Crystal Ball (detector)
Encyclopedia
The Crystal Ball is a hermetic
particle detector
used initially with the SPEAR
particle accelerator
at the Stanford Linear Accelerator Center
beginning in 1979. It was designed to detect neutral particle
s and was used to discover the ηc meson. Its central section was a spark chamber surrounded by a nearly-complete sphere of scintillating
crystal
s (NaI(Tl)), for which it was named. With the addition of endcaps of similar construction, the detector covered 98% of the solid angle
around the interaction point
.
After its decommissioning at SLAC, the detector was carried to DESY
, where it was used for b-physics experiments. Currently it is located at Mainz Microtron
facility, where it is being used by the A2 Collaboration for a diverse program of measurements using energy tagged Bremsstrahlung
photons.
Hermetic detector
In 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...
particle detector
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...
used initially with the SPEAR
SPEAR
SPEAR was a collider at the SLAC National Accelerator Laboratory. It began running in 1972, colliding electrons and positrons with an energy of...
particle accelerator
Particle accelerator
A 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...
at the Stanford Linear Accelerator Center
Stanford Linear Accelerator Center
The SLAC National Accelerator Laboratory, originally named Stanford Linear Accelerator Center, is a United States Department of Energy National Laboratory operated by Stanford University under the programmatic direction of the U.S...
beginning in 1979. It was designed to detect neutral particle
Neutral particle
In physics, a neutral particle is a particle with no electric charge. This is not to be confused with a real neutral particle, a neutral particle that is also identical to its own antiparticle.-Stable or long-lived neutral particles:...
s and was used to discover the ηc meson. Its central section was a spark chamber surrounded by a nearly-complete sphere of scintillating
Scintillator
A scintillator is a special material, which exhibits scintillation—the property of luminescence when excited by ionizing radiation. Luminescent materials, when struck by an incoming particle, absorb its energy and scintillate, i.e., reemit the absorbed energy in the form of light...
crystal
Crystal
A crystal or crystalline solid is a solid material whose constituent atoms, molecules, or ions are arranged in an orderly repeating pattern extending in all three spatial dimensions. The scientific study of crystals and crystal formation is known as crystallography...
s (NaI(Tl)), for which it was named. With the addition of endcaps of similar construction, the detector covered 98% of the solid angle
Solid angle
The 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...
around the interaction point
Interaction point
In particle physics, an interaction point is the place where particles collide. One differentiates between the nominal IP, which is the design position of the IP, and the real or physics IP, which is the position where the particles actually collide...
.
After its decommissioning at SLAC, the detector was carried to DESY
DESY
The DESY is the biggest German research center for particle physics, with sites in Hamburg and Zeuthen....
, where it was used for b-physics experiments. Currently it is located at Mainz Microtron
Mainz Microtron
The Mainz Microtron , abbreviated MAMI, is an electron accelerator of the microtron type, in which electrons are accelerated to relativistic velocities. It is operated by the Institute for Nuclear Physics of the Johannes Gutenberg University of Mainz. Its purpose is the generation of polarized...
facility, where it is being used by the A2 Collaboration for a diverse program of measurements using energy tagged Bremsstrahlung
Bremsstrahlung
Bremsstrahlung is electromagnetic radiation produced by the deceleration of a charged particle when deflected by another charged particle, typically an electron by an atomic nucleus. The moving particle loses kinetic energy, which is converted into a photon because energy is conserved. The term is...
photons.