6 Calorimetry
243
introduced in the liquid volume. At present, one of the largest size detectors using
light from noble liquids is the xenon calorimeter of the MEG experiment [73] (see
also Sect. 6.7.1). As already mentioned in 6.2.3, the search for dark matter has
triggered the development of several large size experiments using liquid xenon.
These experiments [74] exploit both the scintillation and the ionization signal of the
sought for nuclear recoils. Ionization electrons are preferentially transported to the
surface of the liquid bath where, in a high electrical field region, they are extracted
with high efficiency [74] and accelerated in the gas phase, giving in turn rise to
(delayed) light emission. One example is described in Sect. 6.7.2.
Future long baseline neutrino experiments of very large size, like the DUNE
[75] project at Fermilab envision liquid argon detectors of several tens of kilotons.
DUNE will exploit both the scintillation and the ionization signals. In one of the
read-out options, called “single-phase”, the ionization signal is directly collected by
a set of wires, each equipped with a readout chain, in order to have access to details
of all secondary produced particles. The other option, “dual-phase”, is close to what
is described above for dark matter searches.
Liquid scintillators have been used abundantly in neutrino experiments, either in
totally active large volume detectors, like Kamland and SNO, or as a large array of
tubes filled with doped mineral oil.
The most recent example of the latter is NOvA [76] in which each tube is read
out by means of a wavelength shifting fiber connected to a single pixel of an APD.
The chapter on neutrino detectors provides further details.
Plastic scintillator plates, such as Polymethylmetacrylate (PMMA) doped with
organic scintillator, have been used for electromagnetic and even more extensively
for hadronic sampling calorimetry. The principal difficulty using this technology
is the light extraction. The dimension of scintillator tiles of typically 10 cm ×
10 cm size and 0.5 cm thickness would require light guides of typically 10 cm ×
0.5 cm section in order to extract the light while preserving the emission phase space
(respecting Liouville’s theorem), a very difficult task in realistic detector layouts.
An elegant solution is the use of wavelength shifters [77, 78] in which due to their
isotropic emission a constant fraction of the light is transported from the scintillating
tile to a small rod, or even a plastic fibre separated from the tile by an air gap. The
principle is shown in Fig. 6.33. Many calorimeter facilities at colliders were built
following this principle, see also Sect. 6.7.
In a further development, detectors capable of accommodating smaller transverse
granularities (like 5 cm × 5 cm) were proposed, like the “Shashlik” concept in which
readout fibres cross the scintillating tile and the passive converter perpendicularly to
their faces [79]. Originally considered in CMS, this scheme was later chosen by the
LHCb experiment at the LHC for its electromagnetic calorimeter. A sketch of the
arrangement of absorbers, scintillating tiles and fibers is shown in Fig. 6.34.
Even more ambitious was the “Spaghetti” calorimeter [80, 81] in which each
calorimeter cell (typically 1 × 1 ρ M transverse size and 25 X 0 deep) is built out of
scintillating fibres embedded in a lead matrix, oriented parallel to the long side of the
block. The electromagnetic calorimeter of the KLOE [82] experiment at the DAFNE
243
introduced in the liquid volume. At present, one of the largest size detectors using
light from noble liquids is the xenon calorimeter of the MEG experiment [73] (see
also Sect. 6.7.1). As already mentioned in 6.2.3, the search for dark matter has
triggered the development of several large size experiments using liquid xenon.
These experiments [74] exploit both the scintillation and the ionization signal of the
sought for nuclear recoils. Ionization electrons are preferentially transported to the
surface of the liquid bath where, in a high electrical field region, they are extracted
with high efficiency [74] and accelerated in the gas phase, giving in turn rise to
(delayed) light emission. One example is described in Sect. 6.7.2.
Future long baseline neutrino experiments of very large size, like the DUNE
[75] project at Fermilab envision liquid argon detectors of several tens of kilotons.
DUNE will exploit both the scintillation and the ionization signals. In one of the
read-out options, called “single-phase”, the ionization signal is directly collected by
a set of wires, each equipped with a readout chain, in order to have access to details
of all secondary produced particles. The other option, “dual-phase”, is close to what
is described above for dark matter searches.
Liquid scintillators have been used abundantly in neutrino experiments, either in
totally active large volume detectors, like Kamland and SNO, or as a large array of
tubes filled with doped mineral oil.
The most recent example of the latter is NOvA [76] in which each tube is read
out by means of a wavelength shifting fiber connected to a single pixel of an APD.
The chapter on neutrino detectors provides further details.
Plastic scintillator plates, such as Polymethylmetacrylate (PMMA) doped with
organic scintillator, have been used for electromagnetic and even more extensively
for hadronic sampling calorimetry. The principal difficulty using this technology
is the light extraction. The dimension of scintillator tiles of typically 10 cm ×
10 cm size and 0.5 cm thickness would require light guides of typically 10 cm ×
0.5 cm section in order to extract the light while preserving the emission phase space
(respecting Liouville’s theorem), a very difficult task in realistic detector layouts.
An elegant solution is the use of wavelength shifters [77, 78] in which due to their
isotropic emission a constant fraction of the light is transported from the scintillating
tile to a small rod, or even a plastic fibre separated from the tile by an air gap. The
principle is shown in Fig. 6.33. Many calorimeter facilities at colliders were built
following this principle, see also Sect. 6.7.
In a further development, detectors capable of accommodating smaller transverse
granularities (like 5 cm × 5 cm) were proposed, like the “Shashlik” concept in which
readout fibres cross the scintillating tile and the passive converter perpendicularly to
their faces [79]. Originally considered in CMS, this scheme was later chosen by the
LHCb experiment at the LHC for its electromagnetic calorimeter. A sketch of the
arrangement of absorbers, scintillating tiles and fibers is shown in Fig. 6.34.
Even more ambitious was the “Spaghetti” calorimeter [80, 81] in which each
calorimeter cell (typically 1 × 1 ρ M transverse size and 25 X 0 deep) is built out of
scintillating fibres embedded in a lead matrix, oriented parallel to the long side of the
block. The electromagnetic calorimeter of the KLOE [82] experiment at the DAFNE