the European strategy

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Members of the Roadmap Committee, 2008
Elena Aprile
Laura Baudis
Jose Bernabeu
Pierre Binetruy
Christian Spiering (chair)Franz v. Feilitzsch
Enrique Fernandez
Andrea Giuliani
Werner Hofmann
Uli Katz				Paul Kooijman 		
Paolo Lipari 				Manel Martinez
Antonio Masiero
Benoit Mours
Francesco Ronga
Sheila Rowan
André Rubbia
Subir Sarkar
Günther Sigl
Gerard Smadja
Jenny Thomas
Lucia Votano

Editorial Board
Maurice Bourquin
Stavros Katsanevas
Arnaud Marsollier
Deborah Miller
Christian Spiering
Rob van der Meer

Graphic design
Arnaud Marsollier
Didier Rouable

Aspera Working Group Leads
Dark Matter:
Gabriel Chardin
Nigel Smith
Neutrino Mass:
Andrea Guiliani
Fabrice Piquemal
Stefan Schönert
Megaton Detector:
Aldo Ianni
André Rubbia
Charged Cosmic Rays
Andreas Haungs
Günther Sigl
Gamma Rays
Werner Hofmann
Manel Martinez
High Energy Neutrinos
Uli Katz
Gravitational Waves
Harald Lück
Michele Punturo

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Towards a European Strategy for Astroparticle Physics
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Astroparticle Physics is a rapidly growing field of research at the intersection of astrophysics, particle and nuclear physics and cosmology. It addresses questions like the nature ofdark matter and dark energy; the stability of protons and the physics of the Big Bang;the properties of neutrinos and their role in cosmic evolution; the interior of the Sun or
supernovae as seen with neutrinos; the origin of cosmic rays and the view of the sky atextreme energies; and violent cosmic processes as seen with gravitational waves.

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The past two decades have seen the development of the technologies to address thesequestions with a dramatically increased sensitivity. For several of the questions we are at
the threshold of exciting discoveries which will open new horizons. However, the high cost of frontline astroparticle
projects requires international collaboration, as does the realisation of the infrastructure. Cubic-kilometre neutrino
telescopes, large gamma ray observatories, Megaton detectors for proton decay, or ultimate low-temperature devices
to search for dark matter particles or neutrino-less double beta decay are at the hundred million Euro scale. Cooperation is the only way to achieve the critical mass for projects which require budgets and manpower not available toa single nation, to avoid duplication of resources and infrastructure, and to keep Europe in a leading position.
To promote cooperation and coordination, in 2001 ApPEC (Astroparticle Physics European Coordination)
was founded, as an interest grouping of several European scientific agencies. Since 2006 it has been flanked by
ASPERA, a European Union ERANET project. In 2007, a Phase-I stage of a roadmap, Status and Perspectiveof Astroparticle Physics in Europe, was presented by its Roadmap Committee, describing the status and desirable
options of European astroparticle physics for the next decade. For the present document, more precise timelines
and updated cost estimates have been compiled by working groups set up by ASPERA for each of the sub-fields,
and the funding landscape was mapped in more detail. We have shared our views and findings with the CERN
Council Strategy Group which formulated a European Strategy for Particle Physics, and with the astrophysics
community which produced a Science Vision for European Astronomy and an Infrastructure Roadmap for European
Astronomy. The process also included several all-community meetings. As a result, the Roadmap Committee
presents proposals for the high priority experiments, for the phasing of large projects and for international cost
sharing (see for more detailed information about individual experiments and about cost the long write-up at
http://www.aspera-eu.org which is presently being compiled). Our proposals fit within a funding scenario witha smooth factor of two increase over the next 8-10 years. The present document is intended to establish the casefor increased activity and investment, as part of the first common European strategy for astroparticle physics.
New exciting discoveries lie ahead; it is up to us to take the lead on them in the next decade.
Specifically, the Roadmap Committee proposes seven types of major projects, on different time scales:•
Ton-scale detectors for dark matter search•
A ton-scale detector for the determination of the fundamental nature and mass of neutrinos•
A Megaton-scale detector for the search for proton decay, for neutrino astrophysics andfor the investigation of neutrino properties•
A large array of Cherenkov Telescopes for detection of cosmic high energy gamma-rays•
A cubic kilometre-scale neutrino telescope in the Mediterranean Sea•
A large array for the detection of charged cosmic rays•
A third-generation underground gravitational antenna1.

Astroparticle physics: the European strategy

CONTENTS

1. A century of exploration and discovery			4 			

2. The six questions of astroparticle physics			

10				

3. Dark matter & dark energy

12

4. Properties of neutrinos

18

5. Underground physics on the Megaton scale

22

6. The high-energy Universe				26					

7. Gravitational waves						38							8. The infrastructures for astroparticle physics 		

42				

9. Technological innovation			46						10. Coordination of astroparticle theory					48							11. Education and outreach						50						12. Astroparticle physics coordination in Europe
13. Recommendations

		

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1. A century of exploration and discovery

The term astroparticle physics was coined about thirty years ago and has
only been used as a commonly accepted label since the nineties. But its
roots reach back a century, and the story of this century is a story of remar
remarkable explorations and discoveries. We describe some highlights below.

showed stronger signals the higher he moved.
He concluded that a steady rain of somethingionizing fell to Earth from outer space, something different from light and meteorites, theonly cosmic messengers known at that time. It
took some years to realize that these cosmic rays
essentially consist of protons, light and heavier
nuclei, with a minuscule admixture of electrons.
Two decades later, in 1932, the first antiparticle – the positive electron or positron – wasdiscovered in cosmic rays (Nobel Prize 1937).

August 1912: Victor Hess after his highest balloon
flight. Hess’ discovery of cosmic rays was acknowledged with the 1936 Nobel Prize in Physics.

Cosmic rays
In 1911 and 1912, Austrianphysicist Victor Hess performeda series of high-altitude balloon
flights in order to measure
how ionising radiation
would change with altitude. Contrary to initialexpectations, his small
radiation
detectors

One of the first positron tracks in a cloud chamber, recorded
by Carl D. Anderson in 1932.

The next was the heavy brother of theelectron, the muon, discovered in 1937,
followed in 1947 by the pion, the first
representative of the immense family of
the so-called mesons (Nobel Prize 1950)

Astroparticle physics: the European strategy

The Sun as seen in neutrinos.The picture is composed from several thousand neutrinos recordedby the Japanese Super-Kamiokande detector.

Until the early fifties, cosmic rays remained
the main resource for discovering newparticles. At that time, particle accelerators took over and replaced cosmic rays as
the main tool to explore the micro-cosmos.

The solar neutrino puzzle
The emergence of accelerator based research was
not the end of cosmic particle physics. Most
notable was the attempt to better understandthe interior of the Sun by detecting neutrinos.
Wolfgang Pauli had postulated the existence of
these ghostly particles in 1932, in an desperateattempt to explain the apparent deficit in theenergy released in radioactive beta decays. He
assumed that their interaction probability was so
small that they were undetectable. But in 1956,
American researchers Frederick Reines und Clyde
Cowan succeeded in recording a handful of thebillions and billions of antineutrinos escaping froma nuclear reactor in the USA (Nobel Prize 1995).
It was soon realised that neutrinos could be very
special cosmic messengers. As hard as they are todetect, as easily they escape from compact celestial bodies like the Sun. Indeed, the Sun is fuelled
by nuclear fusion reactions, and the only particles
produced in its core which can carry undisturbed
information from there to the Earth are neutrinos.

In the early seventies, the lengthy attempts torecord solar neutrinos paid off: Raymond Davis(USA) succeeded in recording solar neutrinos
in a deep underground detector, well shieldedagainst noise by more than a kilometre of rock.
The surprise was that he measured only a thirdof the expected flux. Was his measurement
wrong? Did the Sun work differently than
expected? The solar neutrino puzzle was born.
In the end, the solar neutrino deficit was
confirmed by other experiments and eventually explained by a mechanism which
Bruno Pontecorvo (USSR) had proposed as
early as 1957. He assumed that the different types of neutrinos can transform into
each other. Today, this effect is known as
neutrino oscillation. The Davis detector had
only responded to one of the three types,
electron neutrinos. The Sun produces exclusively electron neutrinos, and their partial
transformation into the two other types led
to the observed deficit. It was only in 2001
that this explanation was confirmed beyond
any doubt, and that by combining datafrom many experiments all other hypotheses
could be excluded. Oscillations have a fundamental consequence: they are only possible
if neutrinos have mass, and this is the firstsign of physics beyond the Standard Modelof elementary particles. It is remarkable that
this hint did not come from an accelerator
experiment but from astroparticle physics.

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1. A century of exploration and discovery

Grand Unified Theories:
The cosmic bridge
The real thrill in the cosmic arena came only inthe early eighties when some pioneers attempted
to test Grand Unified Theories of particle physics(GUTs). These theories aim at a coherent description of three fundamental forces of physics.
Actually, conditions when the striking differences
between these forces were negligible existed only
during the Big Bang. Therefore, GUTs span afascinating grand bridge between the worlds ofthe smallest and the largest. GUTs predict that
protons, the basic block of ordinary matter, would
not live forever. The simplest GUTs predicted
proton lifetimes of 1029-1032 years, 1020 times theage of the Universe.

In spite of this long lifetime, decays of protons
could be detectable, for instance by observing
1033 protons corresponding to roughly 3000
tons of water, in the volume of the Kamiokande
detector in a deep Japanese mine. Kamiokande
failed to see proton decays, and actually thelower limit for proton decays is now nearly 1034
years, ruling out a lot of the simplest GUTs.

The birth of neutrino astronomy
Instead of seeing proton decays, on February
23, 1987, Kamiokande recorded 12 neutrinos
from a supernova explosion in the Large MagelThe Large Magellanic Cloud before and after the supernova
explosion. The arrow marks the position of the exploding star.

Inside ‘Super-Kamiokande’, the successor of Kamiokande. The walls are paved with 11000 photo sensors.
The water tank is just going to be filled with 50000 cubic meters of water. At the bottom a small boat.

7.

1. A century of exploration and discovery

lanic Cloud, a small satellite galaxy of the
Milky Way. The particles had made a 160 000
year journey and spectacularly confirmed thecalculations about the processes deep in acollapsed star. This discovery came out of theblue and it was made by three detectors simultaneously, the others being located in the USA
and in the USSR. February 23, 1987 is therefore considered as the real birth of neutrino
astronomy. Raymond Davis and Kamiokande’s Masahiro Koshiba were honoured withthe 2002 Nobel Prize for physics, “for opening
The high energy gamma ray sky, 1996 and 20088.

a new window to the Universe” – the windowof neutrino astronomy.

The past decade: gaining speed
The detection of solar and supernova
neutrinos is not the only new window to the
Universe opened by astroparticle physics.
Another is that of high energetic gamma rays

Astroparticle physics: the European strategy

recorded by ground based Cherenkov telescopes – a particularly fruitful field over thelast decade. The wavelength of these gamma
rays is roughly twelve orders of magnitude
shorter than that of visible light. Their energy(many Tera-electronvolts, or TeV) is similar
to that of the Large Hadron Collider, themost powerful particle accelerator ever built.
From the first TeV gamma source detected
in 1989, over three sources known in 1996,
about 40 sources identified by the end of
2006, up to the present 75, the high energy
sky has revealed a stunning richness of new
phenomena and puzzling details.

10 000Sensitivity
relative to 1980

1 000
100
10

Other branches of astroparticle physics did not
yet provide such gold-plated discoveries but
moved into unprecedented sensitivity regionswith rapidly increasing discovery potential –like the search for dark matter particles, thesearch for sources of high energetic cosmic
rays or neutrinos or the attempts to detectgravitational waves. Many of the branches ofastroparticle physics have moved from infancy
to technological maturity, and the attainablesensitivities are improving with a speed far
exceeding that of the previous two decades.
The improvement of sensitivities alone isarguably not enough to raise expectations. On
top of this, we are entering territories witha high discovery potential, as predicted bytheoretical models. For the first time experimental and theoretical techniques allow – orare going to allow – forefront questions to be
tackled with the necessary sensitivity. A long
pioneering period during which methods andtechnologies have been prepared is expectedto pay off over the next five to fifteen years!

11980 1985 1990 1995 2000 2005 2010 2015

Sensitivity in many branches of astroparticle physics has
improved over the last 30 years. A meagre factor 3 per
decade has turned into a factor 10-100 per decade.

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2. The questions of Astroparticle Physics

What is the inventory of the Universe? What is dark matter? Do protons
live forever? How did neutrinos influence cosmological evolution? Whatis the origin of cosmic rays and what is the view of the sky at extreme
energies? What will gravitational waves tell us about the Universe?

Astroparticle physics links phenomena
over a vast distance scale – from the infinitesimally small worlds of subatomic
particles to the billion light year distancesof the whole Universe. It marks the intersection of cosmology, astrophysics andparticle and nuclear physics. Cosmology
is devoted to the very grand mysteries of
the Universe. After centuries of relying on
philosophical reasoning and astronomical
observations, cosmology increasingly uses
concepts of particle physics. Astrophysics,
when exploring the most violent cosmic
events, needs particle physics technologies to record the messages from these
events, and particle physics theory todescribe them. And particle physics, atthe end, is rejuvenated by questions
asked in cosmology and astrophysics,
and by the recent spectacular results
obtained with astroparticle physics
experiments.
Given the interdisciplinary
approachofastroparticle
physics and its overlap withastrophysics, particle physics
and cosmology, a concise
definition of which experiments may be considered“astroparticle physics” isdifficult and perhaps
not even desirable.

For the purpose of this roadmap, historicalassignments used in most European countries have been adopted. Recommendations
for the evolution of the field over the next
decade were formulated by addressing a
set of basic questions. An answer to any ofthese questions would mark a major breakthrough in understanding the Universe andwould open an entirely new field of researchon its own.
1)
     

What is the Universe made of ?
In particular: What is dark matter?

2)

Do protons have a finite life time?

3)
     

What are the properties of neutrinos?
What is their role in cosmic evolution?

4)

What do neutrinos tell us about theinterior of the Sun and the Earth,and about supernova explosions?

5)

What is the origin of cosmic rays?
What is the view of the sky atextreme energies?

6)

What will gravitational waves tell us
about violent cosmic processes andabout the nature of gravity?

The following chapters describe the tools to
address these questions.

First arguments for dark matter have been derived by the Swiss scientist Fritz Zwicky in 1933,
after evaluation of the movements of galaxies in larger clusters. In the seventies, the rotational
curves of galaxies suggested that 90% of most galaxies is made from invisible matter.

11.

Dark side of the Universe

3. Dark matter & dark energy

Normal matter appears like small ships sailing on an ocean of dark
matter and dark energy. Particle physics provides possible candidates
for dark matter, but as yet no clear idea exists for what dark energy
might be. A next generation of experiments will provide new answers.

The cosmic inventory
Since the 1930s, astronomers came torealise that most of the Universe is invisible and made of matter different fromthe ordinary stuff we see as stars andgalaxies. This invisible matter makes up
90% of the mass of our Galaxy, the visible
mass being just 10%. In the Universe asa whole, normal matter only contributes
5%! About 23% is attributed to dark
matter which reveals itself by its gravitational attraction. Since 1998, anotherpiece of inventory was introduced, inorder to explain an apparent acceleration in the expansion of the Universe:
dark energy. At 72%, it seems by far
to dominate the rest and may ultimately dictate its fate.

particle physics. The prime suspect of mostexperts is a particle which is weakly interacting, similarly to neutrinos, but much heavier
than the proton: a WIMP (Weakly Interacting Massive Particle). Such a particle is alsosuggested by super-symmetric theories ofparticle physics. Other candidates are conceivable, among them axions, also a theoretically
predicted particle.

What is dark matter?
For particle physicists, thehunt for dark matter is closely
connected with the search
for new particles. These
particles would not only
provide important clues
in understanding theearly Universe, but also
would fill “gaps” in

If this jar of jelly beans was the Universe, ordinary matter
would be represented by the coloured ones, composing only
5% of the whole. The Universe is mostly dark. 95% consistof dark matter and dark energy.

Astroparticle physics: the European strategy

With an array of 31 photomultipliers, theZeplin III detector in the Boulby Underground
Mine (UK) records light flashes in liquid xenon.
It also measures the related electrical current.

From a technical point of view, the question can betackled in three ways, each exploiting the tools of
nuclear and particle physics.
“Direct methods” look for signals from nuclei
kicked on by a WIMP. Since WIMPs interact
rarely and the signals are feeble, the detectors areoperated deep underground, well shielded against
noise and ambient radioactivity which may mimic
WIMP signals. “Indirect methods” look for particles such as neutrinos, gamma rays or antiparticles
that would emerge from WIMP annihilations incelestial high-density regions, like the Sun or thecentre of the Galaxy. Last but not least, dark matterparticles may be produced in high energy particle
interactions at the Large Hadron Collider.

Devices for direct
dark matter detection
Some of the direct-search underground detectors aim to detect the light flashes emitted when a
WIMP strikes a nucleus, some the released heat andsome the feeble electric current of that interaction.
The DAMA collaboration is studying light flashes
in NaI crystals and reports an intriguing annual
modulation of their event rate. Such an effectcould be a consequence of the Earth’s revolution
around the Sun since the strength of head-on
collisions depends on the relative velocity between
the “sea” of WIMPs and the target nuclei in thedetector. However, in order to prove whether thismodulation is indeed due to dark matter particles
rather than to some other annual effect, it must
be confirmed by other experiments.
Deviation from average

How to detect dark matter?

500

1000

1500

2000

2500

3000

3500

4000
4500
Time (day)Annual modulation of the counting rate observed by the
DAMA experiment in the Italian Gran Sasso Laboratory– first with 100 kg (larger error bars), later with 250 kg
detector mass (small error bars).

The combination of two of the aforementioned
signatures provides the best rejection of fake signals.

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3. Dark matter & dark energy

Detecting light or electric current together with theheat released in ultra-cold crystals is one way, detecting electric current together with light in detectors filled with noble liquids another. Present best
sensitivities have been obtained with the cryogenic
CDMS detector in the USA, and with XENON,
a USA-European liquid xenon detector operated in
the Gran Sasso underground laboratory in Italy.
No clear WIMP signal has been identified with theexisting two-signature detectors of several kilograms
mass. Therefore, the need for larger masses and evenbetter noise reduction is obvious. European dark
matter teams working with cryogenic techniques arefocussing their efforts towards a ton-scale detector,
EURECA, with dramatically improved rejectionof noise signals. Collaborations using noble liquid
detectors filled with argon and xenon are presently
constructing devices on the 100-kg scale and envisage next generation detectors of a ton and beyond.

The CRESST detector in the Gran Sasso Laboratory searches
for a combination of light and heat signals in crystals cooled
down to about 20 milli-Kelvin.

Dark matter strategy

Towards the 100 kg scale: The XENON team is installing alarger detector.

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We recommend supporting the current roundof these experiments at a high priority, as wellas the technology development towards theirnext-generation versions on a ton scale. These
detectors will exceed the sensitivity of present
detectors by about three orders of magnitude
and therefore will have a fair chance of discovering WIMP dark matter. A recommendation on which of the technologies – noble
liquid or cryogenic crystals – should firstmove to a next stage can only be made afterAstroparticle physics: the European strategy

A combination of heat and electrical current ingermanium crystals is recorded by the Edelweiss
detector in the Laboratoire Souterrain deModane (France).

first results from the present experiments in
the 10 to 100 kg target mass range become
available and after noise rejection and sensitivity/cost ratio for ton-scale detectors can be
judged on a more realistic basis. This milestone can be reached by 2010 or 2011.
As soon as one of the technologies turns out
to be clearly superior in sensitivity, cost, andtiming, we suggest promoting this technology with priority.

The central part of a 100-litre liquid argon detector being
installed by the WARP collaboration in the Gran Sasso
Laboratory.

Artist’s view of the planned EURECA experiment, joining
expertise from predecessors CRESST and Edelweiss.

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3. Dark matter & dark energy

Artist’s view of a possible design for a European space mission EUCLID.

Dark energy
Particle physicists have been engaged in the field of
dark energy since the beginning. They contributedwith their experience of handling large data sets andwith cutting-edge technologies. Since the construction of future instruments – large telescopes andspace missions – depends on choices beyond
the single authority of the agencies charting thisroadmap we refer to the Infrastructure Roadmap for
European Astronomy for a more complete overview
of projects related to dark energy. Looking beyond
existing instruments, a next generation of cosmology missions is already in preparation. Examples

are the European Planck mission on a satellite exploring the 2.7 Kelvin radiation with unprecedented
sensitivity, and the ground-based Dark Energy
Survey (DES), the latter with European participation from Spain and UK. Projects to be started
after 2013 include the Large Synoptic Survey Telescope, LSST, and the space based missions JDEM
(NASA/DOE) and EUCLID (ESA). At present,
there is a growing number of European institutions
planning to participate in these projects. Worldwide, a variety of other projects are envisaged orare being prepared, like SKA, the Square Kilometre
Array, which appears as an entry in the European
Roadmap for Research Infrastructures, ESFRI.
Needless to say, many of these devices support avariety of standard astronomical tasks and are notlimited to dark energy surveys. Given the profound
implications for fundamental physics, dark energy
missions find the strongest support from the astroparticle physics community.

The Large Synoptic Survey Telescope LSST

Computer-simulated image of dark matter clumps which act as seeds for the later formation of galaxies.

17.

Elusive neutrinos

4. Properties of neutrinos

Neutrinos by far outnumber atoms in the Universe. They may have helped shape the Universe and may well be the reason that we are here.
Most of what we know about these ghostly particles we have learned
during the last decade, but some fundamental questions remain.

“Almost nothing”
and almost everything
When Pauli postulated the neutrino, he
was not only convinced that they were notdetectable at all, but also could not imagine
that they are related to our own very existence. Truly, the neutrino’s tendency tointeract with matter is tiny: among the 60
billions of solar neutrinos which cross every
square centimeter on Earth per second,
only a handful collides with an atomic
nucleus; the rest passes the Earth unaffected. However, this «almost nothing» isessential for our life and for the Universe
as a whole:• Neutrinos helped to cook the lightelements in the early Universe.
• Neutrinos tell us how the Sun
shines.
• Without neutrinos dying stars
would likely not explode andfertilize the cosmos with heavy
elements, a necessary ingredientof our existence.
• Neutrinos may have been
essential for the disappearance of antimatter. A
tricky mechanism named
leptogenesis could haveproduced an excess ofanti-neutrinos in the early Universe, eventuallyleading to the dominance of matter particles
like protons, neutrons and electrons and leaving
the Universe without antimatter.

Oscillating neutrinos
Neutrinos appear in three species: electron
neutrinos, muon neutrinos and tau neutrinos.
In the Standard Model of particle physics,
neutrinos should have no mass, like photons.
This assumption was questioned when electron
neutrinos were shown to disappear on their
way from the Sun to the Earth. As we know
today, the electron neutrinos change their identity to one of the other species, the latter escaping detection. A similar effect popped up in
the Earth’s atmosphere: neutrinos produced bycosmic rays change their species during their trip
to the detector. This change is dubbed neutrino
oscillation, or mixing, and it can occur only ifneutrinos have a mass. Therefore, oscillations
herald first physics beyond the Standard model.
Experiments at nuclear reactors and accelerators
have confirmed these findings and also provided
independent knowledge about the strength bywhich the three neutrino species mix with eachother. Unfortunately, oscillations are unable toprovide us with the values of these three masses:
we know «only» the differences between thesquares of any pair of them.

Astroparticle physics: the European strategy

Neutrino oscillations: neutrinos are not only
ghosts but also chameleons.

Neutrino masses:
single beta decay
How can we determine the absolute valuesof neutrino masses, rather than just the massdifferences? In the traditional method, one
measures the electrons from tritium beta
decay, where a neutron inside a nucleus
transforms into a proton, an electron andan antineutrino. From these experiments weknow, that the heaviest of the three neutrinos
is lighter than 2.3 eV, i.e. about 4 millionthof the electron mass.
KATRIN, the KArlsruhe TRItium Neutrino
experiment, will have a tenfold improved
sensitivity and either determine the mass
value or improve the upper limit down to 0.2
eV. If KATRIN fails to see an effect, alternative methods might come to the rescue. Inan approach named MARE, physicists plan
to cool small radioactive crystals to milliKelvin and measure the tiny temperature
increase from decay electrons interacting in
the crystal.

Neutrino-less double beta decay
In normal beta decay, a neutron inside a nucleus
transforms into a proton (which stays bound in
the nucleus), an electron and an antineutrino. Let
two neutrons in a nucleus decay simultaneously,
releasing two electrons and two antineutrinos.
Then you have a rare (but observed) process called
double beta decay. In its neutrino-less version,
only electrons are released, no antineutrinos. This
process is only possible if neutrinos are their own
anti-particles (Majorana neutrinos) and if they
have a mass. The consequences of a possible Majorana nature of neutrinos would be fundamental.
It is, for instance, the condition that leptongenesis
leads to the observed dominance of matter overantimatter in the Universe.

The NEMO-3 detector in the Laboratoire Souterrain deModane (France).

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4. Properties of neutrinos

Installation of the GERDA detector
in the Gran Sasso Laboratory.

So far, only one group claims to have observed
neutrino-less double beta decays – from 76Ge
nuclei – and claims a neutrino mass in therange of 0.2 to 0.6 eV. The interpretation of
the measurement is controversial and calls
for replication. This is being attempted with
the GERmanium Detector Array, GERDA,
which will measure 76Ge decays with a more
massive device and better noise suppression.
In its first phase (start 2009, Gran Sasso
Underground Laboratory) it will comprise 18
kg germanium crystals, later 40 kg, and reacha sensitivity of 0.1 to 0.3 eV. Existing experiments like CUORICINO (also Gran Sasso)
and NEMO-3 (Modane Laboratory in the
Frejus tunnel) use other nuclei and are exploring mass ranges of the order of 0.2-0.7 eV.
They also have their more massive follow-ups:
CUORE comprising 204 kg tellurium 130Tein the form of dense packed, super-cooled
TeO2 crystals with 740 kg total mass (planned
start 2011) and SuperNEMO comprising
sandwiches of radioactive material with tracking chambers (planned start 2012-13), withplanned final sensitivities of 0.03-0.1 eV. Twoother projects are EXO in the US, with Swiss
participation, using 136Xe as an isotope, and
COBRA, a project in its early development
stage, using the cadmium isotope 116Cd.

The strategy for
double beta decay experiments
We give priority to the experiments expected
to start operation within the next five years:
GERDA (phase I and II), CUORE and SuperNEMO. Complementary nuclei and measurement methods are essential to judge any positive
claim or any upper limit. These experiments
will be capable of scrutinizing the claimed
evidence in 76Ge. They will approach a mass
range preferred by certain theoretical models(the “inverted hierarchy” range) and keep European leadership in this field. Other methods
may become competitive in the future.
At the same time, the next goal should be envisaged, an experiment on the 1-ton-isotope
scale, which will peer deep into the inverted
hierarchy mass range. From today’s perspective,
it can be accomplished with two options, bothto be realized with a worldwide cost sharing.
GERDA-III could be a merger of the GERDA
project with the USA germanium project Majorana. CUORE-II could change from natural toenriched tellurium, with USA participation. A
major milestone would be the decision on theisotopes/ techniques to be taken by 2013.

Precision manoeuvre for a precision experiment: The huge KATRIN vacuum vessel merely passes a narrow street
on its way from the factory to the Research Centre in Karlsruhe.

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Underground physics

5. Underground physics on the Megaton scaleWith a huge multi-purpose detector, physicists will search for decaying
protons, study the interior of the Sun and the Earth, obtain incredibly
detailed information about a possible galactic Supernova and also study
neutrinos from accelerators.

Underground astroparticle physics has
resulted in huge detectors, the largest
being Super-Kamiokande (or just “SuperK”), a tank in a Japanese mine filled with
50,000 tons of ultra-pure water. Its walls
are paved with 11,000 20-inch photodetectors recording the tiny light flashes
from particle interactions. Super-K is
one of the most successful devices inmodern physics, and it is a true multipurpose device. It accounts for the precision measurements of solar neutrinos,
the detection of neutrinos from thesupernova 1987A, the confirmation ofneutrino oscillations with neutrinos
from the Sun and the Earth’s atmosphere, and for the best upper limits
on the lifetime of protons.

Proton decay
Grand Unified Theories (GUTs)of particle physics predictthat the proton has a finite
lifetime. The discovery of
proton decay would be oneof the most fundamental
discoveries for physics
and cosmology. The
related physics may beclosely linked to the physics of the Big Bang,the cosmic matter-antimatter asymmetry anda mechanism called baryogenesis. Data fromSuper-K constrain the proton lifetime tobe larger than 1034 years, tantalizingly close
to predictions of certain “super-symmetry”
GUT versions. A sensitivity improvementof an order of magnitude would requirewater-filled detectors on the Megaton scaleor detectors filled with scintillating liquid or
liquid argon on the 100 kiloton scale.

Neutrinos from spaceand Earth: a synoptic view
Proton decay detectors can also detectcosmic neutrinos. Solar neutrinos, burst
neutrinos from the supernova SN1987A,
reactor neutrinos, neutrinos generated in the
Earth’s crust and in the Earth’s atmospherehave already been detected. Measurements ofneutrinos in this energy range – MeV to GeV– would be vastly improved in a next-stage
proton decay detector.
Even higher energies are the domain of
detectors underwater rather than underground. Neutrinos from Active Galactic
Nuclei (AGN) and collisions of ultra-energetic protons with the 2.7 Kelvin cosmic
microwave radiation (marked GZK) will

Astroparticle physics: the European strategy

View into the BOREXINO detector
being filled with 100 tons of ultra-purescintillator.

likely be detected by neutrino telescopes in
the next decade (see section 6). No realistic
idea exists how to detect 1.9 K cosmologicalneutrinos, the analogue to the 2.7 Kelvinmicrowave radiation.
Solar neutrino astronomy has turned into
precision science, with eminent input fromthe GALLEX detector in Gran Sasso. Europe’s
excellent tradition in this field is presently
continued by the BOREXINO liquid scintillation detector that started operation in2007 and determines, for the first time, theflux of the 7Be neutrinos.

Flux (cm–2 s–1 sr–1 MeV–1)

1024
1020

Cosmological ν

1016

Solar ν1012

Supernova burst (1987A)

10

8Reactor anti-ν104

Background from old supernova

1
10–4
Terrestrial anti-ν

10–8

Atmospheric ν

10–12
10

–16

The strategy
The rich legacy of underground neutrino
physics is intended to be continued witha worldwide effort towards one or two
multi-purpose detectors in the mass scaleof 100-1000 kilotons. Such a facility will
increase the sensitivity to proton decay byan order of magnitude, would provide incredibly detailed information on the early phaseof supernova core-collapse processes, andwill allow the study of details of the standard
solar model with percent accuracy. Highstatistics studies of atmospheric neutrinos
will improve our knowledge of the neutrino
mixing, and the study of geo-neutrinos will
improve our understanding of the Earth’s
interior. Next generation undergroundobservatories will also allow long baseline
neutrino experiments with beams from accelerators to be performed with unprecedented
precision.

ν from AGN

10–20
10–24

GZK ν

10–28
10–6
μeV

10–3
meV

1
eV

103
keV

106
MeV

109
GeV

1012
TeV

1015
PeV

1018
EeV

Neutrino energy

A synoptic view of neutrino fluxes.
Underground detectors are tailored to the energy range of
100 keV to 100 GeV. This is also the focus of detectors on
the Megaton scale described in this chapter. The extremely
low fluxes at higher energies can be only investigated with
detectors of Gigaton rather than Megaton masses. They aredescribed in chapter 6.

A new giant underground observatory
will be global in nature and has to follow
worldwide coordination and cost sharing.
LAGUNA, a common design study within
the 7th European Framework Program(FP7), is presently underway. It evaluates
three detection techniques: water Cherenkov
detectors, liquid scintillator detectors andliquid argon imaging detectors. The study23.

5. Underground physics on the Megaton scale

will also address the costs of undergroundinfrastructures in several potential locations
in Europe. With related efforts underway in
the USA and Japan, the necessity of a coherent approach is obvious.
The three concepts of the LAGUNA design study: a 700
kiloton water detector (MEMPHYS), a 100 kiloton liquidargon detector (GLACIER) and a 50 kiloton liquid scintillator detector (LENA).

24.

The LAGUNA design study should provide,on a time scale of 2010, the key information on the discovery potential for the different options and sites and then converge to
a common proposal. We recommend additional support to complete the detector R&D
programmes that could not be fully supported
within the FP7 Design Study. Input to thephysics perspectives and feasibility of a large

Astroparticle physics: the European strategy

The Double Chooz experiment inFrance studies neutrinos from anuclear reactor.

underground facility is expected from present
experiments, like BOREXINO (liquid scintillator) and ICARUS-T600 (liquid argon)
in Gran Sasso. Evidence for a non-vanishingmixing between the lightest and heaviest
neutrinos from the long-baseline experiments
Double Chooz (France) and T2K (Japan,
with strong European participation) would
boost our understanding of CP violation. The
observation of different oscillation behaviourof accelerator-generated neutrinos and anti-

neutrinos would have fundamental consequences for matter-antimatter asymmetry in
the Universe. These observations would impact
plans for studying accelerator neutrinos with a
Megaton detector and also motivated proposals for dedicated liquid argon detectors, e.g.
MODULAR at Gran Sasso.

Artist’s view into the inner volume of LENA. The walls are
paved with large photo-sensors.

25.

se
The high-energy Univer

6. The high-energy Universe

The origin of cosmic rays, the most energetic particles everobserved, is going to be revealed in the coming years. Huge
observatories for high energy cosmic rays, gamma rays andneutrinos will open an unprecedented view on the violent Universe.

From the Hot to the Extreme

Radio continuum
Infrared IRAS satellite

Most of the visible cosmic matter is in a state
which physicists call “thermal equilibrium”,
characterised by a certain temperature. The
prime cosmic example is our Sun: analysing
its spectrum, we can easily conclude that its
surface temperature is about 6000 Kelvin.
The spectra of hotter stars, extending far to
the ultraviolet or the X-ray range, indicate
temperatures up to 50000 Kelvin. In the
X-ray range, some strange objects begin toappear on astronomer’s sky-maps. They do
not fit into the equilibrium scheme but
emit considerably more energetic particles than expected for a body with a welldefined temperature. It is here that therealm of the “non-thermal” Universeof extremely high energies begins: therealm of cosmic accelerators.

The realm of
cosmic accelerators
The first obvious proof ofsomething beyond thethermal Universe wasprovided by charged
cosmic rays. They consistof protons, light andOptical
X-Ray ROSAT satellite
Gamma Ray> 100MeV, EGRET, satellite

The galactic plane as seen in different wavelengths.

heavy nuclei, with a minuscule admixture ofelectrons. Some of these particles reach breathtaking energies – about 100 billion GeV (1020eV)! This dwarfs any ground-based accelerator:
it corresponds to about 10 million times thebeam energy of the Large Hadron Collider.
1000 times the LHC – the CRAB nebula is a remnant
of a supernova exploded in the year 1054. At the fronts ofthe expanding cloud, particles are accelerated to close to the
speed of light.

Astroparticle physics: the European strategy

10 000 000 times the LHC? – Artist’s viewof an active galaxy: matter falls to a supermassive black hole in the centre, part of it
makes its way to the jets. Places of acceleration
are the vicinity of the black hole and the jets.

A threefold attack:multi-messenger astronomy
Cosmic rays with energies up to some million
GeV are probably accelerated at the shock
fronts of galactic supernova explosions. Indeed,radio emissions and X-rays give direct evidence
that these fronts accelerate electrons to nearly
the speed of light. However, the evidence thathigh-energy protons and nuclei – the main
component of cosmic rays – have the same
origin is only circumstantial and needs confirmation. How do these particles propagate
through the Universe? What is the maximum
energy achievable by galactic sources such as
supernova remnants or binary star systems?
If the ten-million GeV range is a puzzle, thenthe 100-billion GeV range is a mystery! Are
particles with these energies due to cosmic acceleration in the vicinity of super-massive black
holes or around star crashes? Or are they due
to something totally different, like the decay ofsuper-heavy relic particles from the Big Bang?
Accounting for these extreme energies is one of
the greatest challenges in astroparticle physics.

Cosmic rays give clear evidence that something extremely energetic is happening in the
Universe. But they do not tell us where. Since
they are electrically charged, their paths curveas they travel through cosmic magnetic fields.
They don’t point back to their sources, except
at the very highest energies where deflection
becomes small. Fortunately, the suspectedsources are also predicted to emit by-productparticles which travel in straight lines: gamma
rays and neutrinos. Indeed, gamma rays withenergies up to a hundred thousand GeV havebeen observed from a variety of sources. In mostcases, however, it is not clear whether they are
produced in high-energy proton interactions
with the ambient matter, or whether they areradiated by electrons. Here, neutrinos may
come to the rescue: they can only be produced
in processes including protons and nuclei. Witha threefold attack – charged cosmic rays, gamma
rays and neutrinos – there is a good chance that
we will unveil the mystery of cosmic rays before
the centenary of their discovery in 1912, andafterwards fully explore the landscape of theextreme Universe.

27.

6.1 Cosmic rays

Birth of a mystery
Cosmic rays collide with atmospheric molecules at 15-20 km altitude and trigger avalanches of secondary particles. In 1912, Victor
Hess measured the secondary particles. The
primary particles can only be measured fromstratospheric balloons and satellites.

28.

With increasing energy, the flux of primaryparticles becomes so low that the small detectors in balloons are not even able to collecta few particles. However, in 1938 Pierre
Auger demonstrated that avalanche particles from very high-energy parents can reachthe ground. This was his recipe: arrange a
Registration of high-energy cosmic rays: particle detectors record
the avalanche particles reaching the ground, special telescopes
measure the light emitted along the avalanches in the air.

Astroparticle physics: the European strategy

Argentina is the host of the Southern
Pierre Auger Observatory

large array of detectors at ground level andregister the punch-through particles which
fire several of the detectors in coincidence.
It took another 24 years until the Volcano
Ranch array in the USA recorded a cosmic
ray event of 1020 eV: the mystery, as it stands
today, was born!

The cosmic ray spectrum
The cosmic ray spectrum extends over 32
orders of magnitude. At 100 GeV, one particle

per square metre per second bombards theatmosphere. At one million GeV it is only
one particle per square metre per year. And
in order to catch one per year of the tenbillion GeV grenades, one needs a full square
kilometre!
Still, much can be learned at GeV energies with detectors on satellites like Pamela(launched in 2006) and AMS, the Alpha
Magnetic Spectrometer Experiment; forexample about primary mass composition, or
about the contribution of anti-particles andtheir possible relation to dark matter. Going
higher in energy, the KASCADE detector
in Karlsruhe has provided new insight intogalactic cosmic rays of up to 1017 eV, withcomplementary information coming in from
IceTop at the South Pole and from the Siberian Tunka array. The focus of forthcoming
research, however, is on the very highest
energies, likely to be entirely of extragalactic
origin. This is the domain of the terrestrial
Pierre Auger Observatory and space-bounddetectors monitoring huge volumes of theatmosphere for traces of high energy particles. Two smaller projects address energies
between KASCADE and Auger: the Japan-led
Telescope Array presently under construction
in Utah/USA, and a planned air shower arrayin China.
The flux of cosmic rays.

29.

6.1 Cosmic rays

The Pierre Auger Observatory

atmosphere. The combination of two techniques excludes many uncertainties fromwhich predecessor instruments had suffered;
the large area allows the collection of morethan just a few events in the 10 20 eV range.
This is where bending in cosmic magnetic
fields becomes smaller and back-tracing of
cosmic rays to their sources realistic.
Actually, from their first data, Auger physicists already report tantalising correlationsof cosmic ray directions with cosmic matteraccumulations, and this may be the first step
towards true cosmic ray astronomy. Moredata are being taken with the completed
detector and are expected to improve thestatistical significance of the observation.

Auger North
The direction of air showers can be derived from the particle
arrival times in the Auger water tanks and from theavalanche pattern recorded with the telescopes (not shownhere).

The Southern Pierre Auger Observatory is
located in the Pampa Amarilla in Western
Argentina. Researchers have carpeted 3000
km² of the prairie with 1600 water tanks.
The array is overlooked by four clusters offluorescence telescopes which record thelight flashes emitted by air showers in the30.

Encouraged by this first glimpse, the Auger
collaboration envisages a 20 000 km² arrayin Colorado, USA. The case for “AugerNorth” is strong: high statistics astronomy
with reasonably fast data collection calls
for a substantially larger array than Auger
South, full sky coverage calls for a Northernsite. A larger array would also allow a moredetailed inspection of the high energy
cut-off of the particle spectrum, which
recently has been firmly established byAstroparticle physics: the European strategy

Sky-map of the publised 27 highest-energy Auger events (black
circles), compared to positions ofactive galactic nuclei (red crosses).

Auger-South. Is it due to the omnipresent
sea of 2.7-Kelvin photons, the relics of the
Big Bang, which slow down ultra-energetic
particles when they travel for more than 100
million years? Or is it just due to cosmic
accelerators running out of power? Auger-

North, the clear priority project for charged
cosmic rays for the next decade, will help
answer these questions and further populate
the sky map of cosmic accelerators.
A water tank of the Pierre Auger Observatory, with theAndes in the background.

31.

6.2 Exploring the Universe with gamma rays

The last decade has witnessed the birth of a new
field of astronomy – Very High Energy (VHE)
gamma ray astronomy – expanding wavelength
coverage of astronomical instruments by another10 octaves towards the highest energy radiation.
These gamma rays are produced when high energy
cosmic rays bump into interstellar gas, creating
a bunch of elementary particles. Unlike charged
cosmic rays, the gamma rays travel on a straightpath and point back to the point in the sky where
they were produced. Apart from serving as tracersof cosmic rays, speculation is that some VHE
Registration of gamma ray-initiated avalanches in the atmosphere with Imaging Atmospheric Cherenkov Telescopes.

32.

gamma rays may result from decays of relic particles with have survived since the Big Bang, such as
the mysterious dark matter particles; detection ofsuch gamma rays would give first hints towards thenature of dark matter.

Imaging Atmospheric
Cherenkov Telescopes
Very High Energy gamma rays are absorbed in the
Earth’s atmosphere, creating a cascade of secondary elementary particles, most of which neverreach the ground. Satellite instruments such as
AGILE and Fermi (the former GLAST), now inorbit, detect gamma-rays before they enter theatmosphere, but their size is too small to capture
enough of the highest-energy gamma rays. Afterlong development, a ground-based detection
technique pioneered by the American Whipple
telescope and perfected by the European-led
H.E.S.S. and MAGIC instruments has brought a
break-through: Imaging Atmospheric Cherenkov
telescopes. These telescopes collect and image
the bluish light emitted by the particle cascades
created by a VHE gamma ray in the atmosphere.
Light from a single VHE gamma ray illuminates a“light pool” of about 150 m radius on the ground,hence a single telescope will detect gamma
rays incident upon an area of a few 10000 m2,
compared to the sub-m2 area of satellite detectors.
Latest generation Cherenkov telescope systems

Astroparticle physics: the European strategy

The remnant of a supernova, as seen in TeV gamma rays.
The brightest region top-right marks a molecular cloud.
The gamma rays from this spot are likely produced in collisions of nuclei accelerated at the shock fronts of the supernova. A first convincing image of a cosmic ray accelerator?

use multiple telescopes to provide stereoscopic
viewing of gamma-ray induced particle cascades,
for improved determination of impact directionand energy of a gamma-ray.
Cherenkov telescopes are flanked by detectors
recording the shower particles which reach theground, like the ARGO/YBJ detector in Tibet,
or the American MILAGRO instrument and its

planned successor HAWC. Although inferior insensitivity, they provide an important complementin that they continuously monitor large parts of thesky and allow the study of extended cosmic sources,
including the band of the Milky Way.
One of the four 11-meter mirror dishes of the H.E.S.S. telescopein Namibia. In 2009, a fifth dish with 25 meter diameter will
be installed and improve the low-energy sensitivity of the array.

33.

6.2 Exploring the Universe with gamma rays

A rich harvest
VHE gamma-ray astronomy is becoming partof mainstream astronomy, with surveys of the
Galaxy revealing dozens of VHE gamma-ray
emitting cosmic-ray accelerators.

Objects discovered include supernova remnants,
binary systems, pulsars, stellar associations anddifferent species of active galaxies, hostingsuper-massive black holes at their centres.

The first of the two huge 17-meter dishes of the MAGIC telescope at La Palma with its excellent coverage of lower energies.

34.

Astroparticle physics: the European strategy

The band of the inner parts of the galactic plane as scannedwith the H.E.S.S. telescope. The plane turns out to be linedwith sources of TeV gamma radiation, some of them notknown from any other wavelength.

The future: CTA
So far, Cherenkov telescopes such as H.E.S.S. or
MAGIC are considered “experiments”, requiring
dedicated experts to analyse and fully exploit theirdata. Both the communities of astronomers andof astroparticle physicists feel that the time is ripe
to construct a next-generation VHE gamma-ray
observatory, which on the one hand boosts sensitivity and resolution beyond that of the current
instruments, and also provides observatory services
and tools thus making VHE gamma-ray astronomy
accessible to the entire community. This resulted in
the proposal for the Cherenkov Telescope Array
CTA, composed of a large number of Cherenkov
telescopes covering the gamma-ray energy range
from some 10 GeV to beyond 100 TeV. Combinedwith a 10-fold improvement of sensitivity and asignificant improvement in resolution, CTA is
expected to reveal about one thousand sources of
VHE gamma rays and to explore their spatial struc-ture and energy spectra. Ultimately, a Northernand a Southern CTA instrument, operated under acommon framework, should provide full-sky coverage. Operational overlap with the Fermi satellite
mission will provide seamless coverage of 20 octavesof the spectrum. CTA is the priority project in thefield of European gamma-ray astronomy. Coordination with similar efforts in the USA (AGIS
concept) is underway. CTA is on the ESFRI list of
emerging projects and has been proposed as a full
ESFRI entry. It is also listed as a priority entry in the
ASTRONET infrastructure roadmap. We recommend the design and prototyping of the CTA andselection of site(s), and proceeding rapidly towards
the start of deployment in 2012.
A possible design of CTA, the Cherenkov Telescope Array. Largemirrors in the centre collect enough light to catch dim showers
from low-energy gamma rays. To collect large statistics at highenergies, where particles are rare but the associated showers arebright, smaller mirrors cover an area of a few square kilometres.

35.

6.3 High-energy neutrino astronomy

Going deep, looking deep

Detectors in water and ice

As of today, the sky-map of extraterrestrial
high energy neutrinos is still empty – a challenging terra incognita. Such neutrinos must
be emitted as a by-product of high- energy
collisions of charged cosmic rays with matter.
Since they can escape much denser celestial bodies than light, they can be tracers ofprocesses which stay hidden to traditional
astronomy. Undisturbed by anything, theyreach us from the remotest regions of the
Universe and may let us peer deeper into
the universe than with any other messenger.
Nevertheless, at the same time their extremely low interaction probability makes theirdetection extraordinarily difficult.

In neutrino interactions in water or ice, feeble
Cherenkov light flashes are produced which canbe registered by light sensors arranged over a large
volume. This principle was first conceived in thelate fifties. In the mean time, first-generation detectors are being operated in the Siberian Lake Baikal(NT200), in Antarctic ice (AMANDA) and mostrecently in the Mediterranean Sea (ANTARES).

Detectors for solar neutrinos are buried deep
underground in order to shield them against
noise which could mimic their rare interactions. Only neutrinos can penetrate deep
enough to reach these devices undisturbed.
In order to detect the low fluxes from thesuspected distant sources of high-energy
neutrinos, immense detectors of cubic kilometre volume are required. They cannot be
arranged underground but only in deep
oceans, lakes or glacial ice where available
space is no issue.

36.

A muon is generated in a neutrino interaction and emits
a cone of bluish Cherenkov light. The light is recorded by
sensors in pressure tight glass spheres.

However, even the sky-map of AMANDA, with
6595 neutrinos collected over seven years, does
not reveal statistically significant spots localising cosmic accelerators. Nearly all of theseneutrinos seem to be produced in the Earth’s
atmosphere, in the avalanches of particles

Astroparticle physics: the European strategy

Sky map composed of 6595 neutrinos recordedwith AMANDA. Colours indicate thestrength of the local excesses. Yet, none of theobserved excesses is statistically significant.

initialised by charged cosmic ray interactions.
To realise the dream of high-energy neutrino astronomy one needs detectors of a cubic kilometre
scale or beyond. The construction of these detectors in now underway (IceCube at the South Pole)or planned (KM3NeT in the Mediterranean Sea).

Towards cubic kilometre
telescopes
European physicists play a strong role in the mostadvanced neutrino project, IceCube. IceCube ispresently taking data with half a cubic kilometre
instrumented volume and will be completed in
January 2011. In parallel, a broad community
works towards KM3NeT, a cubic kilometre scale
neutrino telescope in the Mediterranean Sea,
with the recent commissioning of ANTARES(close to Toulon) defining a milestone towards
the next generation telescope. Prototype devices
with alternative designs have been or are operated
close to the Peloponnesus (NESTOR) and to
Sicily (NEMO). In parallel, Russian physicists
plan an array with sensitivity somewhere between
present detectors and KM3NeT.
KM3NeT is the priority project of high energy
neutrino astronomy in Europe. It is on the ESFRI
list, has obtained funds for an FP6 design study
and has recently started a FP7 Preparatory Phase. It

is also listed as a priority entry in the ASTRONET
infrastructure roadmap. KM3Net will complement
IceCube at the South Pole: IceCube will preferentially observe the Northern sky – with neutrinos
having crossed the Earth; KM3NeT will preferentially observe the Southern sky. Resources fora Mediterranean detector should be pooled into asingle optimised design for a large research infrastructure. The KM3NeT Technical Design Reportis expected in late 2009, defining the configuration, deciding between competing technologicalsolutions and providing site arguments. The sensitivity of KM3NeT will substantially exceed that of
all existing neutrino detectors including IceCube.

Artist’s view of a possible KM3NeT configuration.

37.

Probing gravity

7. Gravitational waves

Most of the phenomena predicted by Einstein’s General Theory of Relativity have been confirmed, but one has resisted a direct experimental
proof: the emission of gravitational waves by accelerated bodies.

Proving Einstein

Messengers of catastrophes

When Einstein formulated his General
Theory of Relativity, he predicted a numberof stunning phenomena related to the curvature of space-time. Most of them have been
confirmed in the meantime, but one of themhas resisted direct experimental proof. It is
the emission of gravitational waves by accelerated bodies, ripples in space which propagate at the speed of light and rhythmicallycompress and stretch the distances between
objects. Their existence has been indirectly
confirmed by the change of the orbiting speed of two close stars, a discovery
acknowledged with the 1993 Noble Prizein physics. Einstein considered them too
weak to be ever detected directly: even asupernova collapse in a neighbourhood
galaxy would change the distance
between Earth and Sun by only thediameter of a hydrogen atom, andeven this for only a few milliseconds. However, after decades ofdevelopment, researchers havedeveloped tools so sophisticatedand sensitive that the definitive detection of gravitational waves is within reach.
Within a decade, we should
see true gravitational wave
astronomy flourishing.

Gravitational waves must be emitted by the
coalescence of two orbiting compact objects
like neutron stars or black holes, or whena star is sucked into a massive black holeat the centre of a galaxy. The observationof gravitational waves from binary mergers
out to extreme distances would strongly
impact cosmology. These events can be usedas distance markers and help to map thecomplete expansion history of the Universe in
a way complementary to methods of standard
astronomy, thus providing completely independent information on dark energy. Last
but not least, the Big Bang filled the cosmos
with a faint background of gravitational
waves, similar to the 2.7-Kelvin microwave
background. On a long-term basis, detectionof this ultimate first picture is conceivablewith devices in space.

Modelling of gravitational waves produced by the merging
of two black holes.

Astroparticle physics: the European strategy

Cylinders and interferometers
First attempts to detect gravitational waves usedvery massive metallic cylinders and aimed tomeasure the tiny vibrations caused by gravitational waves. Although these instruments
may be able to detect a nearby supernova, theycannot compete with a technique using interferometers. In these devices, light waves are split,
propagate along extended, perpendicular arms,
are reflected back by large mirrors, and finallysuperimposed at the splitting spot. A gravitational wave passing the device would compress
the space along the two arms in a different
way, leading to a flickering of the interference
pattern. Longer arms, higher light power andbetter noise suppression are the keys to improve
the sensitivity of the interferometer. Progresswith light power and noise suppression has been
tremendous over the recent years.

GEO have formed a worldwide consortium which
had a first common data run in 2007. These devices
have collected a substantial amount of data which
are now being systematically mined for periodic
signals or spikes which may be hidden underbackground noise. These devices could detect
the occasional crash of a binary black hole system
up to distances of a few hundred million lightyears, a volume containing thousands of galaxies.
However, since these processes are rare, detections
within a reasonable operation period are not very
likely, although not excluded.

First generation interferometers
At present, there are four large interferometricobservatories: TAMA in Japan (300 metre arms),
GEO-600 in Germany (600 metre arms and asource of many principal innovations), LIGO in
the USA (two 4-km arms and one 2-km arm).
Youngest in the club is Virgo in Italy (3-km arms)
which took first data in 2007. LIGO, Virgo andEurope’s two interferometric gravitational wave observatories: GEO 600 (top) and Virgo (bottom).

39.

7. Gravitational waves

Advanced interferometers
The existing detectors are currently being
upgraded. First, “enhanced” versions of thefirst generation devices will be launched within
the next two years. They will be succeededby “advanced” versions which could be truly
ranked as second generation interferometers.
The advanced detectors will cover a cosmic
volume a thousand times larger than thecurrent ones, with a clear worldwide strategy
to reach this stage around 2014. Observationof gravitational waves is expected within someweeks or months of operation. This will set thestage to start construction of a third-generation interferometer which would propel gravitational wave detection to the level of standard
astronomy, with many thousands of sources
per year.

The future: E.T, the Einstein
Gravitational Wave Telescope
E.T. is the long-term future project of groundbased gravitational wave astronomy. With anobserved volume a thousand times larger thanthat of the second-generation detectors, E.T.
will record many thousands of events per year,
and, in a network arrangement, have an unprecedented sensitivity at 10 Hz to a stochastic

40.

gravitational wave background from the
Big Bang. The European gravitational wave
community is well co-ordinated and plays aworld-leading role in planning for the futureof the field. An FP7 Design Study for E.T.
has commenced, and a first technical design
and associated costing is expected in 2011,
followed by a ‘Preparatory Phase’. A decision
on funding for the construction of E.T. will
most likely be contingent on a first detection,
which may occur during the era of enhanced
LIGO and enhanced Virgo (“Virgo+”) but ismost likely after collecting about a year of datawith advanced LIGO/Virgo in approximately
2014/15. The targeted start of E.T. construction could be 2016 or 2017.
With European participation in upgradedversions of LIGO and GEO confirmed,
full support for the Virgo upgrade towards“Advanced Virgo” still has to be secured. This
would ensure the critical infrastructure for acoherent gravitational wave programme inEurope and lay the ground for E.T.

Astroparticle physics: the European strategy

Measuring ripples in space with
LISA.

Gravitational waves
from space: LISA
The coalescence of super-massive black holebinaries, the spiralling of stars into black holes,
stochastic backgrounds from the early universeand Big Bang quantum fluctuations would
emit waves in the milli-Herz range. This is therealm of space-based interferometers, where
distances are huge and seismic noise is absent.

The priority for a space mission is LISA. This
ambitious project aims to fly three satellites
at five million-kilometre distance, forming
the “arms” of a huge interferometer. A LISApathfinder mission will provide a final proofof the feasibility of the concept in 2010, withthe start of LISA itself being envisaged for 2018.
LISA is complementary to E.T. It will open the
low-frequency window for gravitational wave
observations and make true multi-wavelength
gravitational wave astronomy a reality.

41.

Infrastructures

8. The infrastructures of astroparticle physics

Astroparticle physics relies on a variety of distributed platforms: large underground laboratories, observatories at very remote locations and satellites. Construction and sustainable operation of these infrastructures are of
key importance for future progress.

Astroparticle physics rests on a variety of
distributed platforms. This is different toparticle physics, with CERN supplying theinfrastructure for the majority of European
experimental activities in the field. The
infrastructures for astroparticle physics canbe grouped into underground laboratories,
observatories and space-based platforms.

km East of Rome, 1400 m underground (3700
metres water equivalent, m.w.e.). With threemain halls each covering 2000 m2 it is thelargest of all the underground laboratories.

Underground laboratories
The study of extremely rare phenomena
calls for an environment free of noise
events which might mimic true signals.
Laboratories deep underground, wellshielded against particles from cosmic
rays, meet this requirement. Experiments performed in undergroundlaboratories include the search for
double beta decay, “direct” searches
for dark matter, investigation ofneutrinos from the Sun or supernovae, and detectors searchingfor proton decay. Europe has
four world-class deep underground laboratories:> The Laboratori Nazionali
del Gran Sasso (LNGS)
along the Gran Sasso
Motorway tunnel, 120

View into one the large halls of the Gran Sasso Laboratory
in Italy.

> The Laboratoire Souterrain de Modane, LSM,
along the Fréjus Road tunnel between Italy andFrance. With a depth of 4800 m.w.e. it is thedeepest of all existing laboratories. Its main hall
has an area of 300 m2. After 2011, an extension
in the context of a coming road-tunnel modification could house ton-scale experiments.
Also, a long-term giant excavation to house a
Megaton-scale detector is being discussed.
> The Laboratorio subterráneo de Canfranc, LSC,
along a tunnel connecting Spain and France, at a
depth of 2450 m.w.e. with 850 m2 area.

Astroparticle physics: the European strategy> The Boulby Underground Laboratory ina potash and rock-salt mine on the coast of
England, at 2800 m.w.e., with 1500 m2 laboratory space.
Other sites are being investigated, offering either
larger depths, or larger distance to nuclear reactors (allowing the study of neutrinos from the
Earth’s crust with a low background from artificially produced neutrinos), or larger available
volume. The largest depths are conceivable in amine in Pyhäsalmi, Finland. Present excavations
at this place reach down to a 4000 m.w.e., butlarge caverns at even greater depth are possible.
Salt mines in Sieroszowice/Poland and Slanic/
Romania offer large volumes at shallow depths.
Small laboratories also exist in France and in
the Ukraine. The oldest of the European underground laboratories is the Baksan Neutrino
Observatory in the Russian part of the Caucasus.
At present, it seems less favoured for logisticalreasons and because of the unstable situation inthis geo-political region.

Map of existing and considered European undergroundlaboratories.

Center for Underground Physics in Pyhäsalmi

Polkowice-Sieroszowice

Boulby Underground Laboratory

Laboratoire Souterrain de Modane

Laboratoire Souterrain Bas BruitLaboratori Nazionali del Gran Sasso

Slanic salt mine

Laboratorio Subterráneo de Canfranc43.

8. The infrastructures of astroparticle physics

A cooperative network ofunderground laboratories
Which of the large experiments will be doneat which site has to be decided over the next
years. Significant activities are under way
within the FP6 programme ILIAS, within the
LAGUNA FP7 design study for a Megatonscale detector, in the laboratories and within
the individual experiments. There are clear
advantages to have several deep undergroundlaboratories in Europe and also to exploit
both types of access – with road tunnels and44.

mines. ILIAS and ASPERA promote thisconcept through formation and operation ofa cooperative network of deep undergroundlaboratories with each partner contributing
low-background facilities and specific infrastructures depending on user demands, techniques available and the specific features ofeach site.

The International Space Station provides the infrastructure for many experiments including AMS 02, the Alpha
Magentic Spectrometer, which should be launched in 2010,
will search for antimatter and measure spectrum and composition of cosmic rays.

Astroparticle physics: the European strategy

The CREAM cosmic ray detector atits launch towards a circumpolar
long-duration flight in Antarctica.

Observatories

Space-based platforms

Most cosmic particle detectors of the past
could be considered “experiments”, with arelatively simple infrastructure. In contrast,
several of the present and most of the future
detectors have the character of “facilities”,
with a sustainable mode of operation andadministration, offering research possibilities to a wide community and being run as
open observatories. For instance, a Mediterranean cubic kilometre facility for neutrino
astronomy will also be used by oceanographers, biologists and seismologists, andthe Cherenkov Telescope Array will reservemuch of its observation time for external
users. The infrastructural aspect of many ofthese facilities is further enhanced by theirremote location. Whereas the necessary
infrastructure for IceCube is provided by
NSF’s Amundsen-Scott Station at the South
Pole, other projects have to create most of
their infrastructure themselves, like H.E.S.S.
in Namibia, the Pierre Auger Observatory
in the Argentinean Pampa, just to name two
examples. A first-class infrastructure, withappropriate funding – not only for construction but also for sustainable operation – is a
key aspect of next-generation detectors.

Some of the detectors for cosmic particles aremounted on satellites. They are able to identify
and measure particles before they interact with
the Earth’s atmosphere. The present major experiments orbiting around the Earth are PAMELA(charged particles) and AGILE and Fermi(gamma rays). The Alpha Magnetic Spectrometer, AMS, is expected to be launched in 2010
and will measure both charged particles andgamma rays on the International Space Station.
Several experiments use stratospheric balloons
for short-term flights, such as CREAM or ATIC,
detecting charged particles. While the detector
construction is supported by particle physics
funding agencies, the infrastructures required tolaunch this type of experiment is usually provided
by national or international space agencies.

The Fermi detector (formerly called GLAST ) records
gamma rays from space.

45.

Innovation

9. Pushing the frontier of innovation

Technological innovation has been a pre-requisite for the enormous progress made over the last two decades. It has enabled maturity in many
fields of astroparticle physics. The challenges of the next decade require
further fresh ideas and cutting-edge technology.

Technological innovation has been a prerequisite for the enormous progress made overthe last two decades and has enabled maturity in most fields of astroparticle physics.
The astroparticle programme calls for betterand cheaper solutions for all of the ubiquitous detectors and materials for astroparticle
physics, for example:• photo detectors,• cryogenic detectors working at milliKelvin temperatures,• charge gain amplification devices,• high-purity crystals and noble liquids
and the related isotope purification techniques,• state-of-the-art optical elements forgravitational antennas.

autonomous sensors. On the computing side,
the treatment of large amounts of experimental
data requires GRID-type solutions, as docomputer simulations, for instance of extensive
air showers or of cataclysmic cosmic events.
Many of the experiments are located in hostileenvironments: anchored deep in the Ocean,frozen in Antarctic ice, installed in the desert,
in underground tunnels, on high mountains or
flying on balloons or satellites. The astroparticle
physicists were the first to install a high-bandwidth continuous link with the ocean bottom,
instrument a very large prairie area with a 3000
km² dense grid of solar powered, synchronizeddetectors and develop underground laboratories
of unprecedented radio-purity. Extreme reliability and remote control are the key words forthese applications.

Beyond cutting-edge improvementsof the existing, principally novel
methods are being tested:• Can one efficiently track particles via their radio emission?
• Can one “hear” neutrino interactions at super-high energies?
Electronics and data acquisition are challenged by theneed to instrument hugeareas or volumes withsophisticated,
often

Given the importance of technological innovation, ASPERA envisages common calls for joint

Astroparticle physics: the European strategy

High-purity germanium crystals for dark
matter search.

funding of research and development projects.
Calls will also stimulate cooperation with industry,
which has been and will be a strong element ofdeveloping cutting-edge technology and of transferring innovative developments to industry.
We suggest that about 15-20% of astroparticle
funding should be reserved for small initiatives,
participation in overseas experiments with nonEuropean dominance, and R&D.

Synergy withenvironmental research
In astroparticle physics, the ambient medium isoften used as both interaction target and detector.
But be it water, be it air – its properties changewith time and must be carefully monitored. Environmental monitoring is therefore a key task indetector development. Instrumentation andmonitoring of huge volumes in the atmosphere,
the ocean and the Earth induces strong synergies with the geosciences, oceanography, climate
research and risk monitoring and will lead tofurther innovations:• Underwater monitoring: Remotely operated
or autonomous vehicles do not allow long-term,
continuous exploration of abyssal depths andrequire costly support ships. The neutrino telescope KM3NeT will provide a unique multidisci-

plinary observatory for deep sea science, exploring
the properties of the deep Mediterranean Sea
continuously over many years.
• Underground monitoring: Astroparticle detectors are currently used, for instance, for environmental measurements, for ancient sample dating
and for the tracking of the origin of food. Futureinterdisciplinary networks of underground sensors
will address a wide range of questions, ranging
from imaging groundwater resources to studying
the complex interactions between tectonic stresses,
seasonal infiltration andfault-zone hydro-mechanical stability.
• Atmospheric monitoring: The new generationof air shower experiments requires accurate
atmospheric monitoring.
Already now, the stormy
development of this field
has provided world-class
data. Autonomous distributed systems developedin this field will also fertilize networks for groundand underwater seismic
monitoring.
Setup to test the feasibility of
acoustic detection of neutrinos
in ice.

47.

Theory

10. Coordination of astroparticle theory

Theoretical research is an invaluable source of new concepts, of inspirationfor experimenters and a necessary tool to interpret experimental results.
Theorists are spearheads in combining particle physics, cosmology and astrophysics. Like experiment, theory needs reliable support and coordination.

Even more than for experimental astroparticle physics, the distinctions between
particle physics, cosmology and astrophysics have been blurred for theory. The same
theorists often work on several fields, likehigh energy particles, dark matter, physics
of the early Universe – just to name a few.
Notably, most of them have a backgroundin particle physics.
Theory often motivates experimental
projects, links distinct sub-fields of astroparticle physics, and is indispensable forthe interpretation of experimental results.
In parallel with the ambitious plans for the
next-generation astroparticle experiments
in Europe, the associated theoreticalactivities – apart from project-specificanalysis and computing activities – needstronger support and coordination. As
examples for the need for coherent
actions we mention the assessment
and reduction of the uncertainty of
nuclear matrix elements for double
beta decay experiments, the interpretation of cosmological data andtheir relevance to dark matter anddark energy, and the modellingof high energy processes inviolent environments.

Coherent European activities in theoreticalastroparticle physics are supported by various
means. These include the establishment of aregular common European school for astroparticle physics, building on the experiences with
the International School on AstroParticle Physics(ISAPP). At present, the European Union
supports the “European Network of Theoretical
Astroparticle Physics” (ENTApP), a networking programme of the FP6 Integrated Infrastructures Initiative ILIAS. ENTApP focuseson theory related to the experimental goals of
ILIAS – neutrino-less double-beta decay, dark
matter and gravitational waves.
Theory is an invaluable source of inspiration forexperimenters and a necessary tool to interpret
experimental results, and must be supportedwith the same recognition like experiments.
Among the discussed proposals for improved
support and coordination of astroparticle
theory we mention a Europe-wide common callfor theoretical proposals and a future European
Centre for Astroparticle Theory, with the involvement of an international panel of expert referees. Such a centre could be established either
in one of the European countries or at CERN.
Given the synergy between LHC physics andastroparticle physics, CERN would be a natural
host, particularly in view of several astroparticle
experiments being CERN ‘recognised experiments’.

49.

Education & outreach

11. Education and outreach

The number of young researchers joining astroparticle physics has
steadily increased over the last decade. Astroparticle physics is not
only an important element of teaching at many universities, but also
challenges imagination and curiosity of a broad audience.

The questions of astroparticle physics
address very basic questions, like theorigin and nature of matter, energy andthe Universe. They challenge the imagination and curiosity of a broad audience.
The cutting-edge technology and thesometimes remote, exotic locations add
other factors of fascination. This makes
astroparticle physics an ideal tool to getlaymen interested in basic science. For
the same reasons, an increasing numberof young researchers with brilliant newideas are motivated to join the field.
The number of university positions
on astroparticle physics has been
continuously increasing over thelast decade, reflecting not only thegrowing importance of the field but
also a growing pool of excellent
young researchers challenged by its
questions.

A joint astroparticle physics outreachprogram in Europe (EuroCosmics) brings
together outreach efforts in 12 European
countries and promotes a long term scientific/educational collaboration between
researchers, high-school teachers and highschool students. For instance, Dutch Universities developed a country-wide network ofcosmic ray detectors at the roofs of morethan 50 high schools. The astroparticle
physics community is also in close contact
with the European Particle Physics Outreachgroup which is also working on a networkand forum for outreach activities. Amongthe traditional activities of outreach, “opendays” in the large underground laboratories and popular-scientific TV movies haveturned out to be particular successful.

The Dutch HISPARC project: recording cosmic particles onschool roofs.

Astroparticle physics: the European strategy

To establish a sustainable outreach structure
ASPERA plans to enhance its outreach group
towards a coordination network, allowing
more effective communication and avoiding
duplication of efforts. This network will
make use of the ASPERA web platform as
the area for the exchange of information andideas.

Warped space-time or soap bubbles? Children at an open
day in the Gran Sasso Laboratory.

The implementation of the ASPERA website(www.aspera-eu.org) has turned out to be avaluable platform for internal and external
communication and was visited 50,000
times within 18 months. It allows access to
information on reports, the roadmap, conferences and meetings, press releases, and the
ERA-NET itself. The ASPERA outreachgroup releases a monthly newsletter with
about 800 subscriptions, developed a traveling exhibition for presenting ASPERA at
important events, and installed extended
press relationships. These activities play a
key role in giving greater visibility to astroparticle physics at the European level andbeyond.

The ASPERA travelling exhibition attracts visitors at theEuro Science Open Forum ESOF 2008 in Barcelona.

51.

Coordination in Europe

Coordination in Europe: ApPEC and ASPERA.

The high cost of frontline astroparticle projects
requires international collaboration, as does therealisation of the infrastructure. Cubic-kilometre neutrino telescopes, large gamma ray observatories, Megaton detectors for proton decay,
or ultimate low-temperature devices to searchfor dark matter particles or neutrino-less double beta decay are in the range of 50-800 M€.
Coordination and cooperation are the onlyway (a) to achieve the critical scale for projects
which require budgets and manpower notavailable to a single nation and (b) to avoid
duplication of resources and structures.
ApPEC (Astroparticle Physics European
Coordination) was founded 2001 as an interest grouping of six European scientificagencies. They realised that most of theemergent field of astroparticle physics was
not covered by the coordinating and funding mechanisms of adjacent disciplines, like particle physics or astronomy.
Consequently, ApPEC aimed at:• developing long term strategies andoffering advice to national funding
agencies or other organisations,• expressing the view of European
astroparticle physics in international forums,• establishing a system of peer
review assessment.

Since then, ApPEC has grown to 17 agencies representing 14 European countries.
Its executive body is the Steering Committee (SC), with one leading scientific executive from each country and observers from
CERN, ESO and ESA. Its strategic advisory
body is the Peer Review Committee (PRC).
The PRC reviewed each of the subfields ofastroparticle physics, with topical workshops
in 2002-2004. ApPEC has coordinated thesubmission of the successful proposal ILIAS,
an Integrated Infrastructure Initiative (I3),funded under the European Commission’s
Sixth Framework Programme (FP6). ILIAS
focuses on the searches for double beta decay, for dark matter, and the search for gravitational waves. It also includes a programme
for coordinating, for the first time, the deep
underground laboratories in Europe, and a
network on theoretical astroparticle physics.
Also, ApPEC promoted the successful proposal for a FP6 Design Study for a Mediterranean neutrino telescope, KM3NeT.
By 2005 ApPEC realised that its goals andmethods fitted perfectly to the European
Union ERANET scheme and initiated thesubmission of the ASPERA proposal. ASPERA started in July 2006, funded by theEU with 2.5 M€ for a three-year period. ASPERA has enabled the pursuit of politicaland coordinative goals on a solid operational
basis. Aiming to be a truly European initia-

Astroparticle physics: the European strategy

tive, it consistently works towards extension
to more national agencies. The bodies of ASPERA are the Governing Board, consistingof high level representatives of the agencies,
a coordinator and a co-coordinator, a Joint
Secretariat, consisting of the Work Package
Leaders, and the Roadmap Committee. Actually, the ASPERA Roadmap Committee
emerged from the ApPEC Peer Review Committee (PRC) with part of the old members
replaced by new members and taking accountthe new partner countries.
The work of ASPERA is structured into clear
work packages, with the three of them forming the core activities:a) chart the status of astroparticle physics
funding schemes in Europeb) establish a roadmap and an action planc) link the existing platforms of observation,
establish the best legal schemes for future
infrastructures and find ways to commonly
and manage the new large programs
Under the operational leadership of ASPERA,
the Phase-I stage of a roadmap was finished,describing the status and desirable options
for the next decade. This Status and Perspective of Astroparticle Physics in Europe (http://
www.aspera-eu.org) has been prepared by the
Roadmap committee between October 2005
and January 2007, with questionnaires sent

to the experiments, many committee meetings and several town meetings and withfeedback from the science community.
In a second phase, detailed questionnaires
from subfields and agencies have been collected and timelines and updated cost estimates compiled within ASPERA working
groups each addressing one of the sub-fields.
The outcome has been presented at an international meeting on 20/21 September 2007
in Amsterdam. In the third phase, ending inautumn 2008, a realistic funding scenario has
been worked out. Proposals for priority experiments, for the phasing of large projects
and for international cost sharing are made.
They meet a funding scenario with a smoothfactor of 2 increase over the next 8-10 years(see the recommendations at the end). PhaseIII will officially culminate with a prestigious
international workshop in Brussels on 29/30
September 2008 and the presentation of thepresent document. It will be flanked by a longer write up, becoming available online.
The ASPERA census as of August 2008 (seehttp://www.aspera-eu.org) includes 11 countries: Belgium, the Czech Republic, France,
Germany, Italy, The Netherlands, Portugal,
Spain, Sweden, Switzerland and the United
Kingdom, with detailed information presented on “National Days”. Numbers from
Greece will be added on a National Day in53.

Coordination in Europe: ApPEC and ASPERA.

autumn 2008, and those for the new ASPERA members will follow in 2009.
The total number of Full Time Equivalents(FTE) assigned to astroparticle physics wascounted as 2,325. The total 2006 budget
for astroparticle physics in the 11 countries
amounted to 186 M€; about 96 M€ for investment and running and 90 M€ for salaries. Averaged over recent years, the totalsum for investment is about 70 M€. The tables give the numbers of FTE, the total 2006
budgets and the number of institutions withastroparticle activities (research centres anduniversities) per country (see table).
Normalised to the total government budget
for research, the expenditures amount to 0.5
to 5.5 per thousand, with a large proportionof the Italian budget spent on running theGran Sasso Underground laboratory (seefirst figure).
The ratio of the number of researchers to the
population of each country demonstrates the
support which astroparticle physics has allover Europe (see second figure).

54.

The ASPERA program gave a tremendous
boost to the European convergence of the
field. The process became visible internationally and elicited demands from othercontinents for global coordination, as it iscurrently seen in the OECD Megascience forum under preparation. Next steps in Europe will be common calls for joint funding ofresearch and development initiatives as wellas coordinated joint programming of multimillion programs.
Although a large part of its activities are
now passing through ASPERA work packages, ApPEC decided not to dissolve into
the ERANET but continue its operation ata higher decisional level. The reason is obvious: Astroparticle physics needs sustainable support beyond the few-years duration of
an ERANET program. So ASPERA sees its
sustainable future in a “reinforced” ApPEC,
or, in other words: ApPEC constitutes boththe past and the future of ASPERA.

Astroparticle physics: the European strategy

Astroparticle physics in ASPERA countries:
Number of Full Time Equivalents (FTE), the 2006 budget, and number of
institutions with astroparticle activities (research centres and universities).

Country
FTE		
Budget(M€)#Institutions

BE
17
0.7
4

CH
52
3.6
7

CZ
20
0.4
5

DE
494
44.0
38

ES
168
10.0
13

FR
608
51.5
28

IT
679
58.6
30

NL
55
6.1
9

PT
40
0.5
5

SE
34
2.0
3

UK
158
9.0
19

Ratio of the astroparticle budget to the government research budget.

Ratio of the number of researchers in astroparticle physics to the total population.

Source: 2006

55.

Recommandations

Recommendations

Astroparticle physics is developing with high speed and stands on thethreshold of fascinating discoveries. Below we present the roadmap committee’s recommendations for priority instruments in each of the sevenfields, for support of related activities and for phasing of the big projects.

Direct Dark Matter Search
We recommend the construction and operation of one – possibly two complementary– detectors on the ton scale or beyond withlow background, capable of reaching a 10-10
pb sensitivity, with a European lead role orshared equally with non-European partners.
We recommend a stepwise approach via
100 kg detectors, as presently underway,
and a prioritisation between different
technologies around 2010/2011. We urge
convergence of parallel worldwide efforts.

Proton Decay & Low Energy
Neutrino Astrophysics
We recommend supporting the work towards
a large infrastructure for proton decay and low
energy neutrino astrophysics, possibly also accelerator neutrinos in long baseline experiments,
in a worldwide context. Results of a current FP7
design study (LAGUNA) are expected around2010 and should be followed by work towards atechnical design report. Depending on technology, site and worldwide cost sharing, construction could start between 2012 and 2015.

Neutrino Mass
Depending on the outcome of thepresent generation of double beta
decay experiments being prepared, werecommend the eventual construction and operation of one or two
double beta decay experiments on
the ton-scale, capable of exploring the inverted-mass region,
with a European lead role orshared equally with non-European partners. A decision on
the construction could betaken around 2013.

Gamma Astrophysics
The priority project for VHE gamma astrophysics is the Cherenkov Telescope Array, CTA. We
recommend design and prototyping of CTA,
the selection of sites, and proceeding rapidly
towards start of deployment in 2012.

Charged Cosmic Rays
The priority project for high energy cosmic
ray physics is the Pierre Auger Observatory.
We encourage the agencies in different conti-

Astroparticle physics: the European strategy

ASPERA comprises 18 agencies from 13
countries in Europe funding astroparticle
physics research, and CERN.

nents to work towards a common path forAuger-North. We recommend the construction of such a large array as soon as worldwide agreements allow.

Neutrino Telescopes
The priority project for high energy neutrino astrophysics is KM3NeT. Encouraged by the significant technical progress of recent years, the support
for working towards KM3NeT is confirmed.
Resources for a Mediterranean detector should bepooled into a single optimised design for a large
research infrastructure, with installation starting in
2012. The sensitivity of KM3NeT must substantially exceed that of all existing neutrino detectors
including IceCube.

Gravitational Waves
The long-term priority of ground-based detectors
is the Einstein Telescope, E.T., a large undergroundgravitational wave detector. We recommend support
for R&D work towards E.T., with construction
starting after first discoveries have been made with
LIGO/Virgo/GEO, likely around 2016/17. The
short term priority is the upgrade of the present
generation of gravitational waves detectors, witha particular recommendation to support a fast
upgrade of Virgo to “advanced Virgo”.

We also support:• Earth and space based missions to explore thephenomenon of “dark energy”,• the concept of a cooperative network of deep
underground laboratories,• a common call for innovative technologies in
the field of astroparticle physics,• efforts to intensity the synergy with environmental sciences,• the formation of a European Centre for
Astroparticle Theory.
Starting from the initial cost and profiles suppliedby the experiments, the Roadmap Committee has
looked at possibilities for phasing and cost reduction by inter-continental cooperation. It defined
milestones to decide which experimental method
in any of the first three classes (dark matter search,double beta decay experiments and a large multipurpose detector underground) should get priority
or how competing methods might be combined.
These milestones are explained in the previous chapters. Cost reductions appeared possible in all fields.
For some projects a rich scientific harvest would beguaranteed even with slightly reduced capabilities.
For others, any compromise in capabilities would
jeopardise the success (for instance the observationof point sources in the case of KM3NeT or Auger
North). We assumed that not all of the available
budget should be spent on the flagship projects, but
about 15-20% should be reserved for small initiatives, participation in overseas experiments with
non-European dominance, and R&D. We find57.

Recommendations

that the plans fit into a scheme where the funding
for investment is smoothly doubled over 8-10 years,
amounting to an integrated increase of about 50%
in a ten year period. The estimated increase in thesum for personnel costs is smaller. The figure below
illustrates our findings.

current medium scale detectors and on cost considerations. The construction of a very large undergrounddetector for proton decay and low-energy neutrino
astrophysics could start by the middle of the next
decade, followed by a third generation gravitational
antenna, both in a worldwide context.

Earliest projects on the cost scale of 30 M€ or more
are the high energy observatories, with the European
priority projects CTA and KM3NeT, together with
an Auger-North implementation in a worldwide
context. These projects are based on known technology and their construction could start by 2012.
In the domain of underground science, the present
network of European underground laboratories
should be further strengthened by coordination andextensions. The technology of ton-scale undergrounddetectors for dark matter and neutrino mass will bedecided in 2010-2013, based on the performance of

The technology of the next generation dark matter andneutrino mass detectors, as well as the steps towards
a Megaton scale detector and the next generation
gravitational antenna, will be further defined in thenext version of this roadmap, due in 2010/2011. Thisupdate will be driven not only by issues of technology readiness and design study specifications but also
by the wealth of data and discoveries expected fromrecently launched or soon operating instruments,
for instance the Fermi satellite, the Large Hadron
Collider LHC, the Planck satellite and long baseline
reactor and accelerator neutrino experiments.

M€
A scenario for investment andoperation cost of astroparticle
physics in the ASPERA countries.

58.

Illustration credits

p30. Air shower detection principle: Fermilab
p31. Sky map of Pierre Auger Observatory events: Auger collaboration,

p1. 3 circles: ASPERA/A.Marsollier

Science Magazine, Nov. 2007 - Pierre Auger Observatory people at

p4. Left: Hubble deep field: NASA / ESA - Cloud chamber: Carl D.

work: Auger collaboration

Anderson, Physical Review Vol.43, p491 (1933)

p32. Gamma ray-initiated avalanches: ASPERA/A.Marsollier

p5. Sun in neutrinos: Institute for Cosmic Ray Research, Tokyo

p33. Remnant of a supernova: H.E.S.S. collaboration, Nature, Nov

p6. Supernova 1987A: Anglo-Australian Observatory2004 - H.E.S.S. telescope: H.E.S.S. collaboration

p7. Super-Kamiokande: Kamioka Observatory, ICRR , University of

p34. MAGIC telescope: Robert Wagner, MPI for Physics, MunichTokyo

p35. Galactic plane by H.E.S.S telescopes: H.E.S.S collaboration -p8. The gamma sky: Konrad Bernlöhr, MPIK Heidelberg

CTA: ASPERA/D.Rouable

p9. Sensitivity increasing: ASPERA/C.Spiering/D.Rouablep36. Cherenkov detection principle in water: ASPERA/A.Marsollier

p10. Left: MAGIC telescope / R. Wagner, MPI for Physics, Munich

p37. AMANDA Sky map: AMANDA collaboration - KM3NeT:

p11. M51 galaxy: Hubble Heritage / NASA

Marco Kraan/Nikhef

p12. Left: dark matter distribution: Springel et al. / MPA Garching -p38. Left: gravitational waves simulation: NASA-Modelling of gravi-

Jar of jelly beans: Fermilabtational waves: MPI for Gravitational Physics/W.Benger-ZIB

p13. Dark matter strategies: ASPERA/A.Marsollier - Zeplin III: H.

p39. Water drop: Adam Hart-Davis - GEO 600 interferometer: GEO

Araujo - DAMA: DAMA collaboration, redesign C.Iezzi

600 collaboration/ AEI Hannover - Virgo interferometer: CNRS/

p14.-CRESST experiment: CRESST collaboration - XENON team:

IN2P3

XENON collaboration, E. Aprile

p41. LISA: ESA - Einstein telescope: Nikhef/Jo van den Brand

p15.-EDELWEISS bolometer: EDELWEISS collaboration -WARP

p42. Left: view of ANTARES: F.Montanet, CNRS/IN2P3 andexperiment: WARP collaboration, C.Montanari - EURECA:UJF/D.Rouable - Gran Sasso laboratory: INFN/Volker Steger

EURECA collaboration

p43. European underground laboratories map: ESA/Novapix/S.

p16. EUCLID: DUNE collaboration - LSST: LSST collaboration

Lebrunp17. Dark energy simulation: A. Kravtsov

p44. AMS: NASA

p18. Left: Particle tracks / DESY

p45. CREAM: NASA and University of Maryland Cosmic Ray

p19. Neutrino oscillation: ASPERA/D.Rouable-NEMO-3 detector:

Physics Laboratory - Fermi satellite: NASA/Sonoma State University/

NEMO-3 collaboration

Aurore Simonnet

p20. GERDA: GERDA collaboration

p46. Left: XENON10 PMT array: XENON collaboration - Techni-

p21. KATRIN in narrow streets: KATRIN collaborationcian at work: EDELWEISS-II collaboration/LSM/IN2P3

p22. Left: the Borexino detector / Borexino collaboration / LNGS/

p47. High-purity crystals: EDLEWEISS/CEA/IRFU-Setup for

INFN

acoustic neutrino detection: R. Nahnhauer/DESY

p23. Synoptic view of neutrino fluxes: C.Iezzi, C.Spiering - Borexino

p48. Left: blackboard: Fermilab

detector: Borexino collaboration / LNGS/INFN

p49. Theorist: CERN

p24. LENA/MEMPHYS/GLACIER: LAGUNA collaboration

p50. Left: CMB picture from WMAP: NASA/WMAP Science Team

p25.-LENA inside: J. Winter, TU Munich - Double Chooz experi-- HISPARC detector: HISPARC collaboration

ment: IRFU/CEA

p51. Open day at Gran Sasso: LNGS-INFN - ASPERA exhibition:

p26. Left: cosmic rays: ASPERA/L.Bret - Multi-wavelength view of

ASPERA/A.Marsollier

the galaxy: Crab Nebula: NASA/ESA/ASU/J.Hester & A.Loll

p52. Left: map of Europe: ESA/Novapix

p27. Active galaxy: Aurore Simonnet, Sonoma State University

p56. Left: Artist’s view of an X-ray pulsar: ESA

p28. High-energy cosmic rays: ASPERA/C.Spiering/A.Marsollier

p57. ASPERA countries: ASPERA/S.Lebrun

p29. The flux of cosmic rays: ASPERA/C.Spiering/D.Rouable

Cover: ASPERA/D.Rouable