342
L. Camilleri
8.3 Detection Techniques
Because of the small interaction cross section of neutrinos, neutrino detectors must
be massive. The exception is detectors addressing coherent neutrino interactions
for which the cross section is orders of magnitude larger than for other neutrino
interactions and which will be addressed in Sect. 8.3.1. The nature of these massive
detectors depends on the physics being addressed. It usually involves observing the
resulting hadronic part of an interaction and, if a charged current interaction, the
observation of a charged lepton. If the physics merely requires the measurement of
the total neutrino energy, a calorimetric detector suffices. If individual particles must
be measured, then a more sophisticated tracking device is needed. The measurement
of a final state muon is usually accomplished in a fairly straightforward way with
magnetized iron because of the muon penetrating nature. A final state electron
is more difficult to measure, especially its charge, because of bremsstrahlung
and showering as it propagates through material. Neutrino detectors must then
necessarily be of several types. Techniques must be suitable to detect neutrinos of
energies ranging from a few MeV to about a PeV. They must be fine-grained enough
to measure electrons, identify individual particles and observe secondary vertices of
τ ’s or charmed particles or heavy enough to produce large number of interactions
using calorimetric techniques. It is evident that neutrino detectors use most of the
detecting techniques used in particle physics. They will be outlined in the following
sections.
8.3.1 Totally Active Scintillator Detectors
Scintillator detectors can either use liquid or solid scintillator. If liquid is used
the detector consists of either a single large tank or of tubes filled with liquid.
Solid scintillator detectors usually consist of strips. The first neutrino detector [2]
used by Reines and Cowan was intended to observe the interaction of reactor
antineutrinos of a few MeV. The observation was made, as in subsequent reactor
experiments, using the IBD reaction ¯
ν e + p → e + + n and using a detector
consisting of liquid scintillator viewed by photomultipliers. In addition to observing
light emitted from the positron annihilation, the neutron can be detected by also
observing photons emitted by the neutron capture in the hydrogen of the scintillator.
In order to enhance the neutron capture cross section, they added cadmium to the
scintillator. They observed an excess of events when the reactor was in operation
leading to the first detection of (anti)neutrino interactions and a subsequent Nobel
prize. This technique is still being applied to this day [10], albeit with some
refinements. Several recent experiments which will be described below, used it
to search for ¯
ν e oscillations to another flavour in the domain of the atmospheric
m 2 , 2.5 × 10 −3 eV 2 . Because of the low energy of reactor ¯
ν e ’s, ¯
ν μ ’s or ¯
ν τ ’s
that they potentially oscillate to cannot be observed through their charged current
L. Camilleri
8.3 Detection Techniques
Because of the small interaction cross section of neutrinos, neutrino detectors must
be massive. The exception is detectors addressing coherent neutrino interactions
for which the cross section is orders of magnitude larger than for other neutrino
interactions and which will be addressed in Sect. 8.3.1. The nature of these massive
detectors depends on the physics being addressed. It usually involves observing the
resulting hadronic part of an interaction and, if a charged current interaction, the
observation of a charged lepton. If the physics merely requires the measurement of
the total neutrino energy, a calorimetric detector suffices. If individual particles must
be measured, then a more sophisticated tracking device is needed. The measurement
of a final state muon is usually accomplished in a fairly straightforward way with
magnetized iron because of the muon penetrating nature. A final state electron
is more difficult to measure, especially its charge, because of bremsstrahlung
and showering as it propagates through material. Neutrino detectors must then
necessarily be of several types. Techniques must be suitable to detect neutrinos of
energies ranging from a few MeV to about a PeV. They must be fine-grained enough
to measure electrons, identify individual particles and observe secondary vertices of
τ ’s or charmed particles or heavy enough to produce large number of interactions
using calorimetric techniques. It is evident that neutrino detectors use most of the
detecting techniques used in particle physics. They will be outlined in the following
sections.
8.3.1 Totally Active Scintillator Detectors
Scintillator detectors can either use liquid or solid scintillator. If liquid is used
the detector consists of either a single large tank or of tubes filled with liquid.
Solid scintillator detectors usually consist of strips. The first neutrino detector [2]
used by Reines and Cowan was intended to observe the interaction of reactor
antineutrinos of a few MeV. The observation was made, as in subsequent reactor
experiments, using the IBD reaction ¯
ν e + p → e + + n and using a detector
consisting of liquid scintillator viewed by photomultipliers. In addition to observing
light emitted from the positron annihilation, the neutron can be detected by also
observing photons emitted by the neutron capture in the hydrogen of the scintillator.
In order to enhance the neutron capture cross section, they added cadmium to the
scintillator. They observed an excess of events when the reactor was in operation
leading to the first detection of (anti)neutrino interactions and a subsequent Nobel
prize. This technique is still being applied to this day [10], albeit with some
refinements. Several recent experiments which will be described below, used it
to search for ¯
ν e oscillations to another flavour in the domain of the atmospheric
m 2 , 2.5 × 10 −3 eV 2 . Because of the low energy of reactor ¯
ν e ’s, ¯
ν μ ’s or ¯
ν τ ’s
that they potentially oscillate to cannot be observed through their charged current