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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