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nsf-proposal-19oct06TK

VIEWS: 3 PAGES: 15

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Results from NSF Prior Work
A prior funded proposal, PHY02-18438, with A.K. Mann as P.I. and K.Lande and R.van Berg as
CO-P.I.s was directed at Technical Studies for a Massive Neutrino Detector. The result of this
effort is the detector design discussed in the remainder of this document and resulted in several
publications, Phys.Rev. D68, 012002(2003)16, hep-ex/0306053, Megaton Modular
Multi-Purpose neutrino Detector for a Program of Physics in the Homestake DUSEL17 and
hep-ex/0608023, Proposal for an Experimental Program in Neutrino Physics and Proton
Decay in the Homestake Laboratory 18. In addition, these results were presented to the NuSAG
Panel on May 20, 2006 and formed part of the discussions of a joint BNL-FNAL panel on future
directions for Long Range Neutrino Physics.

Introduction
A large underground detector with an active mass of several hundred kilotons is a key shared
physics research facility for the future U.S. particle, nuclear and astrophysics research programs.
This detector will address questions of fundamental scientific importance, nucleon decay and
matter-antimatter asymmetry amongst neutrinos, while simultaneously and continuously
observing natural sources of neutrinos and cosmic rays.

This large multipurpose detector must have a detector mass in excess of 100kT to provide
strongly improved statistical power to search for nucleon decay, and to collect enough neutrino
events produced by accelerator-based, very-long-baseline neutrino beams to reliably measure the
needed neutrino oscillation parameters. For at least one of the key proton decay modes (p→ e+0),
the detector mass needs to approach 1/2 Mton to ensure competitive future progress. The detector
needs to have a low energy threshold (<5MeV) and good energy resolution to detect supernovae
and solar neutrinos, as well as good pattern recognition, timing and particle identification
capabilities, in order to distinguish electrons from muons and pions. To exploit the full scientific
potential of such a detector, it must be located deep underground to shield it from cosmic ray
background.

A recent U.S. Government policy document, "The Physics of the Universe"1, considers the
science and technology that would be provided by such a detector and concludes that it has high
scientific value and is also judged to be “Ready for Immediate Investment and Direction Known”
(Page 5). Other official documents support this key scientific priority2 and the administration’s
budget policy3.

Scientific Scope of the Large, Multipurpose Underground Detector
A massive underground detector can simultaneously address three key physics topics:
   1) Neutrino oscillations using very long baseline accelerator neutrino beams;
   2) A significantly improved search for nucleon decay;
   3) Detection and study of neutrinos from natural sources such as the Sun, Earth’s atmosphere,
      past or current supernova explosions plus, as yet unsuspected new sources of neutrinos.

Physics Topic 1 – Neutrino Measurements Using Accelerator Produced Beams
In references4,5,6, as well as additional references contained therein, it has been argued that an
intense, accelerator-generated, broad-band muon neutrino beam, coupled with a large
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experimental detector located more than 1000 km away from the beam source, will make precise
measurements of neutrino oscillation properties such as the mass differences, the mass hierarchy,
the mixing parameters, and CP-violation in the neutrino sector. Using currently known values for
the neutrino mass differences and mixing parameters7, several rules of thumb have been
formulated to characterize such an experiment:
 1) It is desirable to observe a pattern of multiple nodes in the energy spectrum of  disappearance
    and e appearance. Such a pattern of oscillations is important for extraction of signal from
    background as well as the precision measurements of parameters. Since the cross section,
    Fermi motion and nuclear effects limit the resolution of interactions below ~1 GeV, a
    wide-band  beam with energies of 0.5-6 GeV and baseline of ~1300 km is needed to see 2 or
    more oscillation nodes.
 2) The appearance spectrum of electron neutrinos from the oscillation of  to e contains
    information about sin2 213, CP, m212 and the ordering of neutrino masses through the matter
    effect. One of the key unknowns in neutrino physics is whether the mass ordering of neutrinos
    is “normal”, resembling the ordering of quark and charged lepton masses ( m1 < m2 < m3 ), or
    “reversed”, in which the masses of states associated with electrons and muons are heaviest (m3
    < m1 < m2). It was shown in our references that the various parameters can be separated out
    and measured using only a single detector in the broad-band 0.5-6 GeV beam with the >1000
    km baseline. In such an experiment, successive oscillation nodes have different dependence on
    the parameters and therefore can lead to a robust measurement of all the required oscillation
    parameters.
 3) For normal mass ordering, the matter effect causes the conversion probability to increase with
    energy and is most pronounced at energies >3 GeV. In contrast the effects of CP fall as 1/E.
    Our references show that this energy dependence can be used to measure the value of CP and
    sin2 213 without requiring anti-neutrino data for the case of normal mass ordering. Neutrino
    and anti-neutrino data together, will be needed to cover both mass ordering possibilities, and
    will lead to a definitive result for CP-violation as well as yield a precision measurement of the
    CP parameter CP. Because the energy dependence becomes larger for longer baseline
    distances, it is advantageous to perform the experiment with a very long ( >1000 km) baseline,
    so that we can then relax the requirements on systematic errors for the flux, cross-sections and
    other oscillation parameters, plus confidently calculate and observe the matter effect.

In Fig. 1 we illustrate calculated neutrino oscillation characteristics including projected event
yields and statistics for the appearance of electron neutrinos using the Fermilab to Homestake
baseline and recently announced Fermilab neutrino beam capabilities, plus the three 100 kT
detector modules described in this NSF proposal. In the calculation, we assume an initial beam of
muon neutrinos that oscillates as predicted by already-measured neutrino mass differences along
with other assumed neutrino oscillation parameters and matter effects4. Several different values of
the CP-violation phase, CP, are illustrated.
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Fig. 1 – CP-violation phase behavior for a broad-band neutrino beam from Fermilab to the
Homestake Underground Laboratory in Lead, South Dakota.

Note that multiple nodes can be observed in the e spectrum and that different values of the
CP-violation phase, CP, are unambiguously distinguishable over this neutrino energy range. This
feature is unique to the very long baseline method using a broad-band beam.

A joint FNAL – BNL study group is engaged in developing a Long Range U.S. Neutrino Beam
Program. The study results, to date, can be seen at http://nwg.phy.bnl.gov/~diwan/nwg/fnl-bnl/.

Physics Topic 2 – Improved Search for Nucleon Decay
While current experiments show that the proton lifetime exceeds about 1033 years, its ultimate
stability has been questioned since the early 1970’s in the context of theoretical attempts to arrive
at a unified picture of the fundamental particles – the quarks and leptons – and of their three forces:
the strong, electromagnetic and weak. These attempts of unification, commonly referred to as
“Grand Unification”, have turned out to be supported empirically by the dramatic meeting of the
strengths of the three forces, that is found to occur at high energies in the context of so-called
“Supersymmetry”, as well as by the magnitude of neutrino masses that is suggested by the
discovery of atmospheric and solar neutrino oscillations. One of the most critical and general
predictions of grand unification is that the proton must ultimately decay into leptonic channels
such as positron-plus-meson, revealing quark-lepton unification for the first time.

Proton decay, if found, will provide us with a unique window to view physics at truly short
distances – less than 10-30 cm, corresponding to energies greater than 1016 GeV – a feature that
cannot be achieved by any other means. Discovering proton decay will provide the missing link to
grand unification in particle physics. Last but not least, it will clarify our ideas about the origin of
the excess of matter over anti-matter, ideas that are crucial to the origin of life itself. We note that
the predictions of a well-motivated class of grand unified theories for proton lifetime are not far
above current limits. This makes very compelling and exciting, an improved search for proton
decay into the νK+ and e+0 modes with lifetimes less than about 2x1034and 1035years, respectively.
The next-generation detector proposed in this document will carry out this search with world
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leading capability.

We now review the current limits on proton decay. The “classical” proton decay mode, p→ e+0,
can be efficiently detected with low background. At present, the best limit on this mode (τ/β >
5.4×1033 yr, 90% CL) comes from a 92 kton-yr exposure of Super-Kamiokande. The detection
efficiency of 44% is dominated by final-state 0 absorption or charge-exchange in the nucleus,
and the expected background is 2.2 events/Mton-yr. The mode p→ νK+, is experimentally more
difficult in water Cherenkov detectors due to the unobservable neutrino and the fact that the kaon
is below Cherenkov threshold. The present limit from Super-Kamiokande is the result of
combining several channels, the most sensitive of which is K+→+ν accompanied by a
de-excitation signature from the remnant 15N nucleus. Monte Carlo studies suggest that this mode
should remain background free for the foreseeable future. The present limit on this mode is τ/β >
2.2×1033 yr (90% CL).

Given the limits just quoted, continued progress in the search for nucleon decay will inevitably
require much more detector mass. The efficiency for detection of the e+0 mode is dominated by
pion absorption effects in the nucleus, and cannot be improved significantly. An order of
magnitude improvement in this mode can only be achieved by constructing an order of magnitude
larger experiment and operating it for many years. The decay modes of the nucleon are a priori
unknown and each produces a quite different experimental signature. Future detectors, therefore,
should be sensitive to most or all of the kinematically allowed decay channels. The baseline
detector proposed here will cover the most important of these. Detector enhancements noted
below could expand sensitivity to other decay channels. Proton decay experiments have already
made a number of fundamental contributions to neutrino physics and particle astrophysics. The
experiment proposed here will strongly continue this proud and productive scientific tradition.

A variety of detector technologies for discovery of nucleon decay have been discussed. Of these,
water Cherenkov appears to be the only one capable of reaching lifetimes of 10 35years or greater.
Cooperative, parallel studies of a future underground water Cherenkov proton decay experiment
are underway in the U.S., Japan and France. The proposed designs range from several hundred
kton to 1 Mton. We propose a water Cherenkov detector of 300 kT as the best option for a U.S.
program. Other techniques, for instance liquid Argon or scintillation, have been discussed and
may have significant efficiency advantages for certain modes that are dominant in a certain broad
class of SUSY theories. Liquid Argon time projection chambers potentially offer very detailed
measurements of particle physics events with superb resolution and particle identification. Liquid
Argon feasibility will be demonstrated in the near future with the operation of a 600-ton ICARUS
detector. If expectations are correct, it should have a sensitivity that is equivalent to a 6000-ton
water Cherenkov detector in the p→νK+ mode.

The liquid scintillator approach is presently being explored with the 1kT KamLAND experiment.
It should also have enhanced sensitivity to the p→νK+ mode by directly observing the K+ by
dE/dx and observing the subsequent K+→+ decay. If the value of the liquid scintillation method
is demonstrated, we have discussed implementation of an enhanced version of our proposed
baseline water Cherenkov detector. We note that our vertical cylinder design readily permits the
insertion of a central cylinder containing liquid scintillator into the water Cerenkov module. The
inserted scintillator cylinder would be viewed by the same PMTs as the surrounding water
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Cerenkov detector and the incremental cost of the resulting dual detector would be modest. We
want to stress that our baseline detector employs the water Cerenkov method and that a
scintillator insert would be considered as a later enhancement.

Our baseline design of a water Cerenkov detector employs a proven technology that has been
perfected over several decades. Water Cerenkov detectors are in operation in Japan (Super
Kamiokande with a total mass of ~50 kT) and in Canada (the Sudbury Neutrino Observatory,
SNO, with 1 kT of D2O and 5 kT of H2O).

Furthermore, detailed Monte Carlo studies, including full reconstruction of simulated data,
indicate that a water detector could reach the goal of an order of magnitude improvement on the
nucleon decay limits achievable in the projected Super-Kamiokande program. With sufficient
exposure, clear discovery of nucleon decay into e+π0 would be possible even at lifetimes of (few) ×
1035 years where present analyses would be background-limited, by tightening the selection
criteria. For instance, with a detection efficiency of 18%, the expected background is only 0.15
events/Mton-yr, ensuring a signal:noise of 4:1 even for a proton lifetime of 1035 years. A water
Cherenkov detector would also provide a decisive test of super-symmetric SO(10) grand unified
theory by reaching a sensitivity of a (few) x 1034 years for the ν K+ mode.

Most of the decay modes that were searched for in the first generation nucleon decay detectors
required only modest depth. The IMB detector operated successfully at a depth of 2000 feet. The
proposed depth for our detector (4850 mwe) will reduce the muon background by about a factor
of 20 with respect to Super-Kamiokande, certainly helping in the observation of modes with a
low energy component or those influenced by fast neutron background. For example, n → ννν can
be searched for by observing the de-excitation of the residual nucleus. This is difficult in a
background of fast-neutron induced low-energy, cosmic ray induced background events.

Physics Topic 3 – Observation of Natural Sources of Neutrinos
The third scientific mission of the proposed detector is in the improvement of existing and
projected future solar and atmospheric neutrino measurements as well as the potential discovery of
unexpected new phenomena in the flux of natural neutrinos. New natural neutrino sources may
appear when the detector mass reaches the hundreds of kilotons scale.

The continued study of atmospheric and solar neutrinos in the large underground detector will
provide useful additions to the program being carried out successfully in existing experiments.
The solar neutrinos have already been observed in the Super-Kamiokande10 and SNO detectors11.
Our proposed 300 kT water Cherenkov detector will increase the observable event rate enough to
clearly observe spectral distortion in the 5 to 14 MeV region. We will also measure the as yet
undetected hep solar neutrinos (with end point of 18.8 MeV) well beyond the 8B endpoint (~14
MeV). A better determination of the solar spectrum as well as detection of the day-night effect
with high statistics will represent a significant advance in solar nuclear physics measurements.
Statistical clarification of the day-night effect for solar neutrinos is another topic that will benefit
from the strongly improved statistics.

The liquid scintillator detector enhancement noted above could provide low energy solar neutrino
sensitivity, similar to that of Borexino and Kamland, but with a fiducial mass that is 40 and 12
times larger, respectively. This order of magnitude increase in fiducial mass will allow statistical
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improvements in all the topics studied and, perhaps, the emergence of new scientific topics. The
liquid scintillator detector enhancement is also of interest because it could allow the detection of
low energy antineutrinos from radioactive decays in the Earth’s lithosphere, thereby opening a
new chapter in geoscience.

The observation of supernova neutrino events in the proposed large neutrino detector is
straightforward and has historical precedent. The SN 1987A supernova, in fact, was seen by two
large water Cerenkov detectors (11 events in Kamikande-II (total mass~3kT) and 8 events in IMB
(total mass~7kT)) that were active in proton decay searches at that time12. The predicted
occurrence rate for neutrino-observable supernovae (from our own galaxy and of order 10 kpc
distant) is about 1 per 20 years, so events will be very rare15. However, the information from a
single event, incorporating measured energies and time sequence for tens of thousands of neutrino
interactions, obtained by a very large neutrino detector, could provide significantly more
information than has ever been obtained before about the time evolution of a supernova. In
addition to obtaining information about supernova processes, the small numbers of SN1987a
neutrino events have been extensively used to limit fundamental neutrino properties. Supernova
processes continue to have very high interest because of the recent detection of the acceleration of
the rate of expansion of the universe using type Ia supernova. Recent work has shown that diffuse
neutrino events from past core collapse supernova (which produce neutrino bursts) could be used
in to gain independent knowledge on the cosmological evolution parameters13. The detection of
supernova neutrinos, either as a burst from a single supernova and as a diffuse source from past
supernovas, is a key mission of the proposed multipurpose detector.

With some 20-100 times the sensitive mass and, hopefully, a lower neutrino energy threshold (a
few MeV), the energy and arrival-time spectra would have statistical power that the earlier
detectors could not provide. The uncertainty of obtaining a supernova event may make this
research topic insufficient to motivate construction of its own detector. But when this topic is
added to the mission of a multipurpose detector, the increased science potential at no additional
cost to the integrated program is very compelling.

Relic supernova and lithospheric neutrinos, have not yet been studied extensively and could, in
principle, be observed by the enhanced detector concept. An initial result in this area has recently
been announced by KamLAND14. Typically, the neutrino energies for these processes are below
10 MeV and are sensitively dependent upon the low-energy threshold capability of the new
detectors. The liquid scintillator detector concepts are likely to have the best opportunities for
advancing these topics.

Finally, we note that there may be galactic sources of neutrinos that are of lower energy and greater
abundance than the ultra high-energy neutrino sources to be explored by detectors such as the ‘Ice
Cube’ Cerenkov detector now being constructed deep under the Antarctic ice sheet by an NSF
sponsored collaboration. Galactic neutrinos have a natural source in inelastic nuclear collisions
through the leptonic decays of charged secondary pions. This source is expected to be of
comparable intensity and energy distribution to the high-energy photons that are born from neutral
pion decays in the same collisions15. Such neutrino sources, currently not detectable with
Super-Kamiokande, could be seen by a megaton-class neutrino detector that runs for several
decades.
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Relationship of the Physics Topics to the DUSEL Project
A large detector facility located in the DUSEL is the optimum way to pursue all three of the above
physics research goals. The important technical capabilities for such a detector are its fiducial
mass, energy threshold, energy resolution, muon/electron discrimination, pattern recognition
capability, time resolution, low-radioactivity detector environment, and depth of the underground
site of the detector. The capital and operating costs for the detector are also a serious concern.

The fiducial mass requirement derives from the precision sought for the CP-violation
measurement (assuming that the value of sin2 213 > 0.01) and from the sensitive target mass
needed to detect nucleon decay. A measurement uncertainty of ~10-20 deg. on the CP phase
angle will require a detector in excess of 100 kT (regardless of the length of the baseline), since
current technology limits the proton beam power to less than about 2 MW. For significant
progress in detecting nucleon decay, it is clear that improvements in the sensitivity of the existing
Super-Kamiokande detector are needed. A new detector with much greater fiducial mass is
required. Therefore, a very large, deep underground detector that is able to combine the
measurement of accelerator-based neutrino oscillation parameters with a sensitive new search for
nucleon decay offers a very compelling component for the DUSEL science mission.

For the neutrino oscillation physics that we propose here, we noted that it is important to obtain
good energy resolution on the neutrino energy, excellent pattern recognition, and a low energy
threshold. The required energy resolution can be achieved by separating quasi-elastic scattering
events, with well-identified leptons in the final state, from the inelastic charged-current and
neutral-current events. One of the key questions under study is how well quasi-elastic events for
muon and electron neutrinos can be separated from other background events. Studies to date
indicate that this separation can be achieved as required.

Lastly, the energy threshold and the depth of the detector will determine the low-energy and
low-rate capability of the detector for the detection of solar, and supernova neutrinos, as well as
detection of atmospheric neutrinos, lithospheric anti-neutrinos and diffuse relic neutrinos from
long past supernovae. The 4200 mwe depth at Homestake is sufficient for these purposes.

Multi-100 KiloTon Module Water Cerenkov Detector
We began planning the construction of a massive multi-module, 3M water Cerenkov detector at
Homestake in 2001, shortly after the announcement of cessation of gold mining at the Homestake
Mine. An initial presentation of these plans was made to a SAGENAP panel in March 2002 and a
proposal for conceptual design of this detector was submitted to NSF. Several descriptions of
these plans were published and the description that follows represents the maturation of our
conceptual design efforts over the past five years.

Detector Module Orientation and Size
The modules in our conceptual design are vertically oriented cylinders, similar to the
SuperKamiokande detector. Vertical cylinder modules make it possible to install and remove
PMTs without draining the highly purified detector fill water. This is very important since each of
the 100 kiloton fiducial volume detectors is filled with about 120 kilotons of water. Underground
storage of this much water would require a spare detector excavation. Pumping this water to the
surface and then bringing an equal amount of surface water back underground to refill the detector
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is disruptive of the surface water system. It will also take several months to pump out, refill and
purify the detector water; an operation that will involve considerable power costs.

Our present, nominal plan is to have a 50 meter diameter by 50 meter high cylindrical fiducial
volume in a 53 meter diameter cylinder. The PMTs will be mounted such that their photocathode
surfaces lie on a 52 meter diameter by 52 meter high cylinder, allowing a one meter gap between
the photocathode surface and the edge of the fiducial volume. The gap between the 52 meter
diameter photocathode diameter and the 53 meter diameter cylindrical chamber wall will be used
as an active veto as is done successfully in Super-Kamiokande.

In this topology, 67% of the PMTs are on the vertical cylinder, 16% on the flat, top surface and
16% on the flat, bottom surface. The side PMTs will slide into the detector on vertical guide rails.
The light shield that separates the main fiducial volume from the side veto region will be part of the
PMT slide system. One of the design issues to be addressed in the proposed work is moving the
cables together with the PMTs without interfering with adjacent PMTs.

The top PMTs are directly below the platform on the top of the detector and so easily accessible.
Accessing the bottom PMT layer is a challenge. The plan is to divide the bottom layer into a
number of subset panels. Each of these panels will be neutrally buoyant, with the weight of the
frame matching the buoyant force of the attached PMTs. Each of these panels will be
independently suspended on transparent nylon cables and able to be raised to the surface. Again,
the management of the electronic cables is an issue that will be addressed in the proposed design
effort.

The maximum reasonable chamber diameter depends on the local rock properties. The Homestake
rock has been extensively studied and is well understood. The first several chambers will be
excavated within 100 – 200 meters of the chlorine solar neutrino detector excavation. That
chamber was excavated in 1965 and has remained stable for the past 40 years, a clear indication of
the quality of the local rock. Nonetheless, we will core directly into the excavation region of each
chamber in order to measure the rock parameters of that specific chamber location. The specific,
local rock strength parameters will be incorporated into the final design of each chamber and the
rock support of that chamber. A proposal for this rock mechanics study is being submitted to NSF
by William Pariseau of the University of Utah and collaborators. These proposed rock studies are
an integral part of the plan for the multi-100 kiloton detectors.

One of the participants in the rock coring and subsequent rock evaluation will be the Hard Rock
Stability Group from NIOSH’s Spokane Laboratory. This group together with William Pariseau
has been studying the stability of large, deep underground excavations at Homestake since the
early 1980’s, when NIOSH was known as the U.S. Bureau of Mines. NIOSH has agreed to make
these studies an official, specific NIOSH effort.

Chamber Excavation
A fairly detailed plan for chamber excavation was prepared in early 2002 by Mark Laurenti, the
last Chief Mine Engineer of the Homestake Mine. This plan is closely resembles the excavation
plan for the Super-Kamiokande detector. It is based on conservative estimates of the properties of
the local rock formation. It was originally designed for a detector complex at the 6950 ft depth and
has now been adapted to the shallower 4850 ft depth. The excavation time for the 100 kiloton
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chamber is 4 years compared to 2.5 years for excavation plus an additional 1 ½ years for
construction of the steel tank for the 40 kiloton Super-Kamiokande detector.

Super-Kamiokande consists of a steel water containing cylinder constructed inside the rock
excavation while our plan has a 50 cm. concrete liner mounted on the inside of the rock excavation.
The inside surface of the concrete liner will have a sprayed on polyurethane (Mine Guard) liner,
similar to that used by SNO, followed by a geotextile polyethylene fabric and then a heat-sealed
polyethylene liner. Both the polyurethane and the polyethylene liners are standard water-tight
liners that are routinely used in the construction of large water containing excavations. Either the
polyurethane spray or the polyethylene liner is sufficient to hold the detector water fill. Using both
provides an extra safeguard against potential leaks.

The concrete liner will be constructed out of sections that are precast on the surface and then
transported underground. These sections will have threaded sockets cast into them for the PMT
installation/removal system and any other mounting components required for the detector.
Although the concrete liner will be mounted against the excavated rock surface, the irregularities
of the rock surface will leave some spaces between rock and concrete. Any water coming out of
the rock will drain through these gaps and will be pumped out at the bottom of the excavation.
Since the Homestake rock is dry, we do not anticipate any significant amount of such drain water.
There was virtually no such drain water in the Chlorine chamber.




Fig. 2 Layout of excavation of one 100 kiloton module. The spiral ramp surrounding the
excavation provides access to various levels during construction and later will be used to connect
the water drain at the bottom of the detector to the purification facility at the top.

Our construction timetable, four years for the preparation of the chamber and one year for the
installation of the PMTs closely matches the 5 year, 1991- 1996, construction time for
SuperKamiokande.

A significant factor in the construction of these modules is the removal and disposal of the
excavation rock, about 400 kilotons per module. Our initial three modules are sited within 300
                                                 10

meters of the Yates shaft, which has two large rock hoisting skips, each of which can handle about
10 tons of rock per trip. At the surface, the excavated rock will be transported to the adjacent Open
Cut, an extremely large (about 108 ton capacity) open pit.

Photomultiplier Tubes
We plan to use 11 – 12 inch diameter hemispherical PMTs rather than the 20 inch diameter PMTs
used in the SuperKamiokande detector. The smaller diameter PMTs have superior characteristics
– a photocathode efficiency of 24% rather than 20% for the 20 inch PMTs, and a higher electron
collection efficiency, 70% vs. 60%. Thus a 25% geometric photocathode coverage with 11-12
inch PMTs is equivalent in light collection efficiency to a 35% geometric coverage with 20 inch
PMTs and should result in a detector threshold about ½ MeV higher than SuperKamiokande and
so ≤ 5 MeV.

In addition, the smaller PMTs are mechanically stronger than the larger PMTs and, in case of
implosion, have only 1/8 the stored energy of the larger PMTs. Finally, there are multiple
manufacturers of the smaller PMTs so that we can avoid the “sole source issue”.

In addition to the improved light collection efficiency discussed above, the 11 – 12 inch PMTs
have a faster rise time, ~ 4ns, than the larger PMTs, ~10 ns, and a better angular resolution, ~ PMT
diameter/ detector radius, permitting improved event reconstruction.

As presently specified, the lowest PMTs in our detector are 53 meters below the surface of the
water and so must be capable of withstanding 5.3 atmospheres of pressure. Hamamatsu’s present
test data on their R7081 hemispherical PMTs is that they survive at least 9 atmospheres of pressure.
We have acquired 32 Hamamatsu R7081 PMTs for more extensive pressure tests. We will first
determine the hydrostatic pressure at which these PMTs fail. Once we have determined the
typical failure pressure from some of these PMTs, we will do long term tests at reduced pressure in
highly purified water to see if long water exposure reduces the failure pressure. Finally, we are
considering tests to see if elastic rather than rigid mounts for these PMTs will reduce the sensitivity
to a possible shock wave produced by a nearby PMT implosion. We intend to carry out similar
tests on PMTs from other manufacturers and request funds for this purpose.

Readout Electronics
There is now extensive experience with readout electronics for large water Cerenkov detectors.
The University of Pennsylvania Electronics Engineering Group was responsible for the electronics
for the early Kamiokande Solar Neutrino Detector and most recently designed and constructed the
electronics for the SNO detector. This group is now looking at the design parameters for the
multi-module Homestake water Cerenkov detectors. In the decade that has passed since the last
large water Cerenkov detector electronics was constructed, the capability of electronics has
increased considerably and the cost has decreased.

Water Purification
Our water purification requirements can be met by available commercial systems. For example,
one of the major water purification companies, Koch Industries, has a 250 gallon/minute
purification system, which costs about $500,000, than can fill one of our detectors in about three
                                                11

months. The exact system requirements cannot be determined until we supply samples of the
water to be purified.

Once the detector is filled, the purification system will continue operating, drawing water from the
bottom of the detector and returning it, after purification, into the top of the detector. This loop
will also permit us to make up for any water losses in the detector.

We are also considering adding a cooling step to the water purification system. The near surface
rock will be cooled by air during the excavation period. Homestake rock is dry and thus has low
thermal conductivity. We anticipate that the detector water will be in the 25 – 300C range. A
lower temperature, say ~100C, will reduce the PMT noise by a factor of at least 2. We plan to
evaluate both capital and operating costs for such cooling with information from the proposed
pre-excavation coring.

Other Proposed Large Water Cherenkov Detectors
There are three other large water Cherenkov detector proposals. One of these, planned for the
Frejus Tunnel between France and Italy, is intended as a detector for a low energy neutrino beam
from CERN. The Frejus plan19 is for vertical modules that are 57 meters diameter by 57 meters
diameter, essentially the same as ours. They are considering 12 inch diameter hemispherical
PMTs, again, the same as our plan. The Frejus cost estimate for PMTs and electronics, when
adjusted to our parameters, is within 5% of our estimate. The excavation estimate for Frejus is
twice ours. Part or much of this cost difference may be due to the cost of rock removal through the
Tunnel and disposal outside the Tunnel. We hope to be in close contact with the Frejus group
during detector design and construction to insure that the best ideas are incorporated into our
detector and, hopefully, into theirs.

There are also two proposals for horizontally oriented water Cherenkov detectors, UNO and
Hyper-Kamiokande. The cross section of the proposed Hyper-Kamiokande detector is 48 meters
by 54 meters, while that of UNO is 60 meters by 60 meters. There is no physical length constraint
on these horizontal cylinder detectors, only cost and excavation time. We have noted some of the
limitations of the horizontal detector orientation, PMT installation and removal while the detector
is filled, and insertion of auxiliary instruments, such as low background counting system and
liquid scintillator. In addition, with a single chamber detector any maintenance involves complete
detector shutdown whereas the multiple detector system permits maintenance or modification of
one detector while the others remain in operation.

Cost and Construction Time
We have made preliminary cost estimates for the construction of either a single module or three
modules simultaneously. Each of these contains a 30% contingency for the excavation and a 35%
contingency for the other components of the detector. Also, each of these costs has been inflation
adjusted to 2007. There are significant savings in excavating three chambers simultaneously
compared to the same number, one at a time. The savings are such that the cost of three
simultaneous excavations is about the same as two done one at a time, or, to rephrase, we can get
three for the price of two.
                                                12

Component                                    One Module Three Modules
Construction (including 30% contingency)          $29.1M              $66.1M
Photomultipliers and Electronics                  $62.1M            $186.3M
Other                                               $7.9M              $7.9M
Contingency (Other + PMT-electronics)             $17.5M              $48.6M
TOTAL                                            $116.6M            $308.9M
The dominant cost is that of the photomultiplier tubes. We have used several bases for this
estimate, including one given by Photonis at a presentation in NNN05 in April 2005. The
electronics cost was based on the cost of the SNO electronics, adjusted to 2007, made by the Penn
Electronics Engineering Group. Based on the similarity of PMT and electronics costs by the
Frejus group, we assume that they have used similar sources for their estimate. The cost of the
water purification system is based on estimates from Koch Industries, a major water purification
company.

Work Plan
1) As we have indicated above, the most critical initial step is the determination of the rock
strength in the specific region of chamber excavation. These measurements will determine the
maximum safe dimensions of the excavated chambers. We intend to be extremely conservative in
setting the excavation dimensions and will do so in consultation with several highly experienced
mining entities. A proposal for this effort is being submitted separately and is being coordinated
by the University of Utah.

2) We need to know the conservative pressure limitations of the PMTs to be used in the detector.
Thus, we must begin these tests as soon as possible and do so for PMTs from several vendors.
PMTs from Hamamatsu are already at Brookhaven and sample PMTs from Photonis will be
ordered as soon the necessary arrangements are made with Photonis and funds are available.
These pressure measurements and the work in item (6) below are being carried out at Brookhaven
National Laboratory. Brookhaven is submitting a proposal to the Department of Energy for this
effort.

3) The measurement of the specific electronic characteristics of candidate PMTs will be carried
out at Columbia University under the supervision of Professor Janet Conrad. Funds for the
Columbia instrument are included in this proposal.

4) Based on the measured PMT characteristics, we will design the PMT deployment and mounting
system. Since the design of the PMT deployment system will effect the design of the chamber, the
two designs should be coordinated and should be completed before the chamber excavation is
carried out. In particular, the PMT deployment system will determine the location of the mounting
supports that must be cast into the concrete chamber lining. This design effort must also include
the access platform at the top of the chamber. This proposal requests salary for a design engineer
who will carry out and supervise this work.

5) The deployment/removal scheme critically impacts the electronic cable system, which, in turn
depends on the fraction of the electronics that is included in the PMT base or adjacent thereto, we
need to, at least, develop a conceptual layout of the electronics system. The initial design of the
                                                13

electronics system will be carried out the University of Pennsylvania High Energy Physics
Engineering Group.

6) We must develop a detailed event reconstruction and analysis program. Of course, this is not
required until data taking commences, but we need to see how these reconstructions and event
recognition are impacted by PMT spacing and arrangement. As indicated above, this work is part
of the Brookhaven proposal to the DOE.

Tasks (2) through (6), above, are not Laboratory site specific, and apply to any suitable
underground site. Task (1), or course, is specific to Homestake, but a similar task would apply to
any other site.

The above initial work plan is included in the budget justification that follows this proposal
description.

Budget Justification

1) Determination of rock characteristics – will be carried

Participants
The August 8, 2006 draft of this proposal, hep-ex/0608023, lists nine participating institutions,
Brookhaven, Brown, Berkeley, Pennsylvania, Princeton, UCLA, Wisconsin, Kansas and Colorado.
Since then several other institutions, Columbia, RPI, Utah, have joined several others have
expressed strong interest in doing so. The rapid participation growth is a strong indication of the
interest in this detector and the scientific program involved. We expect to establish a collaborative
structure in a timely manner and before any major construction decisions are reached.

Outreach
The topics and scope of this program are of broad, general interest and so should interest students
at various levels as well as the general public. A clear demonstration of that interest occurred
during testimony about this scientific program to the South Dakota Legislature at a public hearing
on January 19, 2005 and again at a Special Session on October 14, 2005. Members of the
collaboration will give talks about the goals of this program and how these relate to the
fundamental issues of the evolution of the Universe to both various school groups and to more
general public gatherings. The concept of a very long range neutrino beam traveling through the
Earth only to be detected 1300 km from its originating location is itself fascinating. The story
becomes even more so when neutrinos change characteristics during this flight and that these
changes may be connected the evolution of a Universe with equal amounts of matter and
antimatter into the matter dominated Universe in which we find ourselves.

We anticipate that undergraduates at each of the participating institutions will participate in the
assembly of detector components and will thus become familiar with the range of topics involved
in this program. In particular, we anticipate that elementary and secondary school students in
South Dakota will be exposed to the broad range of ideas encompassed by this program and will
                                                14

begin to recognize the linkages between various scientific topics addressed by this detector
system.
                                                         15



1
  “The Physics of the Universe, a Strategic Plan for Federal Research at the Intersection of Physics and Astronomy ”,
National Science and Technology Council Committee on Science, February 2004,
http://www.ostp.gov/html/physicsoftheuniverse2.pdf .
2
  “Neutrinos and Beyond – New Windows on Nature”, National Research Council Study, National Academies Press,
2003.
3
  “FY 2007 Administration Research and Development Budget Priorities”, J.H. Marburger, III and J.B. Bolten,
Executive Office of the President Memorandum, July 8, 2005,
http://www.ostp.gov/html/budget/2007/ostp_omb_guidancememo_FY07.pdf .
4
  M. Diwan et al., Phys. Rev. D. 68, 012002 (2003).
5
  M. Diwan, "The Case for a Super Neutrino Beam". Proceedings of the
Heavy Quarks and Leptons Workshop 2004, San Juan, Puerto Rico, 1-5, June (2004). hep-ex/0407047.
6
  W. Marciano, “Extra Long Baseline Neutrino Oscillations and CP Violation”, arXiv:hep-ph/0108181 v1, 2001.
7
  A. Strumia & F. Vissani, hep-ph/0503246 IFUP-TH-2005-06, Mar 2005.
8
  UNO EOI, http://nngroup.physics.sunysb.edu/uno/publications.shtml
9
  LAr Detector homepage, http://www.aquila.infn.it/icarus/exp.html
10
   Super Kamiokand detector homepage, http://www-sk.icrr.u-tokyo.ac.jp/sk/index_e.html
11
   SNO detector homepage, http://www.sno.phy.queensu.ca/
12
   C.B. Bratton et al., Phys. Rev. D 37, 3361 (1988); K. Hirata et al., Phys. Rev. D 38, 448 (1988)
13
   Probing Dark Energy via Neutrino & Supernova Observatories. Lawrence J. Hall, Hitoshi Murayama, Michele
Papucci, Gilad Perez (LBL, Berkeley & UC, Berkeley) . e-Print Archive: hep-ph/0607109
14
   T. Araki, et al., Nature Vol 436, No. 7050 (2005) p499.
15
   M.L. Constantini and F. Vissani, e-Print Archive: astro-ph/0508152


16
   M. Diwan, D. Beamis, M. Chen, J. Gallardo, R. Hahn, S. Kahn, H. Kirk, W. marciano, W. Morse, Z. Parsa, N.
Samios, Y. Semertzidis, B. Viren, W. Weng, P. Yamin, M. Yeh, W. Frati, K. Lande, A. Mann, R. van Berg, P.
Wildenhain, J. Klein, I. Mocioiu, R. Shrock, K. McDonald, PhysRev D68, (2003) 012002, also hep-ex/0303081
17
   M. Diwan, R. Hahn, W. Marciano, B. Viren, R. Svoboda, W. Frati, K. Lande, A. Mann, R. van Berg, J. Klein,
hep-ex/0306053
18
   M. Diwan, S. Kettell, L. Littenberg, W. Marciano, Z. Parsa, N. Samios, S. White, R. Lanou, W. Leland, K. Lesko, K.
Heeger, W. Lee, W. Frati, K. Lande, A. Mann, R. van Berg, K. McDonald, D. Cline, P. Huber, V. Barger, D. Marfatia,
T. Kirk, hep-ex/0608023 also BNL-76798-2006-IR
19
   A. de Bellefon, et. al., http://arxiv.org/PS_cache/hep-ex/pdf/0607/0607026.pdf

								
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