726
D. Froidevaux
The integration of a hermetic and high-precision calorimeter system into the
overall design of the ATLAS detector and its magnet systems has been a task of
high complexity where compromises have had to be made, as will be shown in the
first part of this section, which describes the basic requirements and features of the
calorimeters. As illustrated in the second part, which highlights some aspects of the
construction of the most critical element, namely the electromagnetic calorimeter,
and of its measured performance in test beam, the impact of the main design
choices and of the technology implementations on the performance has been very
significant. A few examples of the overall performance expected in the actual
configuration of the experiment are presented in Sect. 16.8.2, where it is also
compared to the expected performance of the CMS calorimeter system.
16.4.1 General Considerations
16.4.1.1 Performance Requirements
The main performance requirements from the physics on the calorimeter system can
be briefly summarised as follows:
• excellent energy and position resolution together with powerful particle identification for electrons and photons within the relevant geometrical acceptance (full
azimuthal coverage over |η| < 2.5) and over the relevant energy range (from a
few GeV to several TeV). The electron and photon identification requirements are
particularly demanding at the LHC, as already explained in Sect. 16.2.1. These
considerations induce requirements of high granularity and low noise on the
calorimeters. One has to add to this the operational requirements of speed of
response and resistance to radiation (the electromagnetic calorimeters will have
to withstand neutron fluences of up to 10 15 n/cm 2 and ionising radiation doses
of up to 200 kGy over 10 years of LHC operation at design luminosity).
• excellent jet energy resolution within the relevant geometrical acceptance, which
is similar to that foreseen for the electron and photon measurements (see above).
The quality of the jet energy resolution would play an important role in the case
of discovery of supersymmetric particles with cascade decays into many hadronic
jets [24].
• good jet energy measurements over the coverage required to contain the full
transverse energy produced in hard-scattering collisions at the LHC. A calorimetry coverage over |η| < 5 is necessary to unambiguously ascribe the observation
of significant missing transverse energy to non-interacting particles, such as
neutrinos from W-boson decay or light neutralinos from supersymmetric particle cascade decays. With adequate calorimetry coverage providing precise
measurements of the missing transverse energy, the experiments will be able
to reconstruct invariant masses of pairs of hadronically decaying τ -leptons
produced for example in the decays of supersymmetric Higgs bosons. They
D. Froidevaux
The integration of a hermetic and high-precision calorimeter system into the
overall design of the ATLAS detector and its magnet systems has been a task of
high complexity where compromises have had to be made, as will be shown in the
first part of this section, which describes the basic requirements and features of the
calorimeters. As illustrated in the second part, which highlights some aspects of the
construction of the most critical element, namely the electromagnetic calorimeter,
and of its measured performance in test beam, the impact of the main design
choices and of the technology implementations on the performance has been very
significant. A few examples of the overall performance expected in the actual
configuration of the experiment are presented in Sect. 16.8.2, where it is also
compared to the expected performance of the CMS calorimeter system.
16.4.1 General Considerations
16.4.1.1 Performance Requirements
The main performance requirements from the physics on the calorimeter system can
be briefly summarised as follows:
• excellent energy and position resolution together with powerful particle identification for electrons and photons within the relevant geometrical acceptance (full
azimuthal coverage over |η| < 2.5) and over the relevant energy range (from a
few GeV to several TeV). The electron and photon identification requirements are
particularly demanding at the LHC, as already explained in Sect. 16.2.1. These
considerations induce requirements of high granularity and low noise on the
calorimeters. One has to add to this the operational requirements of speed of
response and resistance to radiation (the electromagnetic calorimeters will have
to withstand neutron fluences of up to 10 15 n/cm 2 and ionising radiation doses
of up to 200 kGy over 10 years of LHC operation at design luminosity).
• excellent jet energy resolution within the relevant geometrical acceptance, which
is similar to that foreseen for the electron and photon measurements (see above).
The quality of the jet energy resolution would play an important role in the case
of discovery of supersymmetric particles with cascade decays into many hadronic
jets [24].
• good jet energy measurements over the coverage required to contain the full
transverse energy produced in hard-scattering collisions at the LHC. A calorimetry coverage over |η| < 5 is necessary to unambiguously ascribe the observation
of significant missing transverse energy to non-interacting particles, such as
neutrinos from W-boson decay or light neutralinos from supersymmetric particle cascade decays. With adequate calorimetry coverage providing precise
measurements of the missing transverse energy, the experiments will be able
to reconstruct invariant masses of pairs of hadronically decaying τ -leptons
produced for example in the decays of supersymmetric Higgs bosons. They