OPAL experiment

OPAL was one of the major experiments at CERN's LEP. OPAL studied particles and their interactions by collecting and analysing electron-positron collision events at LEP, the Large Electron-Positron collider. LEP was the largest particle accelerator in the world. There three other experiments at LEP were: ALEPH, DELPHI and L3. ^[1]

The Detector

OPAL was one of the four large detectors on the Large Electron-Positron collider (1989-2000). The detector was dismantled in 2001 to make way for construction of the Large Hadron Collider (LHC).

The OPAL detector was about 12 m long, 12m high and 12m wide. The detector components were arranged around the beam pipe, in a layered structure like that of an onion. The tracking system of OPAL consisted of a silicon microvertex detector, a vertex detector, a jet chamber, and z-chambers (from the beam pipe out).

The silicon microvertex detector and the vertex chamber were used to locate decay vertices of short-lived particles, and to improve the momentum resolution. The central jet chamber identified particles from how much ionization they caused, and how far they curved in the magnetic field. These chambers worked well to identify tracks in the plane perpendicular to the beam axis. They were complemented by so called "z-chambers" at the outside edge of the jet chamber, to provide precise measurements of the perpendicular coordinates of the tracks.^[2]

Further out from the beam pipe, OPAL's calorimeter system was divided into electromagnetic calorimeters (for the electrons identification), hadron calorimeters (for hadrons) and forward calorimeters placed around, and close to, the beam pipe at the two ends of the detector to catch particles thrown forwards by collisions in LEP. Muon detectors formed the end caps of the detector.

In its first phase of operation from 1989 to 1995, electrons and positrons collided in LEP at 91 GeV. The aim was to produce Z bosons. OPAL accumulated millions of these Z events for high-precision measurements. In LEP's second phase from 1996 to 2000, the collider's collision energy was increased to make pairs of W bosons, and to search for possible new particles and new physics.^[3]

References

External links

Scientific publications of the OPAL Collaboration on INSPIRE-HEP

European Organization for Nuclear Research (CERN)

Large Hadron Collider (LHC)	List of LHC experiments ALICE ATLAS CMS LHCb LHCf MoEDAL TOTEM

Large Electron–Positron Collider (LEP)	List of LEP experiments ALEPH DELPHI OPAL L3 LEP5 LEP6

Super Proton Synchrotron (SPS)	List of SPS experiments CNGS NA48 NA49 NA58/COMPASS NA60 NA61/SHINE NA62 UA1 UA2

Proton Synchrotron (PS)	PSB LEIR BEBC^[1] PS212/DIRAC PS215/CLOUD Gargamelle ↑ Later an SPS experiment

Linear Accelerators	AWAKE CTF3 LINAC 1 LINAC 2 LINAC 3 LINAC 4

Other Accelerators	AD ISR ISOLDE ISOLTRAP MISTRAL WITCH LEAR PS210 n-TOF

Non-Accelerator Experiments	CAST OSQAR

Future projects	High Luminosity Large Hadron Collider Very Large Hadron Collider International Linear Collider Compact Linear Collider

Related	LHC@home Safety of high-energy particle collision experiments CERN Courier CERN openlab Worldwide LHC Computing Grid Microcosm exhibition Streets in CERN The Globe of Science and Innovation Particle Fever (2013 documentary)

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