8 Neutrino Detectors
369
to allow the use of stand alone techniques in which the emulsions were scanned
without external information.
The latest scanning microscopes developed in Japan and Italy can measure at an
average speed of 50 and 20 cm 2 /h respectively. In addition to providing very precise
spatial reconstruction emulsions, because of the large number of measurements
along a track, can provide momentum measurements, as described above, and
particle identification using ionization measurements, especially near the end point
of stopping tracks. Please refer to Chap. 5 of this volume which addresses emulsion
techniques in more details.
8.3.5 Hybrid Detectors
NOMAD [105] was a detector, Fig. 8.17, built to search for ν μ → ν τ oscillations
by observing ν τ interactions in the same ν μ beam as used by CHORUS. However,
unlike CHORUS, it intended to identify τ ’s not through the reconstruction of its
separate decay vertex, but through kinematic criteria such as the missing transverse
momentum arising from the unobserved neutrinos produced in τ decay. This
demanded very good momentum resolution. The τ decay modes used in the analysis
were τ − → ν τ +hadrons and τ − → ν τ + ¯
ν e +e − . The latter mode was particularly
useful as its main background is CC interactions of the intrinsic ν e in the beam
but this background is greatly suppressed because of the small ν e contamination,
∼1%. However this mode did require very good electron identification. This latter
Muon
chambers
Neutrino
beam
V8
Hadronic
calorimeter
1 metre
Trigger planes
Drift chambers
Electromagnetic
calorimeter
Front
calorimeter
Dipole magnet
TRD
modules Preshower
Veto planes
Fig. 8.17 The NOMAD hybrid detector used at CERN in the search for ν μ → ν τ oscillations
369
to allow the use of stand alone techniques in which the emulsions were scanned
without external information.
The latest scanning microscopes developed in Japan and Italy can measure at an
average speed of 50 and 20 cm 2 /h respectively. In addition to providing very precise
spatial reconstruction emulsions, because of the large number of measurements
along a track, can provide momentum measurements, as described above, and
particle identification using ionization measurements, especially near the end point
of stopping tracks. Please refer to Chap. 5 of this volume which addresses emulsion
techniques in more details.
8.3.5 Hybrid Detectors
NOMAD [105] was a detector, Fig. 8.17, built to search for ν μ → ν τ oscillations
by observing ν τ interactions in the same ν μ beam as used by CHORUS. However,
unlike CHORUS, it intended to identify τ ’s not through the reconstruction of its
separate decay vertex, but through kinematic criteria such as the missing transverse
momentum arising from the unobserved neutrinos produced in τ decay. This
demanded very good momentum resolution. The τ decay modes used in the analysis
were τ − → ν τ +hadrons and τ − → ν τ + ¯
ν e +e − . The latter mode was particularly
useful as its main background is CC interactions of the intrinsic ν e in the beam
but this background is greatly suppressed because of the small ν e contamination,
∼1%. However this mode did require very good electron identification. This latter
Muon
chambers
Neutrino
beam
V8
Hadronic
calorimeter
1 metre
Trigger planes
Drift chambers
Electromagnetic
calorimeter
Front
calorimeter
Dipole magnet
TRD
modules Preshower
Veto planes
Fig. 8.17 The NOMAD hybrid detector used at CERN in the search for ν μ → ν τ oscillations