354
L. Camilleri
quote their measurement of θ 13 as a range of values driven by the allowed CP
phase values. Combining this range of θ 13 with the precise reactor experiments
measurement of θ 13 , allows to limit the possible values of the CP violation phase.
Several long baseline projects based on the water Cerenkov technique have
been proposed to measure the mass hierarchy and the CP phase via ν μ → ν e
oscillations. However because of the low signal event rate expected, detectors of
the order of the megaton are needed. This would enable these detectors to continue
the very successful non-beam physics programme of SK, namely atmospheric
and solar neutrino physics, proton decay searches and supernovae watches. The
MEMPHYS [47] project was planned in the context of a potential neutrino
beam [48] from CERN to a new laboratory in the Frejus tunnel. It consists of 3
cylindrical water Cerenkov counters placed in contiguous caverns for a total of 0.5
megatons. Hyper-Kamiokande(HK), described in their Letter of Intent [49], is a
natural extension of SK and would use the same beam as SK (600 MeV off-axis at
2.5 ◦ ) but with its power upgraded from 0.75 MW to 1.35 MW, mostly by increasing
the JPARC main ring repetition rate to 0.86 Hz. In their latest design the beam would
impinge on a 0.52 Mton (0.38 Mton fiducial) water Cerenkov detector consisting of
two 74 m diameter and 60 m high cylinders located 295 km from J-Parc in a cavern
650 m underground and 8 km south of SK. The Cerenkov light would be observed
by 80,000 50 cm diameter Hamamatsu R12860 photomultipliers of a new Box and
Line design providing 40% coverage with single photons detected with a 24%
efficiency and a 1ns timing resolution. The photomultipliers have survived extensive
pressure and implosion tests. Alternative sensors are also being investigated such
as Hybrid Photo Detectors and the multi-photomultipliers concept developed for
KM3Net [72]. The extrapolation of the water Cerenkov technique to a megatonsized detector is driven to a large extent by the cost of the optical sensors and
their production schedule, making the spacing and size of the sensors of prime
importance. Similar detectors were considered for installation at SURF DUSEL [50]
in order to observe neutrinos from a new beam from Fermilab. However, as will be
discussed below, the liquid argon technique has been adopted instead.
A test [52] in the Super-Kamiokande detector demonstrated that neutrons from
the IBD reaction ¯
ν e + p → e + + n could be detected with the addition of
gadolinium in the water. A 2.4 L acrylic vessel was filled with a 0.2% GdCl 3
mixture. A BGO crystal containing an Am/Be radioactive source was placed in its
middle. The α particles emitted by the ameritium interacted in the beryllium via
α + 9 Be → 12 C ∗ + n. By immersing the vessel in the SuperKamiokande detector
and using the 4.43 MeV carbon deexcitation photon as a trigger it was demonstrated
that the neutron could be detected via its absorption in the gadolinium, as described
earlier in Sect. 8.3.1, with an efficiency of 66.7% with a 3 MeV threshold for delayed
events. It was estimated that a background reduction of 2 × 10 −4 could be achieved
at a 10 MeV prompt event analysis threshold for ¯
ν e . This opens the way for the use
of the water Cerenkov technique for the detection of ¯
ν e ’s of geological or reactor
origin.
Detectors that measured a deficit in the solar neutrino spectrum were all sensitive
to ν e only. In order to definitely prove that the deficit was due to a flavour
L. Camilleri
quote their measurement of θ 13 as a range of values driven by the allowed CP
phase values. Combining this range of θ 13 with the precise reactor experiments
measurement of θ 13 , allows to limit the possible values of the CP violation phase.
Several long baseline projects based on the water Cerenkov technique have
been proposed to measure the mass hierarchy and the CP phase via ν μ → ν e
oscillations. However because of the low signal event rate expected, detectors of
the order of the megaton are needed. This would enable these detectors to continue
the very successful non-beam physics programme of SK, namely atmospheric
and solar neutrino physics, proton decay searches and supernovae watches. The
MEMPHYS [47] project was planned in the context of a potential neutrino
beam [48] from CERN to a new laboratory in the Frejus tunnel. It consists of 3
cylindrical water Cerenkov counters placed in contiguous caverns for a total of 0.5
megatons. Hyper-Kamiokande(HK), described in their Letter of Intent [49], is a
natural extension of SK and would use the same beam as SK (600 MeV off-axis at
2.5 ◦ ) but with its power upgraded from 0.75 MW to 1.35 MW, mostly by increasing
the JPARC main ring repetition rate to 0.86 Hz. In their latest design the beam would
impinge on a 0.52 Mton (0.38 Mton fiducial) water Cerenkov detector consisting of
two 74 m diameter and 60 m high cylinders located 295 km from J-Parc in a cavern
650 m underground and 8 km south of SK. The Cerenkov light would be observed
by 80,000 50 cm diameter Hamamatsu R12860 photomultipliers of a new Box and
Line design providing 40% coverage with single photons detected with a 24%
efficiency and a 1ns timing resolution. The photomultipliers have survived extensive
pressure and implosion tests. Alternative sensors are also being investigated such
as Hybrid Photo Detectors and the multi-photomultipliers concept developed for
KM3Net [72]. The extrapolation of the water Cerenkov technique to a megatonsized detector is driven to a large extent by the cost of the optical sensors and
their production schedule, making the spacing and size of the sensors of prime
importance. Similar detectors were considered for installation at SURF DUSEL [50]
in order to observe neutrinos from a new beam from Fermilab. However, as will be
discussed below, the liquid argon technique has been adopted instead.
A test [52] in the Super-Kamiokande detector demonstrated that neutrons from
the IBD reaction ¯
ν e + p → e + + n could be detected with the addition of
gadolinium in the water. A 2.4 L acrylic vessel was filled with a 0.2% GdCl 3
mixture. A BGO crystal containing an Am/Be radioactive source was placed in its
middle. The α particles emitted by the ameritium interacted in the beryllium via
α + 9 Be → 12 C ∗ + n. By immersing the vessel in the SuperKamiokande detector
and using the 4.43 MeV carbon deexcitation photon as a trigger it was demonstrated
that the neutron could be detected via its absorption in the gadolinium, as described
earlier in Sect. 8.3.1, with an efficiency of 66.7% with a 3 MeV threshold for delayed
events. It was estimated that a background reduction of 2 × 10 −4 could be achieved
at a 10 MeV prompt event analysis threshold for ¯
ν e . This opens the way for the use
of the water Cerenkov technique for the detection of ¯
ν e ’s of geological or reactor
origin.
Detectors that measured a deficit in the solar neutrino spectrum were all sensitive
to ν e only. In order to definitely prove that the deficit was due to a flavour