angles, one of the ancient Germanic ...

as a tool for particle identification at a B-Factory, and the design was first used by the BaBar collaboration at SLAC. 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 the panda), is a bear species endemic to China. It is characterised by its bold black-and-white coat and rotund body. The name "giant panda" is sometimes use ...

, and GlueX. 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 ...

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

See also