reply to the recommendations of the scientific standing ...mjg/km3net/esfri/km3net...
TRANSCRIPT
Reply to the recommendations of the Scientific Standing Committee
V2.4
KM3NeT
11/20/2012
Contents Executive summary .............................................................................................................................1
Status of the project ...........................................................................................................................2
Agreement on the baseline technology .......................................................................................2
Technical description of the baseline technology ........................................................................3
Concept of building blocks ..........................................................................................................4
Reliability ....................................................................................................................................5
Cost ............................................................................................................................................6
Funding .......................................................................................................................................7
Sites ....................................................................................................................................................8
Visibility ......................................................................................................................................8
Water transparency ....................................................................................................................8
Optical background ................................................................................................................... 10
Atmospheric muon background ................................................................................................ 12
Summary................................................................................................................................... 13
Recommendation 1........................................................................................................................... 14
Recommendation 2........................................................................................................................... 18
Recommendation 3........................................................................................................................... 20
Recommendation 4........................................................................................................................... 21
Recommendation 5........................................................................................................................... 23
Recommendation 6........................................................................................................................... 24
Recommendation 7........................................................................................................................... 25
Recommendation 8........................................................................................................................... 26
Recommendation 9........................................................................................................................... 27
Recommendation 10 ......................................................................................................................... 28
Bibliography...................................................................................................................................... 29
1
Executive summary
KM3NeT is a large international effort with a challenging and compelling objective: The discovery of
neutrino sources in the Universe. The strong scientific case of KM3NeT has been recognised in
national and European roadmaps, in particular those of ApPEC, ASTRONET and ESFRI. The
infrastructure will be shared by a multitude of other sciences, including oceanography, geophysics,
and marine sciences. The total costs of the construction of the infrastructure is estimated at 220 M€.
Following the EU funded Design Study (2006–2009) and Preparatory Phase (2008–2012), the
consortium has agreed to use the available funds (40 M€) for the first construction phase. To this
end, an agreement on the baseline technology was reached and a memorandum of understanding
(MoU) will be presented to the Funding Agencies shortly. The phase-1 MoU is a first step towards the
intended establishment of a European Research Infrastructure Consortium (ERIC). It constitutes a
stepping stone towards the realisation of phase-2: The completion of the infrastructure.
Based on reasonable modelling of known astrophysical sources, the figure of merit of KM3NeT
phase-2 can be summarised as a 5-sigma discovery of a neutrino source within 5 years. Three
suitable sites in the Mediterranean Sea have been identified, namely Capo Passero, Pylos and
Toulon. The optical backgrounds have been measured at the three sites, the previous data on the
water transparency have been scrutinized and the effects of the optical and the atmospheric muon
backgrounds have been quantified. The costs for the construction and operation of the infrastructure
have been worked out and the financial consequences of using more than one site have been
addressed. The overall conclusion is that the advantage of additional funding and human resources
resulting from adopting a multi-site solution significantly outweighs any financial or scientific
advantage from adopting a single site solution. The operational costs of a distributed network of
neutrino telescopes in the Mediterranean is estimated to be about 3% per year of the total
investment. The feasibility of neutrino astronomy with a detector in the Mediterranean Sea was
proved by the successful deployment and operation of the ANTARES prototype detector. KM3NeT
phase-1 will demonstrate the feasibility of a distributed network of neutrino telescopes in the
Mediterranean Sea. KM3NeT phase-2 can be realized by 2020, depending on the availability of
additional funds . A case study for low energy neutrino detection (ORCA) will be presented in a
separate document.
In the framework of the Preparatory Phase, the progress of KM3NeT has been reviewed by an expert
panel: The Scientific Standing Committee (SSC). In February 2012, the SSC produced a report
containing ten recommendations. This document summarises the work that has been done and the
decisions that were taken in addressing these recommendations.
2
Status of the project
Agreement on the baseline technology
As the major deliverable of the KM3NeT Design Study (2006–2009), a Technical Design Report (TDR)
was completed and publicised in 2010 (1). It describes three alternative technical solutions for the
detection units of the KM3NeT neutrino telescope, specifies the requirements and conceptual design
of the seabed network and the shore infrastructure and presents integration/construction
procedures and cost breakdowns.
During the KM3NeT Preparatory Phase (2008–2012) technical work was pursued towards pre-
production models of optical module and detection unit. According to an agreement concluded in
2009, this work concentrated on an optical module design with multiple small (3-inch)
photo-multiplier tubes (PMTs) and integrated front-end electronics (so called multi-PMT digital
optical modules) and on detection units with horizontal bars interconnected by a tetrahedral
arrangement of ropes (flexible towers). In parallel, also the option of strings (two parallel ropes
supporting single optical modules) was pursued in compliance with SSC Recommendation 2b.
In late 2011 it became clear that about 40 M€ will be available for a first construction phase of
KM3NeT. More than 50% of this amount is provided through the European Regional Development
Funds (ERDF), implying that this money must be spent until end 2014 and that regional restrictions
apply for tenders and orders. Specifically, 21 M€, 8 M€, 8.8 M€ and possibly 2 M€ are available in
Italy, France, the Netherlands and Romania, respectively; of these, 21 M€ and 4 M€ come from ERDF
sources in Italy and France.
In June 2012 the scientific representatives of countries with confirmed funding commitments met in
Erlangen to shape a common project under consideration of these constraints and the current status
of the technical work. The following was concluded at this meeting and endorsed by the Funding
Agencies at a meeting in Paris in July 2012:
‒ The string with multi-PMT optical modules is considered as the baseline KM3NeT detection
unit design. This decision – which revises the agreement of 2009 – was mainly motivated by
technical problems related to the integration of multi-PMT optical modules into the tower
structure.
‒ The Italian regional budget will be used to realize a seafloor network at the Capo Passero
site, and several detection units (towers and strings). The seafloor network at the Capo
Passero site will be made compliant with both strings and towers. The towers will be
equipped with single-PMT optical modules (TDR design). Their deployment serves two
purposes: (i) demonstrate to the Italian authorities construction activity as soon as possible
to secure the ERDF funding and (ii) validate the tower structure as a fallback option for the
spending of the Italian ERDF funding should the string technology not be validated in time.
The tower construction will be planned in a staged way in order to switch to the string design
at any time and as soon as it has been validated. The Italian groups will contribute to the
validation of the string design in order to adopt this technology as soon as possible.
3
‒ The seafloor network at the Capo Passero site will accommodate an additional number of
strings produced by the KM3NeT collaboration, at least equal to the number of strings
realized with the Italian regional budget.
‒ The French budget for a neutrino telescope in the scope of the KM3NeT-MEUST project will
be used to realize a shore station, a seafloor network in the Toulon area and several string
detection units. The seafloor network at the Toulon site will be designed to accommodate
string detection units.
‒ Netherlands and Romanian budgets will be used for the construction of string detection
units.
It was decided that this agreement will be the basis for a Memorandum of Understanding (MoU) for
KM3NeT phase-1. This MoU will not cover activities related to the validation and realization of
towers. These will be covered by a separate Italian project. It was recognised that the MoU must
allow groups that have not received funding yet to join the KM3NeT phase-1 collaboration with a
status appropriate to their expected contributions and commitments during phase-1. In particular
the groups in Germany, Greece and Spain will be invited to join the collaboration.
Meanwhile, multi-PMT optical module prototypes are about to be integrated in ANTARES, deployed
and operated. A string-design detection unit prototype will be connected to the ANTARES seabed
infrastructure in 2013. Another deployment of this prototype is foreseen at the Capo Passero site.
Technical description of the baseline technology
The KM3NeT infrastructure will consist of a large number (about 10,000) of optical modules that will
be deployed in the Mediterranean Sea at a depth between 2 and 5 kilometres. An optical module
consists of a 17 inch glass sphere housing 31 small PMTs, various instruments and all necessary
electronics. Each PMT has a low-power base for HV, signal amplification and signal discrimination.
The TDC functionality is implemented inside an FPGA that has a time resolution of 1
12ns. All
analogue pulses that pass a preset threshold (typically 0.3 photo-electrons) are digitised and all data
are sent to shore where they are processed real-time using a farm of computers. This concept is
commonly referred to as “All-data-to-shore”. Each optical module requires about 10 W of power and
has 1 Gb/s readout bandwidth. The different readout channels are multiplexed using DWDM
technology. A detection unit consists of two vertical ropes with a length of about 1 kilometre which
support up to 20 optical modules with a spacing of 30–40 metres. This configuration is referred to as
a string. A cable is required for the fibre-optic readout and electrical power of the optical modules of
a string. This cable, referred to as the vertical electro-optical cable, runs along the ropes and has a
break-out at each optical module.
4
Concept of building blocks
The detector can be considered as a 3 dimensional array of optical modules. In general, the
configuration of such an array is defined by 1) the number of optical modules on each string, 2) the
vertical spacing between the optical modules along a string, 3) the number of strings and 4) the
horizontal spacing between strings. A study has been made of the detection efficiency as a function
of these four parameters for various absorption lengths (2). It was found that for an assumed signal
from RXJ1713-39.43 and fixed horizontal (100 m) and vertical (40 m) spacing , the detection
efficiency – normalised to the number of optical modules – gradually improves with the number of
optical modules per string and the number of strings up to a certain point where it flattens out.
Beyond 18 optical modules per string and 120 strings per detector block, the normalised detection
efficiency no longer improves. This result is primarily due to the assumed energy spectrum which is
rather hard and has a well defined end-point. Such a spectrum is, however, characteristic for that of
any known candidate source in our Galaxy, such as Super Nova Remnants. Hence this result generally
applies to the most promising neutrino sources.
A similar result was found in earlier studies in which detector geometries with a fixed number of
towers subdivided into independent blocks composed of 50, 100 and 154 towers were investigated.
It was found that the time needed for a discovery decreases with the number of towers per block up
to about 100 towers and then flattens out (3).
The limited size of an optimally efficient detector compared to the envisaged size of the complete
infrastructure (about 1/5) makes it thus possible to define building blocks. A building block is the
smallest size detector with an optimal efficiency. These building blocks can then be distributed in
compliance with the funding constraints without loss of the figure of merit. The overall impact of a
multi-site solution is thus limited to finances and management.
5
Reliability
The KM3NeT infrastructure should operate for at least 10 years, without significant degradation, at
depths up to 4.5 km in the chemically aggressive deep-sea environment. This imposes the necessity
of strict quality standards on each subsystem within the detector. To meet these standards, a quality
assurance (QA) system is being implemented to cover each step of the detector production,
transportation, deployment and operations. A detailed discussion on these issues has already been
presented in the TDR.
The experience obtained during the construction phase of the ANTARES telescope has demonstrated
the utmost importance of a strict QA framework. In particular, the establishment of local quality
control supervisors at the various production sites, a thorough follow through of non-conformities
and detailed tracking of the logistics via a database, proved invaluable for the successful completion
of ANTARES. The return of experience from the operation of the ANTARES telescope during the last
seven years demonstrates that such a large scale infrastructure can indeed be operated over long
time scales. For example, the ANTARES junction box is operational since 2002 and the first detection
line since 2006.
Compared to the ANTARES design, the KM3NeT baseline technology offers many improvements in
reliability, which include:
‒ The number of potential leak points (e.g. glass feed-throughs) has been reduced by a factor
of four;
‒ The complexity of the offshore electronics has been considerably reduced and in particular
the DWDM communication lasers are now all located onshore;
‒ The vertical electro-optical cable incorporates individual fibres for each optical module, so a
fibre breakage only induces a loss of single optical module;
‒ The lower operational gain of the PMTs will reduce ageing effect;
‒ The operating temperature of the electronics is reduced;
‒ The floatation is distributed along the length of the string, consequently a failure of the buoy
is not dramatic;
‒ The deployment of a furled string rather than a unfurled string also significantly reduces the
safety risks associated to the deployment procedure.
The use of more than one site also offers advantages. For example, a failure of a deep-sea cable
limits the loss of data to a single building block. Different sites allow for multiple deployment
capabilities. Consequently, the unavailability of a remotely operated submarine vehicle (ROV) or boat
only delays construction of a single building block. Finally, multiple sites offer redundancy in the case
of rare events such as Earthquakes, subsea landslides, whale collision with infrastructure, fishing net
entanglement, exceptional bioluminescence activity, etc.
6
Cost
The relative costs of the various detector components are summarised in Table 1 for a detector
consisting of multi-PMT optical modules and strings (3).
% total costs
Shore station (incl. computing) 6
Deep-sea cable network 12
Deployments 13
Detection units (without PMTs) 34
PMTs (incl. base and lens) 35
Table 1: Relative costs of components.
As can be seen from Table 1, the relative cost of the PMTs is 35%. The larger this fraction is for a fixed
price per unit photo-cathode area, the more cost effective is the design. In comparison, it is about
1.5 times better than for a detector consisting of optical modules with one large PMT. This result is a
feature of the multi-PMT optical module design. There is simply three times more photo-cathode
area inside a single glass sphere compared to an optical module with one large PMT. So, for a
detector with the same total photo-cathode area, one needs three times less glass spheres which
reduces the overhead of feed-throughs , cables, mechanical components, etc. In first order, the
performance of the detector scales linearly with the photo-cathode area. Hence, a detector
consisting of multi-PMT and strings yields, for the same price, a sensitivity that is 1.5 times better
than a detector consisting of large PMTs.
Three manufacturers have been identified that can make PMTs for KM3NeT. ETEL, Hamamatsu and
HZC have agreed to develop a new PMT with a low price. Both ETEL and Hamamatsu have produced
PMTs that comply with the specifications. HZC will deliver the first PMTs before the end of 2012.
Today, the price of small PMTs per unit photo-cathode area is competitive (if not better) than that of
large PMTs.
The relatively low cost of the detection units is partially due to a home-made vertical electro-optical
cable (a commercial cable would be about five times more expensive). At the moment of this writing,
the first in situ tests of this cable are ongoing. In compliance with the validation program of the
baseline technology (see below), this cable should be validated mid 2013.
It should be noted that the costs of the deep-sea cable network consist of two components, namely
the main cable to shore and the network to connect the detection units to a junction box. In any
distribution of the building blocks, i.e. single- or multi-site, one main cable is required for each
building block either for practicability or for redundancy. Furthermore, the cost for the network is to
good approximation proportional to the total number of detection units. Also the costs for the real-
time computer farm scales approximately with the total number of detection units. Finally, the costs
for the civil engineering for the shore stations in Toulon and Capo Passero are already partly covered.
As a result, the cost difference between single- and multi-site is small and estimated to be less than
10% (3). It should be noted that this cost difference can, to a large extent, be attributed to the costs
of parallel sea operations. The additional costs may therefore speed up the construction. If so, this
will in turn reduce the quoted cost difference. The cost difference between single- and multi-site is
7
therefore inconsequential and a central management is foreseen to handle any additional complexity
due to a multi-site solution (see Recommendation 6).
The All-data-to-shore concept has been implemented successfully in ANTARES. The main features
include the simultaneous operation of different triggers without dead time and access to all data for
every triggered event. For KM3NeT, the access to all data (rather than only local coincidences) yields
a net gain of the detection efficiency of about 50% for neutrinos with energies in the range 1–10 TeV.
The cost of the complete readout system is about 10% of the total costs whereas the gain is 50%.
Hence, the implementation of the All-data-to-shore concept is cost effective.
In general, the number of persons to operate a neutrino telescope is small. It typically requires one
or two persons for a fraction of the day. Most of the time, data are autonomously taken and sent to a
computer centre. The operational costs of (a distributed network of) neutrino telescopes in the
Mediterranean is therefore small. It is estimated to be about 3% per year of the total investment.
The low operational cost is in part the result of the design (low power consumption and high level of
reliability) and in part the result of cheap access to the shore stations. The remote access to the
facility makes it possible to operate the detector and analyse data from home and further reduce the
operational costs. As an example, ANTARES is operated remotely for more than 50% of the time.
Funding
‒ The Netherlands have committed 8.8 M€ to KM3NeT of which 1.7 M€ is earmarked for
prototyping, 0.8 M€ for setting up of assembly lines, 5.7 M€ for production of detector units
and 0.6 M€ for deep-sea instrumentation. A proposal to re-allocate 0.7 M€ of the available
funds for the instatement of the KM3NeT head quarters in the Netherlands was approved.
‒ France has committed 8.0 M€ to KM3NeT phase-1 with the following allocation: local
infrastructure 3.8 M€, prototyping 0.8 M€, detector units 2.4 M€ and sea science 1.0 M€.
‒ Italy has already invested about 8 M€ in the construction of KM3NeT related infrastructures:
shore station in Capo Passero, deep-sea cable, prototype of the power system and
acquisition of a 4000 m depth rated ROV. A funding of 20.8 M€ was obtained for the
construction of a first part of the KM3NeT infrastructure in Sicily. These are structural funds
allocated within the 2007–2013 programme and have, therefore, to be spent before the end
of 2014. Of these funds, 6 M€ will be used for the construction of a first set of towers as
described previously, the rest will be committed to KM3NeT phase-1 with the following
repartition: 8 M€ for strings with multi-PMT optical modules (pending validation of the
baseline technology in time for the funding time frame), 3 M€ for the seafloor network
(adapted to host both towers and strings), 3 M€ for sea operations and 0.8 M€ for additional
personnel and a dedicated training programme for young scientists.
8
Sites
For a given design of the detector, the question arises how the figure of merit (e.g. for a discovery of
a point source) depends on the site. The answer is primarily determined by i) the visibility of an
astrophysical source, ii) the water transparency, iii) the optical background and iv) the background
due to wrongly reconstructed atmospheric muons. Three suitable sites in the Mediterranean Sea
have been identified, namely Capo Passero, Pylos and Toulon. They are described in the Technical
Design Report (1).
Visibility
The visibility of a source depends only on the geographical location of the detector and the position
of the source on the sky.
Water transparency
The transparency of the water has been measured at the Capo Passero and Pylos sites with a
designated setup. The results are published in reference (4) and summarized in Table 5.3 in the TDR
(1). The results are referred to as the transmission length. The measured transmission lengths as a
function of the wavelength of the light are shown in Figure 1 together with the attenuation length at
the Toulon site. The attenuation length at the Toulon site is determined from comparisons between
data and Monte Carlo simulations of the response of the ANTARES detector to muons and LED
beacons. Because the scattering length is similar or longer than the absorption length and the
distribution of the scattering angles strongly peaks in the forward direction (the average cosine of
the scattering angle is about 0.8), the attenuation and transmission lengths are very similar. This
similarity is demonstrated in a recent study on the interpretation of the measurements of the water
transparency (5).
Figure 1: The measured transmission length at the Capo Passero (CP1) and Pylos (NP4.5) sites as a function of the
wavelength of the light. Also shown is the attenuation length that is used in the simulation of the response of the ANTARES
detector to muons and LED beacons.
9
The long scattering length and the very forward peaked angular distribution makes it hard to
accurately measure the scattering parameters. At present, there is no evidence that the scattering of
light is different at the three sites. The FWHM of the arrival time of Cherenkov light due to dispersion
and scattering is typically 5 (10) ns at a distance of 50 (100) m away from the muon. The optical
properties of the sea water make it possible to reconstruct the direction of the muon very accurately,
despite the optical background. With the ANTARES detector, an angular resolution of about
0.4 degrees has been obtained for neutrinos with an energy above 100 TeV. The angular resolution
of the KM3NeT detector is expected to be 0.1 degrees.
The dependence of the detection efficiency on the absorption length has been quantified (2). In this,
the absorption length was varied by simply scaling the values from reference (6) with one of the
following fixed values: 0.9, 1.0, 1.1 or 1.2. For this, a detector module consisting of 120 strings and 18
optical modules per string is considered. Indeed, such a module represents the smallest size of a
detector without loss of signal detection efficiency (see
Concept of building blocks). The detection efficiency is defined as the number of events with at least
5 L1 hits (L1 refers to a coincidence of two (or more) hits from different PMTs in the same optical
module within a fixed time window). This definition corresponds to the typical configuration of the
foreseen online data filter. Hence, these events are written to disk and will be available for offline
analysis. The assumed signal corresponds to a flux of neutrinos from RXJ1713-39.43. For each value
of the scaling factor applied to the absorption length, the number of signal events per year as a
function of the vertical spacing between the optical modules and the horizontal spacing between the
strings has been determined. The detector configuration that yields the largest number of signal
events per year is then taken. The resulting number of signal events per year as a function of the
scaling factor applied to the absorption length is shown in Figure 2.
As can be seen from Figure 2, the number of signal events per year depends linearly on the scaling
factor applied to the absorption length. To good approximation, this also applies to the optical
Figure 2: The number of signal events per year as a function of the scaling factor applied to the absorption length. The
detector configuration has been optimised for each absorption length separately. A flux of neutrinos from RXJ1713-39.43 was
assumed.
10
background and the background of atmospheric neutrinos. Hence, the number of years to make an
observation should scale linearly with the inverse of the absorption length. (This should not be
confused with the commonly used term “sensitivity” which scales approximately as N N B , with
N (B) the number of signal (background) events.) Indeed, a complete analysis of the problem,
including the reconstruction of the muon and the background due to atmospheric neutrinos but only
applied to the optimal detector configurations, yields the same linear dependence.
Optical background
The optical backgrounds observed in the deep sea comprise two contributions; a continuous
component from radioactive decays of 40K and possibly bacteria plus a bursting component due to
macroscopic organisms. The 40K concentration in the sea is essentially constant and independent of
location. The biological light emission can vary in time and location. The intensity and variability is
not well understood. The ANTARES site has been continually monitored with many 10 inch PMTs for
a period of seven years (2006–2012).The optical background was measured at the Pylos and Capo
Passero sites during the year 2010 using two independent moorings. The mooring details are
summarised in Table 2.
Site Latitude Longitude depth [m] deployed recovered
Pylos 36o37.657’N 021o24.907’E 4450 15/12/2009 30/01/2011
Capo Passero 36o29.555’N 015o54.826’E 3320 18/12/2009 25/01/2011
Table 2: Mooring details of optical background measurements in 2010.
Each system consisted of two 3 inch PMTs, two data loggers and batteries, housed in a standard
17 inch glass sphere. The count rates of each PMT were measured every 30 minutes with a dynamic
range of 0–40 kHz. The expected rate due to potassium decays was calculated beforehand for a
standard Bialkali photo-cathode and estimated to be 5 kHz with an uncertainty of 10%. The actual
photo-cathode was composed of so-called super Bialkali yielding a higher quantum efficiency (QE).
The dark counts of these PMTs depend strongly on the temperature and to some extent on the
history of the PMT. The dark counts were measured and found to vary between 4 kHz and 50 kHz. So,
the dark counts could compromise the rate measurements. However, the conditions in the deep sea
are extremely stable. Indeed, an analysis of the correlation between the observed count rates in the
deep sea and the sea currents indicate that the data from the moorings contain useful information
(7). The available data were therefore analysed based on the following two assumptions:
1. The count rate of the optical background due to potassium decays ranges from 6–9 kHz;
2. The observed baseline rate can be attributed to the optical background due to potassium
decays and the dark count;
The assumed range of the optical background covers an uncertainty of the QE of super Bialkali in the
range of 1.2–1.8 times that of standard Bialkali. Any increase of the observed rate with respect to the
calculated baseline rate is then attributed to bioluminescence. In the following, the ratio between
the observed rate and the baseline rate is referred to as “normalised rate”. Three out of the four
data sets could be used for this analysis. In one data set, the observed baseline rate was too high to
11
observe bioluminescence with sufficient dynamic range. The results of two data sets are presented in
Figure 3. One data set was used as a cross check. The data for the Toulon site were obtained from
the measured count rate of a 10 inch PMT mounted on the ANTARES instrumentation line. The
ANTARES instrumentation line was operated non-stop during the full period of the two moorings.
This measurement allows for a much larger dynamic range than the measurements using the
moorings.
Figure 3: Fraction of the time that the observed rate is a factor higher that the calculated rate due to potassium decays. Left
Pylos, middle Capo Passero and right Toulon. The areas correspond to the uncertainty on the QE of the PMTs (see text). The
data for the Toulon site have been taken with a 10 inch PMT that was mounted on the ANTARES instrumentation line.
As can be seen from Figure 3, the probability that the count rate is a factor two higher than the
baseline is less than 1% in Pylos, about 1% in Sicily and about 30% in Toulon.
An ANTARES optical module typically has a baseline counting rate of 50–60 kHz with occasional
bursts, of up to few seconds duration, that can attain MHz rates. The probability of the occurrence of
bursts is observed to be correlated with the velocity of the sea current, presumably due to stresses
on bioluminescent organisms induced by turbulence or impacts on the infrastructure. Furthermore,
during some years an enhanced level of bioluminescence has been observed during the spring
period. Due to the limited bandwidth of the ANTARES data acquisition system, a high-rate veto is
implemented that prevents data from any optical module to be transmitted to shore while its singles
rate exceeds 400 kHz. This feature introduces missing information randomly distributed throughout
the detector which increases as the mean rate increases. For example with a mean rate of 400 kHz
the fraction of missing data is typically 20%. Due to concerns about PMT ageing, it was decided that
during the years (5 out of 7 of the years) in which the spring bioluminescence was very high
(≥ 500 kHz mean rate) the high voltage of the PMTs was reduced or switched off. Averaged over all
years a downtime of 10% is attributed to this origin.
12
The optical background may induce a degradation of the detection efficiency or the angular
resolution. Depending on the analysis considered, the final selection cuts represent the optimum
trade off in efficiency, resolution and background rejection. The dependence of the detection
efficiency on bioluminescence has been quantified in the following way. The count rates of all PMTs
in the ANTARES detector are measured with a sampling frequency of 10 Hz. In the run-by-run Monte
Carlo simulation, a random background according to the recorded count rates is superimposed on
each simulated event. The standard analysis procedure developed for the point source search is
applied, assuming a flux of neutrinos from RXJ1713-39.43 with the appropriate energy spectrum. The
resulting sensitivity, ɛ, as a function of the normalised count rate, R, can roughly be formulated as:
For R > 5, the sensitivity is boldly (and pessimistically) set to . This includes the effect of the
above mentioned high-rate veto and the downtime of the detector due to excessively high
bioluminescence. For KM3NeT, however, these effects will have much less impact. A convolution of
this expression with the observed spectrum of count rates (Figure 3) is used as an estimate of the
effect of bioluminescence.
Extrapolating the effects of bioluminescence from ANTARES to KM3NeT is not completely
straightforward and a dedicated simulation study on this issue is planned. Nevertheless, it is
expected that use of the multi-PMT optical module should increase significantly the robustness of
the track reconstruction against bioluminescence due to the fact that it provides a clear separation
between single photons (dominantly background) and multiple photons (dominantly signal).
Furthermore, the enhanced directional information provided by the multi-PMT should help to
exclude photons that are incompatible with the expected direction of photons emitted from a muon
trajectory. In addition, the larger bandwidth afforded by the KM3NeT readout scheme should reduce
the loss of data induced by a high rate veto.
Atmospheric muon background
In general, the background due to wrongly reconstructed atmospheric muons depends on the depth
to the detector. For a point source search, events are typically selected with the cosine of the zenith
angle in the range -1 to 0, with an angular error (from the fit) less than 1 degree and finally with a cut
on the likelihood of the fit. The optical properties of the deep-sea water in the Mediterranean are
such that the slope of the likelihood distribution due to atmospheric muons is very steep at the cut
position. A crude estimate of the dependence of the detection efficiency of neutrinos on the depth
can be made assuming that the rate of wrongly reconstructed muons scales in the same way as the
overall rate. Increasing the depth from 2 km to 4 km, would then improve the detection efficiency by
about 20%, for a flux of neutrinos from RXJ1713-39.43.
13
Summary
The optical backgrounds have been measured at the three sites, the previous data on the water
transparency have been scrutinized and the effects of the optical and the atmospheric muon
backgrounds have been quantified. The results are summarised in Table 3.
Site Visibility Water transparency Depth Bioluminescence
Capo Passero (CP1) 0.71 1 0.9 0.93±0.03
Pylos (NP4.5) 0.71 1.1±0.1 1.0 0.97±0.01
Toulon 0.78 1.0±0.1 0.8 0.70±0.10 Table 3: Summary of the characteristics of the three sites in the Mediterranean Sea.
The values in the column “Visibility” correspond to the fraction of time RXJ1713-39.43 is below the
local horizon. This depends only on the geographical location of the detector and the position of the
source on the sky (e.g. for Vela X, the visibility is 100% for Toulon and about 80% for the other two
sites). The values in the column “Water transparency” correspond to the scaling parameter to be
applied to a benchmark attenuation length, arbitrarily defined as the measured attenuation length at
the Capo Passero site. The values in the column “Depth” and the column “Bioluminescence”
correspond to the above mentioned estimates of the impact of the atmospheric muon and the
optical backgrounds. These values are subject to improvements in the analysis and availability of
more data.
14
Recommendation 1
The KM3NeT Consortium is urged to perform Monte Carlo optimization studies on a variety of fronts
to reduce by roughly a factor of two their figure of merit. The Consortium has defined as their FoM
the number of years required for a 5σ discovery of muon neutrinos from a selected group of
theoretically favorable galactic point sources (see Annex 3, chapters 3.1 and 3.2). The calculated
FoMs range from 7 to 15 years assuming 100% hadronic production mechanism. Reducing the FoM
by a factor two will place the potential for discovery in a less model-dependent range and enhance
the viability of KM3NeT as a discovery project. One or two additional FoMs may be warranted, in
particular one for neutrino-induced showers, from a diffuse flux of extraterrestrial neutrinos. The
chosen FoM(s) should be calculated for each site, assuming the same underlying detector hardware
components, but with detector geometries (e.g., tower spacing and bar length) optimized for each
site.
Due to its location in the Northern hemisphere, Galactic sources are the prime science objective of
KM3NeT. It is in this region that KM3NeT can make unique and significant contributions to neutrino
astronomy.
In the TDR, the sensitivity to point-like cosmic sources of neutrinos was estimated for a flux spectrum
with a E-2 dependence. This represents a reasonable assumption for extra-galactic sources but not
for galactic sources. The energy spectrum of galactic sources has an energy cut-off that is typically in
the range of 10–100 TeV. Because galactic sources are relatively nearby, their appearance extends up
to 1 degree. Therefore the detector design has been optimised to increase the discovery potential for
galactic sources.
Amongst the galactic objects, Super Nova Remnants are probably the most promising ones. As a
representative example the Super Nova Remnant RXJ1713-39.43, which at present is the best
measured object of this type in the high-energy gamma-ray band, was chosen to evaluate the
KM3NeT performances. This source has a radial extension of about 0.6° with rather complex shell
type morphology and hot spots. The energy spectrum of the observed gamma-rays extends up to
about 100 TeV but it is suppressed significantly compared to a pure power-law spectrum at energies
above 10 TeV (8).
A flux of neutrinos from RXJ1713-398.46 has been simulated following the Kelner parameterization
for the energy spectrum (9) and assuming a homogenous disk with 0.6° radius centred at the source
position. This last assumption is rather conservative and has a negative impact on the figure of merit.
First estimates of the sensitivity and the discovery potential have been obtained using a directional
reconstruction based on the knowledge of the source position and a binned analysis. The
minimisation is performed with respect to the fit quality, the number of hits, which represents a
rough estimate of the muon energy, and the search-bin size. Results were presented to the SSC in
detail in reference (3). Here we just report that the figure of merit (i.e. the time needed to make a
5-sigma discovery with 50% probability) estimated with the prescription outlined above amounts to
6.2 years for a 620 string detector with 100 m spacing between detection units, assuming a flux of
neutrinos according to reference (9). These simulations did not take into account double random
coincidences from 40K background in the optical modules. This effect leads to an increase of the
15
number of spurious coincidences, especially at the trigger level, and are now taken into account in all
simulations.
Several improvements both on the trigger (considering also coincidences between nearby storeys
and nearby detection units) and on the reconstruction have been implemented. A new approach in
the reconstruction is represented by the scanning of the full solid angle to determine the best start
value for the final fit. In the scanning method the results strongly improve with the grid density at the
expenses of a large increase of CPU time. Preliminary results have been obtained considering a 3°x3°
grid in theta and phi covering the full solid angle.
In the following we report the state of art of discovery capability for a detector made of 620 strings
with 20 optical modules at 40 m vertical spacing. Detector configurations with various spacing
between detection units are explored. In Figure 4 and Figure 5 , the 1 year sensitivity and the number
of years for discovery of a neutrino flux from RXJ1713-39.43 are reported as a function of the
distance between strings, respectively. The reported values have been obtained using a
reconstruction based on the scanning procedure explained above and a binned analysis. The best
sensitivity and more evidently the best discovery potential correspond to a distance between
detection units of 100 m.
Figure 4: One year sensitivity to RXJ1713-39.43 for a flux of neutrinos according to reference (9). The sensitivity is shown as
a function of the horizontal distance between strings. K0 is the normalisation constant of the neutrino flux. The dashed line
indicates the expected K0 value derived from H.E.S.S. gamma-ray data under the hypothesis of 100% hadronic emission.
The reconstruction based on scanning can be easily used also as a starting point for an unbinned
analysis that is expected to provide better results as already demonstrated by IceCube and ANTARES.
The main drawback of the unbinned analysis is the large increase of the needed CPU time. In this
case, first results based on 1 year of observation time, indicate that 3-sigma significance can be
reached after 1.6 years and 5-sigma significance after 4.8 years (preliminary results).
The inclusion in the simulations of the source morphology extracted from the high-energy
gamma-ray map measured by H.E.S.S. is in progress. This will provide a more realistic description of
the spatial extension of the source.
16
Figure 5: Number of years needed for a 5-sigma discovery of RXJ1713-39.43 as a function of the horizontal distance
between strings. The full circles correspond to a binned analysis, while the red star corresponds to a preliminary estimate
from an unbinned analysis (see text).
Such an approach is appropriate also for the investigation of some other candidate sources. In fact
the most intense ones, Vela X and Vela Junior, have a large spatial extension with a complex
morphology. The discovery potential for these sources, as well as a stacking analysis of several
candidate galactic sources, are being investigated. A preliminary estimate has been obtained for the
Vela X, which has been measured by H.E.S.S. in several observation campaigns. In particular, the
results based on the first observations (10) have recently been updated with data from the 2005–
2007 and 2008–2009 observation campaigns and a more accurate method for the background
subtraction has been used (see arXiv:1210.1359v1). The new data are characterised by a higher
gamma-ray flux and a harder energy spectrum. Emission of very high-energy gamma-rays from an
outer ring 0.8°–1.2° has also been investigated. This contribution is not (yet) considered in estimating
the neutrino emission. The neutrino emission spectrum has been derived from the gamma-ray
spectrum using the prescription from references (11), (12) and (13) based on the hypothesis of a
transparent source and 100% hadronic emission. For the RXJ1713-39.43, this prescription provides
results very similar to ones obtained with the Kelner spectrum (9). The source extension was
simulated assuming a flat distribution within a radius of 0.8°. Our binned analysis indicates that a
5-sigma discovery is reached after 2.8 (5.2) years for the updated (old) spectrum. Vela Junior is
another intense source of very-high energy gamma-rays with a complex morphology. The energy
spectrum was measured by H.E.S.S. up to 20 TeV and a shows a spectral index of -2.24. This source is
under study.
Other promising candidate neutrino sources are the Fermi bubbles recently discovered in an analysis
of Fermi-LAT data that has revealed an intense gamma-ray emission from two large areas above and
below the Galactic centre (14). The detected gamma-ray emission is homogeneous within the
bubbles and shows a spectrum, measured from 1 GeV to 100 GeV, compatible with a power-law
spectrum (15) and a very high intensity (d/dE = K0 E-2 , with K0 = 3–6 x 10-7 GeV cm-2 s-1 sr-1).
Currently, the observed features cannot be fully explained by leptonic processes. An alternative
proposal exists in which the underlying process is hadronic (15). A cosmic ray population associated
17
with long-time scale star formation in the Galactic centre (of the order of 1010 years) was
hypothesised to have been injected into the bubbles where it interacts with the ambient matter and
produces high-energy gamma-rays through π0 decay. Under the hypothesis that the source is
transparent to gamma-rays and that the mechanism responsible for the gamma-ray emission is
hadronic, the intensity of the neutrino flux was estimated to be K0 = 10-7 GeV cm-2 s-1. In the analysis,
a power law spectrum with a spectral index of -2 and an exponential cut-off at 100 TeV have been
considered.
Detailed simulations have been performed to evaluate the detection potential of KM3NeT for high-
energy neutrinos from the Fermi bubbles. Details on simulations and results are presented in a
dedicated paper that is accepted for publication in Astroparticle Physics (16). The main result is that,
for a geometry based on two blocks of 154 towers with a distance of 180 m, the discovery (5 C.L.,
50% probability) of neutrinos is expected in about one year of data taking for a E-2 neutrino spectrum
with a cut-off at 100 TeV. The first evidence (3 C.L., 50% probability) could already be obtained after
a few months of data taking.
Neutrino reaction channels other than charged−current interactions of muon neutrinos produce final
states (with or without neutrinos) that induce electromagnetic and/or hadronic particle cascades
(also referred to as showers). These showers show a longitudinal profile that extends several metres
in water. This should be compared to the range of a muon which is more than one kilometre for a
muon with an energy of 1 TeV. Nevertheless, high-energy cascades are sources of intense Cherenkov
light that is emitted over a broad angular range but peaked at the Cherenkov angle. Detecting this
light allows for reconstructing the events with good energy resolution but limited precision in
direction. Early simulation studies in ANTARES have demonstrated that shower events that are
contained in the instrumented volume can be reconstructed with an angular resolution of the order
of 10 degrees. This event class is particularly useful for identifying down-going neutrinos with
energies above some 100 TeV, where the Earth becomes opaque to neutrinos. The main background
source for such neutrino signatures is due to atmospheric muons undergoing catastrophic
Bremsstrahlung. Due to the steepness of the energy spectrum, this background is expected to be
small at these energies. Nevertheless, a veto on muon tracks penetrating the detector from above
may increase the sensitivity. Designated simulation studies to determine the KM3NeT sensitivity for
shower events are in progress but need more time to be completed.
The site dependence of the figure of merit is addressed in Section Sites.
18
Recommendation 2
The following points should be further developed and tested as elements of a complete design of the
detector
a. To demonstrate the claimed superiority of the multi-PMT option the Consortium should: i.
build a complete unit, ii. perform adequate tests including deep-sea deployment, iii. produce
a reliable cost estimate, iv. include in the comparison the OMs already developed in previous
experiments, v. evaluate the performance, including the, site dependent, detection
probabilities for minimum ionizing tracks vs. distance.
b. Further studies are needed to prove the superiority of the bar tower. It should be noted, in
particular, that if having pairs of modules close enough to see coincidences but not so close
as to see individual 40K events, a single string with smaller vertical spacing works as well.
c. We think thereby that the trade-off study ought to be with close pairs of strings to achieve
the horizontal reconstruction leverage versus the bars.
d. As already requested by the SSC (KM3NET-SSC-R&Q2, 4b), the optimization of the detector
taking into account the characteristics of its site should be fully developed. This is a
necessary process for a proper evaluation of performance and costs in different sites.
a. i-ii) The first operational multi-PMT optical module has been built in 2012. After successful
tests in the laboratory, it was mounted on the ANTARES instrumentation line which is now
ready for deployment. Following the connection to the ANTARES junction box, a detailed
comparison can be made between the in situ performance of one KM3NeT optical module
and the equivalent system consisting of three optical modules, each with one large PMT.
Although the instrumentation line will be operated for a long time, the main results of the
test of the multi-PMT optical module will be concluded shortly after the connection. A
prototype string with a limited number of optical modules (probably three) will be deployed
spring 2013. After the operation of this prototype, an evaluation will be made before a full
string will be built. According to the present planning, the first full string should be deployed
in 2014.
iii) See reference (3) and Section Cost.
iv-v) The photon counting with a multi-PMT optical module is primarily based on counting
the number of hits within a certain time window, rather than measuring the charge of an
analogue pulse. As a result, the purity of identifying hits with multiplicity 2 (5) is better by a
factor 10 (100). A quantitative comparison between a system consisting of three optical
modules, each with one 10 inch PMT, and one multi-PMT optical module has been presented
to the committee. The detection efficiency of a multi-PMT optical module is a factor of 1–2
better, depending on the direction of the neutrino and the number of coincident photons.
Furthermore, a set of small PMTs with limited fields of view allows for pointing the detected
photon back to the muon trajectory. This improves the detection efficiency by about 30% for
neutrinos with energies in the range 1–50 TeV. For the site dependence, the reader is
referred to Section Sites.
19
b. For the detection of muons and showers, the time-position correlations that are used to filter
the data follow from causality. A solution to filter the data exists that does not require local
coincidences between optical modules. In the following, the level-zero filter (L0) refers to the
threshold for the analogue pulses which is applied off shore. All other filtering is applied on
shore. The level-one filter (L1) refers to a coincidence of two (or more) L0 hits from different
PMTs in the same optical module within a fixed time window. The scattering of light in deep-
sea water is such that the time window can be very small. A typical value is T = 10 ns. A
general solution to trigger an event consists of a scan of the solid angle combined with a
directional filter (17). In the directional filter, the direction of the muon is assumed. For each
assumed direction, an intersection of a cylinder with the 3 dimensional array of optical
modules can be considered. The diameter of this cylinder (i.e. the road width) corresponds to
the maximal distance travelled by the light. It can safely be set to few times the absorption
length without a significant loss of the signal. The number of PMTs to be considered is then
reduced by a factor of 100 or more, depending on the assumed direction. Furthermore, the
time window that follows from causality is reduced by a similar factor. (Only the transverse
distance between the PMTs should be taken into account because the propagation time of
the muon can be corrected for.) This improves the signal-to-noise ratio (S/N) of an L1 hit by a
factor of (at least) 104 compared to the general causality relation. With a requirement of five
(or more) L1 hits, this filter shows a very small contribution of random coincidences. The field
of view of the directional filter is about 10 degrees. So, a set of 200 directions is sufficient to
cover the full sky. By design, this trigger can be applied to any detector configuration.
Alternative signals with different time-position correlations, such as slow monopoles, can be
searched for in parallel. It is obvious but worth noting that the number of computers and the
speed of the algorithms determine the performance of the system and hence the physics
output of KM3NeT.
c. For the real-time filtering of the data, there is no need for local coincidences (see b).
Furthermore, it was found that a more homogeneous distribution of the strings improves the
performance of the reconstruction. Hence, a detector configuration with close-by strings
does not improve the figure of merit.
d. The detector configuration has been optimised for the water properties that are typical for
the Mediterranean Sea (see Section Sites). It is interesting to note that the optimal
configuration lies well within the boundaries imposed by the chosen technology. For
example, the length of a string and the horizontal distance between the strings complies
straight off with the maximal deviation of a string due to sea currents. The optimal
configuration represents a genuine optimum, i.e. the dependence of the detection efficiency
on various parameters is small. As a result, the optimal configuration does not significantly
change with site. However, the funding depends strongly on the use of different sites (e.g.
ERDF). So, one may argue that the multi-site solution is driven by funding and not by
technology or science.
20
Recommendation 3
Since important elements of the newly developed technology are largely untested in the deep ocean
environment, for the next phase of the project we recommend development and deployment of a
“Demonstrator” detector, with enough modules to prove that the new technical concepts reliably
survive deep-sea conditions for an extended period of time. Technology arguments like “towers”
versus “strings” may lead to the development of more than one demonstrator. Therefore, the
alternative detector architecture proposed by the Consortium, which is based on single strings
without bars, could also be tested in this phase as a separate demonstrator as it may be less sensitive
to complications during unfurling.
An agreement on the baseline technology was reached (see Section Agreement on the baseline
technology). The validation program for the baseline technology has been defined (18). In this, a set
of milestones is planned, namely:
1. PMT qualification;
2. Pre-production model of an optical module;
3. Test of vertical electro-optical cable;
4. Deployment tests with dummy detection units;
5. Pre-production model of a detection unit;
As indicated above, the first milestone is passed. The second and third milestones are about to take
place. For the deployment tests with dummy detection units, a sea campaign is scheduled in spring
2013. Finally, the test of a complete pre-production model (in compliance with Recommendation 2.a)
will follow shortly. The construction of KM3NeT phase-1 will start after successful tests of the
pre-production model and a product readiness and cost review by an external peer review
committee (see also the reply to Recommendation 8).
ANTARES has already demonstrated the feasibility of a neutrino telescope in the Mediterranean Sea.
KM3NeT phase-1 will demonstrate the feasibility of a distributed network of neutrino telescopes in
the Mediterranean Sea.
21
Recommendation 4
The SSC recommends that the KM3NeT Consortium establish criteria and a process to clearly identify
the best single site for the deployment of the full detector. A consistent set of measurements of
important site properties are needed to allow for an independent and conclusive review of the
results. All the relevant unpublished results should be published in refereed journals and used for
comparing sites and optimizing the design.
The site-dependent figure of merit for the installation of the KM3NeT neutrino telescope is a
combination of the following criteria:
‒ Quality: Which physics sensitivity can be obtained for a given investment volume;
‒ Cost: What does the installation of a given number of detection units at this site cost,
including the required local infrastructure, logistics, personnel and operation;
‒ Time: On which time scale can the neutrino telescope be constructed and become
operational.
Cost and time will depend on criteria beyond the scientific realm, i.e. the local infrastructure, political
and regional support, proximity of harbours, airports etc. These criteria are listed in detail in
reference (3), Section 5. The impact of these criteria on the overall cost still needs to be investigated
in detail. This process will strongly profit from the experience gained in KM3NeT phase-1.
As mentioned above, as truly conclusive study of the site properties requires continuous long-term
measurements covering several years in the optimal case. In that sense, decisions on detector
construction may/will have to be taken before knowing the site properties with ultimate accuracy.
Such decisions will be based on the measurements presented in the TDR and supplementary data
accumulated thereafter or retrieved from old records. It is of particular importance to investigate
and understand the uncertainties of the site properties, both in terms of experimental effects and of
time dependences not covered by the measurements.
In addition to the data reported in the TDR, the following data are or will become available:
1. Results of a previous Italian campaign to measure the water optical properties in the Ionian
sea;
2. Results of a one-year monitoring of the optical background rates at the Capo Passero and the
Pylos sites with autonomous instruments on long-term moorings;
3. Long-term results from the ANTARES site on bioluminescence rates, water properties and
currents;
4. Long-term results on optical backgrounds at the Capo Passero site (once the preproduction
string will be deployed and operated there).
These results will be scrutinized and published if this is appropriate.
The time scale must be aligned with the available funding. This aspect can only be assessed once the
funding and in particular its spending profile for the construction of the full detector can be specified,
which is currently not the case.
22
The performance question has two aspects, which both need to be addressed: (i) which site would
yield the highest sensitivity if chosen for the construction of the full detector; (ii) what is the effect of
a distributed installation in terms of sensitivity. The financial and operational aspects of point (ii) are
discussed in the reply to Recommendation 5. To evaluate the physics performance, the following
steps are to be taken:
1. Determine the physics figure of merit for the KM3NeT neutrino telescope (given its technical
design and the geometrical arrangement of the detection units), as a function of the water
optical properties (absorption and scattering), depth, optical background rates and
geographic location typical for the three candidate sites.
2. Determine the error margin of the results induced by uncertainties in the water optical
properties and the bioluminescence rates and their time dependence.
3. Determine these results for a range of the number of detection units assumed for the
telescope.
4. Determine how many detection units one could install at each site for a given, fixed
investment volume.
The studies will be done using the existing simulation programs and cost tables. The existing
knowledge of the site characteristics will be taken into account, assigning an appropriate uncertainty
to them (we remind the reader that in numerous measurement campaigns in preparation of the
ANTARES project no indication was found that the bioluminescence rates can be as high as actually
observed - i.e. only long-term, continuous measurements will give sufficiently solid answers).
Once all answers are available, the physics performance of a single detector at one of the candidate
sites, as well as of a distributed installation at multiple sites can be easily determined.
23
Recommendation 5
The SSC recommends that the Consortium evaluate accurately and quantitatively the scientific (loss
of FoM) and financial (more infrastructural and running costs) consequences of using more than one
site. The effects of bioluminescence that are different from site to site should be carefully considered
in the evaluation of the FoMs.
The optical backgrounds have been measured at the three sites, the previous data on the water
transparency have been scrutinized and the effects of the optical and the atmospheric muon
backgrounds have been quantified. The results are summarised in Table 3 in Section Sites. The total
figure of merit is approximately equal to the sum of the sizes of the building blocks at each site
weighed with the product of the values in Table 3. The financial consequences of using more than
one site are addressed in Section Cost. In short, the advantage of additional funding and human
resources resulting from adopting a multi-site solution significantly outweighs any financial or
scientific advantage from adopting a single site solution.
The KM3NeT infrastructure will be shared by a multitude of other sciences, making continuous and
long-term measurements in the area of oceanography, geophysics, and marine sciences possible.
These sciences will greatly benefit from using more than one site.
24
Recommendation 6
As the various groups within KM3NeT are not cooperating in a sufficiently coherent manner, a
stronger, centralized and site-neutral leadership is needed in the next phases of the project. The
governance structure and the management plan should be elaborated according to the best
practices in use for projects of the KM3NET scale. A Memorandum of Understanding should be
defined on that basis by the parties (the ministries and funding agencies). A coherent, consensus-
building path towards a well-led and well managed project needs to be established.
The KM3NeT collaboration has drafted a Memorandum of Understanding (MoU) for collaboration on
the implementation of the first phase of the KM3NeT research infrastructure distributed on multiple
sites. Its purpose is to define the programme of work to be carried out for this phase and the
distribution of charges and responsibilities among the parties and institutes for the execution of this
work. It sets out the organisational, managerial and financial guidelines to be followed by the
collaboration as well as the external scientific and technical review processes. Parties who have not
yet secured funding will be invited to join as associate member. The MoU is the first step towards the
intended establishment of a European Research Infrastructure Consortium (ERIC) which would
eventually supersede the MoU. It has been agreed that the Netherlands will host the KM3NeT ERIC.
Both the MoU and the ERIC will allow for full members as well as associate members. It is expected
that the spirit of the MoU will be agreed shortly, although the formal signature process by the
funding agencies will take significantly longer. The elections of the executive management
(spokesperson, deputy spokesperson, physics and software coordinator and technical coordinator) is
planned to take place before March 2013. An interim management has been put in place to bridge
the period until the instatement of an elected management.
25
Recommendation 7
An independent scientific and technical advisory committee should be appointed by the agencies to
follow all the phases of the project with continuity of committee membership sufficient to allow a
coherent perspective over project lifetime. A project cost review should be undertaken by the
committee. The purview of this panel should include a survey of OM design, deep ocean technology,
DAQ, reliability, maintenance, and deployment. The panel should include reviewing the risk analysis
for all of these elements. The result of such a review will bolster confidence that a Project
Implementation Phase would be successful in cost, schedule, and performance. Both detector
sensitivity and construction costs of any demonstrator should also be quantified and thoroughly
documented.
Two external committees are foreseen in the Memorandum of Understanding (MoU) for KM3NeT
phase-1: an Resource Review Board (RRB) and a Scientific and Technical Advisory Committee (STAC).
The IRB will be set up by the parties participating in the MoU to supervise the work for
KM3NeT-phase1. The role of the IRB includes:
‒ Reaching agreement on the Memorandum of Understanding;
‒ Monitoring the general financial and human resource support;
‒ Monitoring the Common Projects and the use of the Common Fund;
‒ Endorsing the annual budget of KM3NeT-phase1.
The STAC will be setup by the IRB. The STAC will monitor and evaluate the progress in the definition
of scientific objectives, priorities and output, and technical decisions related to these issues. A
project cost review will be undertaken by the STAC. The STAC will report to the IRB and makes
recommendations to the collaboration.
Although the signature of the MoU will take some time, it is the intention of the collaboration to
have these committees established in the shortest possible time to follow the progress of the project
and advise the collaboration as soon as possible.
26
Recommendation 8
As already detailed in the previous points, more studies are needed to bring the project to the stage
of the final construction approval, including the production of a more advanced (at the above
mentioned level) “Technical Design Report” with all the data that are necessary for such a decision
and the development of a full resource loaded schedule, in terms of labor and funds, in analogy to
projects of similar scale. The process leading to that, including the reviews mentioned in point 7,
should be precisely defined as soon as possible.
As mentioned in the findings 8, the existing Technical Design Report – elaborated as the main
deliverable of the Design Study – presents a rather detailed description of the baseline technology
for KM3NeT and sketches a development and implementation plan, which however needs to be
updated and worked out in more detail (1).
The neutrino telescope design is modular and consists of the following basic assembly groups
(each including the appropriate deployment tools and procedures):
‒ the detection unit with its components;
‒ the sea-floor network including the main cable(s) to shore;
‒ the shore infrastructure including online computing facilities;
‒ the nodes for the earth and sea sciences.
Observing that the interfaces between these assembly groups are standardised, commercial
products (e.g. deep-sea connectors), the technical validation and review process can be
performed independently for each group. Similar arguments may apply to subcomponents of the
assembly groups (e.g. the validation of the mechanical behaviour of a detection unit under water
can be performed independently from the validation of the optical module functionality).
Currently, the ongoing work focuses on the technical validation of the detection unit and its
components (see introduction and reply to Recommendation 2). The seabed network is expected to
consist of commercial components (cables, connectors, penetrators) and custom-designed
junction boxes for which a separate validation process is in preparation.
For each of the abovementioned assembly groups, the following steps will be preceding the
tendering and construction phase:
1. technical validation with respect to the functionality, specifications and reliability
requirements laid down in the TDR (or, if not included there, in a complementary document);
2. production of a technical documentation describing specifications, design (including PBS),
assembly and test procedures (including WBS), resources and production time schedule;
3. a product readiness and cost review by an external peer review committee, organised under
oversight of the Scientific and Technical Advisory Committee (STAC).
The technical documentation documents will, in combination, represent a technical proposal and
correspond to the improved “Technical Design Report” mentioned in the recommendation.
Optionally, a first engineering subset of the full installation during KM3NeT phase-1 may be part of
the technical validation process.
27
Recommendation 9
The collaboration will need to expand. In the nearer term, more effort should be employed in the
critical effort of simulations. In the longer term, a number of strong groups should be recruited to
this challenging project. Non-European collaborators should be encouraged.
The gathering together of the ANTARES, NEMO and Nestor neutrino collaborations already
represents a community of about 400 persons distributed over 40 institutes and 10 countries. The
ANTARES telescope is currently taking data and is foreseen to continue operation to at least 2016.
The ANTARES collaboration offers an open door policy to all KM3NeT members and indeed common
ANTARES/KM3NeT meetings are now being organised. On the short term, sufficient analysis effort on
ANTARES must be preserved to maximise the physics return from the experiment while at the same
time providing an invaluable training ground for future KM3NeT analyses. On the longer term, as the
ANTARES physics reach saturates it is expected that the ANTARES analysis efforts will migrate
towards KM3NeT. At this stage an eventual merging of ANTARES and KM3NeT would be natural.
We recognize the current need for more simulation studies, in particular in view of the new data on
Super Nova Remnants, the development of shower reconstruction software and the studies for low
energy neutrino detection (ORCA). These efforts are currently limited by lack of human resources.
Although the current available manpower is considered sufficient for the implementation of KM3NeT
phase-1, the collaboration is very aware that additional financial and manpower resources are
desirable to facilitate the construction, operation and analysis of data from the full size (phase-2)
research infrastructure. Such additional resources could potentially be forthcoming from both
European and non-European Countries not currently involved in KM3NeT. For Europe, contacts
within the UK, Scandinavian and Belgium are currently being explored. For non-European countries,
contacts with China, Japan and Russia are also being actively pursued. For example, the interest of
the Chinese to provide small PMTs for KM3NeT has opened the opportunity to discuss with them the
possibility of involvement of Chinese research institutes in the project; with this in mind, a workshop
in China has been organized for the 13th December 2012 in Beijing, under the auspices of the
ASPERA.
The attractiveness of KM3NeT to new collaborators will clearly be enhanced once KM3NeT phase-1
has been successfully operated and hopefully the detection of non-terrestrial neutrinos has been
established by IceCube (or possibly even ANTARES). The KM3NeT collaboration is currently studying
the possibility to make a measurement of the neutrino mass hierarchy with KM3NeT phase-1 (ORCA
feasibility study). If indeed this is proven feasible and adopted as the physics focus of KM3NeT
phase-1, it should certainly attract some of the low energy neutrino community (both in countries
already involved and not involved in KM3NeT) to the project. The neutrino astronomy community is
actively discussing the establishment of a MoU for a Global Neutrino Observatory (GNO) to foster
cooperation between the various high energy neutrino telescopes involved in the field (USA-IceCube,
Russia-Baikal/GVO, Mediterranean-ANTARES/KM3NeT). In its ultimate form GNO would represent a
single research infrastructure, with detectors distributed over several continents. Within such a
framework it is anticipated that R&D efforts can be shared and certainly data analysis would be
distributed amongst a significantly larger manpower base.
28
Recommendation 10
The observation or non-observation by existing ongoing projects should be used to further optimize
the design, especially in terms of required detection volume and sensitivity.
We note that currently the identification and investigation of Galactic neutrino sources is the priority
physics objective of KM3NeT. The sensitivity of corresponding measurements can be relatively
precisely determined from existing high-energy gamma-ray measurements (in particular from
H.E.S.S. and Fermi) if we assume that the observed gamma-ray fluxes originate from purely hadronic
emission processes. The relevant neutrino energy range is roughly 1-100 TeV. The IceCube findings
are only weakly related to this objective since, due to its geographic location, IceCube cannot
observe with sufficient sensitivity neutrinos from the largest part of our Galaxy in that energy range.
The KM3NeT optimisation for Galactic point source searches is therefore based on available gamma-
ray data.
Other KM3NeT science cases are directly related to the following observations (or non-observations)
of ongoing projects:
1. IceCube: An observation of neutrinos of extragalactic origin (be it point sources or diffuse
flux) would imply that KM3NeT could scrutinise the finding and investigate it with improved
statistics. This would probably require a re-optimisation for higher energies and for the
detection of cascade events. With excitement we are awaiting further IceCube results
complementing the intriguing findings presented at the Neutrino 2012 conference in Kyoto.
In this context, it should be noted that locating the origin of neutrinos with cascade events is
hampered by the degraded angular resolution.
2. Recent neutrino oscillation measurements indicate that the mixing angle 13 is large and that
therefore the neutrino mass hierarchy might be measurable with a densely instrumented
neutrino telescope using atmospheric neutrinos in the energy range 3-20 GeV. This option is
investigated in the ORCA feasibility study. A corresponding KM3NeT phase-1 setup will be
considered if such a measurement should turn out to be possible. This might also yield
sensitivity to indirect WIMP searches and therefore relate to possible LHC,
IceCube/DeepCore and direct search results.
An optimisation of the KM3NeT layout – according to current schedules – will in principle be possible
until about mid-2013 for phase-1 and until about a year prior to the construction for phase-2. All
simulations indicate that, to leading order and for given distances between optical modules, the
KM3NeT sensitivity is determined by the product of the overall photo-cathode area deployed and the
quantum efficiency. This indicates that design optimisations beyond layout/geometry do not need to
be considered.
29
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