ALEPH was a

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 ...

at the Large Electron-Positron collider (LEP) at

CERN The European Organization for Nuclear Research, known as CERN (; ; ), is an intergovernmental organization that operates the largest particle physics laboratory in the world. Established in 1954, it is based in Meyrin, western suburb of Gene ...

. It was designed to explore the physics predicted by the

Standard Model The Standard Model of particle physics is the Scientific theory, theory describing three of the four known fundamental forces (electromagnetism, electromagnetic, weak interaction, weak and strong interactions – excluding gravity) in the unive ...

and to search for physics beyond it.

Detector

The ALEPH detector was built to measure events created by

electron The electron (, or in nuclear reactions) is a subatomic particle with a negative one elementary charge, elementary electric charge. It is a fundamental particle that comprises the ordinary matter that makes up the universe, along with up qua ...

positron The positron or antielectron is the particle with an electric charge of +1''elementary charge, e'', a Spin (physics), spin of 1/2 (the same as the electron), and the same Electron rest mass, mass as an electron. It is the antiparticle (antimatt ...

collisions in LEP. It operated from 1989 to 1995 in the energy range of the Z particle (around 91 GeV) and later (1995 to 2000) above the threshold of W pair production (up to 200 GeV). Typical events have many particles distributed in jets over the entire detector volume. The event rate ranged from around 1 Hz at the peak of the Z to at least a factor hundred smaller at the highest energies. The ALEPH detector was therefore designed to accumulate, for each event, as much information over as much

solid angle In geometry, a solid angle (symbol: ) is a measure of the amount of the field of view from some particular point that a given object covers. That is, it is a measure of how large the object appears to an observer looking from that point. The poin ...

as was practical. This was achieved by a cylindrical arrangement around the beam pipe with the electron-positron interaction point in the middle. A

magnetic field A magnetic field (sometimes called B-field) is a physical field that describes the magnetic influence on moving electric charges, electric currents, and magnetic materials. A moving charge in a magnetic field experiences a force perpendicular ...

of 1.5 Tesla was created by a

superconducting Superconductivity is a set of physical properties observed in superconductors: materials where electrical resistance vanishes and magnetic fields are expelled from the material. Unlike an ordinary metallic conductor, whose resistance decreases g ...

coil 6.4 m long and 5.3 m in diameter. The iron return yoke was a dodecagonal cylinder with two end-plates that left holes for a focusing magnet (quadrupole) of the LEP machine. The iron was 1.2 m thick and was subdivided into layers that left space for the insertion of layers of streamer tubes. In this way the iron yoke was a fully instrumented

hadron In particle physics, a hadron is a composite subatomic particle made of two or more quarks held together by the strong nuclear force. Pronounced , the name is derived . They are analogous to molecules, which are held together by the electri ...

calorimeter A calorimeter is a device used for calorimetry, or the process of measuring the heat of chemical reactions or physical changes as well as heat capacity. Differential scanning calorimeters, isothermal micro calorimeters, titration calorimeters ...

(HCAL), which was read out in 4608 projective towers. Outside the iron, there were two double layers of streamer tube chambers to record the position and angle of

muon A muon ( ; from the Greek letter mu (μ) used to represent it) is an elementary particle similar to the electron, with an electric charge of −1 '' e'' and a spin of ''ħ'', but with a much greater mass. It is classified as a ...

s that had penetrated the iron. Inside the coil was the electron-photon

(ECAL), designed for the highest possible angular resolution and electron identification. It consisted of alternating layers of lead and proportional tubes read out in 73,728 projective towers, each subdivided into three depth zones. The central detector for charged particles was the

time projection chamber In physics, a time projection chamber (TPC) is a type of particle detector that uses a combination of electric fields and magnetic fields together with a sensitive volume of gas or liquid to perform a three-dimensional reconstruction of a particle ...

(TPC), 4.4 m long and 3.6 m in diameter. It provided a three dimensional measurement of each track segment. In addition, it provided up to 330

ionisation Ionization or ionisation is the process by which an atom or a molecule acquires a negative or positive charge by gaining or losing electrons, often in conjunction with other chemical changes. The resulting electrically charged atom or molecule i ...

measurements for a track; this was useful for particle identification. The TPC surrounded the inner track chamber (ITC); an axial-wire drift chamber with inner and outer diameters of 13 cm and 29 cm and a length of 2 m. It provided 8 track coordinates and a trigger signal for charged particles that came from the interaction point. Closest to the beam pipe, was a silicon strip vertex detector. For each track, this measured two pairs of coordinates, 6.3 cm and 11 cm away from the beam axis over a length of 40 cm along the beam line. The beam pipe, made out of beryllium, had a diameter of 16 cm. The vacuum inside was about 10⁻¹⁵ atm. ALEPH Website
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References

External links

Record for ALEPH experiment
on

INSPIRE-HEP INSPIRE-HEP is an open access digital library for the field of high energy physics (HEP). It is the successor of the Stanford Physics Information Retrieval System (SPIRES) database, the main literature database for high energy physics since the 1 ...

{{DEFAULTSORT:ALEPH Experiment CERN experiments Particle experiments