8 Neutrino Detectors
359
of the scintillation light emitted in the argon by the products of the interaction and
recorded by photomultipliers. A track deposits energy along its trajectory and this
is recorded as pulse heights in the wires. The pulse height distribution provides
particle identification through the ionization pattern whereas the pulse height sum
is a measure of the particle energy. The latter can also be obtained by range.
ICARUS [76], was the first to develop and use this technique. It was located
at the Gran Sasso LNGS laboratory and was exposed to neutrinos produced by
the CNGS beam 732 km away at CERN. It consists of two 300 ton modules each
3.6 × 3.6 × 19.9 m 3 . Each module includes a central high voltage plane and, along
each of its long sides, three sets of detection wire planes, with orientation at 0 ◦
and ±60 ◦ . Electrons drift over a maximum distance of 1.5 m in the electric field
perpendicular to the wire planes. This very complete detector relies on long drift
distances and therefore requires high purity liquid argon. The purity achieved [77]
during a technical run was such as to allow an electron drift lifetime of 1.8 ms
equivalent to an electron mean free path of 280 cm. The electron drift velocity at
89 ◦ K increased from 0.5 mm/μs at an electric field of 0.1 kV/cm to 2 mm/μs at
1.0 kV/cm.
In the US, the first liquid argon TPC used in a physics experiment was
ArgoNeuT [82], a 0.35 ton detector installed upstream of the MINOS near detector
in the NUMI beam line at Fermilab. It produced significant low energy neutrino
energy results as well as providing a test bed for subsequent larger liquid argon
detectors.
The liquid argon technique has since been adopted for SBN [83], the Short
Baseline Neutrino beam program at Fermilab, intended to investigate the possibility
of additional, sterile, neutrinos. It uses the Booster Neutrino beam and consists
of three liquid argon TPC detectors: SBND at 110 m from the neutrino source,
MicroBooNE at 470 m and ICARUS at 600 m. The first to be installed was MicroBooNE [84], approved to observe electrons and photons and determine the origin
of the low energy electromagnetic excess observed by MiniBooNE (Sect. 8.3.1).
It’s good spatial resolution would allow it to distinguish converting photon showers
which are not associated to the primary vertex and are twice minimum ionizing at
the conversion point from prompt electrons which are connected to the vertex and
are singly ionizing. This should result in a good electron/photon discrimination.
The TPC is inserted in a foam insulated cylindrical cryostat. It is 10.4 m long,
2.3 m high and 2.5 m wide. Electrons drift horizontally over a maximum of 2.5 m
(corresponding to a maximum drift time of 2.25 ms) in a 0.273 kV/cm electric field
and are recorded by two induction and one collection successive wire planes inclined
respectively at ±60 ◦ and 0 ◦ to the vertical. The experiment was the first liquid argon
TPC experiment to fill its cryostat without prior evacuation. It has achieved [85] an
electron drift-lifetime of 18 ms corresponding to an O 2 equivalent contamination of
17 ppt and a loss of signal of 12% over the 2.5 m drift length. It also placed preamplifiers and shapers in the cold to reduce connection lengths and hence electronic
noise. The amplified signals exit the cryostat and are digitized in warm ADCs before
entering the DAQ electronics for Huffman compression and storage. This is done
in two independent streams. The first stream records all the data occuring over
359
of the scintillation light emitted in the argon by the products of the interaction and
recorded by photomultipliers. A track deposits energy along its trajectory and this
is recorded as pulse heights in the wires. The pulse height distribution provides
particle identification through the ionization pattern whereas the pulse height sum
is a measure of the particle energy. The latter can also be obtained by range.
ICARUS [76], was the first to develop and use this technique. It was located
at the Gran Sasso LNGS laboratory and was exposed to neutrinos produced by
the CNGS beam 732 km away at CERN. It consists of two 300 ton modules each
3.6 × 3.6 × 19.9 m 3 . Each module includes a central high voltage plane and, along
each of its long sides, three sets of detection wire planes, with orientation at 0 ◦
and ±60 ◦ . Electrons drift over a maximum distance of 1.5 m in the electric field
perpendicular to the wire planes. This very complete detector relies on long drift
distances and therefore requires high purity liquid argon. The purity achieved [77]
during a technical run was such as to allow an electron drift lifetime of 1.8 ms
equivalent to an electron mean free path of 280 cm. The electron drift velocity at
89 ◦ K increased from 0.5 mm/μs at an electric field of 0.1 kV/cm to 2 mm/μs at
1.0 kV/cm.
In the US, the first liquid argon TPC used in a physics experiment was
ArgoNeuT [82], a 0.35 ton detector installed upstream of the MINOS near detector
in the NUMI beam line at Fermilab. It produced significant low energy neutrino
energy results as well as providing a test bed for subsequent larger liquid argon
detectors.
The liquid argon technique has since been adopted for SBN [83], the Short
Baseline Neutrino beam program at Fermilab, intended to investigate the possibility
of additional, sterile, neutrinos. It uses the Booster Neutrino beam and consists
of three liquid argon TPC detectors: SBND at 110 m from the neutrino source,
MicroBooNE at 470 m and ICARUS at 600 m. The first to be installed was MicroBooNE [84], approved to observe electrons and photons and determine the origin
of the low energy electromagnetic excess observed by MiniBooNE (Sect. 8.3.1).
It’s good spatial resolution would allow it to distinguish converting photon showers
which are not associated to the primary vertex and are twice minimum ionizing at
the conversion point from prompt electrons which are connected to the vertex and
are singly ionizing. This should result in a good electron/photon discrimination.
The TPC is inserted in a foam insulated cylindrical cryostat. It is 10.4 m long,
2.3 m high and 2.5 m wide. Electrons drift horizontally over a maximum of 2.5 m
(corresponding to a maximum drift time of 2.25 ms) in a 0.273 kV/cm electric field
and are recorded by two induction and one collection successive wire planes inclined
respectively at ±60 ◦ and 0 ◦ to the vertical. The experiment was the first liquid argon
TPC experiment to fill its cryostat without prior evacuation. It has achieved [85] an
electron drift-lifetime of 18 ms corresponding to an O 2 equivalent contamination of
17 ppt and a loss of signal of 12% over the 2.5 m drift length. It also placed preamplifiers and shapers in the cold to reduce connection lengths and hence electronic
noise. The amplified signals exit the cryostat and are digitized in warm ADCs before
entering the DAQ electronics for Huffman compression and storage. This is done
in two independent streams. The first stream records all the data occuring over