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P. Jenni and T. S. Virdee
The solution to charged particle tracking was to opt for a small number of precise
position measurements of each charged track (~13 each with a position resolution
of ~15 μm per measurement) leading to a large number of cells distributed inside a
cylindrical volume 5.8 m long and 2.5 m in diameter: 66 million 100 × 150 μm 2
silicon pixels and 9.3 million silicon microstrips ranging from ~10 cm × 80 μm to
~20 cm × 180 μm. The 198 m 2 area of active silicon of the CMS tracker is by far
the largest silicon tracker ever built.
Finally the hadron calorimeter, comprising ~3000 projective towers covering
almost the full solid angle, is built from alternate plates of ~5 cm brass absorber
and ~4 mm thick scintillator plates that sample the energy. The scintillation light
is detected by photodetectors (hybrid photodiodes) that can operate in the strong
magnetic field.
6.4.4 Installation and Commissioning
The two very different and complementary detector concepts, ATLAS and CMS,
resulted in two different strategies for the underground installation of these experiments.
Given its size and its magnet structure, the ATLAS detector had to be assembled
directly in the underground cavern. The installation process began in summer 2003
(after the completion of civil engineering work that started in 1998) and ended in
summer 2008. Figure 6.4 (top) shows the completion of the barrel toroid magnet
system with the insertion of the barrel calorimeters. Figure 6.4 (bottom) shows one
end of the cylindrical barrel detector after 3.5 years of installation work, 1.5 years
before completion. The ends of four of the barrel toroid coils are visible, illustrating
the eightfold symmetry of the structure.
The iron yoke of the CMS detector is divided into five barrel-wheels and three
endcap disks at each end, giving a total weight of 12,500 tons. This structure
enabled the detector to be assembled and tested in a large surface hall while the
underground cavern was being prepared. The sections, weighing between 350 tons
and 2000 tons, were then lowered sequentially between October 2006 and January
2008, using a dedicated gantry system equipped with strand jacks: a pioneering
use of this technology to simplify the underground assembly of large experiments.
Figure 6.5 top shows the lowering of the heaviest and central section, supporting the
superconducting coil. Figure 6.5 bottom shows the transverse section of the barrel
part of CMS illustrating the successive layers of detection starting from the centre
where the collisions occur: the inner tracker, the crystal calorimeter, the hadron
calorimeter, the superconducting coil, and the iron yoke instrumented with the four
muon stations. The last muon station is at a radius of 7.4 m.
Individual detector components (e.g. chambers) of both experiments were
built and assembled in a distributed way all around the globe in the numerous
participating institutes and were typically first tested at their production sites, then
after delivery to CERN, and finally again after their installation in the underground
P. Jenni and T. S. Virdee
The solution to charged particle tracking was to opt for a small number of precise
position measurements of each charged track (~13 each with a position resolution
of ~15 μm per measurement) leading to a large number of cells distributed inside a
cylindrical volume 5.8 m long and 2.5 m in diameter: 66 million 100 × 150 μm 2
silicon pixels and 9.3 million silicon microstrips ranging from ~10 cm × 80 μm to
~20 cm × 180 μm. The 198 m 2 area of active silicon of the CMS tracker is by far
the largest silicon tracker ever built.
Finally the hadron calorimeter, comprising ~3000 projective towers covering
almost the full solid angle, is built from alternate plates of ~5 cm brass absorber
and ~4 mm thick scintillator plates that sample the energy. The scintillation light
is detected by photodetectors (hybrid photodiodes) that can operate in the strong
magnetic field.
6.4.4 Installation and Commissioning
The two very different and complementary detector concepts, ATLAS and CMS,
resulted in two different strategies for the underground installation of these experiments.
Given its size and its magnet structure, the ATLAS detector had to be assembled
directly in the underground cavern. The installation process began in summer 2003
(after the completion of civil engineering work that started in 1998) and ended in
summer 2008. Figure 6.4 (top) shows the completion of the barrel toroid magnet
system with the insertion of the barrel calorimeters. Figure 6.4 (bottom) shows one
end of the cylindrical barrel detector after 3.5 years of installation work, 1.5 years
before completion. The ends of four of the barrel toroid coils are visible, illustrating
the eightfold symmetry of the structure.
The iron yoke of the CMS detector is divided into five barrel-wheels and three
endcap disks at each end, giving a total weight of 12,500 tons. This structure
enabled the detector to be assembled and tested in a large surface hall while the
underground cavern was being prepared. The sections, weighing between 350 tons
and 2000 tons, were then lowered sequentially between October 2006 and January
2008, using a dedicated gantry system equipped with strand jacks: a pioneering
use of this technology to simplify the underground assembly of large experiments.
Figure 6.5 top shows the lowering of the heaviest and central section, supporting the
superconducting coil. Figure 6.5 bottom shows the transverse section of the barrel
part of CMS illustrating the successive layers of detection starting from the centre
where the collisions occur: the inner tracker, the crystal calorimeter, the hadron
calorimeter, the superconducting coil, and the iron yoke instrumented with the four
muon stations. The last muon station is at a radius of 7.4 m.
Individual detector components (e.g. chambers) of both experiments were
built and assembled in a distributed way all around the globe in the numerous
participating institutes and were typically first tested at their production sites, then
after delivery to CERN, and finally again after their installation in the underground