8 Neutrino Detectors
377
be identified in the same detector by time of arrival, itself related to the timing
separation of μ + and μ − bunches in the storage ring. In a triangular geometry
two straight sections could point to two detectors. The physics envisaged with
this project is the observation of ν e → ν μ oscillations using the ν e ’s produced
in μ + decay. The signal is the observation of a μ − as opposed to the copious μ + ’s
produced by the interaction of the ¯
ν μ also produced in μ + decay. The identification
of the charge of these wrong sign muons necessitates the use of a magnetic
detector. A 50 kton magnetized iron detector [130] coupled with scintillator or
RPC’s lends itself to this. Less dense detectors such as liquid argon TPC’s and
emulsion detectors [131] using the OPERA technology are also being considered
to observe respectively electrons and τ leptons. These would allow the observation
of additional oscillation channels which would be useful in removing ambiguities in
the determination of oscillation parameters. With the higher energies and distances
being considered the resolution of the mass hierarchy could be envisaged in addition
to the search for CP violation.
The very high intensity proton beams needed to produce an adequate neutrino
flux impose strong restrictions on the type of material used for the proton target.
MERIT [132] is an R&D experiment at CERN intending to investigate the effectiveness of a mercury jet in a solenoidal field as a target. The constant flow of
mercury would circumvent the problems related to stress and heating of a solid
target. Muon cooling is being studied by MICE [133] at RAL with its strong synergy
with MUCOOL [134] at Fermilab, with a setup including capture solenoids, liquid
hydrogen absorbers and RF cavities. Incoming and outgoing spectrometers measure
the effectiveness of the cooling.
8.4.3 High Current Cyclotrons
The present accelerator based long baseline experiments intend to compare oscillations of ν μ to oscillations of ¯
ν μ . However the ¯
ν μ beam has much more ν μ
background than the ν μ beam has ¯
ν μ background. This is because of the π +
to π − ratio at the proton target being larger than unity and because of the ν
interaction cross section being larger than the ¯
ν cross section. DAEδALUS [135]
is an experiment aiming to remedy this situation by using the decay at rest of pions
to produce a very pure source of ¯
ν that would illuminate a detector also exposed to
a long base line ν μ beam. A beam of 800 MeV protons produced by a high current
cyclotron impinges on a thick target producing pions which stop in the target, with
the π − being captured before decaying resulting in a beam dominated by the decay
of π + . As a consequence there will be essentially no π − → μ − → e − ν μ ¯
ν e
and hence any ¯
ν e interaction observed must be from a ¯
ν μ to ¯
ν e oscillation. The
DAEδALUS project proposes installing three sources of pions at rest: one at 20 km
from the detector which, for an average neutrino energy of 45 MeV, would be at the
maximum oscillation probability and at the same L/E as the long baseline beam, one
at 8 km to observe the rise in ¯
ν e appearance and one at 1.5 km for flux normalization.
377
be identified in the same detector by time of arrival, itself related to the timing
separation of μ + and μ − bunches in the storage ring. In a triangular geometry
two straight sections could point to two detectors. The physics envisaged with
this project is the observation of ν e → ν μ oscillations using the ν e ’s produced
in μ + decay. The signal is the observation of a μ − as opposed to the copious μ + ’s
produced by the interaction of the ¯
ν μ also produced in μ + decay. The identification
of the charge of these wrong sign muons necessitates the use of a magnetic
detector. A 50 kton magnetized iron detector [130] coupled with scintillator or
RPC’s lends itself to this. Less dense detectors such as liquid argon TPC’s and
emulsion detectors [131] using the OPERA technology are also being considered
to observe respectively electrons and τ leptons. These would allow the observation
of additional oscillation channels which would be useful in removing ambiguities in
the determination of oscillation parameters. With the higher energies and distances
being considered the resolution of the mass hierarchy could be envisaged in addition
to the search for CP violation.
The very high intensity proton beams needed to produce an adequate neutrino
flux impose strong restrictions on the type of material used for the proton target.
MERIT [132] is an R&D experiment at CERN intending to investigate the effectiveness of a mercury jet in a solenoidal field as a target. The constant flow of
mercury would circumvent the problems related to stress and heating of a solid
target. Muon cooling is being studied by MICE [133] at RAL with its strong synergy
with MUCOOL [134] at Fermilab, with a setup including capture solenoids, liquid
hydrogen absorbers and RF cavities. Incoming and outgoing spectrometers measure
the effectiveness of the cooling.
8.4.3 High Current Cyclotrons
The present accelerator based long baseline experiments intend to compare oscillations of ν μ to oscillations of ¯
ν μ . However the ¯
ν μ beam has much more ν μ
background than the ν μ beam has ¯
ν μ background. This is because of the π +
to π − ratio at the proton target being larger than unity and because of the ν
interaction cross section being larger than the ¯
ν cross section. DAEδALUS [135]
is an experiment aiming to remedy this situation by using the decay at rest of pions
to produce a very pure source of ¯
ν that would illuminate a detector also exposed to
a long base line ν μ beam. A beam of 800 MeV protons produced by a high current
cyclotron impinges on a thick target producing pions which stop in the target, with
the π − being captured before decaying resulting in a beam dominated by the decay
of π + . As a consequence there will be essentially no π − → μ − → e − ν μ ¯
ν e
and hence any ¯
ν e interaction observed must be from a ¯
ν μ to ¯
ν e oscillation. The
DAEδALUS project proposes installing three sources of pions at rest: one at 20 km
from the detector which, for an average neutrino energy of 45 MeV, would be at the
maximum oscillation probability and at the same L/E as the long baseline beam, one
at 8 km to observe the rise in ¯
ν e appearance and one at 1.5 km for flux normalization.