16 Integration of Detectors into a Large Experiment: Examples from ATLAS. . .
705
• the position of the ATLAS solenoid just in front of the barrel electromagnetic
calorimeter limits to some extent the energy resolution in the region 1.2 < |η| <
1.5;
• the position of the CMS solenoid outside the calorimeter limits the number of
interaction lengths available to absorb hadronic showers in the region |η| < 1;
• the muon spectrometer system in ATLAS provides an independent and highaccuracy measurement of muons over the full η-coverage required by the physics.
This requires however an alignment system with specifications an order of
magnitude more stringent (few tens of μm) than those of the CMS muon
spectrometer. In addition, the magnetic field in the ATLAS muon spectrometer
must be known to an accuracy of a few tens of Gauss over a volume of close to
20,000 m 3 . The software implications of these requirements are non-trivial (size
of map in memory, access time);
• the muon spectrometer system in CMS has limited stand-alone measurement
capabilities and this affects the triggering capabilities for the luminosities
envisaged for the LHC upgrade.
In terms of construction, the magnet systems have each turned out to be a major
project in its own right with very direct and strong involvement from the Technical
Coordination team [15] and from major national laboratories and funding agencies.
A detailed account of the construction of these magnets is beyond the scope of this
review and this section can be concluded by simply stating that during the course
of the past few years, all these magnets have undergone very successfully extensive
commissioning steps, sustained operation at full current, in particular for cosmicray data-taking in 2008/2009, and stable operation with beam in the LHC machine
at the end of 2009.
16.2.2.1 Radiation Levels
At the LHC, the primary source of radiation at full luminosity comes from collisions
at the interaction point. In the tracker, charged hadron secondaries from inelastic
proton-proton interactions dominate the radiation backgrounds at small radii while
further out other sources, such as neutrons, become more important. Table 16.4
shows projected radiation levels in key areas of the detector.
In ATLAS, most of the energy from primaries is dumped into two regions: the
TAS (Target Absorber Secondaries) collimators protecting LHC quadrupoles and
the forward calorimeters. The beam vacuum system spans the length of the detector
and in the forward region is a major source of radiation backgrounds. Primary
particles from the interaction point strike the beam-pipe at very shallow angles,
such that the projected material depth is large. Studies have shown that the beamline material contributes more than half of the radiation backgrounds in the muon
system. The deleterious effects of background radiation fall into a number of general
categories: increased background and occupancies, radiation damage and ageing of
705
• the position of the ATLAS solenoid just in front of the barrel electromagnetic
calorimeter limits to some extent the energy resolution in the region 1.2 < |η| <
1.5;
• the position of the CMS solenoid outside the calorimeter limits the number of
interaction lengths available to absorb hadronic showers in the region |η| < 1;
• the muon spectrometer system in ATLAS provides an independent and highaccuracy measurement of muons over the full η-coverage required by the physics.
This requires however an alignment system with specifications an order of
magnitude more stringent (few tens of μm) than those of the CMS muon
spectrometer. In addition, the magnetic field in the ATLAS muon spectrometer
must be known to an accuracy of a few tens of Gauss over a volume of close to
20,000 m 3 . The software implications of these requirements are non-trivial (size
of map in memory, access time);
• the muon spectrometer system in CMS has limited stand-alone measurement
capabilities and this affects the triggering capabilities for the luminosities
envisaged for the LHC upgrade.
In terms of construction, the magnet systems have each turned out to be a major
project in its own right with very direct and strong involvement from the Technical
Coordination team [15] and from major national laboratories and funding agencies.
A detailed account of the construction of these magnets is beyond the scope of this
review and this section can be concluded by simply stating that during the course
of the past few years, all these magnets have undergone very successfully extensive
commissioning steps, sustained operation at full current, in particular for cosmicray data-taking in 2008/2009, and stable operation with beam in the LHC machine
at the end of 2009.
16.2.2.1 Radiation Levels
At the LHC, the primary source of radiation at full luminosity comes from collisions
at the interaction point. In the tracker, charged hadron secondaries from inelastic
proton-proton interactions dominate the radiation backgrounds at small radii while
further out other sources, such as neutrons, become more important. Table 16.4
shows projected radiation levels in key areas of the detector.
In ATLAS, most of the energy from primaries is dumped into two regions: the
TAS (Target Absorber Secondaries) collimators protecting LHC quadrupoles and
the forward calorimeters. The beam vacuum system spans the length of the detector
and in the forward region is a major source of radiation backgrounds. Primary
particles from the interaction point strike the beam-pipe at very shallow angles,
such that the projected material depth is large. Studies have shown that the beamline material contributes more than half of the radiation backgrounds in the muon
system. The deleterious effects of background radiation fall into a number of general
categories: increased background and occupancies, radiation damage and ageing of