508
J. Apostolakis
11.5 Case Studies
The discovery of the top quark [106, 107] involved detector simulation only in a
minimal and indirect way. Detector simulation was undertaken by CDF and D0 in
the optimization phase of the design of their detectors. In D0 it informed the design
of the interface between the central and end calorimeters [108]. Subsequently, simplifications were made for the detector simulation used in production, to reduce the
computing time per event. The individual calorimeter plates were replaced by a large
block, which contained a mixture of the absorber and active material. Optionally
the response of particles below 200 MeV was parameterized. Comparisons with
test beam determined that the full detailed plate setup agreed well; the simplified
mixture setup was found to agree less well with test beam measurements, but judged
adequate for most purposes.
Events simulated using the D0 simulation program were used in the later
observation of the production of single top quarks [109]. However, the detector
simulation was found to have significant limitations; these appear to have stemmed
both from the simplifications of the modeling of the detector and its response
and from the intrinsic limitations of the simulation tool. Several corrections were
required, including a factor for the efficiencies of the trigger reconstruction, and for
the efficiency to identify and select particles and jets.
In the LHC experiments, simulation was first utilized to model the response of
the calorimeters to muon, electron and hadron beams. One key application has been
the detailed calibration of the energy response of the electromagnetic calorimeter, to
obtain an estimate of the energy of the incoming particle as a function of the inferred
visible energy measured as signal in the different calorimeter compartments.
The ATLAS calorimeter system is complex, utilizing different detector materials,
geometrical structure and technologies for the different rapidity regions. The
insensitive material between parts of a detector distorts the energy signal due to
tracks crossing this region. Simulation is used to obtain correction factors for the
energy of the incident particle or jet.
ATLAS has undertaken an extensive comparison of test beam results with Monte
Carlo simulation. Simulation utilising GEANT 3.21 in the 1990s was used for
detector design studies and the first test beam comparisons. Progressively from
2000 onwards, test beam results were compared mostly with GEANT4, and in 2004
a Geant4-based simulation was declared the official ATLAS ‘production’ detector
simulation in 2004.
Comparisons were undertaken first with the test beam results for individual
detectors. A typical comparison started with muons, as minimum ionizing particles,
to make a first verification of the material description and geometry of active
parts. Next, measurements of electrons were compared, verifying the detector
description of passive parts. This determines the factor for conversion of the
deposited energy into the signal measured by each detector, its electromagnetic
scale, by comparison with a beam of a particular energy, typically 100 GeV. Key
J. Apostolakis
11.5 Case Studies
The discovery of the top quark [106, 107] involved detector simulation only in a
minimal and indirect way. Detector simulation was undertaken by CDF and D0 in
the optimization phase of the design of their detectors. In D0 it informed the design
of the interface between the central and end calorimeters [108]. Subsequently, simplifications were made for the detector simulation used in production, to reduce the
computing time per event. The individual calorimeter plates were replaced by a large
block, which contained a mixture of the absorber and active material. Optionally
the response of particles below 200 MeV was parameterized. Comparisons with
test beam determined that the full detailed plate setup agreed well; the simplified
mixture setup was found to agree less well with test beam measurements, but judged
adequate for most purposes.
Events simulated using the D0 simulation program were used in the later
observation of the production of single top quarks [109]. However, the detector
simulation was found to have significant limitations; these appear to have stemmed
both from the simplifications of the modeling of the detector and its response
and from the intrinsic limitations of the simulation tool. Several corrections were
required, including a factor for the efficiencies of the trigger reconstruction, and for
the efficiency to identify and select particles and jets.
In the LHC experiments, simulation was first utilized to model the response of
the calorimeters to muon, electron and hadron beams. One key application has been
the detailed calibration of the energy response of the electromagnetic calorimeter, to
obtain an estimate of the energy of the incoming particle as a function of the inferred
visible energy measured as signal in the different calorimeter compartments.
The ATLAS calorimeter system is complex, utilizing different detector materials,
geometrical structure and technologies for the different rapidity regions. The
insensitive material between parts of a detector distorts the energy signal due to
tracks crossing this region. Simulation is used to obtain correction factors for the
energy of the incident particle or jet.
ATLAS has undertaken an extensive comparison of test beam results with Monte
Carlo simulation. Simulation utilising GEANT 3.21 in the 1990s was used for
detector design studies and the first test beam comparisons. Progressively from
2000 onwards, test beam results were compared mostly with GEANT4, and in 2004
a Geant4-based simulation was declared the official ATLAS ‘production’ detector
simulation in 2004.
Comparisons were undertaken first with the test beam results for individual
detectors. A typical comparison started with muons, as minimum ionizing particles,
to make a first verification of the material description and geometry of active
parts. Next, measurements of electrons were compared, verifying the detector
description of passive parts. This determines the factor for conversion of the
deposited energy into the signal measured by each detector, its electromagnetic
scale, by comparison with a beam of a particular energy, typically 100 GeV. Key