DELPHI (DEtector with Lepton, Photon and Hadron Identification), is a detector for e+e- physics, with special emphasis on powerful particle identification , three-dimensional information, high granularity and precise vertex determination. It is installed at LEP (Large Electron and Positron collider) at CERN where it has operated since 1989.
The Vertex Detector
) - nearest the collision point -
is an advanced silicon detector providing very precise tracking, principally in
order to detect very short lived particles by extrapolating the tracks back
towards the interaction point.
The old VD has been made longer by 24 cm and is now the barrel part of the Silicon Tracker. It consists of tree coaxial cylindrical layers of AC coupled silicon strip detectors at average radii of 6.3, 9.0 and 10.9 cm. At present the polar angle coverage extends down to 25 degrees.
The Inner Detector ( ID ) - shown as the smallest green cylinder - is located between the Vertex Detector and the Time Projection Chamber and provides intermediate precision position and trigger information. It consists of two parts: the JET chamber and the Trigger Layers (TL). The JET chamber provides points per track between radii of 12 and 23 cm and the polar angle coverage extends down to 15 degrees.
The Time Projection Chamber ( TPC ) - shown as the big blue cylinder - is the principal tracking device of DELPHI. As well it helps in charged particle identification by measuring the dE/dX. It is a cylinder of 2x130 cm situated between the radii 29 cm and 122 cm. The detector provides points per particle trajectory at radii from 40 to 110 cm between polar angles from 39 to 141 degrees. At least three pad rows are crossed down to polar angles from 20 to 160 degrees.
The Outer Detector ( OD ) - shown as the narrow navy-blue cylinder - consists of five layers of drift tubes located between radii of 197 and 206 cm. The active length of the detector corresponds to polar angles from 42 to 138 degrees. It provides a final precise and direction measurement after the Barrel Ring Imaging Cherenkov detector.
The Forward Chamber A ( FCA ) - shown as the smaller blue component in the forward part - is distant from the interaction point of about 160 cm in z. The chamber covers polar angles from 11 to 32 degrees and from 148 to 169 degrees.
The Forward Chamber B ( FCB ) - shown as the bigger blue component in the forward part - is a drift chamber at an average distance of | z | = 275 cm from the interaction point. The sensitive area of the chamber corresponds to polar angles from 11 to 36 degrees and from 144 to 169 degrees.
The Very Forward Tracker ( VFT ) is located on both sides vertex detectors. It is covers the polar angle from 10 to 25 degrees and from 155 to 170 degrees. The VFT is the forward part of the Silicon Tracker.
The Muon Chambers
(MUC = MUB + MUF + SMC)
are farthest the collision point, since muons are the only charged particles that
can traverse the lead and iron of both calorimeters essentially unaffected. Most
muons of momenta above 2 GeV/c are expected to penetrate to The Muon Chambers
,whereas other charged particles are stopped by this material.
Muon identification is achieved by comparing the extrapolations of the reconstructed tracks with the hits in the Barrel ( MUB that covers polar angles from 53.0 to 88.5 degrees and from 91.5 to 127.0 degrees ) and Forward ( MUF that covers polar angles from 20 to 42 degrees and from 138 to 160 degrees ) muon drift chambers. In 1994 a layer of Surrounding Muon Chambers ( SMC ) based on limited streamer tubes was installed outside the endcaps to fill the gap between the barrel and forward regions.
The High-density Projection Chamber ( HPC ) - shown as the big green cylinder - is the barrel eletromagnetic calorimeter and is installed as a cylindical layer outside the Outer Detector. It is mounted on the inside the solenoid. The HPC is a cylinder of 2x254 cm situated between the radii 208 cm and 260 cm and consists mainly of lead. The polar angle coverage is from 43 to 137 degrees.
The Forward ElectroMagnetic Calorimeter ( FEMC ) - shown as the green disk component in the forward part - is the forward electromagnetic calorimeter and consists of two 5 m diameter disks (made of lead-glass). The front faces are placed at | z | = 284 cm, covering the polar angels from 8 to 35 degrees and from 145 to 172 degrees.
The hadron calorimeter
HCAL ) - shown as the red component of the DELPHI
detector - is a sampling gas detector incorporated in the magnet yoke (it
consists mainly of iron), the barrel part covering polar angles from 42.6 to
137.4 degrees, and two end-caps from 11.2 to 48.5 degrees and from 131.5 to 168.8
The hadron calorimeter provides calorimetric energy measurements of charged and neutral hadrons (strongly interacting particles). In addition is implemented a system to read out the HAC tubes as well as the pads, in order to give a more detailed picture of the hadronic showers and thus better distinction between showers caused by neutral and charged hadrons and better muon identification.
The Barrel RICH Detector ( Barrel-RICH ) - shown in yellow - is located between the Time Projection Chamber and the Outer Detector. It is a 350 cm long cylinder with inner radius 123 cm and outer 197 cm, divided into two halves by a central support wall, 6.4 cm thick. It covers polar angles between 40 and 140 degrees.
The Forward RICH Detector ( Forward-RICH ) - shown as the yellow disk component in the forward part - is located between 1.7 m < | z | < 2.7 m and covers polar angles between 15 and 35 degrees.
The Small angle TIle Calorimeter ( STIC ) is a sampling lead-scintillator calorimeter formed by two cylindrical detectors placed on either side of the DELPHI interaction region at a distance of 220 cm, and covers a wider angular region between 29 and 185 mrad in polar angle (from 6.5 to 42 cm in radius).
The Very Small Angle Tagger ( VSAT ) consists of 4 calorimeter modules. Each such module is composed of 12 silicon diodes. It detects electrons and positrons coming from Bhabha scattering between 5 and 7 mrad.
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