ILD Detector Systems
2D view (left) and 3D view (right) of ILD
The ILD detector systems have many layers surrounding the point where the beams collide. The description of each system is described below, ordered by the distance from the beam collision point (closest first).
Vertex Detector (VTX)
The two possible options for the Vertex Detector: five single layers (left) versus three double layers (right).
Just outside the beam pipe, the Vertex Detector sits at a radius of a few centimeters. It will consist of multiple layers of state-of-art silicon pixel sensors, which enables the measurement of the position of charged particles with excellent accuracy. Much R&D has gone into reducing the thickness of each layer, which reduces the distortion of the path of the incoming particles.
Time Projection Chamber (TPC)
Outside the vertex detector lies the Time Projection Chamber, which also measures the position of charged particles. The TPC consists of two chambers filled with gas, with a high voltage applied across the length of the TPC. The passage of charged particles results in ionized gas molecules which drift toward the end plate caps, where they are captured and detected. The drift time is used to calculate the position of the ionization.
Although the TPC is less accurate than the VTX, it has the advantage of being able to track the continuous volume inside the detector, whereas the VTX is only sensitive where the silicon wafers are located. The TPC can also cover a large volume of space relatively easily.
Electromagnetic Calorimeter (ECAL)
ECAL barrel and end caps (left) and one module from the barrel (right)
The Electromagnetic Calorimeter consists of interleaved layers of absorbing material (tungsten) and position sensors. The ECAL measures photons and charged particles, both of which will leave a shower of secondary particles as they interact with tungsten. The position sensors detect these secondary particles. The original particle type can be identified by an analysis of the shapes of the shower.
There are two candidates for the position sensors. One option is to use silicon pixel or pad sensors. The other is to use scintillator plastic strips. R&D efforts are ongoing to determine the performance and the cost of each option.
Hadronic Calorimeter (HCAL)
The HCAL barrel and end caps (left) and one module from the barrel (right).
The Hadronic Calorimeter measures the energy deposited by charged and neutral hadrons. The HCAL consists of steel absorber material, which slows down the hadrons, and an active medium, which measures the resulting showers. There are two options being considered for the active material: scintillator tiles and gaseous devices.
The charged hadrons can be measured very precisely by the tracking detectors (VTX and TPC), which makes the HCAL the most important detector for measuring neutral hadrons.
Special calorimeters are to be placed in the forward region (close to the beam pipe). The LumiCal will be used for precise measurement of the luminosity, while the BeamCal will be used for a fast estimate of the luminosity. The LHCal will extend the angular coverage of the HCAL endcap. The GamCal is placed about 100 m in the downstream of the detector (not shown in the picture) will be used to tune the beams.
Coil and Return Yoke
The coil which lies outside the HCAL provides the magnetic field necessary to bend the charged particles inside the detector. The coil is a superconducting solenoid designed to produce a magnetic field of 3.5-4.0 Tesla. Outside the coil lies the iron yoke design to close the magnetic field lines close to the detector. The return yoke also doubles as a muon detector, as described next.
Because muons are relatively unaffected by the calorimeter systems, the outermost region of the detector makes it an ideal place to place the muon detector. The muon detector consists of a thick layer of instrumented iron (the return yoke). The showers resulting from the passing of muons are detected by gas detectors or scintillator strips (to be decided).