370
L. Camilleri
requirement as well as the requirement of good momentum resolution dictated the
use of a light detector. The detector consisted of 49 drift chamber modules each
one providing three coordinates with sense wires at 0 ◦ , +5 ◦ and −5 ◦ degrees to
the vertical. The chambers were built out of honeycomb panels made of aramid
fibres sandwiched between two kevlar skins. These panels provided the target
material, 2.7 tons, for neutrino interactions. The average density of the target was
0.1 g · cm −3 , close to that of a hydrogen bubble chamber and the drift chambers
provided measurements every 2% of a radiation length (X 0 ). The spatial resolution
was 150 μm providing a momentum resolution of σ p /p =
0.05 √
L
0.008p √
L 5 , with the
momentum p and the track length L expressed in GeV/c and meters respectively.
The chambers were complemented by 9 modules of transition radiation detectors
consisting of polypropylene foils and straw tubes containing an 80% xenon–20%
methane gas mixture. These modules together with a 1.6 X 0 lead and proportional
tube preshower and a 19 X 0 lead glass array provided the necessary e/π separation.
These detectors were housed in a 7.5 × 3.5 × 3.5 m 3 dipole magnet providing a
0.4 T horizontal magnetic field. The lead glass array, being inside the magnetic
field, was read by tetrodes with a gain of 40 and had an energy resolution E/E =
(3.02/
√
E(GeV )+1.04)%. An iron-scintillator hadron calorimeter was located just
outside the magnet coil and was followed by two muon detection stations consisting
of large area drift chambers located after 8 and 13 interaction lengths.
Silicon is another technique that provides very precise track localization and
hence, secondary vertex identification as has been proved repeatedly in hadronic
interactions. NOMAD-STAR [106] was a 45 kg prototype of a possible application
of this technology to neutrino interactions. It consisted of 4 plates of boron carbide
providing the interaction mass interleaved with five planes of silicon detectors. Each
plane consisted of ten 72 cm long ladders of 12 silicon-strip detectors with a pitch
of 50 μm. It was exposed to a neutrino beam within the NOMAD detector and,
in conjunction with the rest of the detector, it was able to reconstruct 45 charm
decays. The hit to noise ratio was 17:1 and the hit finding efficiency 98%. The
impact parameter resolution of the μ − produced in a ν μ CC interaction relative to a
hadronic jet consisting of at least three charged particles was 33 μm.
The magnet used by NOMAD is now being used in the T2K experiment as part of
the hybrid near detector [107] located 280 m from the target. The magnet houses:
• Scintillator planes interleaved with lead or brass optimized for photon detection
and π 0 reconstruction.
• Three time projection chambers (TPC) using Micromegas modules for the drift
electrons amplification and readout.
• These TPC’s are interleaved with fine-grained detectors consisting of strips of
scintillator providing target mass.
• A scintillator and radiator electromagnetic calorimeter.
• Scintillator planes housed in the slots located in the return yoke providing a muon
range detector
L. Camilleri
requirement as well as the requirement of good momentum resolution dictated the
use of a light detector. The detector consisted of 49 drift chamber modules each
one providing three coordinates with sense wires at 0 ◦ , +5 ◦ and −5 ◦ degrees to
the vertical. The chambers were built out of honeycomb panels made of aramid
fibres sandwiched between two kevlar skins. These panels provided the target
material, 2.7 tons, for neutrino interactions. The average density of the target was
0.1 g · cm −3 , close to that of a hydrogen bubble chamber and the drift chambers
provided measurements every 2% of a radiation length (X 0 ). The spatial resolution
was 150 μm providing a momentum resolution of σ p /p =
0.05 √
L
0.008p √
L 5 , with the
momentum p and the track length L expressed in GeV/c and meters respectively.
The chambers were complemented by 9 modules of transition radiation detectors
consisting of polypropylene foils and straw tubes containing an 80% xenon–20%
methane gas mixture. These modules together with a 1.6 X 0 lead and proportional
tube preshower and a 19 X 0 lead glass array provided the necessary e/π separation.
These detectors were housed in a 7.5 × 3.5 × 3.5 m 3 dipole magnet providing a
0.4 T horizontal magnetic field. The lead glass array, being inside the magnetic
field, was read by tetrodes with a gain of 40 and had an energy resolution E/E =
(3.02/
√
E(GeV )+1.04)%. An iron-scintillator hadron calorimeter was located just
outside the magnet coil and was followed by two muon detection stations consisting
of large area drift chambers located after 8 and 13 interaction lengths.
Silicon is another technique that provides very precise track localization and
hence, secondary vertex identification as has been proved repeatedly in hadronic
interactions. NOMAD-STAR [106] was a 45 kg prototype of a possible application
of this technology to neutrino interactions. It consisted of 4 plates of boron carbide
providing the interaction mass interleaved with five planes of silicon detectors. Each
plane consisted of ten 72 cm long ladders of 12 silicon-strip detectors with a pitch
of 50 μm. It was exposed to a neutrino beam within the NOMAD detector and,
in conjunction with the rest of the detector, it was able to reconstruct 45 charm
decays. The hit to noise ratio was 17:1 and the hit finding efficiency 98%. The
impact parameter resolution of the μ − produced in a ν μ CC interaction relative to a
hadronic jet consisting of at least three charged particles was 33 μm.
The magnet used by NOMAD is now being used in the T2K experiment as part of
the hybrid near detector [107] located 280 m from the target. The magnet houses:
• Scintillator planes interleaved with lead or brass optimized for photon detection
and π 0 reconstruction.
• Three time projection chambers (TPC) using Micromegas modules for the drift
electrons amplification and readout.
• These TPC’s are interleaved with fine-grained detectors consisting of strips of
scintillator providing target mass.
• A scintillator and radiator electromagnetic calorimeter.
• Scintillator planes housed in the slots located in the return yoke providing a muon
range detector