The CMS Detector
Answering the above key questions is the objective behind the
creation of the Compact Muon Solenoid (CMS) at the LHC
[1]. Construction
of this multipurpose detector is a joint effort of scientists from 32
countries forming an international CMS collaboration.
The physics objectives require precise measurements of the parameters
of detected particles with high energy and momentum resolution in over
a broad range of energies. The CMS detector (Fig. 1) is based on the
superconducting solenoid magnet, whose internal diameter and field are
about 6 m and 4 Tesla, respectively. A return yoke surrounds the magnet.
The mass of the yoke is 12000 ton. Inside the solenoid, a tracker, a
forward muon station, and calorimeters are located. The magnet yoke
serves as an absorber and as a support for the rest of the chambers of
the muon system. Such a configuration is compact, and provides for an
efficient identification, detection, and parameter measurements of muons
with pseudorapidities ranging up to 2.4. The set-up is structured into
the barrel and endcap modules including the forward calorimeters (HF).
Starting from the interaction point, the following modules are located
in successive layers: the inner tracking system, the preshower detectors,
the electromagnetic calorimeters (ECAL), the hadron calorimeters (HCAL),
and, lastly, the detectors of the muon system.
In the barrel, the muons are detected by four stations, each of which
consists of multilayer drift chambers. The endcap muon stations consist
of cathode strip chambers that are capable to operate in the presence
of high particle rate. Each station includes the trigger planes of the
resistive chambers. The inner tracker serves to detect and match all the
reconstructed tracks of muons and electrons, and to recognise all tracks
with transverse momentum exceeds 2 GeV. The silicon microstrip and pixel
detectors are to guarantee the required resolution at the highest luminosity
of LHC. The electromagnetic calorimeter (ECAL) based on the lead tungstate
crystals serves for identification and precise energy measurement of photons
and electrons. Preshower detector based on the strip silicon detectors is
to separate the photons and to reject the background originating from
neutral pion decays, and to measure the photon direction. It achieves
the above results without deterioration of the resolution of the di-photon
masses. The hadron calorimeters (HCAL) identify and measure the energy and
direction of the particle jets. They are to achieve hermetic measurement
of the energy flow needed to determine the missing transverse energy.
Complying with the physics at CMS requires the uses of modern high
precision technologies in the construction of the above detectors.
Fig. 1:
Overall view of the Compact Muon Solenoid (CMS).
Weight 14500 ton, outer diameter 14.60 m,
length 21.60 m, solenoid magnetic field 4 T.
The insertion shows the system which Russia and
Dubna member states (RDMS) CMS collaboration is responsible for.
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