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%  SNO-ARC Science Subcommittee Report for December 1999 Meeting
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%  Versions
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%	0.1  12/12/99  Initial framework distributed to committee
%	0.2  14/12/99  Add Ed Kearns to list
%	0.9  15/12/99  Incorporate all the first drafts
%       1.0  23/12/99  Suggestions from first round of review
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\begin{document}
\title{The 1999 NSERC and SNO-ARC Science Review of SNO \\
{\small Version 1.0}}
%
\maketitle
%
\section*{Executive Summary}
%
A review of the Sudbury Neutrino Observatory was carried out on
8-9 December 1999 by a joint committee from NSERC (GSC-19 site visit)
and SNO-ARC (science  subcommittee).  We are pleased to report that SNO
has been commissioned and  began taking physics data in October 1999. 
This is the culmination of many years  of hard work and we extend our
congratulations to the collaboration.  The  science potential of SNO
continues to be high and the experiment should provide a solution to the
solar neutrino problem in the next 2-3 years. The committees  recommend
that funding both for site operations and for the Canadian university
groups be continued and that two year grants would be appropriate at this
time.

This year saw much progress at SNO.  A working solution to the potentially
serious high voltage breakdown problem was found in March, allowing 
commissioning to proceed.  The committees recommend that work continue on 
establishing a permanent solution, in case the connectors start to fail
prematurely. Several calibration runs have been done,
indicating that the detector is working very well and that the detector
can be operated at the necessary low energy trigger threshold.  The
required low levels of radioactivity have been attained in most cases
and where they have not (e.g. radon), the  collaboration is successfully
taking steps to continue to reduce them.  The analysis of the data is
progressing well, with emphasis given to calibrations and the 
identification of algorithms to eliminate background and/or spurious
events. The  analysis effort is well organized but suffers from a lack of
personnel, which is not unusual for a large project in transition
between construction, commissioning and data taking.  More scientific
effort, however, will have to be diverted to the data analysis in the
near future.

The collaboration has produced a long range plan extending over 3-4 years 
with roughly one year each allocated to running with pure \DtwoO, \DtwoO\
plus  MgCl$_2$, and pure \DtwoO\ with the $^3$He detectors.  Running with
light water is also planned once the heavy water is returned to AECL.  It
is crucial that  the lease agreement with AECL be extended to 2004, and it
is expected that this  will be settled by June 2000. The long range
plan should be improved by  setting clear milestones and criteria for
switching between the three running  configurations.

The collaboration has reorganized its management structure to address 
upcoming retirements and the reduction in the onsite presence of
senior  managers.  Deputies and/or assistants have been identified to
allow a smooth transition to a new management team.

In summary, the SNO experiment is now on-line and taking data.  The
remaining problems are typical for an experiment this size, and are
being  dealt with efficiently.  The biggest challenge facing the
collaboration is  the transition to the analysis phase of the
experiment.  The committees look  forward to seeing physics results from
SNO in the not too distant future.

\section{Introduction}
%
The NSERC Subatomic Physics Grant Selection Committee (GSC 19) and SNO
Agency Review Committee (SNO-ARC) commissioned independent reviews of the
Sudbury Neutrino Observatory (SNO) in fall 1999.  The NSERC review
follows on similar annual reviews that have been arranged by GSC 19 in
the context of the project grant renewals for the Canadian SNO
collaborators.  The SNO-ARC review was performed by a ``science
subcommittee,'' which has been recently established to give advice to both
SNO-ARC and SNO on the science and management of the project.  The
memberships of the two committees are listed in Appendices B and C.

These two committees coordinated their reviews so that a common set of
presentations by SNO collaborators were made to both committees on 8
December 1999. The committees then split up on December 9 for
presentations on funding (GSC committee) and more detailed discussions
on specific issues such as calibration and the long range plan
(SNO-ARC subcommittee).  The agenda for the two-day review is provided in
Appendix D.  A common set of recommendations on scientific and
technical matters was arrived at by the two committees, and so this
report documents the findings of the review.  In the case of the NSERC
review, Appendix A of this report details the committee's funding
recommendations to GSC 19.

The committees wish to thank the SNO collaborators and NSERC staff for
arranging a productive two-day review.  In the opinion of the two
committees, the needs of an NSERC GSC review and the SNO-ARC science
subcommittee review are so similar that a more efficient
process could be established.  Since the SNO-ARC science subcommittee
is an ongoing one, it is suggested that this committee be augmented by
two GSC members to perform the funding review in the future.

This report is organized as follows:  Section 2 describes the status of
the current science issues that SNO was designed to address.  Section 3
gives a brief status report on the various aspects of the experiment. 
Section 4 addresses issues related to the physics analysis effort,
section 5 addresses management issues and section 6 address the schedule
and long-range plan.  Section 7 summarizes the status of the HV
connectors and section 8 comments on the longer term science
opportunities of the SNO detector and site.  In section 9, we summarize
our recommendations.

\section{The Science}
%
A series of experiments, covering almost three decades of neutrino
observations of the sun, have established an electron neutrino
($\nu_e$) flux from the sun of about half the expected value.  The set of
available data cannot easily be reconciled with standard solar model (SSM)
calculations because they are incompatible with the existence of the
so-called $^7$Be neutrinos.  Moreover, the SSM appears robust from the
theoretical point of view and has been confirmed by helioseismology
studies.  Therefore, the assumption has been
that the solution to the ``solar neutrino problem'' resides with the
particle physics of the neutrino and not with the astrophysics of the
sun.  SNO has the potential to reveal the properties of neutrinos
responsible for the deficit in flux, with neutrino oscillations providing
the best motivated explanation.  The prospect that SNO provides the first
conclusive evidence for $\nu_e$\ oscillations has been reinforced by the
recent indirect observations of $\nu_\mu$\ oscillations in the atmospheric
neutrino flux.

In the last year, the chances that the competing SuperKamiokande
experiment will determine that the source of the solar neutrino deficit is
due to a specific oscillation scenario has
all but faded. Their much larger detector has made impressive
observations of the solar neutrino flux, confirming once more, the
$\nu_e$ deficit. But hints provided by the time and energy dependence of
the solar neutrino flux have not converged on a particular solution with
sufficient statistical or systematic accuracy. SNO has the next
opportunity, over the three-year timeframe described in its current
scientific plan, to resolve the solar neutrino problem as being due to
neutrino oscillation. It must make good use of this time, because new
experiments such as Borexino and KamLAND will turn on in this 3-year
period and have the potential to identify certain oscillation scenarios.

Using \DtwoO\ as a target, SNO has the unique capability to measure
both the flux of electron neutrinos via the charged current
(CC) interaction as well as the flux of other neutrino flavours via the
neutral current (NC) interaction.\footnote{The elastic scattering
process (ES) is an important third process that SNO has sensitivity to
at a significantly lower level than the CC and NC processes.}  SNO can
therefore observe the reappearance of the oscillating
$\nu_e$\ as a neutrino with a different flavour.  

The SNO collaboration has proposed a four-stage run plan that spans
the next 3-4 years to make these measurements.  In the first stage,
SNO will run with pure \DtwoO\ and make a CC measurement.  After
approximately one year of running, magnesium salt (MgCl$_2$) will be
added to the \DtwoO\ in order to raise the NC detection efficiency to
83\%.  The collaboration expects to take data for approximately one year
in this configuration.   In the third stage of the scientific plan,
neutron detectors (NCDs) will be inserted in the SNO detector to replace
the magnesium salt, resulting in a lower NC detection efficiency but a
potentially better separation of the NC events from events resulting
purely from $\nu_e$\ interactions.  The fourth stage would be a run with
just light water.

Even before a precise measurement of the NC rate is made in the second and
third phases, information about which oscillation models are viable could
be obtained with several thousand events recorded in pure \DtwoO. 
However, this observation alone is unlikely to be compelling or
definitive.  It is therefore important to determine how one decides the
duration of the pure
\DtwoO\ data taking with a stable and well-understood detector before
moving on to the definitive NC measurements.  During this
period, SNO will also provide information on the possible ``high-energy
anomaly'' observed by the SuperKamiokande collaboration in the form of an
excess of events with neutrino energies ($E_{\nu_e}$) above 12 MeV.  

Another path to identifying neutrino oscillation as the source of the
solar neutrino puzzle is to measure a distortion in energy spectrum,
which is well predicted by the nuclear physics of $^8$B beta decay.
Although the SuperKamiokande collaboration has not observed a
statistically significant distortion, it is hampered by the poor
neutrino-electron energy correlation in charged current electron
scattering. With an neutrino energy threshold of about 2 MeV, SNO has the
unique ability to use the CC absorption reaction (with a 1.44 MeV
$Q$-value) to recognize distortion in the neutrino energy spectrum due to
vacuum oscillations or certain matter-enhanced solutions. In addition,
the 2 MeV threshold provides additional leverage not available to
SuperKamiokande (currently triggering at a approximately 4.5 MeV and
analyzing data above 5.5 MeV). The SNO experiment should recognize this
opportunity and continue with their extensive calbration plan for the
lowest possible energy systematic uncertainty. Naturally, they should
also achieve the lowest possible analysis threshold.

In the near term, the SNO experiment can readily study the high energy end
of the $^8B$ spectrum, which should be more free of background. By
studying events above 13-14 MeV, they can potentially identify an
enhanced hep neutrino flux.

SNO has several other science missions that include measuring the
properties of atmospheric neutrinos and the detection of galactic
supernovae.  The scientific importance of observing a supernova with a
detector like SNO far outweigh the low probability that such an event
will occur during its lifetime.  The participation in the SNEWS early
warning network clearly enhances SNO's science reach, as it
will allow astronomers to make the important early observations that were
not possible with SN1987A. 

In summary, with its ability to detect neutrinos through their CC and NC
interactions, SNO holds the key to solving the solar
neutrino problem.  It will possibly provide the first direct observations
of solar neutrino oscillations.  The detector has started data taking
with an adequate time window to deliver results before competing
detectors will be commissioned.

\section{Detector Commissioning Status}
%
\subsection{Operations}

The SNO collaboration has made very good progress in commissioning the
detector over the last seven months since the water fill was complete. 
This was evidenced in all aspects of the experiment.  The team now is
focussed on understanding the detector and optimizing its performance.
Since the water fill was completed at the end of April 1999, all
detector subsystems have been commissioned and brought
into routine operation. Significantly, the last major changes to detector
configuration were made in the middle of October (the photomultiplier
tube (PMT) high voltage was increased by 100 V). Since then, the
collaboration has been operating the detector with increasing
efficiency, while at the same time calibrating the detector and measuring
background rates.

The significant problems with the high-voltage (HV) connectors seem to
have been solved (see Section 7).  An annoying source of of background
light has been traced to sparks arising from charging of the acrylic
vessel.  These have been largely eliminated and are no longer affecting
detector operations.

The electronics and data acquisition (DAQ) systems are operating smoothly,
with typical trigger rates in the neighbourhood of 15-20 Hz. 
The detector is operating with a trigger that requires at least
18 PMT's above pedestal threshold, corresponding to an energy threshold
near 2 MeV.  The ``livetime'' of the detector -- in this case the
fraction of time that the detector was ready to detect supernovae events
-- was reported to have reached 94\%\ in the month of November, an
impressive figure given the complexity of the detector.  Livetime for
solar neutrino collection was significantly lower due to conflict between
certain operations during calibration and normal data taking.  

The reviewers recommend that the collaboration determine the 
livetime for solar neutrino data-taking,  accounting for the effects
of calibrations and other activities that interrupt normal data-taking.  A
target livetime should be determined that optimizes the requirement to
fully calibrate the detector and collect the maximum amount of solar
neutrino data. 

The operations team appears to be well-managed and highly competent.  The
committees are confident that the necessary structure is in place to
operate the detector, although overall personnel resources are stretched
when one accounts for the large number of parallel tasks that must be
underway to support the calibration, operation and analysis activities.

\subsection{Calibration}
%
The SNO detector has an arsenal of calibration sources designed to
measure the optical response of the detector, its energy resolution and
background rates.   An understanding of the optical transmission and
detection of photons is a fundamental issue, and must be established
before a detailed energy calibration can be completed.  The optical
calibration, performed using a laser source and a diffuser ball suspended
in the \DtwoO, appears to be well understood, although this work is not
yet complete. The committees were shown preliminary results,
demonstrating that the agreement between observed
performance of the detector and the Monte Carlo (MC) predictions was at
the few percent level.  The non-uniformities of the illumination of the
source remain to be completely resolved, though a reasonable plan exists
to address this issue.

Three calibration runs using a $^{16}$N source
(producing a 6.1~MeV $\gamma$) have been performed, providing an energy
calibration at this energy with an uncertainty better than 6\%.  The
ultimate goal is an understanding of the energy calibration to an
uncertainty of 1\%, which requires periodic $^{16}$N runs and the
deployment of additional sources.  These calibration sources are:
\begin{itemize}
\item U and Th sources to measure the characteristics of the principle
backgrounds in the \DtwoO,
\item a ${\rm (p,t\gamma)}$\ source that provides a 20 MeV
$\gamma$\ calibration point,
\item a $^8$Li source to provide a $\beta$\ source with a continuous
spectrum to measure the efficiency of the ``data cleaning'' operations and
test the understanding of the detector's energy response, and
\item a number of lower-energy sources for background studies and
low-energy calibration points.
\end{itemize}
The collaboration's highest priorities are the analysis of the
existing calibration data and the deployment of the U, Th, ${\rm
(p,t\gamma)}$, and $^8$Li sources in order to meet its initial physics
milestones.  The reviewers agree with this strategy.

The collaboration noted that personnel resources may limit its ability to
implement these additional calibration sources on a schedule consistent
with the  milestone of June 2000, when the initial optical and energy
calibrations of the detector will have been completed.  The committees are
not convinced that the schedule is credible either, given the limited
number of personnel involved in the calibration effort.  The reviewers
recommend that the collaboration make every effort to identify additional
scientific personnel for this task to ensure that these additional
calibration sources are deployed and the calibration data are analyzed
promptly.

\subsection{D$_2$O, H$_2$O and Radioactive Backgrounds}
%
The  key to  the  SNO detector  is  the 1000  tonnes  of 
\DtwoO\ suspended  in a  spherical acrylic vessel  at the  centre of
7000 tonnes of light water (H$_{2}$O) shielding.  The light and heavy
water both  must be maintained  ultrapure for optical clarity  and low
background radiation.   The radioactivity in the water  is required to
be less  than one uranium disintegration  per day per  tonne of water.
The heavy water is valued at  \$300M and therefore has to be
accurately accounted for.  The heavy water is
insured against a catastrophic loss or  dilution with  light water, but
the cost  of restoring heavy water that has been  downgraded (diluted by
light water) or lost through normal operation is  considered part  of the
normal operating  and decommissioning costs.

The heavy  water itself is on loan  from AECL to the end of 2000. 
Negotiations  are underway to extend the loan, first to the end of 2001
and then to the end of 2004. The first  date is  well in hand and the
collaboration  is optimistic about achieving the second.

The  SNO water handling  team has  done a  highly professional  job of
designing,  building, commissioning and  operating the  water systems.
Moreover, they  have met a number of  significant challenges including
some unsuspected experimental conditions that became apparent once the
water was in place.  The most difficult task has been controlling radon
ingress from the mine air leaking into the gas volume above the light
and heavy water surfaces.

The  water  operations  require   a  specially 
trained  team  of  six operators, four assistants and  three others in
charge of maintenance, cleaning  and other  functions.  The  team works 
six  twelve-hour day shifts  and  three twelve-hour  night  shifts  per 
week.  The water system may only be run when there are at  least two
operators underground at  the experiment.  The ongoing  operations
include  running the  circulation systems  for the heavy  and light
water  and making  radioactive assays.   Recently the water team  has
moved one technician  to the surface to  help with the assay  chemistry.

The radiation  levels in the  water have improved and  are approaching
design.   Radon  levels are  an  important  indicator  of the  uranium
content of  the water, and weekly assays are scheduled.  Radon levels in
the \DtwoO\  have dropped to approximately the design criteria following
the stable  application of a flowing nitrogen cover gas for  the
\DtwoO.  This results in a  loss of 200~ml of 
\DtwoO\ per  day (\$60), an acceptable short-term consequence but clearly
not optimal.  The  radon in the  light water is nearing  design 
specification, with the largest source of radon appearing to  be from air
entering from the mine.  The  water  team  is working  on  sealing leaks
into the  light  water cover-gas volume. 

Assays for radium contamination in the \DtwoO\ are made to  estimate the
amount of uranium ($^{226}$Ra) and thorium ($^{224}$Ra) using MnO$_x$ and
seeded ultrafiltration techniques.   The uranium  assays  are at 
$10^{-15}$ gram U per gram water, well  below the required  levels.  The
thorium  assays have only  yielded upper limits that are  consistent with
the  required  levels.  A direct observation  confirming the thorium 
concentration is required, and the collaboration is working on a high 
flow system  with eight parallel  columns of
MnO$_x$\ to solve this problem.  A system to detect
lead is also being developed.

The  water team is  also developing  the plant  that will  produce the
MgCl$_2$ brine  and remove  it from the \DtwoO.  This  operation is
critical for  the NC measurement of  the second phase of  the SNO
experiment.  The system will be  reviewed in the next couple of weeks.
The schedule  calls for  the brine to  be produced and  underground by
September 2000.

The total inventory of heavy  water received from Ontario Hydro
is 1,106,484  kg.  The  isotopic purity of  the bulk water  is checked
regularly and  has not changed significantly.   Approximately 170 kg of 
heavy water has been  lost, mostly by  absorption in the acrylic  vessel. 
Further losses from evaporation  are expected to be 73 kg  per year.  The
cost of replacement  is approximately \$300  per kg.  Another 2025  kg
have been isotopically downgraded  as part of the initial  setup and due
to ongoing assays.   There is a further  30 kg that  is isotopically pure
but contaminated.  This water can be cleaned on site.

The downgraded water can be returned to Ontario Hydro for upgrading at
a cost of  \$8 per kg, so that the cost of upgrading the present
inventory  will be about
\$20~000.   The  SNO  collaboration  would  like  to 
start returning degraded  water to Ontario Hydro to reduce their stored 
inventory, but Ontario Hydro has requested a delay while it develops an
appropriate facility. Over  the longer  term, upgrading  costs are 
expected  to be  roughly \$10~000 per year.

\subsection{Neutral Current Detectors}
%
Construction of the neutral current detectors (NCDs) is proceeding well,
after the collaboration resolved a number of problems affecting the
series production of the counters over the last year.  Currently, 165 of
the required 300 detectors are completed and now underground in the mine.
Completion of the remaining counters is scheduled for fall 2000, well in
advance of when they would be required for insertion in the \DtwoO\
volume.


\section{Physics Analysis}
%
The SNO collaboration has put together a comprehensive
analysis plan, consisting of a series of ``supporting analyses'' and
a set of ``physics analyses.''  Working groups have been established for
each of the supporting analyses, although the personnel effort in many of
these groups is limited to only one individual (who in many cases has
multiple responsibilities).  Convenors have been identified for
organizing each working group, and a Gantt chart detailing the analysis
effort over the next three years has been developed.  Each  group
has clear goals and is working toward a common schedule and set of
milestones.

The organization of this analysis effort is an impressive first step
toward getting science out of SNO, and the reviewers applaud the
collaboration for the commitment to this structured process.  The
reviewers endorse the collaboration's commitment to use the SNOMAN
framework as the basis for all ``final, publishable analyses.''  The
collaboration was able to report significant progress on all major
analysis fronts: software and databases, detector support, calibrations,
data flow, data cleaning and event characterization.  They have set as
important milestones the completion of the optical calibration by April
2000, the energy calibrations by July 2000 and a preliminary measurement
of the CC and ES flux by February 2001.

However, much remains to be done and personnel resources appear to
be a limiting factor in analysis progress.  There are approximately 10
full-time personnel working on solar neutrino analyses, an additional 6
physicists working part-time on solar neutrinos, 4 physicists involved in
analyses of through-going muons, and 2 physicists working full-time on
the supernova watch.  Of these analysis efforts, the reviewers were
satisfied that sufficient resources were allocated to the latter two
topics.  However, the reviewers were very concerned that the analysis
effort on solar $\nu$'s was too dispersed and not sufficiently focussed. 
The collaboration reported that four independent groups were involved in
solar neutrino analyses.  Although it is important to have several
independent analyses on this topic, given it is where SNO is expected to
have the greatest scientific impact, the reviewers believe that four such
analyses are simply too many given the limited physicist
resources.  The reviewers recommend that the solar neutrino physics
analysis efforts be more focussed with a smaller number of independent
efforts.

\section{Management Issues}
%
The SNO collaboration has taken significant steps over the last year
to improve its management structure.  The Scientific Management Committee
and the Senior Executive Committee were replaced by a Scientific Board (SB)
that meets at least monthly.  The SB includes one representative from
each SNO institute, the national spokepersons, the scientific officers
(director, two associate directors and the analysis coordinator) and key
group leaders.  Two members are elected at large by the collaboration,
with the intent that they represent the junior members of the
collaboration. The scientific board is responsible for setting policy on
topics such as the length of data runs in each configuration of SNO, run
plans within each configuration, and publication and conference talks. 
The board's decision must be ratified by the collaboration.  This
management scheme seems to be working well.

The collaboration has also reorganized the supervision of the operation
of the water systems and the detector.  David Sinclair was appointed
as Associate Director - Science with overall responsibility for running
the experiment.  Tony Noble replaced Sinclair as Associate Director of
underground operations with main responsibility for the water systems.
Richard Van de Water is the head of the detector working group and is
responsible for the day-to-day operation of the detector systems.
Finally, Josh Klein is continuing as analysis coordinator.  This team
is effective and the committees feel that SNO operations run smoothly.

Last year's GSC site review committee expressed concern over the long
term staffing of key management positions related to the fact that
several individuals would have to return to teaching duties, or to 
retirements.  The SNO collaboration has responded to this issue by 
designating replacements and/or deputies for these key individuals,
and the situation seems to be in hand.

\section{Schedule and Longer Range Science Plan}
%
The SNO Collaboration presented to the review committees a four-stage
running plan.  In essence, the plan proposes taking data over the next
three to four years to attack the solar neutrino problem in four 1-year
periods:
\begin{enumerate}
\item running with pure \DtwoO,
\item adding MgCl$_2$\ to the \DtwoO\ to enhance NC detection,
\item deploying the $^3$He Neutral Current Detectors (NCD's) in pure
\DtwoO, and
\item running with pure H$_2$O.
\end{enumerate}
This plan is consistent with the overall scientific goal of SNO, which is
to determine independently the total flux of ``active'' neutrinos from
the neutral current (NC) interactions in \DtwoO\ and to compare this
with the flux determined only from the charged current (CC) interactions.

The scientific goals for each of the four stages outlined above are clear,
and are detailed below.

\subsection*{Running in Pure D$_2$O}
%
The scientific objectives for running with pure heavy water are:
\begin{itemize}
\item to measure the integral $\nu_e$\ flux with the CC interaction for
$\nu_e$\ with $E_{\nu_e}>7.5$~MeV,
\item to measure the energy spectrum with the CC interaction for $\nu_e$\
with $E_{\nu_e}>7.5$~MeV,
\item to measure the integral $\nu_e$\ flux with the 
ES interaction for neutrinos with $E_{\nu_e}>7.5$~MeV,
\item to make an initial measurement of the ES/CC ratio, and
\item to make an initial measurement of the NC/CC ratio.
\end{itemize}
This last measurement will require a proper understanding of the
radioactive
backgrounds.

This is a sensible initial programme, which will allow experience to be
gained with running the detector over an extended period in stable
conditions, and will also test the calibration, data reduction and data
analysis techniques. The results from the ES interactions could be compared
to the SuperKamiokande data.

A sufficiently precise measurement of the spectral shape could, in
principle, yield valuable information on the origins of neutrino
oscillations, but this probably requires a longer run than can otherwise
be justified given the importance of the NC measurements. There is a
risk that a measurement of the ES or NC rate, combined with the CC rate
and the SuperKamiokande data, will allow almost anyone to do ``quick and
dirty'' analysis to ``resolve'' the solar neutrino problem. The
collaboration therefore needs to have a clear strategy for deciding what
data can be shown publicly, consistent with the imperative to publish
important results as quickly as possible.

\subsection*{Adding MgCl$_2$}
%
By adding salt (MgCl$_2$) to the \DtwoO, the sensitivity to neutral
current events
is significantly enhanced. Techniques have now been developed that allow
the NC/CC ratio to be deduced statistically from the data, making this a
robust technique. The operation is relatively quick - it should take about
a
week to introduce the salt though a brine solution - and reversible -
it should talk about a month to remove the salt by reverse osmosis. This
should yield the first statistically significant measurement of the NC/CC
ratio.

Given that this procedure is relatively quick and could be repeated should
problems or inconsistencies arise, it makes sense to perform this test
early.  

The committees note that some concerns have been raised
earlier about the impact of the magnesium salt on the acrylic vessel, but
this issue was not addressed during the review.  The reviewers therefore
recommend that the SNO Collaboration prepare a memo to SNO-ARC that
addresses this issue.

\subsection*{Using the $^3$He Neutral Current Detectors}
%
The NCDs enhance the sensitivity for NC
detection by using $^3$He counters. This allows NC interactions to be
recognised on an event-by-event basis, and may help reduce the systematic
errors on the measurement of the energy spectrum.

The deployment of the NCDs is a major interruption to the schedule, and
is estimated to take about 3 months, during which time the detector will
be more exposed to mine air and SNO will not be able to
participate in the supernova watch.  The deployment is not easily
reversible if problems with their operation should arise.  However, the
NCDs will enhance the science reach of the detector and remain an
important element of the SNO experiment.

\subsection*{Running in pure H$_2$O}
%
The main objectives are to confirm the radioactivity backgrounds and the ES
measurements. It is clearly prudent to plan this at some stage, but for
practical reasons this should be done last.
%
\subsection{Discussion and Recommendations}
%
The proposed long-range plan defines a coherent programme for achieving the
scientific goals of the experiment. However, the Committee was not given
sufficient detail to be able to judge whether this ambitious programme was
realistic in the timeframe suggested.  The committees make the following
comments and recommendations: 
\begin{enumerate}
\item The committees endorse the general strategy for the NC
measurements. In particular, the committees believe that it is essential
that the  MgCl$_2$\ run be completed before deployment of the NCD's.
%
\item The committees are concerned that there is no set of criteria which
determines the time at which the change over from pure \DtwoO\ to
\DtwoO+MgCl$_2$\ takes place.  They recommend that these criteria be
identified.
%
\item The committees recommend that a set of milestones be
developed against which progress for at least the first two stages of the
long-term plan can be measured and monitored. The committees recognise
that this is an ambitious programme, and are concerned that without a
clear schedule against which to operate, the scientific goals might be
compromised.
%
\item The committees believe that it will take until at least 2004 to
complete this programme of work, and that it is therefore important to
negotiate by June 2000 an extension of the lease of the \DtwoO\ until at
least 2004.
\end{enumerate}


\section{Photomultiplers, Bases and the HV Connectors}

In late 1998, very serious problems were observed associated with
``wet-end breakdown'' in the HV connectors leading into the
photomultipler tube (PMT) bases. Since March 1999, when the regassing
with nitrogen of the light water that surrounds the PMTs, the breakdown
problem in the connectors has been dramatically reduced. The detector has
operated stably with minimal problems from high voltage breakdown or tube
loss since that time. The PMT death rate, from all causes, based on about
6 months of operation, is presently 0.4\% per year or about 1 per week,
well in line with other large water detectors. Wet-end breakdowns still
occur so there is no evidence that the HV problems are completely solved
but there is no indication at this time that a connector replacement
program will be needed.

The SNO collaboration has followed the recommendations of the External
Advisory Committee on the High Voltage Connector, which reported to
SNO-ARC in April, 1999.  The first recommendation was to implement
automated tools that would monitor the HV breakdown phenomena.   Several
on-line and near-line monitoring tools have been implemented to track
high voltage effects such as the presence of ``sharkfin'' pulses and
blown terminator resistors in the PMT base to give an early warning of
the onset of problems.

Sharkfins are large charge pulses generated in the absence of light,
which are assumed to be due to micro-discharges in the connector. They
appear as events in the ESUM trigger and can be monitored with the random
PULSE\_GT trigger. As they are characterized by a large ($>100$~mV) pulse
in one channel with pick-up in several nearby channels on the same HV
distribution card, they can be easily identified and separated from the
neutrino interactions during the data cleaning process. The wet-end
breakdowns are known to first blow the 75~$\Omega$\ terminating resistor
in the PMT base after tens of discharges and this can be monitored by
reflection tests or by checking for gain increases in a channel, since
the loss of this resistor causes the gain to double. If the
sparking persists, a 100 k$\Omega$\ series resistor can fail, causing
the tube to become inoperable.  Another potential problem leading to tube
loss is a water leak into the connector or PMT base, which causes a HV
short.

The most serious potential source of background to neutrino data are
``flashers,'' which are believed to be light-emitting breakdowns inside
the PMT. The light is picked up in several surrounding tubes and in tubes
on the opposite side of the detector. These are not related to
problems with the HV connector.  A significant fraction of
the tubes exhibit flasher behaviour, and it has been observed that seismic
activity increases the rate of flasher events. A sufficiently large
number of tubes are involved when a flasher occurs that the event is
likely to satisfy the event trigger and be recorded. The flasher
signature has now been well characterized so that these events can be
removed during the data cleaning, although the efficiency of doing this
has not been determined as yet.

In October 1999, the voltages on all PMTs were increased by 100~V to
improve the signal/noise and provide the design sensitivity threshold of
0.25 photoelectrons. During this increase the HV phenomena were closely
monitored.  Both the sharkfin and flasher rates increased and then
settled to acceptable rates; sharkfin rates increased from 1.5~Hz to
2.5~Hz and flasher rates rose from 30 per hour to 50 per hour. The tube
loss rate since that time has not noticeably increased. There are
presently 160 PMTs not functioning in the detector, with most of these
due to failures before the regassing was carried out in March.

The External Advisory Committee on the HV
Connectors made two other recommendations:  The SNO
collaboration was to develop and test a replacement high voltage
connector, and to produce an implementation plan showing the cost and
time impact if a repair were necessary. A new connector design has been
produced but only variations of this connector have been tested to date.
A draft report on the SNO Detector Connector Repair was submitted to the
SNO collaboration and to the SNO-ARC science subcommittee at this meeting.
The main conclusions/recommendations of the draft report, which still
needs to be reviewed by the collaboration, are as follows:
\begin{itemize}
%
\item If a connector repair is required, a new wet-end male
connector/full cable assembly replacement represents the best
understood methodology at this time. (We note that this is solution
1. as recommended by the External Advisory Committee.)
%
\item A dry repair with full cable assembly replacement will cost 5.18
million 1999 Canadian dollars, and will take 12.5 months of detector
non-operation.
%
\end{itemize}

The committees make the following recommendations:
\begin{enumerate}
%
\item The SNO Collaboration should continue the close monitoring of the
detector HV performance.
%
\item The SNO Collaboration should complete the development and
fabrication of the production prototype of the replacement connector and
test 10-20 of these, first in an initial long-term test to be
completed in 6 months and then in the SNO detector using the Berkeley
underwater test sleds.
%
\item The External Advisory Committee on the High Voltage Connector
should continue to receive bi-monthly reports on the HV performance.
%
\item If a HV connector repair is required, a review of the detector
repair plan be performed.
%
\end{enumerate}

\section{Future Science Opportunities}
%
SNO represents a unique scientific resource, due to the low
radioactive background levels achieved in the clean-room conditions of
the underground laboratory and the low cosmic-ray backgrounds due to its
2-km depth.  In addition, the underground laboratory is a
well-instrumented and serviced location, and is well-integrated into the
SNO surface facility.  It therefore provides numerous scientific
opportunities for future astrophysics and particle physics experiments.
At the same time, one has to keep in mind the significant cost associated
with operating the underground laboratory and the fact that it is located
in an operating INCO nickel mine.

No formal plans are in place for possible future projects that may be
well-suited to the underground laboratory.  The committees therefore
recommend that SNO-ARC initiate discussions with the various
``stake-holders'' in order to assess the quality and scope of possible
extensions of the current scientific mandate of the SNO underground
facility.  These discussions should probably include the SNO
Collaboration, INCO, the various funding agencies and the scientific
community.  This is not urgent, but given the long timescales of typical
astrophysics and particle physics experiments and the expectation that a
long-range planning process will commence in the Canadian subatomic
physics community in 2000, it is appropriate to define a process that
will allow SNO-ARC to understand the potential future value of the
science that can be done in the underground laboratory beyond the current
SNO experiment.

\section{Summary of Recommendations}
The recommendations outlined in the report are summarized here:
\begin{enumerate}
%
\item The collaboration review the personnel requirements for the
deployment of the highest priority calibration sources (U, Th, 
${\rm (p,t\gamma)}$, and $^8$Li) and the associated analysis efforts.
%
\item The reviewers recommend that the collaboration determine the 
livetime for solar neutrino data-taking,  accounting for the effects of
calibrations and other activities that interrupt normal data-taking.  A
target livetime should be determined that optimizes the requirement to
fully calibrate the detector and collect the maximum amount of solar
neutrino data. 
%
\item The collaboration focus the solar neutrino analysis efforts to make
use of limited personnel resources in as effective a way as possible. 
The number of independent analyses should be reviewed and reduced.
%
\item The committees endorse the general strategy for the NC
measurements. In particular, the committees believe that it is essential
that the  MgCl$_2$\ run be completed before deployment of the NCD's.
%
\item The committees recommend that a set of criteria be developed that
determines the time at which the change over from pure \DtwoO\ to
\DtwoO+MgCl$_2$\ takes place.
%
\item The committees recommend that a set of milestones be adopted
against which progress for at least the first two stages of the long-
term plan can be measured and monitored. The committees recognise that
this is an ambitious programme, and is concerned that without a clear
schedule against which to operate, the scientific goals might be
compromised.
%
\item The committees believe that it will take at least until 2004 to
complete this programme of work, and that it is therefore important to
negotiate by June 2000 an extension for the use of the \DtwoO\ until at
least 2004.
%
\item The collaboration prepare a memo to SNO-ARC regarding the effect
of the magnesium chloride on the acrylic vessel.
% 
\item The collaboration should continue the close monitoring of the
detector HV performance.
%
\item The collaboration complete the development and fabrication of the
production prototype of the replacement connector and test 10-20 of
these, first in an initial long-term test to be completed in 6
months and then in the SNO detector using the Berkeley underwater test
sleds.
%
\item The External Advisory Committee on the High Voltage Connector
should continue to receive bi-monthly reports on the HV performance.
%
\item If a HV connector repair is required, a review of the detector
repair plan be performed.
%
\item SNO-ARC initiate a dialogue with the appropriate ``stake-holders''
in order to assess the quality and scope of possible extensions of the
current scientific mandate of the SNO underground facility. The next 12
months would be a suitable timeframe for initiating this discussion.
%
\end{enumerate}

\section*{Appendix A:  Funding Recommendations}
This section is only made available to members of GSC 19.

\section*{Appendix B:  Membership of SNO-ARC Science Subcommittee}
%
\begin{itemize}
	\item Prof. Pekka Sinervo, Department of Physics, University of Toronto
(chair)
	\item Dr. Ewart Blackmore, TRIUMF
	\item Prof. Francis Halzen, Department of Physics, University of
Wisconsin 
	\item Prof. Ed Kearns, Department of Physics, Boston University
	\item Prof. John Martin, Department of Physics, University of
Toronto
	\item Prof. Ken Peach, Particle Physics Department, Rutherford
Appleton Laboratory
%
\end{itemize}

\section*{Appendix C:  Membership of the NSERC SNO Review Committee}

\begin{itemize}

	\item Dr. Michel Vetterli, TRIUMF (chair)
	\item Prof. Enrico Bellotti, Department of Physics, University of Milano
	\item Prof. Patricia Kalyniak, Department of Physics, Carleton
University
	\item Prof. Richard Keeler, Department of Physics and Astronomy,
University of Victoria
	\item Prof. Jim Waddington, Department of Physics, McMaster University
	\item Ms. Kate Wilson, Team Leader for Subatomic Physics and Astronomy,
NSERC (observor)
\end{itemize}

\section*{Appendix D:  Agenda for Review}
\begin{verbatim}
Wednesday, Dec.8th: SNO Project Status
--------------------------------------

 9:00 Committees in camera (15)
       - organisation of the two committees

 9:15 Introduction  A.B. McDonald (15)
 
 9:30 Status of Experiment (35) D. Sinclair
       - overview of commissioning
       - status of outstanding problems from last year
       - what new problems have arisen?
       - prospects for physics results

10:05 Water (35) T. Noble
       - rate of loss of D2O
       - status of degradation
       - assays: time & number
       - contamination levels
       - status of MnO2 fabrication
       - status of MgCl2

10:40 COFFEE

10:55 Detector (30) R. Van de Water
       - PMT's (status of HV breakdown)
       - electronics & DAQ
       - monitoring

11:25 DAQ (15) A. Hamian
       - DAQ status
       - Future development

11:40 Analysis (45) J. Klein

       Organisation

       Technical:
       - status of software & databases
       - status of data reduction
       - online analysis

       Physics:
       - analysis chain & software
       - Monte Carlo studies
       - prospects for physics results

 12:25 LUNCH

 1:25 Calibration (30) A. Hallin
       - what has been done?
       - current development of new sources
       - future sources

 1:55 3He Detectors, U.S. Status H. Robertson (15)

 2:10 Discussion of morning session (20)


 2:30 Scientific Priorities & Strategy (45) A. McDonald
       - Time required for CC measurement
       - Competition
       - Neutral Current Measurement

 3:15 COFFEE

 3:30 Special Topics
       - Supernova Detection (15) C. Virtue
       - Muons, Atmospheric Neutrinos (15) C. Waltham

 4:00 Discussion of afternoon session (30)

 4:30 Committees in camera (60)

 5:30 Close-out meeting

 5:45 Adjourn

 7:00 Working Dinner

Thurday, Dec.9th
----------------

 9:00 Committees in camera (60)

10:00 COFFEE

The two committees will split at this point.

Schedule for GSC Committee
-------------

Operations Grant:
----------------

10:15 Site Operations Grant (60) McDonald, Sinclair, Hepburn,
Noble
       - Services funded by this grant
       - Staffing requirements
       - Budget
       - Organisation

Institutional Grants:
--------------------

11:15 Overview (20) A. McDonald
      - Group responsibilities
      - # of people to satisfy these responsibilities
      - Typical travel costs  

      This information should be given in tables we 
      can refer to in later presentations.  Questions 
      to be reserved for individual groups.

11:35 Queen's (20) A. Hallin

11:55 Carleton (20) D. Sinclair

12:15 LUNCH

 1:15 Guelph (20) J. Simpson

 1:35 Laurentian (20) D. Hallman

 1:55 UBC (20) C. Waltham

 2:15 General Discussion

 2:45 COFFEE

 3:00 GSC Committee in camera (60)

 4:00 Close-out meeting

 4:15 GSC Committee in camera (60+)

      Adjourn when required for travel



Thursday, Dec.9th

Schedule for SNO-ARC Sub-Committee
----------------
 9:00 Committees in camera (60)

10:00 COFFEE

The two committees will split at this point.

SNO-ARC Science Sub-Committee
-----------------------------
10:15 - 11:30  SNO-ARC Committee Meeting in camera

11:30 - 12:15 LUNCH

12:15 - 2:15 

Calibration Details (A. Hallin) (20)
       - Status of all calibration systems
       - Detector tuning 

HV Connectors (R. Helmer) (20)
       - Status of HV connectors

  Run Plan (D. Sinclair) (30)
       - Priorities for next year and schedule
       - Resources plan (personnel, responsibilities)

  Review of Plan for Neutral Current Detection (A. McDonald)(30) 
       - Update on plan and schedule
       - Progress on run sequence

  Discussion of Possible Future Projects (A. McDonald) (20)
       - What experiments are possible to augment SNO
       - New projects running parasitically in mine
       - Proposed strategy for review and approval 

 2:15 General Discussion

 2:45 COFFEE

 3:00 SNO-ARC Committee Meeting in camera

 4:00 Close-out
\end{verbatim}

\end{document}

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