6 Calorimetry
271
hadrons) ≈ 0.20/
√
E(GeV). This sampling frequency is rather coarse for electrons
resulting in an electron energy resolution σ/E (electrons) = 0.18/
√
E(GeV).
H1 and Zeus provided a detailed measurement of electron-nucleon scattering
from which a new generation of parton distribution functions (PDFs) was derived.
These functions have been used, and are still being used extensively for LHC physics
analysis.
6.7.6 Facilities at the LHC and a Future Collider
The research programmes at the LHC and at a possible future Colliders impose a
new level of performance requirements.
6.7.6.1 Facilities at LHC
The two general-purpose p-p experiments, ATLAS and CMS, have developed rather
different approaches for the same physics research, promoted by different groups
of physicists with their personal experience, background and taste, constrained by
realities of funding. In both cases the extraordinary requirements on electromagnetic calorimetry imposed ‘hybrid’ solutions to allow independent optimization
of electromagnetic and hadronic calorimetry. This ‘independence’ led ATLAS to
choose two novel, unconventional detector geometries. The ‘Accordion’ calorimeter
(see Sect. 6.7.4) is followed by a hadronic instrument with scintillator tile/WLS
fibre readout. One of the 64 slices forming a complete and crack-less cylinder is
shown in Fig. 6.49. The unconventional geometry of absorber plates and scintillating
tiles oriented along the direction of the incident particle permits an economic
construction and homogeneous sensitivity [141]. This geometry works because
the preceding ~1.5 λ Accordion calorimeter provides enough hadronic shower
development to permit good sampling in the Tile-geometry. This arrangement
also greatly facilitates longitudinal and transverse segmentation hence permitting
effective longitudinal weighting of the shower energies. Weighting leads to a
resolution of the combined calorimetry system (accordion and Tile calorimeter)
of σ /E ≈ (0.52/
√
E ⊕ 1.6/E) ⊕ 0.03 and a good linearity of response [120]. A
jet energy resolution of σ (jet)/E ≈ 0.6/
√
E(GeV) is estimated, adequate for LHC.
The ATLAS Tile and Extended Tile calorimeter covers |η| < 1.4. For the forward
(‘endcap’) regions (1.4 < η < 3.2) ATLAS had to adopt different solutions to cope
with the even more ferocious radiation levels. An Accordion-type electromagnetic
calorimeter precedes a Cu/Liquid Argon hadron calorimeter. In the very forward
region (3 < η < 5) yet another novel geometry had to be invented: cylindrical
readout elements with narrow LAr-gaps (0.25 to 0.35 mm) as sensitive medium
are embedded in a tungsten absorber, sampling geometrically very tight showers at
adequate readout speeds [120]. Figure 6.50 shows a cut-view through the ATLAS
calorimeter facility.
271
hadrons) ≈ 0.20/
√
E(GeV). This sampling frequency is rather coarse for electrons
resulting in an electron energy resolution σ/E (electrons) = 0.18/
√
E(GeV).
H1 and Zeus provided a detailed measurement of electron-nucleon scattering
from which a new generation of parton distribution functions (PDFs) was derived.
These functions have been used, and are still being used extensively for LHC physics
analysis.
6.7.6 Facilities at the LHC and a Future Collider
The research programmes at the LHC and at a possible future Colliders impose a
new level of performance requirements.
6.7.6.1 Facilities at LHC
The two general-purpose p-p experiments, ATLAS and CMS, have developed rather
different approaches for the same physics research, promoted by different groups
of physicists with their personal experience, background and taste, constrained by
realities of funding. In both cases the extraordinary requirements on electromagnetic calorimetry imposed ‘hybrid’ solutions to allow independent optimization
of electromagnetic and hadronic calorimetry. This ‘independence’ led ATLAS to
choose two novel, unconventional detector geometries. The ‘Accordion’ calorimeter
(see Sect. 6.7.4) is followed by a hadronic instrument with scintillator tile/WLS
fibre readout. One of the 64 slices forming a complete and crack-less cylinder is
shown in Fig. 6.49. The unconventional geometry of absorber plates and scintillating
tiles oriented along the direction of the incident particle permits an economic
construction and homogeneous sensitivity [141]. This geometry works because
the preceding ~1.5 λ Accordion calorimeter provides enough hadronic shower
development to permit good sampling in the Tile-geometry. This arrangement
also greatly facilitates longitudinal and transverse segmentation hence permitting
effective longitudinal weighting of the shower energies. Weighting leads to a
resolution of the combined calorimetry system (accordion and Tile calorimeter)
of σ /E ≈ (0.52/
√
E ⊕ 1.6/E) ⊕ 0.03 and a good linearity of response [120]. A
jet energy resolution of σ (jet)/E ≈ 0.6/
√
E(GeV) is estimated, adequate for LHC.
The ATLAS Tile and Extended Tile calorimeter covers |η| < 1.4. For the forward
(‘endcap’) regions (1.4 < η < 3.2) ATLAS had to adopt different solutions to cope
with the even more ferocious radiation levels. An Accordion-type electromagnetic
calorimeter precedes a Cu/Liquid Argon hadron calorimeter. In the very forward
region (3 < η < 5) yet another novel geometry had to be invented: cylindrical
readout elements with narrow LAr-gaps (0.25 to 0.35 mm) as sensitive medium
are embedded in a tungsten absorber, sampling geometrically very tight showers at
adequate readout speeds [120]. Figure 6.50 shows a cut-view through the ATLAS
calorimeter facility.