Astroparticle physics

The European Roadmap
		© Picture: ASPERA / ESA / L.Bret-Novapix

		w w w. a s p e r a - e u . o r gThis roadmap was worked out by the Scientific
Advisory Committee of ASPERA/ApPEC:
Ad M. van den Berg
Roberto Battiston
Laura Baudis
Jose Bernabeu
Daniel Bertrand
Pierre Binetruy
John Carr
Enrique FernandezFrancesco Fidecaro
Gilles Gerbier
Andrea Giuliani
Andreas Haungs
Werner Hofmann
Steven Kahn
Uli Katz
Paul Kooijman
Hans Kraus
Antoine Letessier-Selvon
Manel Martinez
Benoit Mours
Lothar Oberauer
Rene Ong
Michał Ostrowski
Sheila Rowan
Subir Sarkar
Stefan Schönert
Günter Sigl
Ion Siotis
Christian Spiering (Chair)
Robert Svoboda
Francesco Vissani
Lucia Votano
Roland Walterbecause they have an impressive momentum thatneeds to be maintained, because they enter a phase
Executive Summarywith high discovery potential, because they go handin hand with LHC physics, because they are technologically ready and have a worldwide community behind
them, or finally, because a delay of crucial decisions
Astroparticle physics marks the intersection of and funding could even jeopardize the project. In thisastrophysics, particle physics and cosmology. It spirit, we recommend the following projects and urge
addresses fundamental questions like the nature of dark the agencies to join their forces in order to provide
matter and dark energy, the physics of the Big Bang, effective and substantial support:
the stability of protons, the properties of neutrinos
and their role in cosmic evolution, the interior of the • Gravitational waves: With Advanced VIRGO,
Sun or supernovae as seen with neutrinos, the origin Advanced LIGO and GEO-HF, a discovery in theof cosmic rays, the nature of the Universe at extreme next five years becomes highly probable. This would
energies and violent cosmic processes as seen with open an entirely new window to the Universe. We urge
gravitational waves.
the agencies to continue to substantially support theongoing and planned upgrades to advanced detectors.
Among the spectacular successes of astroparticle physics
in the last 25 years have been the opening of two new • Dark Matter: With the advent of the LHC andwindows to the universe: the neutrino window (the Sun thanks to a new generation of astroparticle experiments
and a supernova) and the window of high-energy gamma using direct and indirect detection methods, therays. The study of cosmic neutrinos also revealed that well-motivated SUSY-WIMP dark matter hypothesis
neutrinos have mass, with fundamental consequences will be proven or disproven within the next 5-10
for the role of these particles in cosmic evolution. years. The highly significant annual modulation signal
Astronomers and physicists have discovered that the observed by DAMA/LIBRA, and its interpretation
expansion of the Universe accelerates (2011 Nobel prize in terms of dark matter interactions, will also be
for physics!). Other branches of astroparticle physics have scrutinized in the next few years. The dramatic progress
greatly improved the levels of sensitivity, something which of the liquid-xenon technology over the past 2-3 years
makes analogous groundbreaking discoveries in the near demonstrates a high momentum, which must be
future likely. This applies to the detection of gravitational maintained. The recently approved XENON1T at
waves and dark matter particles, the study of the origin of Gran Sasso laboratory is expected to start operationhigh energy cosmic rays and neutrinos, the determination in 2014/15. The bolometric experiments CDMS andof the neutrino mass or, later, the observation of proton Edelweiss have recently provided upper limits close
decay and the understanding of dark energy. Compared to those of XENON100 and move towards a closer
to the last version of the ASPERA roadmap in 2008, we US-Europe coordination. We recommend supporting
witness today a remarkable progress on many fronts, the development of EURECA, which envisages one ton
as well as an increased coordination and networking of sensitive mass, eventually in a common US-Europe
on a global scale.
framework. Looking beyond the scale of one ton,
we strongly recommend that DARWIN, a program
Research priorities differ from country to country, aiming to extend the target mass of noble liquids todepending for example on their local infrastructures, several tons, is pursued and supported.
or on their traditions and historically grown strengths
in particular fields. The Scientific Advisory Committee • Neutrino properties: Several highly important(SAC) ranked scientific arguments highest but at the experiments in Europe are either in the commissioning
same time kept in mind that there are also historical phase or in the final years of construction: GERDA,
and political aspects to be considered. We decided to CUORE and the demonstrator for SuperNEMO willclassify our recommendations into two categories: a) search for neutrino-less double beta decay, KATRIN for
medium scale projects or medium scale upgrades being neutrino mass via single beta decay. Double CHOOZ,
at different stages of realization (investment funds in a nuclear reactor experiment, is studying neutrino
the category of tens of M€) and b) large scale projects oscillations. The mentioned experiments build on awhose construction needs to start towards the middle long experience and validation with precursors. Theyof the current decade (investment funds on the scale have been recently joined by NEXT, a new approachof hundreds of M€).
to the search for double beta decay. We renew ourstrong support for these experiments and look forward
In the first category there are a few projects whose to first results. Beyond this, we recommend a phased
funding has to be kept at substantial levels, be it experimental approach in neutrino-less double betadecay with a sensitivity (ton scale masses) that will allow astrophysics and proton-decay detector for astroparticle
to explore fully the mass range predicted by oscillation and accelerator-based neutrino measurements is
experiments for the inverted mass hierarchy.
addressed by the LAGUNA design study. The scientificgoals combine high-risk research addressing several• The underground science program on dark fundamental questions of physics (proton decay, CP
matter and neutrino properties calls for more violation) with exciting neutrino astrophysics (e.g.
underground space. In this context, there is a unique supernova, solar, geo- and atmospheric neutrinos).
window of opportunity to extend the present The committee recommends that the study be pursued
Underground Laboratory of Modane (LSM) by within the LAGUNA-LBNO program, including
taking advantage of the excavation of the safety tunnel options with and without a new neutrino beam.
of the Frejus road tunnel, which has already started. Due to the high cost (350-700 M€, depending on
The new laboratory of 60.000 m3 at a great depth site and type of detector) and the long development
could host several of the proposed large new projects. time, the committee recommends that this program is
We recommend the timely support for the LSM pursued in a global context. Given the close relation toextension.
beam-related neutrino oscillation projects, the urgency
of its realization depends strongly on the output of
The large-scale infrastructures whose construction the current accelerator and reactor programs and inneeds to start towards the middle of the current particular on whether the missing neutrino-mixing
decade include three high-energy projects and one on parameters are in the range that would permit a series
low-energy neutrino astrophysics:of very exciting new measurements (neutrino mass
hierarchy, CP violation etc). If the current indications• TeV gamma-ray astrophysics: The Cherenkov for a large mixing angle θ13 were to be confirmed
Telescope Array (CTA) is the worldwide priority within one or two years, attractive scenarios for the
project of this field. It combines proven technological medium-term CERN strategy open up, LAGUNA
feasibility with a high speed towards prototyping, is therefore clearly at the interface with the CERN
with a guaranteed scientific perspective and a mode European Strategy Update to be delivered by the endof operation and wealth of data similar to mainstream of 2012. As such the LAGUNA project constitutes
astronomy. The cost scale of CTA is 200 M€. We a high astroparticle physics priority to be discussed
recommend the design and the prototyping of CTA, within the CERN strategy update process.
the selection of the site(s), and to proceed vigorously
towards start of construction in late 2013.
The presently conceived start of construction of
KM3NeT, the ground based cosmic ray observatory• High energy neutrinos: In the high-energy neutrino and a low-energy neutrino detector is in the years
domain, the requirements on the necessary sensitivity 2014-2016. We would support a strategy to search
have tightened, but the scientific case for a large neutrino for funding opportunities for these projects – both indetector in the Northern hemisphere remains high. The Europe and worldwide – and promote any one of these
KM3NeT collaboration is working towards a technical projects as soon as a corresponding window appears.
proposal for a neutrino telescope with a substantiallylarger sensitivity than IceCube. The expected cost scale Astroparticle physicists play a major role in manyis 250 M€ and based on pioneering technical work by international dark energy programs, as e.g. thethe European astroparticle community, also provides dominantly US-funded LSST observatory (first light
access to deep-sea research.
ca. 2020) or the ESA satellite EUCLID (launch2019). The committee recommends a strong support• High energy cosmic rays: The cosmic-ray for these participations.
community including the Pierre Auger collaboration
is working towards a next-generation ground-based The path for research in gravitational waves beyond
observatory. These efforts include the development of the advanced detectors foresees two very large-scale
new detection technologies, the search for appropriate projects (costs on the billion Euro scale): thesites, and the attraction of new partners. We reiterate Earth-bound Einstein Telescope (E.T.) and thethe definition of a substantially enlarged ground-based space-bound LISA project. In today’s perspective, E.T.
observatory as the priority project of high-energy construction would start at the end of the decade andcosmic ray physics. The cost scale is 100-150 M€, with after the first detection of gravitational waves with thea substantial contribution from Europe.
advanced detectors. We also look forward to the resultsof LISA-Pathfinder. We renew our strong support of• Low-energy neutrino astrophysics and proton the LISA mission and preparatory work on E.T.
decay: A megaton-scale low-energy neutrino

We finally emphasize the importance of threetransversal aspects:• Theoretical research is an integral part of astroparticle
physics and is indispensable when experimental data
have to be interpreted in the context of models, be it
in terms of possible signals or as constraints. Similar toexperimental activities, theoretical studies will strongly
benefit from a strengthened and more coordinatedsupport. In turn, this will also help to maximally exploit
the impact of astroparticle physics experiments.
• Smaller projects and innovative R&D activities are
essential for the progress of our field and profit frominternational cooperation. ASPERA addressed this bycarrying out a series of calls for R&D activities.
• Most astroparticle observatories, whether they
are located underwater/ice (neutrino telescopes)
or underground (underground laboratories) or on
the ground (air-shower detectors), have developed
strong synergies with geoscience, biological andenvironmental sciences. They provide state-ofthe-art technologies and attractive infrastructures tothe corresponding communities, which in turn will
increase the support of these infrastructures.

Content
1.

Introduction ............................................................................. 3.

2.

The high energy universe ......................................................... 5.
2.1 Introduction ........................................................................... 5.
2.2 Charged cosmic rays ...................................................................... 5.
2.3 Gamma-ray astrophysics ................................................................ 10.
2.4. High-energy neutrinos ................................................................. 14.

3.

Dark matter, neutrino mass,
low energy neutrino astronomy & proton decay ........................ 19.
3.1 Introduction ........................................................................... 19.
3.2 Dark matter .................................................................................. 19.
3.3 Direct measurement of neutrino mass .............................................. 26.
3.4 Neutrino-less double beta decay ..................................................... 28.
3.5 A large detector for proton decay, low energy neutrino astrophysics
and long baseline experiments ..................................................... 32.

4.

Dark energy and gravitational waves ........................................ 38.
4.1 Dark energy ................................................................................... 38.
4.2 Gravitational waves

5.

.......................................................................... 43.

Transversal activities .............................................................. 47.

Appendices............................................................................. 48.

A.1 Letter of Charge to the Science Advisory Committee ............................ 48.
A.2 The 2008 ASPERA roadmap ........................................................ 49.
A.3 From 2008 to 2011 ................................................................... 50.
A.4 Compilation of detailed recommendations from the individual chapters ..... 52.
A.5 Tabularized overview of experiments ............................................... 56.

3

1. Introduction
The term astroparticle physics was created only thirty
years ago, and it took a decade to be commonly accepted.
Its roots, however, reach back a century, whose story
is one of remarkable explorations and discoveries. It
started with the groundbreaking discovery of cosmic
rays in 1912 by Victor Hess (Nobel Prize 1936). Two
decades later, in 1932, the first anti-particle – thepositron – was discovered in cosmic rays (Nobel Prize1937). Next came a heavy brother of the electron, themuon, discovered in 1937, followed in 1947 by thepion, the first representative of the immense family ofthe mesons (Nobel Prize 1950). The “second spring”
of astroparticle physics started with the detection ofneutrinos from the Sun in the 1970s and the spectacularregistration of neutrinos in 1987 from a supernova. In
2002, Ray Davis and Masatoshi Koshiba were awarded
the Nobel Prize for opening the neutrino window to
the Universe, specifically for the detection of neutrinos
from the Sun and Supernova 1987A. Their work wasa unique synthesis of particle physics and astrophysics.
Solar neutrinos also provided the first clear evidence
that neutrinos have mass. The detection of solar andsupernova neutrinos is not the only new window
opened by astroparticle physics. Another one is that ofvery energetic gamma rays recorded by ground-based
Cherenkov telescopes. From the first source detected
in 1989, three sources known in 1996, to over 100
sources identified until 2011, the high-energy sky
has revealed a stunning richness of new phenomena
and puzzling details. At the same time, astroparticle
physics has progressed to levels of sensitivity with highdiscovery potentials. This applies to the detectionof gravitational waves, the search for dark matterparticles and the nature of dark energy (the Nobel
prize for physics in 2011 has just been awarded for the1998 discovery that the expansion of the Universe isaccelerating!), the search for the origin of high-energy
cosmic rays and neutrinos, the determination ofnature, mass and mixing properties of neutrinos andto the observation of proton decay.
We thus are at the threshold of exciting discoveries inseveral key areas. However, the cost for cubic-kilometre
neutrino telescopes, large gamma-ray and cosmic-ray
observatories, megaton-scale detectors for proton decay,
or ultimate low-temperature devices to search for dark
matter particles or neutrino-less double beta-decay ranges
between tens and hundreds of millions of Euros. Such costs
require international collaboration, as does the realizationof the necessary infrastructure. Co-operation is the only
way to achieve the critical mass for projects that requirebudgets and personnel not available to a single nation.
This avoids duplication of resources and structures, andwould also guarantee a leading role for Europe.
ApPEC and ASPERA have been created to promote
this process. ApPEC (Astroparticle Physics European
Coordination) was founded in 2001 as a bodycoordinating the interests of six European scientificagencies. They realized that most of the emergent
field of astroparticle physics is not covered by thecoordinating and funding mechanisms of adjacentdisciplines like particle physics or astronomy.
Consequently, ApPEC aimed at developing long-term
strategies and offering advice to national funding
agencies or other organisations, expressing the view ofEuropean astroparticle physics in international forums,
and establishing a system of peer review assessment.
ApPEC’s executive body is the Steering Committee(SC), with one leading scientific executive from eachcountry and observers from CERN, ESO and ESA.
Realizing that its goals and methods fit ERA-NET, theEuropean Union program for support of national andregional cooperation, ApPEC initiated the submission ofa proposal for an ERA-NET project called “ASPERA”.
ASPERA started in July 2006, funded by the EU with
2.5 M€ for a three-year period, and was prolonged foranother three years in 2009. The bodies of ASPERA are
the Governing Board, consisting of high-level representatives of the agencies, a coordinator and a co-coordinator,a Joint Secretariat consisting of the Work Package
Leaders, and the Science Committee, presently named
Scientific Advisory Committee (SAC). At present,
ASPERA includes 24 partners from 18 countries.
ASPERA issued two European-wide calls for research
projects, the first focusing on gamma-ray astronomy
and dark-matter searches, the second on cosmic ray
projects and neutrino mass experiments, with the goal topromote developments towards large future experiments
and infrastructures and to strengthen the collaboration
between the relevant research groups in Europe.
ASPERA and ApPEC have charged the SAC to update
the previous Roadmap(s) for Astroparticle Physics inEurope. The first phase of a roadmap, Status and Perspectiveof Astroparticle Physics in Europe, has been presented in2007. It described the status and desirable options ofEuropean astroparticle physics for the decade 2007-16,
including detailed physics information. A second
document, Astroparticle Physics – the European Strategy,
was released in autumn 2008. It was directed to a wider
readership than the first one. Moreover, it included more
precise timelines and updated cost estimates, and also
mapped the full funding landscape. This phase ended
officially with a high-profile international workshop in
Brussels at 29-30 September 2008.

4
Because astroparticle physics is a rapidly growing,
dynamic field, it does not come as a surprise that its
landscape has changed already between 2008 and now.
Fortunately, a non-negligible fraction of the necessary
modifications to the 2008 roadmap are for the better.
On the other hand there have also been substantial
delays – which are not unusual for projects on thesecost scales. The dynamics of the research landscape isthe first argument for an updated roadmap.

research priorities will differ from country to country,
depending, e.g. on their local infrastructures or on
their traditions and historical strengths in particularfields. The SAC ranked scientific arguments highest,
but at the same time kept in mind that there are also
historical and political aspects. For instance, we were
careful not to define priorities in such a way thatthey might limit the phase space of national funding
agencies for substantial, positive funding decisions,once such possibilities for a certain project appear on
The second argument for the timing is the planned the national level. We also have had to face the fact
update in 2012 of the European Strategy for Particle that the ApPEC and ASPERA steering bodies did not
Physics which is worked out by the CERN Council define funding envelopes, to which we could have
Strategy Group. Already for the 2008 ApPEC/ tailored our recommendations.
ASPERA Roadmap, we have shared our views andfindings with the CERN Council Strategy Group The present roadmap is composed of the following(as well as with the astrophysics community which parts:
produced a Science Vision for European Astronomy andan Infrastructure Roadmap for European Astronomy). In Section 2 we address the projects of the high-energy
The present Roadmap should provide a qualified input Universe, starting with an introduction to the basic
to the updated document on the European Strategy questions, continuing with projects on charged cosmic
for Particle Physics. This is particularly important rays, then gamma-ray telescopes and ending withsince much of our research goes hand-in-hand with high-energy neutrino detectors.
research at the LHC and other accelerators – startingwith dark matter and supersymmetry, including high In section 3 we cover dark matter searches, experiments
energy interactions and ending with questions like to determine the nature and mass of neutrinos – both
CP-violation in the leptonic sector and cosmology. direct mass measurements and searches for neutrino-lessOur roadmap was also drafted in close relation to the double beta decay – as well as detectors for low energy
Report of the Working Group on Astroparticle Physics for astrophysical neutrinos and proton decay, focussing
the Global Science Forum of the OECD.
on a future detector on the 50 kiloton to 1 Megaton
scale.
In the 2008 roadmap, proposals for priority experiments,
for phasing of large projects and for international cost Section 4 is devoted to dark-energy missions andsharing were made. They met a funding scenario with gravitational-wave detection. The tools used in thesea smooth factor of 2 increase over the next 8-10 years. experiments are rather distinct from the particle andWe were – and continue to be! – convinced that the nuclear physics tools typical of the field discussed inprospects of astroparticle physics merit this increase. On Sections 2 and 3. Because dark-energy missions are to
the other hand we have to face that funding realities in a very large extent defined by US plans, we keep ourmost countries have become more challenging. This is a recommendations on this subject brief.
third argument for a revision of the 2008 recommendations and a critical reality check.
Section 5 addresses activities which are essential for all
fields – starting with theoretical research and ending
Russia – a country with a long tradition in Astroparticle with technology development.
Physics – became an associate member of ASPERA.
Whereas until now Europe, the US and Japan have The Appendices reproduce the letter of charge to thebeen the primary drivers of astroparticle physics, other SAC in A.1, give a reminder on the 2008 roadmap
countries are becoming increasingly involved, amongst (A.2), sketch the development from 2008 to 2011
them China and India. This adds another aspect of (A.3) and list all recommendations given in the text
global cooperation and competition.
(A.4). Tables in A.5 provide summary information on
all relevant experiments.
The mentioned arguments led to the decision to update
the European roadmap for astroparticle physics.
The ApPEC Steering Committee and the ASPERA
Governance Board charged the SAC to prepare thisdocument. The charge does not include the requestof a prioritisation of projects. The SAC is aware that5
2. The High Energy Universe

inter-galactic magnetic fields. Fortunately the sources
are also expected to emit particles that travel in straight2.1. Introductionlines: gamma-rays and neutrinos. Indeed, gamma-rays
with energies up to 1014 eV have been observed from
Cosmic rays were discovered nearly a century ago. They a variety of sources. In most cases, however, it is nothave been the basic source of progress in elementary clear whether they are produced in the interactions
particle physics in the 1930s and 40s, before the of high-energy protons or nuclei with the ambientdevelopment of accelerators. Presently, the primary matter, or whether they are radiated by high-energy
interest in cosmic rays is opening a window to explore electrons. Here, neutrinos may come to the rescue: they
the Universe at the highest energies using all possible can be produced only in processes involving protons
messengers.
and nuclei. With a three-fold approach – charged
cosmic rays, gamma-rays and neutrinos – there is a
Astrophysics Questions: The observation of good chance that the mystery of the origin of cosmic
particles with energies much beyond the beam energies rays will be unveiled and the landscape of the extremeof terrestrial accelerators raises several questions. First, Universe will subsequently be fully explored.
how can cosmic accelerators boost particles to these
extremely high energies? Cosmic rays with energies up Fundamental Physics: Experiments detecting
to about 1016 eV are probably accelerated at the shock high-energy cosmic particles naturally involve particle
fronts generated by galactic supernova explosions or and nuclear physics and can probe new physics beyond
stellar wind collisions. Indeed, radio emissions, X-rays the Standard Model of particle physics. For example,
and gamma-rays give direct evidence that these fronts supersymmetric (SUSY) theories which are to beaccelerate electrons to beyond 1014 eV. However, the tested at the LHC also predict dark matter particles
evidence that high-energy protons and nuclei – the that annihilate into charged cosmic rays, gamma-rays
main component of charged cosmic rays – have the and neutrinos. The latter particles can be observedsame origin as these electrons is only circumstantial by space-based detectors (charged cosmic rays andand needs confirmation. Cosmic rays constitute a gamma-rays) and by Earth-bound detectors (highremarkable part of the galactic inventory and play an energy gamma-rays and neutrinos). With their potential
important role in the thermodynamics of the Galaxy. for indirect dark matter detection these detectors
Another key question concerns the maximum energy provide important complementary capabilities to theachievable by Galactic sources, such as supernova LHC and to direct detection experiments (see Section
remnants or binary star systems. The energy range above 3). Another example is the possibility to probe newa few 1018 eV is likely dominated by extra-Galactic physics at energies much beyond those reached atcosmic rays, because the Galactic magnetic field cannot terrestrial accelerators. For instance, a tiny violation
confine particles of such energy. Most enigmatic are the of Lorentz invariance would affect the propagation ofparticles with energies around and beyond 1020 eV. Are energetic cosmic particles over cosmological distances
particles with such huge energies due to acceleration and lead to observable effects. An abrupt change ofin the vicinity of super-massive black holes or around interaction cross sections at the highest energies due tostellar collapses? Or are some of them due to more the opening of new dimensions is another example.
exotic processes? The flux of protons travelling overlarge cosmic distances should be suppressed above~4×1019 eV where collisions with the cosmic 2.73 K
blackbody photon background results in rapid energy 2.2. Charged cosmic rays
loss within tens of Megaparsecs. Data obtained at
the Pierre Auger Observatory convincingly confirm Cosmic rays can be studied by direct and indirecta spectral suppression at the expected energy. Is this methods. Direct measurements on satellites and balloons
due to the above mentioned so-called GZK effect or record the primary particles before they interact in theis it just because the cosmic accelerators do not reach atmosphere of the Earth. Due to the small area of thesehigher energies?
detectors, however, there are no appropriate statistics in
the TeV range. The higher energies are the domain of
The multi-messenger approach: Because cosmic indirect methods: the detection of air showers initiated byrays are electrically charged, their paths are bent as the primary particles. The best established techniques arethey travel through cosmic magnetic fields. They do ground-based detectors that record the shower particles
not point back to their sources, except at the very arriving at ground level, or record the Cherenkov or
highest energies (more than a few 1019 eV), where fluorescence light from the showers. Indirect methods
the deflection for protons is expected to become for extreme energies include satellite-borne optical or
small according to our current understanding of the radio detectors observing the atmosphere from space,6ground-based radio telescopes observing the lunar crust,or balloon-borne radio detectors observing ice sheets on
the polar caps of the Earth.

its sensitivity to higher energies and with considerablylarger statistics, AMS will shed new light on the
PAMELA positron excess and provide a clearer answer
on its origin and the possible relation to dark matter.
Being complementary to SUSY searches at the LHC,AMS explores some parameter regions that are not
2.2.1. Direct measurements fromaccessible to the LHC. The AMS search for anti-nuclei(such as anti-helium or heavier) is motivated bysatellites and balloons, E < 1014 eV
the possible existence of anti-matter domains in
the Universe, so the observation of anti-helium
The most direct information on the properties of cosmic nuclei above astrophysical background would be anrays is obtained with detectors above the atmosphere important discovery. With the parameters mentioned– on stratospheric balloons or in outer space. Balloon above, the direct anti-matter search is improved by
missions with (minor) European participation have at least three orders of magnitude and extended tobeen TRACER (The Netherlands), ATIC (Germany) energies of 1 TeV. In addition, AMS has significant
and CREAM (Italy), the first in both hemispheres, the sensitivity for the detection of anti-deuterons that
other two in Antarctica. Direct measurements have could provide a very low-background technique ofprovided much of the information on galactic cosmic search for dark matterrays and contributed to the contemporary standard
model of cosmic-ray propagation in the Galaxy. For New since 2008:
instance, TRACER has provided boron-to-carbon
measurements up to almost 1014 eV. Cosmic particles Whereas in 2008 the future of AMS was uncertain
with GeV-TeV energies from Galactic accelerators (due to problems with the US Shuttle program) it wasor from interactions of primary cosmic rays with meanwhile successfully launched and is now taking
interstellar matter, are not only interesting on their data. Originally, AMS was constructed to operate onown, but also constitute the background of searches for the ISS for three years. The operation time of the ISS
physics beyond the Standard Model of particle physics will now be prolonged from 2015 to 2020 (or beyond).
and for the origin of the cosmic matter-antimatter The superconducting magnet of AMS (maximum
asymmetry.
operation time three years) has been replaced by the“warm” magnet already flown with AMS-01 in 1998.
PAMELA and AMS
The PAMELA satellite detector (Italy and other
European countries) was launched in 2006. In
2008, the collaboration reported a tantalizing excess
of positrons over the expected background which
triggered a flurry of discussions on its origin –ranging from the annihilation/decay of dark matter toconventional astrophysics like e.g. nearby pulsars or
supernova remnants.

The committee looks forward to the exciting physics
results expected from AMS.
Other satellite and balloon experiments

There is a gap between the energy range covered bypresent balloon and satellite experiments (up to 1012 eV)and by the range accessible from the ground (1014 eVand higher). Balloon and satellite measurements of thecomposition do not suffer from the large uncertainties
Deeper insight is expected from the Alpha Magnetic of hadronic interaction models which complicate theSpectrometer, AMS. AMS is a multi-purpose particle interpretation of ground-based shower detectors. They
detector deployed at the International Space Station would not only provide unique information on the(ISS) on May 19, 2011 for a mission of about a origin and nature of Galactic cosmic rays but also –decade. The AMS community consists of about 600 via the improved knowledge about cosmic-rays in thescientists, 70% from Europe and 30% from elsewhere “knee” region – lead to a better knowledge of interaction(China, Korea, Mexico, Russia, Taiwan and US). models which is mandatory for interpretation of air
The physics goals of AMS are the indirect search for showers at higher energies.
Dark Matter, the search for cosmic anti-nuclei, theprecise measurement of spectrum and composition of CALET (CALorimetric Electron Telescope) is acosmic rays up to a TeV, and the search for strange mission for the Japanese ISS module. It consists ofquark matter. The goals are a sensitivity to anti-He/He a total absorption calorimeter, a tracking calorimeter=10-10, an e+/p rejection of 10-6, and an accuracy of 1% and a silicon pixel detector. It aims for excellent energy
for composition and spectra of charged particles. With measurement, particle identification and charge

7measurements. CALET will search for dark-mattersignatures in electron and gamma-ray spectra andmeasure fluxes and spectra of nuclei up to Fe and up
to the multi-TeV region. The collaboration partners
come from China, Italy, Japan and US. The planned
launch is 2013.
The Russian satellite project NUCLEON aims at
measuring the spectrum and composition of cosmic rays
between 1012 and some 1014 eV. It will consist of a large
tracking calorimeter. The launch, originally plannedfor 2011, has been shifted by three years to 2014/15(now without the original Italian participation). To
what extent these plans are realistic and compatible
with even more demanding Russian projects withthese goals is hard to judge from the outside.

2.2.2. Galactic cosmic rays
at energies 1014 - 1018 eV
Above ~1014 eV, the showers of secondary particles
created by interactions of the primary cosmic rays in
the atmosphere are extensive enough to be detectablefrom the ground. At around 1015 eV there is a distinct
steepening of the spectrum, which is usually interpreted
as the limit of the acceleration range of Galactic sourcesof cosmic rays. Because the maximum energy attainable
at cosmic-ray sources is proportional to particle charge,
one expects that the average mass of cosmic primaries
increases when passing this “knee”. This energy region
has been explored by a variety of experiments in thelast decade (e.g. EAS-TOP, GAMMA, GRAPES,KASCADE, TIBET, TUNKA-25). Their results havegiven additional support for a rigidity dependence ofthe steepening for different primaries. Nevertheless,in all experiments, inconsistencies have been foundbetween the data and the predictions of the hadronicinteraction models underlying the analyses. Therefore,
further detailed investigations are necessary, inparallel by using new data from the “forward physics”
experiments at the LHC (CASTOR, TOTEM, LHCf )and by dedicated shower measurements.

GAPS (General AntiParticle Spectrometer) is a
proposed project to search for dark matter via theanti-deuteron signature. The instrument would use
a large area Si(Li) tracker that would serve both astarget and detector. Anti-deuterons are detected withhigh efficiency via an exotic-atom technique. GAPS isscheduled to fly a prototype balloon detector in 2011
with a full instrument coming approximately four years
later. GAPS is currently a US-Japan collaboration,
but there is the hope that European groups could be
involved as well.
The situation at energies above 1016 eV is of crucial
importance to our understanding of the origin andAccess to long duration balloon flights around the propagation of cosmic rays in the Galaxy. What is theNorth Pole originating from Kiruna or, even better, mass composition above the iron knee? Is this region
from the Svalbard Islands (higher latitude, resulting in dominated by sources other than supernova remnants?
a lower geomagnetic cut-off) would open a window Why are anisotropies not observed even though cosmic
of opportunity for European groups. Proposals for rays should be diffusing away rapidly from the Galaxy
measuring medium-energy positrons and electrons at such energies? What is the nature of the observed(PEBS) or low energy anti-deuteron (Dbar-SUSY) are “second knee” at ~7×1017 eV? Is there an early onset ofbeing considered for such flight opportunities. There an extragalactic component?
are already corresponding US experiments on balloons
being flown from Antarctica with minor European After KASCADE-Grande has finished its operation,
participation (ATIC, CREAM). US and Dutch groups the main progress for the next years is expected
are preparing a new TRACER mission with increased from IceTop/IceCube at the South Pole, from theaperture.
TUNKA-133 experiment in Siberia and fromthe low-energy enhancements of the Pierre Auger
Observatory in Argentina, all with European
Recommendation: We reiterate the suggestion of the participation. These detectors provide complementary
2008 roadmap, that efforts be directed to achieve an information and therefore an interesting possibility foroverlap between present direct and air-shower detection a coherent investigation of cosmic rays up to the end
methods in order to get a better understanding on of the galactic spectrum and for determining the onset
the mass composition and spectral features of cosmic of the extra-Galactic component. We also note thatrays. This goal may be pursued with large-aperture, KASCADE-Grande analysis continues, using newlong duration flight missions above the atmosphere input from LHC measurements.
(balloons/satellites) and/or by ground-based detectors
with adequate particle identification placed at the New since 2008:
highest altitudes (see next section).
a) The Tunka Cherenkov air-shower array, with 133
wide-angle photomultiplier stations spread over 1

8
km² has been completed and takes data. Detectors formuons and a large-spacing extension towards 4 km²
are planned for 2011/12. Also the 1 km² IceTop arrayhas been completed and records air-shower particles
on the ground, whereas IceCube records the resulting
muons punching down to 2,5 km depth in the ice.
The extensions at the Pierre Auger Observatory
towards lower energies have already been installed(HEAT) or are being installed (AMIGA). Several
efforts are being made at these arrays and elsewhere
to use MHz receivers as a new method to study thelongitudinal profiles of air showers with a 100% duty
cycle (LOFAR, AERA at the Auger site, RASTA at theSouth Pole, Tunka-Radio).
b) The LHC is providing first data, e.g. on total crosssections and multiplicities, which will substantially
improve the interpretation of the air shower data.
c) An interesting physics effect, reported earlier by the
Tibet air shower array, by Super-Kamiokande and by
the American Milagro experiment, was confirmed by
the ARGO/YBJ experiment (China/Italy) in 2008 andby IceCube and EAS-Top in 2009: a ~0.1% anisotropyof cosmic rays on both large and medium angularscales. It is an open question whether this effect is due
to cosmic-ray focussing on local magnetic fields, tonearby sources of cosmic rays, or to something else.
New results are expected from HAWC, the successorof the Milagro-detector that is under construction in
Mexico (without any European contribution).
d) China is constructing a new high altitude air shower
array (LHAASO) that will record cosmic rays andgamma-rays. This hybrid array will include wide-angle
and imaging Cherenkov counters, water pools andscintillation muon counters (see more in the section
on gamma-rays). First European and Russian groups
are discussing to join the project.
The existing experiments IceCube, TUNKA-133
and the low-energy extensions of the Pierre Auger
Observatory (AMIGA/HEAT) should be exploited.
We encourage the further development of MHz
radio wave detection of air showers, e.g. at the large
facilities Auger (AERA) and LOFAR, as well as at theSouth Pole and the Tunka site. There should be close
cooperation with the particle-physics community,in particular with respect to LHC results. An arrayat the highest possible altitude is desirable todetermine the chemical composition in the energy
range overlapping with balloon experiments (10TeV – PeV). At present, the planned LHAASO
experiment in China seems to come closest to thisrequirement.

2.2.3. The highest energies
The Pierre Auger Observatory
The present flagship experiment in the search forsources of ultra-high energy cosmic rays is the Pierre
Auger Observatory (in short “Auger”) in Argentina(450 scientists, ~50% from Europe). This 3,000 km2
array of water tanks, flanked by 27 air-fluorescencetelescopes, measures direction, energy and profile
of giant air showers. Even at energies above 1019 eV,
where the cosmic flux is only about one particle
per year per square kilometre, Auger can collect areasonable number of events. Above this energy, thedeflection of charged particles in cosmic magnetic
fields becomes less important and source tracing islikely to become possible if the observed cosmic rays
are low-Z particles.
Auger has been taking data since 2004 and in its fullconfiguration since 2008. The combination of a large
detector array and fluorescence telescopes provides a
substantial improvement in energy calibration andidentification of primary particles, resulting in data of
unprecedented quality. The observatory is successfully
operating and meets all of its design parameters. The
first results have provided important information on
key questions in the field.
A first breakthrough is the convincing confirmationof the steepening of the spectrum at energies beyond
50 EeV. However, the reason for the effect is not yet
convincingly established. It can be explained either bycollisions of cosmic rays with the cosmic microwave
radiation (“GZK cut-off”) or by a natural maximalenergy of cosmic accelerators. Beyond several tens of
EeV, the Auger Collaboration observes a transition froman isotropic to an anisotropic distribution of the arrival
directions. In 2008, the collaboration published thefirst sky map of events with energies above 55 EeV andreported a correlation of arrival directions with nearby
concentrations of matter as traced by certain Active
Galactic Nuclei (AGN). Such a correlation would be inagreement with theoretical expectations that only twoclasses of objects are able to accelerate particles up to1020 eV or higher – the central black holes or emerging
jets of AGNs, and Gamma-Ray Bursts (GRBs). In
the mean time, the correlation strength has decreased,
although the statistical significance of the reported
correlation has not changed very much. Anotherquestion of great interest is the mass compositionof the primary particles. The Auger results indicate
surprisingly a heavier composition of the primaries
towards the highest energies, where, however, thestatistics are limited. In addition, Auger showed thatthe fraction of primary photons is less than 2% of all9cosmic rays at energies of about 1019 eV, thus rulingout most ‘top-down’ models for the origin of ultra-highenergy cosmic rays. The Auger Collaboration has also
been able to set a stringent limit on cosmic neutrinos
at energies of 1018-1020 eV, complementary to the limit
obtained from the IceCube neutrino detector at theSouth Pole.

Alternative experimental
highest energies

approachesat

An alternative approach to reach the huge detection
volumes necessary for cosmic ray studies at 1020 eV
and beyond are space-based detectors which can record
fluorescence light and reflected Cherenkov light fromair showers. First generation projects are JEM-EUSO(planned launch 2017), with Japanese leadership,
and the Russian project TUS. TUS will have a muchsmaller aperture than JEM-EUSO but is planned to belaunched already in 2012 and may provide interesting
input to JEM-EUSO design parameters. In the further
future (beyond 2018), these devices could be followed
by Super-EUSO and KLYPVE (Russia) or a mergerof both. European participation in JEM-EUSO
makes up about 40% of the associated scientists. The
future development of these devices relies on novel
technologies and requires strong coherent R&D efforts.
In the more distant future, the Square Kilometre Array(SKA) has the potential to record cosmic rays withenergies beyond 1020 eV.

Understanding the primary composition above 1019 eV
and the nature of the high-energy cut-off as well as
identifying individual sources calls for significantly
higher statistics. This is the primary motivation tobuild a much larger array than the present Auger.
From its beginnings, the Pierre Auger Collaboration
envisaged a detector in the northern hemisphere to givefull sky coverage. The plan was to build Auger-Northin the US, an array with seven times the aperture ofAuger-South. Auger-North sited in Colorado would
have profited from the developed infrastructure andthe associated cost reductions. Cost estimates were ona firm ground because they were based on principles
proven by Auger South. The project cost was 130 M$,
with about 50 M$ expected from the US and 40-50%
from Europe. In both the 2006 and 2008 ApPEC Comparison of different detectors
roadmaps, Auger-North was defined as the clear
priority project of the field “charged cosmic rays”.
A next generation ground-based cosmic-ray observatory
could enable full sky coverage and would provide
News on the Pierre Auger Observatory since 2008:a much larger detection area than other northerncosmic-ray experiments, such as the Telescope Array
Whereas the funding prospects for Auger North (US-Japanese-Taiwan experiment in Utah/US) or thein some countries had improved over the last 2-3 Yakutsk array in Russia. It is also based on provenyears, the prospects in the US as host country had hybrid technology (multiple signatures of an event),
stayed open. However, in October 2009, the Particle in contrast to JEM-EUSO which will measure
Astrophysics Scientific Assessment Group (PASAG), fluorescence light only and which will have worse
charged by DOE and NSF, released recommendations capability for particle identification. On the otherfor the fields of Dark Matter, Dark Energy, and hand JEM-EUSO will gather far more statistics at theHigh Energy Cosmic Particles. It recommended the highest energies and will cover both hemispheres offunding of Auger North in a scenario where funding the sky.
for these fields would be doubled over the next ten
years. In 2010 the Decadal Survey for Astronomy
and Astrophysics (Astro2010) was released and Auger Recommendation: In conclusion, we reiterate theNorth was not prioritised. As a consequence, the US definition of a substantially enlarged ground-based
funding agencies will not consider giving funding for cosmic-ray observatory as the priority project of highthe Colorado site. The Pierre Auger Collaboration energy cosmic-ray physics – irrespective of whereconcluded that a new proposal for an experiment of this will be deployed. We encourage the community
the next generation should be prepared. This requires to work towards a global common path for such a
3-5 years of preparation in order to modify the substantially enlarged observatory including thetechnology accordingly and to find an appropriate site, development of new detection technologies. We
including the possibility of a considerable extension recommend that European groups play a significant
of Auger South to a similar scale as had been planned role in preparing a proposal for the next generation
for Auger North. Efforts are being made to exploit not experiment, and after its approval, make a significant
only radio emission dominated by geomagnetic effects contribution to construction and operation. We also
at tens of MHz frequencies, but also the molecular support European participation in JEM-EUSO withBremsstrahlung emission using GHz receivers, as its novel technology. We encourage cross coordination
new methods to study the longitudinal profiles of air between these two approaches.
showers with a 100% duty cycle.

10
2.3. Gamma-ray astrophysics
In contrast to charged cosmic rays, gamma-rays
propagate in straight lines while compared to neutrinos,
their interaction cross section is much higher making
them easier to detect. This has made gamma-rays apowerful tracer of energetic cosmic processes. On theother hand due to their higher cross section, high-energy
gamma-rays are more easily absorbed when travellingover long distances. Similar to charged cosmic rays,
gamma-rays can be studied both with satellite- andEarth-based detectors. MeV and GeV gamma-rays
are the domain of satellite detectors, whereas froma few tens of GeV upwards, Earth-bound telescopes
take over. The physics goals are, to a large extent, thesame:

MeV range, and AGILE and Fermi, targeting energies
in the MeV-100 GeV range.

INTEGRAL (an ESA, NASA and Russian collaboration
with instrument PIs in Denmark, France, Germany,
Italy, Spain and Switzerland) is a medium-class missionof ESA’s ‘Horizon 2000’ program, launched in 2002.
Operations are recommended to be extended to atleast 2014. INTEGRAL carries two main instruments
covering soft gamma-rays from 12 keV to 10 MeV andtwo monitors in the X-ray and optical band. For theexperiments considered in this roadmap, INTEGRAL
is the “next neighbor” towards lower energies. Among
its achievements are the deepest all-sky survey in hard
X-rays, the mapping of the e+-e- annihilation light in
the Galaxy (the origin of which is still unclear), thediscovery of many new hard X-ray sources includinga) investigating the origin and propagation of Galactic new families of X-ray binaries and magnetars, thecosmic rays by classifying gamma-ray sources and detection of obscured AGNs in hard X-rays as well as
by studying shock-wave acceleration in supernova GRBs and the mapping of pulsar magnetospheres.
remnants and other extended sources, pulsar winds
and stellar winds, as well as particle acceleration in We note that in the following, we will focus to energies
pulsar magnetospheres;
above the X-ray range and consider lower energies
as the realm of “classical” astronomy. We will onlyb) studying the physics of compact objects and their occasionally address X-ray missions, e.g. in the context
relativistic outflows on different scales, from pulsars of dark matter search.
and micro-quasars to AGNs and GRBs, in particularprobing the physics of black holes close to the event AGILE, a fully Italian mission, was launched inhorizon and the emergence and composition of jets;
December 2007. It carries a 40×40 cm2 silicon tracker
and a calorimeter covered by a veto counter, an X-rayc) addressing cosmological questions by searching for detector and a small gamma-ray-burst detector.
gamma-rays from Dark-Matter annihilation or decay AGILE has detected many Galactic and extra-Galactic(indirect Dark Matter search), measuring extra-Galactic sources and recorded a series of interesting transient
background light via its interaction with high-energy phenomena.
gamma-rays and probing the accretion history of the
Universe and the formation of the first galaxies;
The Fermi Gamma-ray Space Telescope (US, France,
Germany, Italy, Japan, Sweden) was launched in Juned) analyzing topics in fundamental physics, such as 2008. It carries two instruments, the Large Area
testing the quantum structure of space-time by looking Telescope (LAT) and the GLAST Burst Monitor
for any energy dependence of the speed of light at the (GBM). With a 180x180 cm2 silicon tracker and ahighest energies and from the most distant sources.
calorimeter (also covered by a veto counter), the LAT is
30 times more sensitive than any previous high-energy
gamma-ray experiment flown into space and is expected
to detect thousands of sources during the five-year
2.3.1 Gamma-ray astronomy
primary mission. Fermi has already detected many new
pulsars not seen at any other wavelength, as well asfrom satellites
many other new galactic and extragalactic gamma-ray
sources. It has clearly excluded the galactic ‘excess’ inSpace-bound gamma-ray astronomy was pioneered by GeV gamma-rays which had earlier been reported by
missions like SAS-2 (1972/73) and COS-B (1975-81). EGRET and interpreted as a signal of dark matter. The
In the 1990s, the EGRET detector on the Compton detection of gamma-rays from distant GRBs provided
Gamma Ray Observatory (CGRO) discovered a few significantly improved limits on Lorentz invariancehundred astrophysical sources of GeV gamma-rays. violation. Fermi has revealed Galactic bubbles and
The BATSE detector on CGRO recorded about 2000 put constraints on cosmological magnetic fields. Last
Gamma-Ray Bursts. The legacy of these missions is but not least Fermi has precisely measured spectra offulfilled by INTEGRAL, targeting energies in the keV- cosmic-ray electrons up to a TeV and has confirmed

11
the PAMELA excess of positrons. Very recently, both
Fermi and AGILE reported short flares with up to 30
times the nominal flux from a source that was assumed
to be rather steady (and therefore a ‘standard candle’)– the Crab Nebula.

ARGO/YBJ and HAWC) have a higher threshold andreduced flux sensitivity as well as poorer energy andangular resolution but enjoy, due to their large field ofview, better survey and monitoring capabilities. Thus,
they nicely complement IACTs.

Fermi is certainly one of the most successful
enterprises at the borderline between astronomy andfundamental physics. The initial mission extends up
to 2013, but will likely be extended considerably. The
chances of realization for a Russian Fermi-like mission(“Gamma-400”) are hard to estimate at this time.

Present Imaging Cherenkov Telescopes

Even after INTEGRAL (20 keV–a few MeV) andAgile/Fermi (30 MeV–100 GeV), there remains a
noticeable lack of coverage in the gamma-ray sky in the
1-30 MeV range and a lack of effective area to probe
physical mechanisms in detail. For many sources, themain power output is expected in this range. Several
proposals for missions addressing these energies havebeen submitted to the recent M3 ESA ‘Cosmic Vision’call, but none were selected. On the other hand theLOFT X-ray mission is amongst the four projects having
passed the selection for follow-up studies. The mainscience goal of LOFT is to determine the equation ofstate of dense matter through precise measurement of
the mass and radii of neutron stars, i.e. probing QCD
and nuclear physics (at the surface of the neutronstar) under extreme conditions (density and magnetic
fields). This is clearly a domain at the interface between
astro- and particle physics. The committee recognizes
the importance of these missions.

2.3.2. Gamma-ray astronomy with
Earth-bound detectors
Due to the small area of detectors on satellites there
are no available statistics at energies above a few tens ofGeV. Higher energies are the domain of ground-based
Imaging Atmospheric Cherenkov Telescopes (IACTs),
covering the energy range up to several hundred GeV
with high sensitivity. IACTs record the Cherenkov
light from air showers originating from gamma-ray
interactions in the atmosphere. Large reflectors focus
the light onto cameras of hundreds to a few thousandsof photomultipliers (in future possibly also solid-state
detectors). From the shower image, the direction,energy and character of the primary particle (hadronversus gamma-ray) can be derived. With anothertechnique, the shower particles reaching the ground arerecorded – either via the Cherenkov light they produce
in water pools or via the ionisation in tracking devices.
Compared to IACTs, these detectors (such as Milagro,

The IACT technique was pioneered in the US withthe development of the Whipple Telescope andthe detection of a first source, the Crab Nebula,in 1989. During the last decade European groups
have been central to the progress of the field ofground-based high-energy gamma-ray astronomy.
A large proportion of the new sources have been
discovered by two Europe-led facilities (H.E.S.S.
and MAGIC). VERITAS in Arizona started fulloperations in 2007, with a similar sensitivity to HESS.
All three experiments lead to continuing high rate ofdiscoveries. The measurements provide all the typical
data of astronomical observations: images showing
spatially resolved source morphologies; light curves
showing time variations; energy spectra extending
multi-wavelength spectral energy distributions ofknown sources towards the TeV region; and surveys
discovering unidentified sources and extending source
catalogues.
IACTs have by now revealed more than a hundred
sources of gamma-rays at the 1011 to 1014 eV scale,many of them in the Galaxy and revealing a complex
morphology. Most of the Galactic TeV sources
correspond to objects like binary systems, pulsar
wind nebulae and supernova remnants. Others arestill entirely unknown at any other wavelength andobviously emit most of their energy in the TeV range(“dark accelerators”). Going outside the Galaxy, a large
number of AGNs have been observed and their fastvariability demonstrated.
The present state-of-the-art of IACTs is represented by
the three facilities:- H.E.S.S., an array of four 12 m Cherenkov telescopesin Namibia, which has taken data since 2003 with all
four telescopes. European partners make up 95% of
the 170 members of the collaboration. The telescopes
operate in stereo mode. The extension towards lower
energies by a 28 m telescope, originally planned for
2009, is now envisaged for summer 2012.
- MAGIC, located at La Palma/Spain, was initiallyoperated as a single 17 m telescope. MAGIC-II, asecond 17 m telescope, saw first light in 2009 andallows now also stereo observations. All of the 150
members of the collaboration come from Europe.

12
MAGIC is testing innovative photon detectors as partof the existing cameras. In addition, in summer 2011
the MAGIC-I camera will be replaced by a camera of
MAGIC-II type, and the readout for both cameras
by one with improved performance. Among all threetelescopes, MAGIC has the best sensitivity at energies
below 100 GeV.
- VERITAS is an array of four 12 m telescopes
operating in Arizona/US. The collaboration consistsof 95 scientists, 20% from Europe. VERITAS has
achieved the same sensitivity as H.E.S.S. (1% of the
Crab Nebula in less than 30 hours). VERITAS iscurrently undergoing an upgrade to replace all pixels
with high quantum efficiency PMTs and to improve
the trigger system with a telescope-image trigger. This
upgrade, to be completed in 2012, will significantly
improve the telescope sensitivity at gamma-ray energies
below 100 GeV.

tructed events. The actual design of CTA is still understudy, but it will likely consist of a few large central
telescopes providing superb efficiency below 50 GeV,
embedded in an array of medium-sized telescopes
giving high performance around a TeV, themselves
surrounded by a few-km² array of small dishes to catchthe bright but rare showers at 100 TeV. The minimum
detectable flux in the central energy band at 1 TeV, will
be about 0.1% of the Crab flux, combined with anenergy resolution of 15% and angular resolution down
to 1 arcmin for the best-reconstructed events.

CTA is aimed to cover both hemispheres, with one sitein each. The field of view of the Southern site includes
most of the Galaxy, while the Northern telescope
would instead place the main emphasis on the studyof extra-Galactic objects. At energies above a few tensof TeV and over megaparsec distances, gamma-rays
are absorbed by the cosmic infrared background lightand by the cosmic microwave background above a few
Less powerful telescopes are operated in Australia hundreds of TeV. Therefore high-energy sensitivity is(CANGAROO) and in India (TACTIC). India is less important for the Northern (“extra-Galactic”) siteplanning to build MACE, a telescope array of similar than for the Southern (“general-purpose”) site, whichpower to the present three leading installations, but at should provide full energy coverage and excellent
high altitude (on the Tibetan plateau at 4,300 m).
angular resolution in order to study the morphology
of galactic objects.
While the results achieved with current instruments are
already very impressive, they just give a taste of the TeV We assess the project below with reference to thecosmos. The detailed understanding of the underlying essential criteria: scientific impact, uniqueness/processes and the chance to see more than the tip of complementarity, strength of community, project
the iceberg can be improved dramatically by a much management, cost, technical readiness, risks andlarger array of telescopes based on now well-established industrial involvement.
techniques and observation strategies. The time
has come to make this exciting new astronomical Scientific Impact: The low-energy sub-arrays of CTA
window available to the wider community through would explore a new territory and would bridge thethe construction of a major new facility, which, unlike gap to space-based gamma-ray astronomy. The large
earlier projects, will be run as an open observatory and number of GeV sources detected by Fermi confirms
be made available to astronomers on the same basis the high potential of this energy range. Our present
as optical or X-ray observing facilities. A consortium understanding of the absorption of gamma-rays by
has been formed to work jointly towards the design the extra-Galactic background light (EBL) indicatesand realisation of such an instrument, the Cherenkov that the visibility of the Universe for energies above
Telescope Array (CTA). It involves all groups 100 GeV is limited to redshift z < 1. The low-energy
worldwide currently participating in IACTs, as well as section of CTA would extend the observation range toa large number of additional new partners from both high redshift AGNs with z ~ 3-5. The large accessible
particle physics and astrophysics. CTA is included in cosmic volume would result in a substantiallythe list of projects compiled by the European Strategy increased number of sources, allowing for the first
Forum for Research Infrastructures (ESFRI), and is time cosmological issues such as Dark Energy to be
ranked high in the ASTRONET roadmap and the US possibly addressed.
decadal survey.
Extension of the sensitivity at medium and high energies
will allow sensitive mapping of the Galaxy and a more
The Cherenkov Telescope Array (CTA)
precise study of the high-energy part of the spectra
The goal of CTA is to increase the energy bandwidth of galactic objects and close-by AGNs. Spectra andsimultaneously towards both lower and higher energies, energy-dependence of source morphology in this energy
thus improving the current sensitivity and providing range provides the most important information forlarge statistics of highly constrained and well-recons- distinguishing acceleration mechanisms in the sources.

13
With the increase of the sensitivity in the central-energy
region, fainter objects will be visible. Also, known
objects can be measured on much shorter time scales
and their transient behaviour can be studied in moredetail. The improved angular resolution will provide
much more detailed information on the morphologyof the sources. With one thousand expected sources
between a few tens of GeV and 100 TeV, CTA willturn ground-based gamma-ray astronomy into an
observational discipline comparable to conventional
astronomy.

Matter annihilating to gamma-rays in the Galactic
halo. Low-mass candidates will be well covered bydirect detection experiments, but near or above theTeV mass range CTA would have unique capabilities
for detecting a dark matter signal.

Strength of Community: CTA combines the worldwide
experience of all relevant communities working withatmospheric Cherenkov telescopes: Europe, US,
Japan and India. The groups from US (formerly
AGIS collaboration) and India joined in 2010, with
the US groups proposing a major contribution to theUniqueness/Complementarity:
medium-sized telescopes. The observatory characterof CTA will open this infrastructure to a much wider
CTA vs. H.E.S.S , MAGIC and VERITAS: providing community, which will appear as “users” who apply
an order of magnitude boost in sensitivity and energy for observation time, as in traditional astronomical
coverage and operated as an open observatory, CTA observatories.
is qualitatively different from experiments such as
H.E.S.S., MAGIC and VERITAS and cannot be Project Management: A collaboration based on MoUs
realized by a simple expansion or upgrade of any of was formed in May 2010. A three-year EU-fundedthese instruments.
preparatory phase started on Oct.1, 2010 and a project
office for the preparatory phase was installed.
CTA vs. Wide-angle devices: Wide-angle devices like
HAWC, the successor of the Milagro experiment Cost: The current cost estimated for CTA is on the 200
in the US, will have a higher threshold and worse M€ scale. The goal of the design and prototype phase isflux sensitivity, angular and energy resolution but – to carry out the necessary work to reduce costs as muchdue to their large field of view – better survey and as possible and to ensure that the project is ready formonitoring capabilities, thus nicely complementing the start of construction at the end of the preparatory
CTA. Wide-angle devices may possibly also have the phase. The Southern site will be more expensive
potential to extend the energy range of gamma-ray because it will include the high-energy extension withastronomy into the PeV region.
a much larger number of small telescopes than the
Northern site.
CTA vs. Fermi: Fermi will overlap with CTA in theenergy range of tens of GeV. Combination of data from Technical readiness, challenges and risks: CTA is mostly
the two instruments will provide an unprecedented based on existing and proven techniques, therefore there
seamless coverage of more than seven orders of are no major risks that could prevent the observatory
magnitude in energy. Simultaneous observations over from not working or not providing excellent scientificsuch a wide energy range are a key to understand the results. However, the goals of CTA imply significant
physics of Galactic and extragalactic cosmic accelerators advances in terms of efficiency of construction andand could be essential in the identification of Dark installation, in terms of the reliability of the telescopes
Matter.
and in terms of data preparation and dissemination.
The main challenge is to lower the costs per collected
CTA vs. IceCube/KM3NeT and Auger: CTA has photon as compared to MAGIC/H.E.S.S./VERITAS.
a guaranteed rich scientific output based on clear A risk arises from the possibility that the cost reductions
detection of sources. CTA will be a key element for cannot be achieved within the planned time and themulti-messenger studies with neutrino telescopes and project would either be delayed or be downgraded towith Auger.
meet the cost constraint, the latter with a corresponding
loss in science power.
CTA vs. new radio and x-ray observatories: thesensitivity of CTA will allow matching the accuracy Industrial involvement: Cooperation with industry,of the measurements provided in the radio and X-ray towards largely industrial fabrication of telescope
bands in multi-wavelength observations.
components is well established and covers many areas,such as optimisation of photo sensors, development
CTA vs. H.E.S.S., MAGIC, VERITAS and direct of cost-effective techniques for mirror production, or
detection experiments of Dark Matter: CTA will design/production of telescope structures and drives
expand by a large factor the possibility to detect Dark and control systems.

14
Recommendation: The Cherenkov Telescope Array,
CTA, is the clear worldwide priority project of Very
High-Energy (VHE) gamma-ray astrophysics. We
recommend the design and prototyping of CTA,
the selection of site(s) and to proceed vigorously
towards start of construction in late 2013. We
strongly recommend that the various funding
agencies work together to secure the required funds
for the construction and operation of CTA. The
current IACTs should continue to take data until
CTA has superior sensitivity and sky coverage.

Wide-angle devices
Wide-angle devices have inferior background rejection,
sensitivity, angular and energy resolution and a higher
threshold than IACTs. On the other hand they havea wider field of view and about ten times better duty
cycle. A number of impressive detections have been
made by the Milagro collaboration with a large waterpool in the US, including extended sources that are
harder to cover with IACTs. Also ARGO/YBJ (Italy/
China) has detected several gamma ray sources, theCrab Nebula, Mkr-421 and MGRO J19808+06.
The follow-up project of Milagro is HAWC, the“The High Altitude Water Cherenkov Experiment”,
a wide-field detector of 900 huge water pools and22,000 m² area being constructed in Mexico (US/
Mexico) at 4,100 m altitude. HAWC will be a real
breakthrough – it will map the Galactic diffuse
gamma-ray emission above 1 TeV, will perform an
unbiased sky survey with a detection threshold of ~30
mCrab in two years, enabling the monitoring of known
sources and the discovery of new classes of diffuse andpoint-like TeV gamma ray sources. HAWC would also
be sensitive to transient phenomena (an AGN flare 5
times the flux of the Crab in 10 minutes). Both HAWC
and CTA will profit from a close cooperation.

100 TeV. As an example we mention SCORE (Study
for a Cosmic ORigin Explorer), which is a proposed
project sensitive to gamma-rays above 10 TeV andcosmic rays above 100 TeV. The SCORE principle will
be tested with a test array to be deployed in the next 2-3
years at the Tunka site in Siberia and if feasible, could
serve as a future PeV extension for IACT arrays.
The wide-angle devices are also excellent cosmic-ray
detectors in the energy range from 100 TeV to 1 EeV.
The corresponding center-of-mass energies (1.7 TeV
to 170 TeV) of the interactions of the cosmic rays
with air overlap fully with the LHC energy range andextend well beyond the energies that can be reached byaccelerators on Earth.

2.4. High-Energy Neutrinos
The physics case for neutrino astronomy is compelling:high-energy neutrinos can provide an uncontroversial proof that their astrophysical sources accelerate
hadrons. Moreover they can reach us from cosmic
regions which are opaque to other types of radiation.
However, whereas neutrino astronomy in the MeV
energy domain has been established with the impressive
observation of neutrinos from the Sun and Supernova
SN1987A, extraterrestrial neutrinos with energies of
GeV and above, which must accompany the productionof high-energy cosmic rays, still await discovery. The
focus in this field is on Cherenkov neutrino telescopes
in deep water and ice. At the high-energy frontier they
are extended by methods using acoustic, radio andfluorescence light signals.
Neutrino telescopes address a wide range of astro- andparticle physics topics:a) Exploration of the high-energy universe using
neutrinos. First, searching for astrophysical sourcesof high-energy neutrinos, like supernova remnants,
LHAASO is a proposed 1 km² area, hybrid array microquasars, pulsars, AGNs, GRBs, or even unknown
comprising IACTs, water pools, scintillation detectors phenomena. Second, searching for neutrinos fromand fluorescence telescopes. It addresses Galactic cosmic-ray interactions with inter-galactic mattercosmic-ray studies up to 1018 eV and wide-angle and radiation fields, thereby addressing cosmological
gamma-ray astronomy. It is envisaged to be located questions.
at more than 4 km altitude in Tibet/China. The large
area and the high degree of hybridisation promise b) Study of fundamental physics questions: i) search
important contributions for the highest energies. The for neutrinos from Dark-Matter annihilation/decay; ii)
collaboration is forming, meanwhile including first search for effects of quantum gravity, e.g. possible violation
collaborators from Europe and Russia.
of Lorentz invariance (VLI) or effects of quantum
decoherence, by analysing oscillations of atmosphericIn addition, there are efforts for large-area wide-angle neutrinos or neutrinos from distant sources; iii) search
gamma-ray and cosmic-ray detectors sensitive to for exotic particles like magnetic monopoles, supergamma-rays above 10 TeV and cosmic rays above symmetric Q-balls or nuclearites; iv) measurements

15of neutrino cross-section at ultra-high energies, which
would probe non-perturbative QCD effects as well as
new physics beyond the Standard Model.
c) Cosmic-ray studies, by investigating downward
going muons or (for IceTop/IceCube) by measuring
the spectrum and mass composition of cosmic rays.
d) Monitoring the Galaxy for MeV supernova
neutrino bursts (something which does not belong to
the high-energy universe, but which can be done by
IceCube).
In addition to these central physics topics, the neutrino
telescopes and their infrastructures in the deep polar
ice or lake/sea water are also useful for a wide spectrumof other fields of science, such as marine biology,
oceanography, geology and geophysics, glaciology orenvironmental sciences.
First generation detectors:
NT200, AMANDA, ANTARES
European physicists have played a key role inconstruction and operation of the pioneering neutrino
telescopes, NT200 in Lake Baikal (Russia, Germany),
AMANDA (US, Belgium, Germany, Sweden) at theSouth Pole. ANTARES is an entirely European project,with 200 scientists from France, Germany, Italy,
Netherlands, Romania, Spain and Russia and has broken
the technological wall of operating a deep-sea telescopewith an acceptably small failure rate. Both AMANDA
and ANTARES have shown convincingly the successof the method and that they can detect atmospheric
neutrinos with the predicted rate, angular and energy
distribution. Unfortunately, even with AMANDA andthe highest statistics of high-energy neutrino events
ever collected (over 6,000 in 7 years), no signal of
extraterrestrial neutrinos has yet been identified. In the
coming years ANTARES will collect similar statistics
looking at a different region of the sky, which covers
the central part of the Galaxy, in order to fully exploit
its scientific potential and provide input and testing
grounds for the final design steps of KM3NeT.

European (Belgium, Germany, Sweden, Switzerland
UK). IceCube is recording about 100,000 neutrinos
and about 50 billion down going muons per year andis a member of the Supernova Early Warning Network(SNEWS). IceCube has observed atmospheric neutrinos
up to a record energy of 400 TeV and has put the moststringent limits on fluxes of extraterrestrial neutrinos.
No such signal has been identified until now, puttinga certain pressure on plans for KM3NeT (see below).
The arrival directions of down-going muons fromcharged cosmic rays show a 0.1% anisotropy similar towhat has been observed in the Northern hemisphereby ARGO/YBJ, Milagro and Super-Kamiokande. The
IceCube limits on high-energy neutrinos from theSun place competitive limits on dark matter particles
with spin-independent scattering on nucleons, and infact improve on direct detection experiments for thecase of spin-dependent interactions. Record limits
have also been obtained for magnetic monopoles andpossible effects of the violation of Lorentz invarianceon neutrino oscillations.
IceTop measures air-shower particles from cosmic
rays with primary energies in the range of 1-300
PeV. Combined with muons measured in IceCube, itwill provide unique data on the mass composition ofprimary particles.
The high-density DeepCore nested array will lower
the threshold from 100 GeV down to about 10 GeV.
This will make IceCube sensitive to oscillations ofatmospheric neutrinos. Further increasing the densityof optical modules may lower the threshold to 3 GeV,
allowing for studying matter oscillations, and possibly
even effects that can distinguish amongst the different
mass hierarchy scenarios. A further increase in thedetector density would allow detection of supernova
neutrinos from outside our own Galaxy (see also section
3.5.2). These extensions are presently under study andwill critically depend on the actual performance of theexisting DeepCore installation.
A planned 160 km² in-ice radio detector at the South
Pole will be discussed at the end of this section.

IceCubeGigaton Volume Detector (GVD) in Lake Baikal

The IceCube Neutrino Observatory consists ofIceCube, a 1 km³ neutrino telescope installed at a
depth of 1.5-2.5 km in the polar icecap, and IceTop,a 1 km² air-shower detector at the surface. IceCube
consists of 5160 optical modules on 86 strings. It
was completed December 2010. The 250-member
collaboration consists of 34 institutions, 17 of them

Guided by national history and priorities, the Russian
Baikal Collaboration plans the stepwise installationof a kilometer-scale array in Lake Baikal, the Giant
Volume Detector. GVD will consist of strings grouped
in clusters of eight, each with 24 optical modules.
Prototype strings have been operated in 2009 and2010. Three strings with eight optical modules each

16
and a prototype of the array electronics have been
deployed in spring 2011. An official proposal has
recently been submitted to Russian funding agencies.

The project cost are estimated to be ~250 M€ for a
detector which reaches about five times the sensitivityof IceCube for certain searches.

The GVD configuration is optimized for cascade
detection. The detection volume for cascades above
50 TeV is 0.3-0.8 km³; the detection area for muons
with energy above 10 TeV is 0.2-0.5 km². A thresholdof 10 TeV appears to be rather high when comparedto IceCube and KM3NeT. On the other hand the
optimum energy cut to get the best signal-to-noise
ratio (extraterrestrial versus atmospheric neutrinos)
for the weakest detectable E-2 sources is at a few TeV
for point sources, and in the 100 TeV range for diffuse
fluxes. Therefore, the GVD configuration may turnout to have a favorable physics/cost ratio. Still, thevolume/area is too small to compete with IceCube and
KM3NeT. Building GVD could make sense as partof a global Northern infrastructure, i.e. if KM3NeT
is built. We give no recommendation with respect to
GVD, since no European funding is involved.

Scientific Impact: KM3NeT increases the discovery
potential for neutrino sources and potentially allows
deeper a deeper search into black hole environments
and at energies beyond 100 TeV, further out into the
Universe than possible with gamma-rays. Together
with gamma-ray and cosmic ray observations (and with
IceCube), it could pave the way to real multi-messenger
astronomy. However, in absence of established cosmic
high-energy neutrino sources, it is difficult to assess thesensitivity necessary to achieve these goals. Until now
neither IceCube nor ANTARES have seen any cosmic
neutrino sources. Should this picture pertain for the firstfew years of full-scale IceCube operation, KM3NeT in
its currently planned configuration, being about fivetimes more sensitive than IceCube, may provide only alimited additional discovery window for extragalactic
sources. The abundance and characteristics of such
sources should not differ much between the Northernand Southern skies, but firm flux predictions are absent.
Predictions for Galactic sources are much more firm if
we assume dominantly hadronic emission. In contrast
to extra-Galactic sources, we seem to be close to thediscovery region, therefore here a factor five but with atelescope observing the Southern hemisphere, counts
indeed. With the central part of the Galaxy in its fieldof view, KM3NeT therefore may provide a significant
step beyond IceCube.

KM3NeT
IceCube observes neutrinos from the Northern sky.
Complete sky coverage, in particular of the central partsof the Galaxy with many objects that emit TeV gamma
rays and are promising neutrino source candidates,
requires a detector in the Northern hemisphere withat least the same sensitivity. R&D work towards
such a Northern neutrino telescope on the cubickilometre scale, named KM3NeT, is being pursued bya consortium formed from the three Mediterranean
neutrino telescope projects (ANTARES, NEMO andNESTOR) and sea science/technology institutes. The
consortium includes more than 300 members, all from
Europe.

The gain from KM3NeT for indirect Dark-Mattersearches, exotic phenomena such as magnetic monopoles
or Q-balls, or oscillation studies with atmospheric
neutrinos, is restricted because these phenomena are
not expected to depend on the hemisphere. If, however,
IceCube would see an exotic effect, the confirmation by
KM3NeT would be essential. Given recent constraints
Three candidate sites in the Mediterranean Sea, close to from Fermi-LAT measurements of the diffuse gamma
Toulon (ANTARES), east of Sicily (NEMO), and off radiation in the energy range below about 100 GeV,
the west coast of the Peloponnese (NESTOR) have been the sensitivity of KM3NeT in its current configuration
identified and studied in long-term collaborations.
to cosmogenic neutrinos is expected to be limited, but
might be increased to a significant level by implementing
The European Strategy Forum for Research Infras- (part of ) the detector in a sparse array of several tens
tructures (ESFRI) has included KM3NeT in the of km3.
European roadmap for research infrastructures. An
EU-funded three-year FP6 Design Study has been The KM3NeT infrastructure will also provide accesscarried out. An FP7 Preparatory Phase project is to continuous, real-time deep-sea measurements overongoing until February 2012, its major objective is to long periods. This is of high interest to various scienceaddress the legal, governance, financial, engineering communities, e.g. marine biologists, oceanographers,
and political issues that need to be clarified before geologists and geophysicists, environmental scientists,
construction can proceed. A Conceptual Design etc. It is foreseen that KM3NeT will be one node of aReport for KM3NeT was released in April 2008. A global deep-sea observatory system.
Technical Design Report, summarising the outcomesof the Design Study, is available since June 2010.

17
Scientific groups involved and transnational cooperation(Strength of Community): All research groups currently
KM3NeT vs. IceCube vs. Lake Baikal GVD: KM3NeT involved in deep-sea neutrino telescope projects arewill have the highest sensitivity to neutrino point sources also part of the KM3NeT effort, providing leadingof all three telescopes. It will be the only detector with expertise in all relevant fields. In addition, a number of> 1 km3 volume to observe the Southern sky (and with marine-science and technology institutes have joined
it the central region of the Galaxy) in the neutrino the KM3NeT consortium and KM3NeT cooperates
energy range 1012-1015eV. Together with IceCube, closely with the EMSO project (European MultidisciKM3NeT will provide full-sky coverage over the full plinary Seafloor Observatory). Currently, KM3NeT isenergy range up to energies of cosmogenic neutrino pursued as a pan-European effort.
fluxes. It seems obvious that the early observation or
non-observation of sources by IceCube will impact the Project Management: Currently, the KM3NeT activities
actual size and configuration of KM3NeT. KM3NeT are coordinated and managed through the Preparatory
will be about one order of magnitude more sensitive Phase project. For the time beyond the Preparatory
than GVD in Lake Baikal. GVD could be part of a Phase, a Memorandum of Understanding between
distributed northern infrastructure and add statistics the participating institutions is in preparation. Forwith a detector with different systematics.
management and governance in the construction andoperation phase, the set-up of an ERIC (European Research
KM3NeT vs. CTA and Auger: Even though in Infrastructure Consortium) is under investigation.
contrast to CTA, KM3NeT might likely just scratch
the sensitivity region of interest, it would/could open a Cost: The estimated budget for the KM3NeT research
truly new window, with the occasional surprises related infrastructure lies in the range of 250 M€, with a projected
to new territories. It also represents the one hitherto spending profile peaking in the period 2014-17.
missing frontier of a multi-messenger approach. Evena low-statistics measurement of cosmic neutrino Technical readiness, challenges and risks: The feasibility
signals would provide highly relevant complementary of a deep-sea neutrino telescope has been demonstrated
scientific information to that of CTA and Auger. Thus by ANTARES. The KM3NeT technical design
this is a question of complementarity rather than of represents a major development beyond ANTARES,in particular concerning cost-effectiveness, reliability
competition.
and deployment of state-of-the-art technology.
KM3NeT vs. “new detection methods”: The KM3NeT is expected to be ready for construction by
new detection methods mentioned further below the end of 2012. The major challenge, besides securing(acoustics, radio, etc.) are typically applicable at funding and reaching political agreement, is to keepenergies of 1017-1018eV and beyond. These methods the consortium together and active in the phase before
are therefore complementary to the “traditional” project endorsement. A certain risk is that delays
neutrino-telescope technique. Rather than the physics beyond the current schedule may lead to a drain of keyof cosmic acceleration, their main focus is the detection experts and/or to the implementation of alternative,of neutrinos from cosmic-ray interactions with the “specialised” projects of regional character, which fail2.7 K radiation and from possible exotic relics.
to match the scientific objectives of KM3NeT but tie
up available resources.
Timeliness and schedule/milestones: Following the
publication of the TDR, the KM3NeT Consortium Industrial involvement: Close contacts to industry have
has converged on a technical design, for which now been established, amongst others, in the following
prototyping and test deployment activities are being product fields: photomultipliers, information
pursued. An important milestone is a decision on technology (in particular with optical components),
the deployment site, which has a political dimension deep-sea technology. A substantial fraction of thethrough the link to possible funding sources of local KM3NeT budget will be spent for purchase ofnature, in particular European Regional Development such components from industry. Corresponding
Funds (ERDF) and the constraints concerning their pre-procurement activities are conceived in theuse. This decision is foreseen to be taken towards the Preparatory Phase. Outsourcing of production
end of the Preparatory Phase. A Technical Proposal processes to industry is also considered.
will be presented in 2012, and construction could
commence in 2013/14 if the project is endorsed. It is
expected that construction will take about 4-5 years, Recommendations for IceCube and KM3NeT:
although also a staged implementation over a longer IceCube is now providing data with unprecedented
period might also be possible.
quality and statistics. The European partners should
Uniqueness/Complementarity;

18
be supported in order to ensure the appropriatescientific return.
There is a strong scientific case for a neutrino
detector in the Northern hemisphere, however,with a substantially larger sensitivity than IceCube.
Resources for a Mediterranean detector should
be pooled in a single optimized design for a large
research infrastructure. The KM3NeT collaborationis encouraged to present a technical proposal
matching these requirements and in particular toreach final site and design decisions that would
enable start of construction in 2014.

horizon to search for EeV neutrinos.
The published data from these experiments havelead to limits over an energy range of more than six
decades, starting at 1016-1017 eV and extending beyond
1022 eV. All of them have been established within thelast decade. The exploitation of the full potential ofthese methods needs large-scale R&D work, e.g. fortheir application at SKA.

The next step in radio detection of neutrinos is being
undertaken by two projects in Antarctica: ARIANNA,
planning to deploy radio antennas on the shelf ice, and
ARA, planning to build an 150 km² array at the SouthThe IceCube, ANTARES and KM3NeT collaborations Pole. In Europe, Belgium is taking part in ARA (withare encouraged to strengthen cooperation, with the the centre of activities being in the US and Taiwan).
goal to form a Global Neutrino Observatory that in ARA obtained significant funding in the US and was
the future might also include further projects, such testing equipment for fast drilling, energy generation
as Baikal-GVD.
by wind power and radio detection in the season
2010/11. In the future, the satellite-based Russian
project LORD will be used to observe GHz radiation
Techniques for extremely high energies
from the lunar regolith.
Emission of Cherenkov light in water or ice provides
a relatively strong signal and hence a relatively
low-energy threshold for neutrino detection. However,the limited light transmission in water and ice requiresa large number of light sensors to cover the required
detection volume. Towards higher energies, novel
detectors focus on other signatures of neutrinoinduced charged particle cascades, which can bedetected from a larger distance. Such methods include
recording the Cherenkov radio emission or acoustic
signals from neutrino-induced showers, as well as theuse of air shower detectors such as the Pierre Auger
Observatory, responding to deeply penetrating quasihorizontal showers with a “neutrino signature”. Augeris also sensitive to tau neutrinos that enter Earth below
the horizon and interact to produce energetic tau
leptons, which generate Earth-skimming showers. The
rates for quasi-horizontal and Earth-skimming events
have different dependence on the UHE neutrino
cross-section. Therefore, by measuring both rates, thecross-section can in principle be pinned down, withouteven knowing the cosmic neutrino flux precisely.
The very highest energies are covered by balloon-borne
detectors recording radio emission in terrestrial ice
masses (the ANITA project with some European
participation from the UK) by ground-based radio
antenna arrays, e.g. in Europe at LOFAR with the
NuMoon project observing the lunar regolith (inthe more distant future also SKA). Alternatively, thedetectors of Auger are being used to observe neutrinoinduced air showers, while R&D is ongoing to use
also at this site radio-detection techniques. IceCube
has used extremely energetic muons from above theGiven the recent indirect constraints from Fermion the cosmogenic neutrino flux at 109-1011 GeV,
it seems clear that detectors of many tens of cubic
kilometers will be necessary to record more than a
handful of neutrinos from GZK interactions. We
encourage R&D efforts towards this goal.

19
3. Dark Matter, Neutrino
Mass, Low-Energy NeutrinoAstronomy & Proton Decay
3.1 Introduction
Dark matter interactions, neutrino-less double beta
decay and proton decay – if they exist at all – areextremely rare processes. Interactions from neutrinos
from the Sun have been recorded, but also at a very
low rate. The study of such extremely rare phenomena
calls for an environment free of noise events that can
mimic true signals. Laboratories deep underground,well shielded against particles from cosmic rays, meetthis requirement. Europe has four such world-classlaboratories deep underground:- The Laboratori Nazionali del Gran Sasso (LNGS)
along the Gran Sasso Motorway tunnel, 120 km
East of Rome, 1,400 m underground (3,700 metreswater equivalent, m.w.e.). With three main halls eachcovering 2,000 m2, a total area of 17,800 m² including
bypass tunnels (total volume of 180,000 m³) it is thelargest of all underground laboratories.
- The Laboratoire Souterrain de Modane (LSM)
along the Fréjus Road tunnel between Italy andFrance. With a depth of 4800 m.w.e. it is the deepestof all existing European laboratories. Its main hall has
an area of 300 m2, while the total volume is 3,500 m³.
After 2011, a major extension in the context of aforthcoming road-tunnel modification could houseton-scale experiments.
- The Laboratorio subterráneo de Canfranc(LSC) along a tunnel connecting Spain and France,
at a depth of 2,450 m.w.e. with 1,700 m2 area and11,000 m³ volume. Also for LSC, extensions areplanned.
- The Boulby Underground Laboratory in a
potash and rock-salt mine on the coast of England at
2,800 m.w.e., with 1,500 m2 laboratory space and a
volume of 3,000 m³.
Other sites are 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 reactor neutrinos), or larger
available volume. They include the Pyhäsalmi mine in
Finland the Sieroszowice mine in Poland (SUNLAB)
and the Slanic mine in Romania (see also Section 3.5).

The committee acknowledges the efforts of the three
countries to provide underground laboratory space forastroparticle physics.
In the following, we will discuss searches for Dark
Matter (Section 3.2), the approaches for direct
measurement of the neutrino mass (Section 3.3.),
which is related to neutrino less double beta decay(Section 3.4). In Section 3.5, projects for low energy
neutrino astrophysics and for the search for proton
decay are discussed.
New underground facilities have been built in China(Jinping) and are planned in the US (DUSEL), India(INO) and South America (ANDES).

3.2 Dark Matter
The search for Cold Dark Matter (CDM) candidates
addresses one of the most fundamental problems
in particle physics and cosmology. There are many
hypothetical particles that could play the role of dark
matter, with different interactions and different nature.
Masses spanning from some billionths of eV to millionsof TeV have been considered and actually, the dark
matter halo could even have a multi-component nature.
However, the dark matter candidate that is favoured bymany theorists is a weakly interacting massive particle(WIMP), related to new physics at the TeV scale. Amongthe various WIMP candidates on the GeV-TeV scale,the most appealing one is the lightest super-symmetric(SUSY) particle framed in the Minimal SupersymmetricStandard Model (MSSM). The MSSM postulates that theeffective scale of SUSY breaking is around a TeV and that
there is an additional symmetry called R-parity, which
would keep the lightest SUSY particle stable. Anothertheoretically well-founded dark matter candidate is
the axion. Even though axions are much lighter than
WIMPs, they could still constitute CDM because they
are produced out of thermal equilibrium in the early
Universe and would be non-relativistic. Alternative
candidates include light bosonic particles with axion-like
couplings, nuclei of mirror matter, sterile neutrinos in
the 10 keV mass range, s-neutrinos and Kaluza-Klein
particles or super-symmetric Q-balls. Recently there
has been growing interest in asymmetric dark matter –particles with mass of around 5-10 GeV which have thesame particle-anti-particle excess as do relic baryons –because this provides a natural connection between theobserved abundances of baryonic and dark matter. Such
particles would not be able to undergo annihilations
today but may well have self-interactions that canpotentially solve the problem of excessive sub-structure
expected on small scales for collisionless particles.

20
SUSY particles with masses up to the TeV scale could
be produced in particle interactions at accelerators.
The negative results of current accelerator searches
indicate that even the lightest SUSY particle, likely
the neutralino, is heavier than 50 GeV in the simplest
realizations of the MSSM, even though lower masses
are not ruled out. The LHC will extend the search
for SUSY particles to much higher masses. However,the discovery of a SUSY particle at the LHC alone
does not prove that it is the CDM particle requiredby cosmology, in particular it may be unstable becauseof R-parity violation. For that purpose, the detectionof cosmological WIMPs is necessary. Conversely, thedetection of cosmological WIMPs alone would notprove that they are SUSY particles. For that purpose,
identification and investigation at accelerators isnecessary. The synergy between LHC and next
generation dark matter searches is obvious and opens
an exciting perspective. In the present situation, where
we do not yet have experimental proof of SUSY,
we should not abandon the search for alternative
candidates. Cosmological WIMPs can be detected indirect and indirect searches. In the following we will
discuss the dedicated direct-search experiments andrefer for indirect searches to section 2.

3.2.1 General featuresof a WIMP detector
The direct detection of WIMPs relies on measuring thenuclear recoil produced by WIMP elastic scattering off
target nuclei in underground detectors. A large range oftechniques and target materials are currently being used
to this purpose. The appropriate tool is a low-energy
nuclear detector with the following characteristics:
1. Very low energy threshold for nuclear recoils (given thenearly exponential shape of the energy spectrum, any
gain in threshold corresponds to a relevant increase
in sensitivity). Thresholds of the order of 1-10 keV(or even lower) have been demonstrated in various
approaches.

background for which the energy deposition is detected
via a primary fast electron.
4. Sensitivity to a Dark-Matter-specific observable.
This is necessary for an indisputable signature andmay manifest itself in seasonal modulation of therate, in diurnal modulation of the nuclear recoil
directions and in the correct scaling of the candidate
WIMP-induced recoil spectrum with the mass A of
the target. Typically, such signatures also apply to awider range of candidates.
The hypothetical WIMP-induced events are instrong competition with background events causedby particles which interact electromagnetically, suchas charged particles and gamma-rays originatingfrom residual radioactive contamination or cosmic
radiation. In order to extract a nuclear recoil spectrum
from this dominant electromagnetic background, itsmere reduction through passive methods is usuallyconsidered to be insufficient, so that most experiments
set up methods distinguishing nuclear recoils fromthe electron recoils induced by the electromagnetic
background. If this operation is successful, the only
background source arises from fast neutrons, which,like the WIMP signal, produce slow nuclear recoils.
The neutron background can be kept under control by
combining proper shielding with detector granularity
or spatial resolution. Because the mean free path offast neutrons is normally in the range of centimetresto tens of centimetres, there is a high probability thata fast neutron, unlike WIMPs, undergoes multiple
scattering in a large enough detector or detector array.
The event-by-event identification of nuclear recoils canbe achieved by means of the so-called double read-out
detectors and can be performed using three different
approaches. A fast particle depositing energy in amaterial produces, in general, three types of elementary
excitations in the target medium: electron-hole orelectron-ion pairs (ionisation), phonons (heat) andscintillation photons (light). Instruments with double
read-out are able to provide two distinct signals,
proportional to two distinct classes of excitations. In
these hybrid devices, the ratio between the two signal
amplitudes allows identifying nuclear recoils, since theratio for energy deposited via a primary electron differsfrom that deposited via a primary nucleus. This ratio
plays the role of a recoil-specific observable.

2. Very low intrinsic radioactive background at low
energies. In general, this requires significant expert
effort in terms of material selection and cleaning to
reduce the intrinsic background to below 0.1 events/ (day kg keV). Backgrounds of the order of 0.01 In case of a simultaneous measurement of ionisation andevents / (day kg keV) are expected in the best present heat, the detectors consist of arrays of large germaniumexperiments.
or silicon Ge or Si. detectors with simultaneous
read-out of charge and phonon signal. The detectors
3. Sensitivity to a recoil-specific observable. This allows must be operated at very low temperatures, typically inrejecting ambient and residual electromagnetic the range 10-100 mK, in order to work as bolometers

21
and to be sensitive to the phonons. The arrays usuallyconsist of tens of individual elements, providing ahigh sensitive mass and also the granularity necessary
to reject or assess the residual neutron background.
The raw background and the energy threshold mustbe sufficiently low. Experiments using this approach
are EDELWEISS in Europe and CDMS (and its
expansion SuperCDMS) in the US.

need to have a very low raw background rate and a large
total mass (or exhibit the prospect of scalability). Thiscan make them sensitive to the dark matter signatureof annual modulation (which does depend on specificassumptions on the dark matter model) and thereby
may compensate for the lack of a method for identifying
nuclear recoils. Scintillating crystals like sodium iodide
are a convenient solution for accumulating a large
detector mass. It is however more difficult to achieve
In case of a simultaneous measurement of light and a radio-purity comparable to germanium. NaI-based
heat, the detectors consist of an array of scintillating searches, such as DAMA-LIBRA, or the meanwhile
crystals with an additional phonon sensor. These terminated NAIAD, originally attempted to use
devices are often defined as a scintillating bolometer pulse-shape discrimination to statistically identify aand require the operation of a light detector at very WIMP component in their observed rate. However,
low temperatures, with very low threshold, typically it was found that due to the low number of detectedin the few-photon range. Currently, these light scintillation photons per keV of incident energy, thisdetectors have been implemented through auxiliary method is not feasible at low energies.
bolometers consisting of thin wafers of low specificheat materials and equipped with suitable phonon
sensors. Experiments based on this technology are the A first result exploiting the annual modulation signature
was provided by the DAMA/NaI set-up (about 100 kg
European CRESST and ROSEBUD.
of low-radioactive NaI(Tl) detectors) over seven annual
In case of a simultaneous measurement of light and cycles. The result was confirmed by the subsequentionisation, the detectors use liquid noble elements expansion of the DAMA experiment, named LIBRA,
as dark matter target. These materials are ideal for comprising 232.8 kg of NaI detectors. With muchbuilding large, homogeneous and position-sensitive higher statistics, corresponding to 0.87 ton×y (sixdevices. Liquefied noble gases are intrinsic good annual cycles), the modulation effect was confirmed
scintillators and have high ionisation yields. If a high at an 8.9 σ confidence level. The cumulative DAMA/
electric field (~ kV/cm) is applied, ionisation electrons LIBRA exposure is 1.17 ton×yr, corresponding to 13
can also be detected, either directly or through the annual cycles. The modulation frequency and phasesecondary process of proportional scintillation. are in excellent agreement with what is expected fromSeveral experiments use or plan to use noble elements the interaction of particles composing the Galactic
for WIMP search: XENON and ZEPLIN (both dark matter halo.
in Europe) and LUX in the US use xenon as target;
ArDM and WARP (both in Europe) as well as the
proposed DarkSide experiment (US/Europe proposal In spite of these remarkable correspondences, theto LNGS) use argon as target.
reconciliation of the reported modulation effect withthe published exclusion limits based on other direct
NaI(Tl) scintillating crystals with ultra-high and indirect searches would require some departureradio-purity and very low threshold are operated in from the standard SUSY scenario: the comparison of
the DAMA/NaI and DAMA/LIBRA experiments results from different dark matter experiments is not
and used to investigate the annual modulation as a independent from model assumptions
possible signature of Dark Matter detection. Notably,
this smoking gun signature applies to a large variety of The DAMA-LIBRA collaboration has put forward
dark matter particles and interaction types.
several possible explanations of this modulation interms of dark matter, spanning from WIMP-likecandidates – something resembling SUSY neutralinos–to more exotic models for dark matter particles which
3.2.2 Experiments without
could interact electromagnetically. An independent
cross check using NaI-crystals could be provided by
identification of nuclear recoils
ANAIS (Laboratorio Subterràneo de Canfranc, Spain).
The DAMA-LIBRA results could be scrutinized
When abandoning the implementation of a recoil- further with a similar technology by the Korean groupspecific observable, detectors with simpler structure KIMS, which deployed CsI crystal detectors with athan those based on double readout can be realized. In low detection threshold for direct WIMP search in theorder to be competitive, these single-readout devices Y2L Laboratory. Moreover, a summer/winter effect for22
a Southern hemisphere detector would yield a phaseshift by six months vs. a WIMP-related effect: Thus,
if the present technical test of two NaI-crystal units inan IceCube hole at the South Pole is successful, thiswould provide the option for an additional test of theorigin of the modulation phase.

hit pattern in the top PMT array providing the x-y
position (with a few mm resolution). In addition to
the recoil-specific observable consisting of the lightto-ionisation-signal ratio, the position sensitivity,
along with the self shielding of liquid xenon and an
active liquid xenon veto around the TPC, serves as animportant background-rejection feature.

Recommendation: The committee strongly supports
improving the DAMA/LIBRA experiment in terms ofa lower detection threshold and a lower background,in order to better understand the modulation signal.
A fully independent experiment based on the sameor on a similar technology would be crucial to
cross-check the DAMA/LIBRA effect.

The active target mass is 62 kg of ultra-pure liquid
xenon. The raw background is about two ordersof magnitude lower than the one of XENON10,
because of the selection of low activity materials andthe location of the cryo-cooler (a possible source ofradioactive background) outside the shields and theveto. The dark matter search has started at the end of
2009, and the results from 100 days of data are very
promising, with a limit of 7×10-45 cm2 for 50 GeV
WIMP mass. The sensitivity was limited by 85Kr which
induced three background events in the signal region.
After elimination of this background, the expected
sensitivity would extend down to cross sections of theorder of 2×10-45 cm2 for standard WIMPs inducing
nuclear recoils. In addition, the preliminary runs
exhibit a very low raw background, of the order of
0.02 counts/(ke×kg×day) below 100 keV with 40 kg ofliquid xenon in the fiducial volume. This performance
will enable XENON100 to “switch off” the recoil
identification mode and to look at the raw spectrum
in order to check if a seasonal modulation appears
when searching for particles with electromagnetic
interactions, as in the DAMA experiment.

Among the searches based on a single-readout
approach, non-European experiments based on pureionization Ge detectors with a very low threshold and an
impressively low raw background (CoGeNT in the US
and later TEXONO-CDEX in China) should also bementioned. In spite of their inability to identify nuclear
recoils, these searches reach excellent sensitivities at
low WIMP masses, both for the spin independent andspin dependent channels. Also CoGeNT has recently
reported the indication of an annual modulation,although until now with a confidence of only 2.8σ.
Other single read-out experiments, with noble liquid
targets, are the North-American CLEAN/DEAP (neonand argon, both using pulse shape discrimination, andthe Japanese XMASS (xenon).

3.2.3 Experiments with identificationof nuclear recoils
Experiments based on the simultaneous detectionof ionisation and light in double phase noble liquids
have obtained remarkable results in recent years. The
XENON collaboration, after the successful precursor
XENON10, is now operating the XENON100
experiment, based on the dual-phase time-projectionchamber technique, running in the LNGS. The
detector uses two arrays of UV-sensitive photomultipliers (PMTs) to detect the prompt and proportional
light signals induced by particles interacting in thesensitive xenon volume. The bottom array is locatedbelow the cathode, fully immersed in liquid xenon, andmainly detects the prompt light signal. The PMTs of
the top array are located in the cold xenon gas above theliquid, detecting the proportional light. XENON100
has full 3D position sensitivity: the time separation
between the two pulses of direct and proportional
light provides the event depth of an interaction; theThe encouraging results achieved by XENON100 has
motivated the collaboration to propose an expansionof the experiment named XENON1T, aiming at
operating 1 ton of liquid xenon (fiducial WIMP mass)
with a 100 times reduced background compared to
XENON100. XENON1T has recently been approved
to run in a large water shield in the LNGS.
Other searches exploit both the charge and lightmodes to reject nuclear recoils. Besides XENON, also
LUX (US) and ZEPLIN-III (Boulby mine, UK) use
xenon as the sensitive material. The recent resultsof ZEPLIN-III are competitive with the best-everobtained results with double-readout experiments.
WARP (under commissioning in LNGS) and ArDM
(ready to be installed in the Spanish LSC), are basedon a double-phase argon target. With respect toxenon, argon has an additional tool able to perform
nuclear- vs. electron-recoil discrimination, which is thepulse-shape analysis of the primary scintillation signal.
However, the lower target mass makes the sensitivity
to spin-independent interactions significantly lower.
Recently, DarkSide, a project using depleted argon,

23
has been started in LNGS. At present, a 50-kg detector both the ionisation and heat approaches. The detectors
is under construction. The plan is to commission it at simultaneously detect the phonon and the ionisation
the end of 2012.
signals, allowing discrimination against bulk electron
recoils of better than 99.9% above 15 keV recoil
The existence of two noble liquids with very promising energy. The charge signal is measured by aluminium
potential for WIMP detection (Xe and Ar) and with electrodes sputtered on each side of the target crystal,
nuclear masses significantly different from each other, while the phonon signal is recorded by a germanium
motivates the realization of a set-up with two targets, neutron-transmutation doped (NTD) heat sensor
an essential feature to provide a WIMP-specific glued onto the germanium crystal. The NTD sensors
observation. This is the purpose of DARWIN, a project read out the thermal phonon signal, and hence
aiming to complete the necessary research and design for spatial information is not available. To address this,the construction of a multi-ton scale liquid argon and/ and hence add capability of rejecting close-to-surface
or liquid xenon detector with a sensitivity three orders events, EDELWEISS implemented a new pattern ofof magnitude better than that of existing experiments. charge collection electrodes (InterDigit), allowing
DARWIN brings together several European and US rejection of surface events with high efficiency usinggroups working in the XENON, WARP, DarkSide the ionisation channel. Thanks to these additionaland ArDM collaborations and unites expertise on tools, measurements performed with ten 400 g
liquid noble-gas detectors, low-background techniques, detectors during one year have yielded a limit tocryogenic infrastructure and shielding.
spin-independent WIMP interactions of 4.4×10-44 cm2
at a mass around 80 GeV. This result has brought thisTwo noble-liquid target experiments, CLEAN (argon) experiment into the leading group with XENON andand DEAP (neon) are under preparation at SNOlab in CDMS. The EDELWEISS-II set-up uses a specially
Canada. Though both experiments are single-read-out developed 50 l low-radioactivity dilution refrigerator,
experiments, they will identify nuclear recoil events which will be fitted with forty 800 g detectors inand separate them from electromagnetic interactions the coming year. The collaboration seems to have inby pulse-shape discrimination.
its hands the technology and the means to achievesensitivity better than 10-44 cm2 in the next years.
Recommendation: The last 2-3 years have seen
dramatic progress of the liquid-xenon based
technology for the direct detection of WIMPs. The
100 kg scale has been realised with a low backgroundlevel and the 1-ton scale is currently being planned.
On this basis, the committee recommends thatDARWIN, a program to further extend the target
mass of noble liquids to several tons, is pursued andsupported. The choice in favour of a double-target
option should be taken after a clear experimental
confirmation that a liquid argon target is competitive
with liquid xenon in terms of rejection efficiency,
background and operation reliability.
Experiments based on bolometers were the first to
implement nuclear-recoil discrimination with double
readout. Cryogenic calorimeters satisfy the crucial characteristics required of a high-sensitivity WIMP detector:
low energy threshold, excellent energy resolution and theability to differentiate nuclear- from electron recoils onan event-by-event basis. The phonon signal is recorded
either after phonons reach equilibrium or “thermalise”,
or when they are still out of equilibrium or “a-thermal”,
the latter providing additional information about thelocation of an event.
The EDELWEISS experiment operates germanium
bolometers at 20 mK in the LSM. This search uses

In the US, the experiment CDMS uses a technology
similar to EDELWEISS: the main difference is in thephonon read-out, which is based on fast superconducting transition edge sensors, which can detecta-thermal phonons. This feature allows the rejectionof the dangerous surface events on the basis of time
structure of the phonon signal. The CDMS-II phaseat the Soudan Underground Laboratory has ended,
and recently the SuperCDMS phase using larger
germanium detectors with improved charge andphonon sensors has started. In the next phase,SuperCDMS will use an approach similar to thatdeveloped by EDELWEISS for additional surface-event
identification.
The two collaborations Edelweiss and CDMS havegathered their data into a combined analysis withimproved limits for the high-mass region. Collaborative
work is also ongoing towards the optimization of
EURECA/Phase-1 and Super-CDMS allowing thepossibility to house detectors from one experiment in
the infrastructure of the other.
CRESST is a European collaboration which develops
cryogenic detectors based on CaWO4 crystals, whichshow a higher light yield at low temperatures comparedto other scintillating materials. The detectors are also
equipped with a separate, cryogenic light detector,

24presently consisting of a sapphire wafer of 40 mm
diameter and 0.4 mm thickness, with an epitaxiallygrown silicon layer on one side for photon absorption.
The temperature rise in both the CaWO4 crystals andthe light detector is measured with tungsten superconducting phase-transition thermometers, kept at around~10 mK, within their transition between the superconducting and normal conducting states. A nuclear
recoil has a different scintillation light yield comparedwith an electron recoil of the same energy, allowing
discrimination between the two types of events. The
advantage of the CRESST approach is the low-energy
threshold in the phonon signal and the possibility todiscriminate between recoils of the different nuclei
present in the target. CRESST observes an excess inthe oxygen nuclear recoil region, which is incompatible
with the current understanding of the backgroundfrom gamma-rays, neutrons and alpha particles. The
next step is to scrutinize the reported excess counts inthe oxygen nuclear recoil band by further reducing thebackground and by increasing the exposure.

targets tailored to test the low-mass WIMP region)and to possibly house other rare event searches
based on bolometric technology.

Recommendation: The bolometric techniques haveremained competitive with the noble liquid approachin terms of sensitivity to WIMP interactions. The
results of the EDELWEISS collaboration showed aclear technological advancement with germanium
detectors regarding the rejection of surface beta
background, which was the main limitation in
the “ionisation + heat” option. The CRESST
experiment showed the power of identifying nuclear
recoils from light and heavy nuclei using CaWO4.
The committee recommends therefore supporting
the development of the multi-target approach
EURECA, an apparatus capable of housing 1
ton of bolometric sensitive mass and the ongoingcooperation with the CDMS follow-up projects.
This facility is complementary to the solution
provided by noble liquids, and is versatile enoughto provide a multi-target approach (including low Z

It is worth mentioning also an unconventional
technology, which might lead to an unexpected
breakthrough in the direct search for dark matter.
The idea is to build large WIMP detectors using
superheated liquids. An energy deposition can destroy
the meta-stable state, leading to the formation of
bubbles, which can be detected and recorded bothacoustically and optically. Since a minimal energy
deposition is required to induce a phase transition,these detectors are so-called threshold devices. The
operating temperatures and pressure can be adjusted
such that only nuclear recoils (large stopping powers
dE/dx) lead to the formation of bubbles. COUPP,PICASSO and the European project SIMPLE belong
to this class of experiments. The latter has recently
reported a stringent limit on spin-dependent WIMP
interactions.

The possibility to construct the EURECA set-up isconnected to the provision of a suitable, deep, fully
instrumented, underground space. In the European
scenario, the most natural location would be theplanned extension of the LSM, even though otherpossibilities are not excluded. This extension would
be useful also for other next-generation projects inastroparticle physics.

Recommendation: The recommended projects fordark matter such as EURECA and DARWIN and
SuperNEMO for ββ decay need new available
space, if possible at a deep site. There is a unique
opportunity to extend the present undergroundlaboratory of Modane (LSM) by taking advantageof the excavation of the safety tunnel of the Frejus
road tunnel, which started a year ago. This new
The expertise developed by EDELWEISS, CRESST laboratory of 60,000 m3 would be able to hostand ROSEBUD (another experiment at the LSC recommended projects. LSM has the greatest depth
belonging to the light + heat class) represents the basis of the present underground laboratories in Europe.
of the EURECA project (European Underground Rare The committee therefore strongly recommends
Event search with Calorimeter Array). The EURECA the timely support for this infrastructure. Such afacility will be located in the planned extension of the laboratory - is of the size of one Gran Sasso hall
LSM (France). EURECA, currently carrying out a with six times lower muon flux, in operation by
design study, develops a dedicated cryostat with water 2014 - would enhance the complementarity of theshielding, and is finalizing the design of its detector European Deep Underground laboratories.
modules in the existing EDELWEISS and CRESST
experiments. EURECA will use a target mass of
up to 1 ton, enough to explore WIMP-nucleon
spin-independent cross sections in the region of 3.2.4 Other approaches~ 10-46 – 10-45 cm2. A major advantage of EURECA is
the planned use of more than just one target material. to the direct detection of WIMPs

25
Recommendation: The committee endorses an
expansion of the experiment SIMPLE with a lower
background level in order to further increase its
sensitivity to spin-dependent interactions. Thissearch can be done in synergy with the possibilities
provided by xenon (about 50% nuclei have half
integer spin) and by the bolometric approach which
offers the chance to study different odd-A target
nuclei.
Finally, directional experiments deserve a special
mention. As pointed out above, a diurnal modulation
is expected, because all the nuclear recoils induced
by WIMP events should globally point towards the
Cygnus constellation due to the motion of the Earthin the Galaxy. A strong forward/backward asymmetryis then expected, taking into account the rotation of
the Earth. This is a distinctive signature, which cannot
be mimicked by any conceivable background source.
The challenge is to measure three-dimensional tracks
of low energy nuclear recoils with directional detectors
based on low-pressure gas chambers. Low pressure(of the order of few tens of mbar) are required for theslow nuclear recoil to have an appreciable range. This
makes it quite difficult to increase the sensitive mass.
However, an order of 10 events would be sufficient
to provide a significant signal. The projects belonging
to this class are DRIFT-II, DM-TPC, NEWAGE andMIMAC.
Recommendation: The committee recommends
supporting the R&D activities related to thedirectional detection of WIMPs, in particularaiming at a substantial background reduction, as
this may become essential to confirm the Galactic
dark matter origin of the signal in case of a positive
signal from the high-density target detectors.

3.2.5 Indirect detection of Dark Matter

detect the decay products of these annihilations: an
excess of neutrinos from the center of the Earth or
Sun or a gamma signal from the center of the Galaxy,from the center of galactic halos or from dwarf
spheroidal galaxies. Anti–particles such as positrons
and anti–protons, produced in WIMP annihilation
would be trapped in galactic magnetic fields and be
detected as an excess over the background generated
by astrophysical processes.
Obtaining convincing evidence for dark matterfrom excesses in the measured energy spectrum of
gamma-rays or anti-matter turned out to be extremely
difficult since the astrophysical backgrounds are notwell understood. With extreme assumptions aboutannihilation cross sections and branching ratios,
observations, like e.g. the rise in the energy spectrumof the positron ratio measured by PAMELA can bemade compatible with a dark matter origin, without,
however, providing a real proof of it. Fresh data, e.g.
from AMS and Fermi, may help to clarify the present
situation.
Convincing evidence could be obtained from theobservation of a gamma-ray line that would point
to dark matter annihilating directly to photons. The
Fermi LAT satellite has put stringent constraints on
this signature and will improve the sensitivity byalmost one order of magnitude over the next decade.
For dark matter masses above several hundred GeV,
Cherenkov telescopes, in particular CTA, will provide
significantly improved sensitivity. If dark matterparticles are not completely stable (although having acosmologically long lifetime) one could observe theirdecay via an X-ray or gamma-ray line. The decay signal
would be proportional to the dark matter column
density in a given object (and not to the squared dark
matter density, as in the case of the annihilating dark
matter). As a result, a large variety of astrophysicalobjects of different nature would produce comparable
decay signals. If a candidate line were found, its surface
brightness profile could be measured (as it does notdecay quickly away from the centers of the objects) anddistinguished from astrophysical lines (which usuallydecay in outskirts). This would allow distinguishing
the line due to decaying dark matter from any possible
astrophysical background.

Up to now, only direct detection methods have been
discussed. Complementary signatures could beobtained from indirect dark matter detection. Hereone searches for the annihilation products or decay
products of dark matter particles: X-rays and gamma Another very clean signature of WIMP annihilations
rays, anti-particles and neutrinos.
would be the observation of high energy neutrinos
from the Sun or the center of the Earth. IceCube so
WIMPs can be gravitationally trapped in celestial far has neither found any evidence for an excess ofbodies and eventually accumulate until their density neutrinos from the Sun, nor from the Earth or the
becomes large enough that the self-annihilation galactic halo, but over the next few years will improveof WIMPs would be in equilibrium with WIMP its sensitivity by a factor of 5 and extend the search tocapture. Celestial or satellite detectors would then masses below 50 GeV.

26
Direct and indirect methods are complementary. For
instance, gravitational trapping works best for slow
WIMPs, making indirect searches most sensitive. In
the case of direct detection, however, by kinematic
reasons fast WIMPs are easier to detect. For indirect
searches, the annihilation rates would depend on all
the cosmic history of WIMP accumulation and not
only on the present density, providing another aspectof complementarity to direct searches. Current andupcoming indirect searches in the next 5–10 years
will cover some parts of the Minimal SupersymmetricStandard Model (MSSM) parameter space which are
not accessible by LHC and direct experiments.

with microwave cavities in the mass region below 100
μeV which is preferred for the dark matter hypothesis.
Actually CAST sets a similar limit as that derived fromthe cooling rate of horizontal branch stars. The CAST
experiment, however, plans a new experiment with thegoal to reach as sensitivity of gaγγ ~ 0.5×10-11, and there
are even ideas towards extending sensitivity to gaγγ byanother order of magnitude. This would at least covera non-negligible part of the gaγγ-ma parameter spacepredicted by QCD axion models for axion masses
larger a few meV.

A CAST follow-up is discussed as part of CERN’s
physics landscape. It requires new magnets with
Last but not least it must be mentioned that indirect increased field and aperture, as well as improved
searches do not require dedicated experiments. They cryogenic and X-ray detection devices.
come “for free”, since X-ray and gamma-ray missions Even if not all approaches in this field are strictly
as well as neutrino telescopes, are mainly driven related to dark matter, there is a potential for revealingby astrophysical questions. In addition, cosmic-ray new physics. Therefore, we support the continuation
missions on satellites address a variety of other of the corresponding programs.
fundamental questions.

3.2.6 Axions
Experimental searches for axions or axion-likeparticles (ALPs) build on the coupling of the axion
to two photons. The search for axions of astrophysicalorigin assumes conversions of axions to photons andvice versa in strong electromagnetic fields. Provided
that dark matter is made dominantly from axions, anobservation would determine the value of the coupling
constant gaγγ and vice versa, assuming a certain coupling
constant, a value for the axion density can be derived.

3.3 Direct measurement of theneutrino mass

The determination of the absolute neutrino mass scale
follows a threefold concept. Three methods can infact address directly this crucial parameter: analysisof the cosmic microwave background temperaturefluctuations, search for and measurement of
neutrino-less double beta decay (0νββ) and study ofsingle beta decay. We note that the three approaches
probe different combinations of masses, mixings andphases. The observation of neutrino-less double beta
The American Axion Dark Matter Experiment decay would prove the Majorana nature of neutrinos,(ADMX) searches for axions saturating the dark which would be even more important than information
matter halo of the Galaxy (a “haloscope”). ADMX uses on masses.
a strong magnetic field permeating a cold microwave
cavity. Axions matching the resonant frequency of the The first method is observational, and seeks to measurecavity decay into microwave photons. ADMX has the effect of neutrino mass on the power spectrum of
excluded optimistic axion models in the mass range large-scale structure. Although it is in principle very
1.9-3.5 μeV under the assumption that axions indeed sensitive, it depends critically on untested cosmologicalmake up the dominant part of the dark matter halo.
assumptions (e.g. concerning the primordial power
spectrum of density fluctuations) and requires
Axions (without an imperative connection to dark therefore independent checks. Projected sensitivities
matter) can be produced in the Sun’s core when at the end of the decade reach down to 50 meV for the
X-rays turn to axions in the presence of strong electric sum of all neutrino masses, i.e. about six times better
fields. On Earth, these axions can be converted back than the expectations from the Planck satellite (thein a strong magnetic field. Arriving as axions they present flagship of CMB measurements) alone. If atunnel a wall in a large magnet and appear again as positive effect was detected, it would provide extremely
keV X-rays. This is the approach of the Axion Solar valuable information when combined with laboratory
Telescope (CAST) at CERN and of the Tokyo Axion experiments. For instance, a CMB detection of the
Helioscope, with CAST in a clear lead position. With neutrino mass, not confirmed by double beta decay
gaγγ < 10-10, the present CAST limit cannot compete experiments, would challenge the Majorana nature of

27
neutrinos. Conversely a positive detection by KATRIN(single beta decay spectrometer) of a mass above thecosmological bound, would challenge the standard
cosmological model.
The second and third methods are based on laboratory
searches. The 0νββ searches provide at the moment
sensitivities in the range 0.2-1 eV, but are notsensitive to neutrino masses if e.g. the neutrino is a
Dirac particle. A positive detection would prove theMajorana nature of the neutrino. Single beta decay
endpoint measurements, frequently referred to as direct
searches for neutrino mass, are not able to disentangle
the three values of the neutrino masses (although thisoperation would be possible in principle), because therequired energy resolution and statistics are out of thereach of present technologies. The sensitivity of any
future conceivable experiment hardly reaches the 0.1
eV scale. However, direct searches remain crucial, since
they are the only ones essentially free of theoreticalassumptions about neutrino properties and are reallymodel-independent. Moreover, a complete neutrino
physics program should comprise experiments
addressing all the three variants of the neutrino massscale, because they are not redundant but rather
complementary. They are all required to fully untangle
the nature of the neutrino mass.
Direct neutrino mass measurements are performedby analysing the kinematics of charged leptons and/or pions emitted together with flavour-state neutrinos
in suitable weak decays. The most sensitive neutrinomass measurements to date, involving electron typeneutrinos, are based on the analysis of the shape ofthe beta spectrum near the end-point of the decay.
The limits are ~2.2 eV for electrostatic spectrometers(obtained in Mainz/Germany and Troitsk/Russia withtritium experiments), and ~15 eV for low-temperature
micro-calorimeters (MIBETA and MANU experiments
in Italy). All these results have been obtained several
years ago.
Future experiments on single beta decay:
Two approaches are at the moment experimentally
relevant for the direct measurement of the neutrino
mass, and represent the evolution of the searches thathave obtained the current most stringent limits.
One is based on the study of the tritium (3H) beta
decay, extensively used in the last forty years withmagnetic and electrostatic spectrometers. Tritium
beta decay is an allowed transition with an end pointat 18.6 keV, one of the lowest in nature. Its lifetimeof only 12.3 years allows realizing sources with highspecific activities. Presently the leading technique forthe analysis of the beta electrons uses electrostatic
spectrometers with adiabatic magnetic collimation. In
these devices, the electrons are collimated by means ofa magnetic field with a proper space profile and selectedby an electrostatic potential barrier. Higher energy
resolutions and luminosities can be achieved withrespect to the previous-generation magnetic bending
spectrometers. The most sensitive planned experimentis KATRIN: it exploits this technology at the highest
level and is the only project in the construction phase(in the tritium laboratory in Karlsruhe) in the field of
the direct searches. It is mainly a European project,with German leadership and important Russian
and US contributions (total cost 50 M€). The mainfeatures of KATRIN are a stronger tritium source anda larger main spectrometer (10 m diameter), with ahigher energy resolution (~1 eV) than its predecessors
in Mainz and Troitsk. The simultaneous improvementof resolution and luminosity, together with a better
control of background, lead to a sensitivity of about
one order of magnitude better than the present limit.
The anticipated 90% C.L. exclusion limit is 0.2 eV
and the 5σ discovery sensitivity is 0.35 eV. The firsttritium runs are planned for 2012. In parallel, theTroitsk experiment is being upgraded to achieve asensitivity below 1 eV.
Recently, a new idea has emerged in the US for the
precise determination of the energy of the tritium
beta electrons, consisting of the measurement of
the radiofrequency they emit when propagating
on cylindrical helices in a static magnetic field. An
R&D activity is being conducted in the experiment
PROJECT-8.
The second approach uses low-temperature microcalorimeters with a very low transition-energy source
embedded in them. The MARE project is based on
this technology, already developed in the MIBETA
and MANU precursors. MARE plans to study thebeta decay of 187Re, whose transition energy is only
2.47 keV, the lowest known in nature. The beta decayrate in natural rhenium is of the order of 1 Bq/mg,
ideally suited to bolometric detection. Sensitivities
similar to those achievable by KATRIN are possible
if the bolometric performance meets the expectations.
In addition, the modular approach intrinsic tothe bolometric technology does not set intrinsic
limitations to the expansion of the experiment. In theintense R&D activities performed in the last years,
it was not possible however to achieve the plannedenergy resolution. Since this may be due to limitations
intrinsic to the Re-based materials, another promising
approach is under study by the MARE and the ECHO
collaborations, which foresees the embedding of a

28
light neutrino exchange, the decay rate is proportional
to an exactly calculable phase space factor, to the
nuclear matrix element (whose calculation represents
a severe challenge for nuclear theorists), and to theso-called Majorana mass. This parameter contains all
the neutrino physics, being a linear combination of thethree neutrino masses mi, weighted with the square of
the elements of the first row of the neutrino mixing
We note that the non-observation of masses above matrix. The presence of the phases of these elements (the0.2 eV would have also its good aspects, since only for so-called Majorana phases) makes cancellation of terms
low masses one could distinguish the sequence of the possible: the effective Majorana mass could be smaller
neutrino mass states.
than any of the neutrino masses. As already stated at the
beginning of Section 3.1, the results on the Majorana
mass need to be cross-checked with the information
Recommendation: The KATRIN beta spectrometer coming from cosmology and the direct searches for ais expected to provide unique results on the direct full comprehension of the neutrino properties.
measurement of the neutrino mass starting from2013, testing the degenerate mass region at the 0.2 It is important to note that other mechanisms caneV level. At the moment, no other technology seems induce 0νββ, such as the exchange of heavy neutrinos,
to be really in competition. Since with KATRIN the virtual SUSY particles or V+A currents. In these cases,
maximum feasible size seems to have been reached, constraints discussed in section 3.3. do not necessarily
no larger electrostatic spectrometer is currently apply. However, signs of the associated new physics
being planned, but improvements with respect to could be detected at the LHC.
resolution and other parameters are conceivable. On
the other hand the bolometric approach followed The uncertainties related to the calculation of thein MARE is modular and can in principle be nuclear matrix elements are critical for a complete
extended arbitrarily. Therefore, we recommend the interpretation of 0νββ results, and also for thecontinuation of R&D activities on the bolometric comparison of the physics reach of future searches
approach, regarding both 187Re (beta decay) and using different nuclei.
163Ho (electron capture) sources.
163
Ho source in optimised bolometers with very highenergy resolution. This nucleus decays by electron
capture and the mass of the emitted electron neutrino
can be measured by studying the end point of thespectrum of the total visible energy produced in the
decay. Sensitivities similar to those achievable in therhenium case can be achieved.

Recommendation: The committee notes progressin the calculation of the nuclear matrix elements
3.4 Neutrino-less Double Beta Decayfor 0νββ, with clear signs of convergence and witha validation of the traditional methods through a
Double Beta Decay (DBD) is rare nuclear transition, new approach. The committee confirms therefore
in which a meta-stable isobar changes into a more the importance of continuing this fruitful program,stable one, by the simultaneous emission of two which is based on both theoretical and experimental
electrons and two electron antineutrinos. Such process investigations.
can take place in principle for 35 naturally occurring
even nuclei, whose ordinary β decay is energeticallyforbidden or severely hindered by a large change of Thanks to the information we have from neutrino
the nuclear spin-parity state. DBD is a second-order oscillations, it is useful to express the Majorana massprocess of the weak interactions and has consequently a in terms of three unknown quantities: the mass scale,very low probability, which leads to extraordinary long represented by the mass of the lightest neutrino, and thelifetimes for the candidate nuclides. The two-neutrino two independent Majorana phases. It is then common
process (2νββ) already observed in several nuclides, is to distinguish three mass patterns: normal hierarchy
fully consistent with the standard model (SM). The (NH), where m1 < m2 < m3, inverted hierarchy (IH)
neutrino-less channel (0νββ), which involves only the where m3 < m1 < m2, and the quasi-degenerate mass
two electrons in the final state, violates lepton number spectrum (QD), where the differences between theconservation and would definitely imply new physics masses are small with respect to their absolute values.
beyond the Standard Model of particle physics.
The 0νββ process has the potential to provide essential
information on nature’s choice on mass ordering ofOf primary interest is the process mediated by the neutrinos. In fact, if one can experimentally establish
exchange of light Majorana neutrinos interacting that the Majorana mass is larger than 50 meV, one canthrough the left-handed V-A weak currents. In case of conclude that the QD pattern is the correct one. On

29
the other hand if this parameter lies in the range 20-50
meV, the pattern is likely to be IH. Eventually, if one
could determine that the Majorana mass is smaller
than 10 meV but non-vanishing (which is unlikely
in a foreseeable future), one could conclude that the
NH pattern holds. Therefore 0νββ is important at
two fronts: the comprehension of fundamental aspectsof elementary particle physics and the contribution
to the solution of hot astroparticle and cosmologicalproblems, related to both the neutrino mass scale andits fundamental nature.

3.4.1 General featuresof a 0νββ decay search
From the experimental point of view, the shape ofthe two electron summed energy spectrum enables us
to distinguish among the two relevant decay modes.
In case of 2νββ, this spectrum is expected to be acontinuum between zero and the transition energy Q
with a maximum around Q/3. For 0νββ, the spectrum
is just a peak at the energy Q, enlarged only by the finite
energy resolution of the detector. Additional signatures
for the various processes are the single electron energy
distribution and the angular correlation between thetwo emitted electrons. Q ranges from 2-3 MeV forthe most promising candidates. The importance of
having such a high Q-value, in terms both of the phasespace for the process and of reduced contribution ofradioactive backgrounds at higher energies, limits
drastically the number of candidate nuclei that areexperimentally relevant. As a reminder: 130Te (Q=2527
keV), 116Cd (Q=2802 keV), 76Ge (Q=2039 keV), 136Xe(Q=2479 keV), 82Se (Q=2995 keV), 100Mo (Q=3034
keV), 150Nd (Q=3367 keV) and 48Ca (Q=4270 keV).
The experimental strategy to investigate 0νββ consistsof the development of a proper nuclear detector, withthe aim of revealing the two emitted electrons in realtime and the measurement of their summed energy
spectrum as minimal information. Additional pieces
of information can be provided in some cases, likethe single electron energies and initial momenta. The
desirable features of this nuclear detector are:

3 Large source, in order to monitor many candidate
nuclides. Present sources are of the order of 10 kgof isotope in the most sensitive detectors, while thenext generation experiments aim at sources in the
100-1,000 kg scale.
4 Event reconstruction method, useful to rejectbackground and to provide additional kinematicalinformation on the emitted electrons.
Normally, the listed features cannot be met
simultaneously in a single set-up. The practicalexperimental approaches privilege some properties
with respect to others.
The searches for 0νββ can be further classified into two
main categories: the so-called calorimetric technique,in which the source is embedded in the detector itself,
and the external-source approach, in which source anddetector are two separate systems.
The calorimetric technique has been proposed andimplemented with various types of detectors, such as
scintillators, bolometers, solid-state devices and gaseouschambers. It can provide high efficiency, large sources
and with a proper choice of the detector, a very highenergy resolution (of the order of 0.1%). A drawback
is that it is difficult to reconstruct event topology (withthe exception of liquid or gaseous xenon TPCs, andwith novel germanium detectors). Recent proposals todissolve the investigated isotopes in a huge amount ofliquid scintillator belong to this class as well.
In the external-source approach, many different
detection techniques have been combined also :scintillation, gaseous TPCs, gaseous drift chambers,
magnetic field for momentum and charge sign
measurement, time-of-flight. In this case, large
source masses are not easy to achieve, because of selfabsorption in the source so that the present limit isaround 10 kg, and normally the energy resolution islow (of the order of 10%), intrinsically limited by thefluctuations of the energy the electrons deposit in thesource itself. However, a neat event reconstruction
is possible, enabling an excellent background
identification capability.

The present experimental situation is dominated by
1 High energy resolution, since a 0νββ peak must be three experiments: Heidelberg-Moscow, Cuoricino
identified over an almost flat background.
and NEMO3. All have set limits on the Majorana
mass of the order of 0.2 – 1 eV. However, the search
2 Low background, which requires underground for the 0νββ transition has been spurred on by adetector operation, very radio-pure materials (the claim made by a part of the Heidelberg-Moscow
competing decays from natural radioactivity have collaboration. The 76Ge half-life best value quoted bytypical life-times at least 15 orders of magnitude them is 1.5×1025 y (or (0.8 - 18.3)×1025 y at 95% c.l.),shorter than those predicted for 0νββ).
which can be interpreted in terms of a Majorana mass

30
of 0.39 eV (or 0.05 - 0.84 eV at 95% c.l. including
nuclear matrix element uncertainties). NEMO3 (with
100Mo) and especially Cuoricino (with 130Te) havepartially scrutinized the range of the claim, but were
not able to exclude it because of the nuclear matrix
element uncertainties.
New generation experiments are just starting or
will begin data taking in the next few years. All ofthem should be in a position to scrutinize fully the
Heidelberg-Moscow claim, and many aim to attack
the IH region of the neutrino mass pattern.

3.4.2. Calorimetric 0νββ searcheswith US leadership, uses the same basic technology andwill consist of an array of enriched germanium diodes
operated in conventional copper cryostats. Merging
with GERDA is foreseen in anticipation of a 1-ton
set-up.
LUCIFER is a European project consisting of anarray of ZnSe scintillating bolometers operated at 20
mK. The proof of principle with ~10 kg enriched Se
is foreseen in 2014 in the LNGS. The proven energy
resolution is better than 1% FWHM. LUCIFER
is in the R&D phase and can be considered as ademonstrator for a possible upgrade of CUORE,
however with a considerable sensitivity by itself (~100meV to Majorana mass).

A second class of future experiments is based ona conversion of existing large liquid undergrounddetectors, dedicated so far to direct detection ofFour planned projects are characterized by a neutrinos. The approach is still calorimetric, but withcalorimetric approach with high energy resolution.
low energy resolution and no tracking capability. We
report here on two non-European projects in which
CUORE, a natural expansion of Cuoricino, will be an very large statistics and a full understanding of thearray of natural TeO2 bolometers arranged in 19 towers background sources can compensate for the low energy
and operated at 10 mK in the Laboratori Nazionali resolution. Similar plans (xenon loading of liquid
del Gran Sasso. The source will correspond to 200 kg scintillator) have been considered for BOREXINO
of the isotope 130Te, the only one which has a natural for a long time and still represent a future option.
abundance enough high (34%) to enable competitive
experiments without an expensive enrichment process. SNO+ is an upgrade of the homonymous solar
It will take advantage of the Cuoricino experience. neutrino experiment (Canada, with some European
The proven energy resolution is 0.25% FWHM. The contribution), aiming at filling the SNO detector
sensitivity to the Majorana mass is 50 meV, and is with neodyme-loaded liquid scintillator to investigate
limited mainly by surface alpha background. CUORE the isotope 150Nd. Crucial points are Nd enrichment
is in the construction phase and data taking is foreseen and purity. Another issue concerns the 150Nd nuclear
to start in 2014. A test module of the CUORE detector, matrix elements, whose calculation is made difficult bycomprising a single tower and named CUORE-0, started nucleus deformation, which could lead to an importantdata taking in 2011.
suppression. The present plan is to use 0.1% w/w
natural Nd-loaded liquid scintillator in 1,000 tonnes,
GERDA is an array of enriched Ge diodes operated in providing a source of 56 kg of 150Nd, which should
liquid argon and shielded by an active water Cherenkov lead to a sensitivity of 100–200 meV to the Majorana
veto. The experiment, installed in the LNGS, investigates mass. Data taking is foreseen in early 2012.
the isotope 76Ge, with the possibility to scrutinize the
Heidelberg-Moscow result in just one year. The energy KamLAND-Zen is an upgrade of the KamLAND
resolution measured during the Phase-I commissioning set-up in Japan (no European contribution). The idea isruns is 0.18% FWHM. and 0.14% for Phase-II to convert it to neutrino-less Double Beta Decay search
prototype detectors. The first phase (currently under by dissolving 400 kg of enriched xenon gas in the liquid
preparation) consists of 18 kg of enriched (86%) Ge scintillator, contained in a mini-balloon immersed in
detectors. The performance of the detectors in liquid the main vessel. The data taking should have started inargon is excellent, but a known background source (the 2011, with a final sensitivity of about 50 meV.
cosmogenic isotope 42Ar) turned out to be higher than
expected. Mitigation techniques have been developed
to make sure that 42Ar does not limit the sensitivity ofthe experiment. The second phase foresees 40 kg ofisotope. The predicted sensitivity to the Majorana massis 190-390 meV in the first phase, and 75 – 150 meV
in the second phase. The MAJORANA experiment,

without tracking capability

31
3.4.3. Double Beta Decay
with Tracking /Topology Capability
This category comprises calorimetric or external-source
experiments based on detectors which compensate thelow energy resolution with tracking or some form of
event-topology capability.
SuperNEMO, which is foreseen to be installed in
the planned extension of the LSM, implements theexternal-source approach at the most sophisticated level.
It will provide excellent track reconstruction, ensuring
the unique capability to measure single electronenergy distribution and angular correlation, preciousfeatures for a possible identification of the 0νββmechanism. It will be composed by several modules
containing source foils, tracking (drift chamber inGeiger mode) and calorimetric (low-Z scintillator)
sections. A magnetic field is present for charge signidentification. SuperNEMO will take advantage of
the NEMO3 experience, and will investigate 82Se
and possibly 150Nd and 48Ca in a second phase. The
proposed configuration foresees 20 modules with 5 kg
source for each module, providing 100 kg of isotopes.
The projected energy resolution is 4% FWHM. The
project is in an advanced R&D phase: the first module,
operating as a demonstrator, is scheduled for 2013.

EXO is mainly an US experiment (with Swiss
participation), consisting of a TPC of enriched liquidor high pressure gaseous xenon, for the investigationof the isotope 136Xe. The set-up will provide event
position and topology. In prospect, the tagging of Ba
single ion (ββ decay daughter) is foreseen with optical
spectroscopy methods. The first step (EXO-200), undercommissioning, consists of 200 kg of enriched liquid
xenon and will not use the Ba tagging approach. It is
located in the WIPP facility, in the USA. EXO-200
sensitivity to the Majorana mass is anticipated to
be 133 – 186 meV. The proven energy resolution is3.3% FWHM (improved thanks to simultaneous
measurement of ionization and light). Further steps
foresee source masses in the 1 – 10 ton range.

Recommendation: The European detectors GERDA
and CUORE will explore in the next years thedegenerate region of the neutrino mass pattern.
CUORE will probe also part of the mass range
predicted by neutrino oscillation experiments for thecase of the inverted mass hierarchy. In case of discovery
at the degenerate mass level, there is a clear path for“precision measurements”, with possible evidence
from three different nuclei and the opportunity
provided by SuperNEMO to investigate the leading
DBD mechanism. The committee recommends a
prompt realization of the SuperNEMO demonstrator.
NEXT is a 100 kg high-pressure gaseous-xenon TPC, to Whereas GERDA, CUORE and SuperNEMO rely on
be located in the LSC, Spain. The extension to 1 ton is the long-term experience with precursors and extensively
technically possible. Clear two-track signature is achievable, validated techniques, NEXT is a comparatively new
thanks to the use of gaseous rather than liquid xenon. approach, with a steep time gradient, combining
The energy resolution extrapolated from measurements construction of a full detector with basic R&D.
with a prototype is better than 1% FWHM, achieved The committee encourages the collaboration to
thanks to the electroluminescence signal associated to the demonstrate all aspects of the technology and moveionisation electrons produced in the double-beta decays. ahead toward NEXT-100.
The experiment is in the R&D phase. Three prototypes,
all dubbed NEXT-1, have been completed in Spain and at
LBNL (USA). A conceptual design report for NEXT-100 The community is working to improve the sensitivity
has been recently released and the ambitious plan is of these experiments, with the aim to fully cover thepredicted to start running in 2014.
inverted hierarchy region, a crucial element for thedetermination of the neutrino mass hierarchy in synergy
COBRA is a proposed array of 116Cd-enriched CdZnTe with the next stages of the neutrino oscillation program.
semiconductor detectors operated at room temperature. The general requirement for this task is 1 ton of isotope
Nine ββ isotopes are under test, but 116Cd is the only and a background at the level or below 1 count/(yrcompeting candidate. The final aim of the project is to ton-isotope) in the region of interest. This challenging
deploy 117 kg of 116Cd with high granularity. Small scale objective can be accomplished either by the technologies
prototypes have been realized in LNGS. The proved of the experiments running or in construction (this optionenergy resolution is 1.9% FWHM. The project is in would provide the advantage of a phased approach) or by
R&D phase. Recent results on pixellization show that new promising technologies which are currently under
the COBRA approach may allow an excellent tracking study (LUCIFER, COBRA pixel detectors, pulse shapecapability (solid state TPC).
discrimination in bolometer experiments, argon instrumentation in GERDA, Cherenkov light in TeO2).
The three mentioned experiments are located inEurope.

32
Recommendation: The committee recommends thatthese options are pursued at the R&D level in viewof a final assessment of the most effective approaches
for the 1 ton scale. As the required financial
resources are substantial for ton scale experiments,
the committee endorses their realisation in theframework of worldwide collaborations. This
would allow the investigation of more than one
double beta isotope, which is essential to provide
an unambiguous signature of neutrino-less double
beta decay and to determine the effective Majorana
mass.
For future DBD experiments on the ton scale,enrichment at high production rate is a central
issue. While this operation is possible for isotopes
which are gaseous, or form gaseous compounds atroom temperature (like 76Ge, 82Se, 100Mo, 116Cd,
130
Te, 136Xe), radon background free isotopes (like150
Nd, 96Zr and 48Ca) require innovative techniques.
Enrichment technology is presently dominated by
Russian companies.
Recommendation: We
encourage Westerncompanies and laboratories to continue R&D
on the enrichment of new isotopes (like 150Nd)by centrifugation technology or by laser isotopic
separation.

3.5 A large detector for proton decay,
low energy neutrino astrophysics & next
generation long baseline neutrino
experiments
The successful detection of neutrinos from the supernova
SN1987A by the Kamiokande detector (Japan), IMB
detector (US), and Baksan detector (Russia) and thedetection of solar neutrinos by the Homestake detector(US) and Kamiokande detector (Japan) opened the fieldof neutrino astronomy. Both of these accomplishments
were recognized with a Nobel Prize in 2002. Actually,
these opened a 30-year long tradition of incredibly rich
physics with large underground detectors, including
solar physics, the discovery of neutrino oscillations
by studying Solar (GALLEX/GNO, SAGE, SuperKamiokande, SNO, BOREXINO) and atmospheric
neutrinos (SuperKamiokande, MACRO, Soudan,
Baksan), and the confirmation of these results using

reactor neutrinos (KamLAnd CHOOZ, Palo Verde) andaccelerator neutrinos (K2K, MINOS, OPERA). Moreambitious physics topics, like Grand Unification, havealso been explored. The limits for the lifetime of protons
have been pushed to nearly 1034 years. Last but not least,in 2005 KamLAND announced the first indicationof geo-neutrinos, and BOREXINO confirmed thisresult with a better (>5σ) significance. At present andin the near future, the mass-flavour mixing matrix forneutrinos is studied with more intense neutrino beams
from the Japanese KEK/J-PARC accelerator complex
to Super-Kamiokande (T2K experiment) and fromFNAL to Ash-River (NOvA) to measure the last,
unknown mixing parameter defined as θ13, opening
the path towards measurement of CP-violation in the
leptonic sector. The CERN-LNGS program with aneutrino beam to OPERA and ICARUS in LNGS iscontinued. In addition, the Double-CHOOZ reactor
neutrino experiment in France has started data-taking,whereas Daya Bay in China and Reno in the South
Korea are being constructed. They will measure electron
disappearance to search for the unknown mixing
parameter defined as θ13 as well. Double-CHOOZ isa principally European experiment with significant
overseas participation. T2K sees a very large European
contribution with more than half collaborators comingfrom European institutions from France, Germany, Italy,
Poland Spain, Switzerland and United Kingdom. There
are also European collaborators in Super-Kamiokande
and MINOS (neutrino beam from Fermilab to the
Soudan mine).
New since 2008: Several important physics andtechnological results have been obtained since the2008 roadmap. BOREXINO has measured Solar 7Be
neutrinos with improved accuracy (and also the 8Bcomponent), provided essential data in the transition
region between vacuum and matter oscillations andconfirmed the absence of a day-night effect. BOREXINO
has also measured convincingly geo-neutrinos, with amuch smaller background from reactor neutrinos than
KamLAND. BOREXINO performs as expected withrespect to all parameters, in particular with respect to thecritical question of purity and background rejection. In
2010, the 600-ton liquid argon TPC ICARUS in Gran
Sasso became operational. It demonstrated that the liquidargon technology yields impressive imaging performanceand can also be reliably operated in an undergroundenvironment. Also of note in 2010, the OPERA
experiment detected its first candidate for a tau neutrino
event, adding strong evidence of neutrino oscillationfrom muon to tau neutrinos. Previously, the only direct
evidence was a statistical analysis of atmospheric neutrino
events in Super-Kamiokande. Furthermore, a set ofanomalies in the neutrino sector (LSDN, SAGE and
GALLEX registration of neutrinos from Cr sources, Bugey

33
and Mini-Boone) has been extended by results from theanti-neutrino measurement with Mini-Boone and the
SAGE-argon measurement. Although none of these hints
for physics beyond the Standard Model are particularly
convincing, theorists have tried to accommodate themin models which invoke sterile neutrinos interacting
only via gravity. The models also make use of recent
cosmological observations. To test such ideas we needa new experimental campaign which will falsify theanomalies, or in fact discover new physics. Last but notleast, the T2K experiment reported a tempting indication
for a non-vanishing mixing angle θ13.

3.5.1 Present andnear term measurements
Solar neutrinos: Once GALLEX/GNO (Gran Sasso
Laboratory), KamLAND (Japan) and SNO (Sudbury
Laboratory, Canada) have terminated their extremely
successful operation or moved on to other physics
topics, there will remain worldwide three devices withan active solar neutrino programme:

Supernova neutrinos: If today the signal from asupernova would arrive, the prospects for neutrino
detection would be incomparably better than in 1987.
At that time, three detectors (Kamiokande, IMBand
Baksan) recorded a total of 22 events. Scaled to asupernova at the center of the Galaxy, this corresponds
to ~700 events. Today, a SN1987A-type supernova
at 10 kpc distance would result in nearly 10,000
neutrinos detected worldwide:- Super-Kamiokande (8500) and KamLAND (350)in Japan,- LVD (400), BOREXINO (100) and ICARUS (50)in the LNGS in Italy,- MiniBOONE (200) in the US,- the Baksan detector (70) in Russia.

Numbers in brackets give the approximate number of
events (dependent on emission model).The possibility
to detect supernova neutrinos of all flavors via theelastic reaction ν+p→ ν+p gives scintillation detectors
like BOREXINO and KamLAND a crucial role inmeasuring the temperature of a supernova. A few
1) Super-Kamiokande (22 kt fiducial volume water millions of interactions would be detected in IceCube,
however, not as reconstructed events, but only as an
Cherenkov, Japan, 8B-neutrinos)
increased dark count rate. A counting rate alone does
2) BOREXINO (270 t scintillator, Gran Sasso not give information on energy and direction, but theLaboratory, Italy, 7Be neutrinos)
time profile of the supernova pulse would be measured
with great accuracy and contribute to the understanding3) SAGE (GaGe radiochemical detector, Russian of the early phase of the supernova explosion.
Baksan Laboratory, pp neutrinos)
The observation of spectral changes due to neutrinoThe scientific programme includes measurement of neutrino interactions and matter effects could be an
the predicted matter effects from neutrino oscillations independent way to determine the ordering of the(the solar neutrinos pass through significant matter in neutrino masses. It is also possible that an early cut-off
their path from the core of the Sun and through the of the neutrino emission could provide the first direct
Earth at night), precision measurement of solar fusion evidence of the formation of a black hole.
processes, and long-term monitoring of the solar fusion
process. In 2011, first indications for pep neutrinos Geo-neutrinos: BOREXINO has successfully detectedhave been reported. The main goals of the present 8B neutrinos, 7Be neutrinos, and geo-neutrinos and will
solar neutrino experiments which can be within reach continue to improve these important measurements.
in a few years are: measurement of the up-turn of the The future goals of geo-neutrino measurements are:survival probability; improved measurement of the determination of the total Uranium content within
pep flux and first measurement of the CNO flux and the Earth through a spectroscopic observation;
possibly of the pp flux by BOREXINO; resolving the determination of the radiogenic heat from the mantle;
direct determination at 5% accuracy of the Thorium andmetallicity controversy.
Uranium ratio. The last aim can be achieved only by afuture super-massive detector such as LENA.
Recommendation: The committee strongly endorses Atmospheric neutrinos: IceCube has collected byfurther support for the BOREXINO program, far the largest statistics of atmospheric neutrinos and iswhich is now unique in the world. BOREXINO continuing data taking. With its inner array DeepCore,
could be able to detect CNO neutrinos at 30% level energies low enough to study neutrino oscillations will
be reached.
in a timescale of two years.

34
Accelerator neutrinos: Both the OPERA experimentin Europe and the MINOS experiment in the US willcontinue their programme of tau neutrino and precisionoscillation measurements for the next few years. In
addition, new experiments have started: T2K experimentis now operating and a first result of neutrino oscillation
via θ13 is expected within the year. T2K aims at leading
the worldwide θ13 exploration and is expected to reacha sensitivity sin2(2θ13)<0.014 by summer 2014. In 2013
the NOvA experiment will start data taking with thepossibility to test matter effects in long baseline neutrino
oscillations for favourable values of θ13 as well.

liquid scintillators, with the goal to perform very shortbaseline oscillation experiments. The BOREXINO
collaboration is considering such an option.

3.5.2 Next-generation detectors
Large underground detectors have produced an
extremely rich harvest of discoveries. This legacy
is intended to be continued by one or several
multi-purpose detectors on the mass scale of 50-500
ktons. The physics potential of a large multi-purpose
facility would cover a large variety of questions:

A discovery of θ13 in the coming years would provide
a tremendous boost for next generation long baseline a) The observation of proton decay would be one of theaccelerator experiments looking for CP violation in most fundamental discoveries for physics and cosmology.
the leptonic sector.
The verification of GUT models calls for a proton decay
sensitivity to be improved by up to one order of magnitude
OPERA achieved the first direct detection of a tau neutrino and that alternative decay modes be explored.
candidate produced from oscillation of a muon neutrino
beam. Due to the fact that other existing neutrino beams in b) A galactic supernova would result in several ten
the world operate below the threshold for tau production, thousands of fully reconstructed neutrino events which
the CERN/LNGS beam is the only facility capable of would provide incredibly detailed information on themaking this measurement. ICARUS, which claims a tau early phase of the supernova explosion.
appearance sensitivity similar to that of OPERA, should
also confirm this measurement. In this context we also c) Neutrinos from nuclear reactors and/or particle
mention the proposal to restore the CERN PS neutrino accelerators could be detected over a long baseline
beam and measure oscillations with ICARUS placed at a between neutrino source and detector. By theseθ13 could bevery short distance. This is focused on physics beyond the measurements the sensitivity to
substantially improved. 1
Standard Model e.g. sterile neutrinos.
It is recommended that OPERA and ICARUS are d) The diffuse flux from past supernovae would probe
continued as planned in order to obtain a more the cosmological star formation rate and the averagefeatures of neutrino emission.
significant evidence for tau appearance.
Reactor neutrinos: The Double-CHOOZ Far
Detector has recently started operation and will measureelectron neutrino disappearance to provide data on θ13
vastly improved from the original CHOOZ experiment.
To achieve full sensitivity and to be competitive withother experiments worldwide, it is critical that the
Near Detector be completed as soon as possible.

e) The details of the processes in the solar interior can bestudied with high statistics and the details of the Standard
Solar Model determined with per cent accuracy. 2

Knowledge of θ13 is important to define the path todiscovery of the CP violation in the leptonic sector,
Earth matter effects and perhaps even supernova
neutrino emission. It will provide import input onlong baseline options for Megaton-scale detectors.
Radioactive sources: This approach is motivatedby deficits which were measured in GALLEX andSAGE for neutrinos from strong radioactive sources
and by the recently discussed reactor anomaly, as well
as by speculations on a fourth, sterile neutrino family
deduced from cosmological and accelerator data. It
foresees to place extremely strong radioactive sources ing) The high-statistics study of atmospheric neutrinos
will further improve our knowledge on the neutrinomass matrix and might provide information on theneutrino mass hierarchy.

f ) Geo-neutrinos could be measured with a much-increased
statistical accuracy compared to today, which should
help discriminate among various geophysical models.

h) The study of neutrinos of medium energy fromthe Sun and the centre of the Earth could reveal signs
for low-mass dark matter which is not detectable bydeep-water/ice detectors.
Several conceptual ideas for next-generation very
massive, multi-purpose underground detectors have

35
emerged worldwide and in Europe over the last few years.
All the designs consist of large liquid volumes observed
by detectors which are arranged on the inner surfaces ofthe vessels. The liquid simultaneously acts as the target
and as the detecting medium. First, MEMPHYS relieson the concept of Super-Kamiokande and uses water.
Second, LENA extrapolates experience gained inreactor experiments and BOREXINO and uses liquid
scintillator. The third detector is GLACIER, buildingon the pioneering efforts of ICARUS and useing
Liquid Argon. The physics return of a next-generation
underground facility could be maximized if one could
incorporate sub-detectors of different technologies. A
proposal on site(s) and technologies necessarily has tobe tackled globally, in particular taking into accountthe plans in the US and Japan. In this context one
may also think of a “global observatory” which relies
on infrastructures at several sites.
From a practical point of view, the most straightforwardliquid is water. Water is a cheap medium, therefore thedominant costs are in excavation and photomultipliers.
The possibility of building a water Cherenkov detector
with a fiducial mass of 200-500 kton volume is currently
being also studied for the DUSEL Laboratory in the
US (LBNE project) and for the Kamioka site in Japan(Hyper-Kamiokande). Both projects are also conceived
as Long Baseline Experiments (Hyper-Kamiokandewith a beam from the T2K experiment with a planned
power upgraded neutrino beam from KEK/J-PARC to
the Kamioka site, LBNE using a new neutrino beamfrom Fermilab). Water-Cherenkov detectors have a highsensitivity to proton decays with three Cherenkov rings,
like for example the channel p → e+ πo.

chamber. Thanks to their imaging capability, liquid
Argon detectors can provide improved sensitivities to theproton decay channels where backgrounds are serious in
the Water Cherenkov detectors, like for example for p→anti-ν + K+. It also provides the best performance andbackground rejection for reconstructing neutrino events
above 1 GeV, as encountered in long baseline neutrino
oscillations. GLACIER is a novel design for a newgeneration double phase liquid Argon TPC presently
being developed by a European-Japanese effort, aiming
at a detector concept scalable up to at least 100 kton.
Different detector locations are being considered at thisstage: along the planned power upgraded KEK/J-PARC
neutrino beam at Okinoshima (Japan) and in Europe
along a new neutrino beam from CERN. A 17 kton
single phase detector, like ICARUS, is being consideredby the LBNE project in the US.
The three mentioned detector types represent a varietyof complementary aspects (see also the table below):• MEMPHYS would have the largest mass and collect
the largest statistics.
• GLACIER would have the best pattern recognitionand perform best for multi-GeV neutrino events fromneutrino beams.
• LENA would have the lowest energy threshold andprovide the best measurement of MeV neutrinos• MEMPHYS and LENA are superior in anti-neutrino
detection while GLACIER is best in neutrino detection.
Neutrinos and anti-neutrinos together provide the full
information to study supernovae.
• MEMPHYS has complementary sensitivity to LENA
and GLACIER on proton decay flavour signatures• LENA physics requires deep detectors, MEMPHYS
can be shallower but needs large volumes.

With respect to its proven feasibility (BOREXINO,KamLAND), a high purity liquid scintillator detector
comes next. The scintillator technology for LENA
is based on the pioneering developments within the
BOREXINO experiment. The light yield of a scintillator
is much larger than that of Cherenkov light produced inwater and has therefore a lower threshold. The Cherenkov
rings used in water to identify events cannot be imaged, __________________________
however it has been shown to be effectively replaceable
by precise timing, for example in the context of the 1 Results from OPERA. T2K and reactor experiments (Double-Chooz, Daya Bay andsearch for proton decays in the p → K+ν channel. This Reno) will contribute in guiding the next steps worldwide in long baseline neutrino
technique could also detect remnant diffuse supernovae physics. Positive results from these experiments will signify the direct experimental
neutrinos, geo-neutrinos emitted from the Earth and proof of the fully 3x3 nature of the PMNS matrix and the correctness of its formalism
reactor neutrinos. At present the maximum volume of to describe lepton flavor violation in nature. In this case, the coherent next step willsuch a detector seems to be limited by financial reasons be the proof of the complex nature of the mixing matrix via the measurement of theto several tens of kilotons.
δ phase and the determination of the neutrino mass hierarchy.
CP

The third possibility is a liquid Argon Time Projection
Chamber as pioneered in Europe with many years of
R&D in the ICARUS program. This technology is able
to image the rare events with the quality of a bubble-

2

We expect that most issues of solar physics will be covered by BOREXINO andSNO+ in the next years. What likely will stay unresolved is the detection of supernova
relic neutrinos (item d) for which a next gene-ration scintillation detector appears tobe the best option.

36
Physics potential of the 3 types of detectors for proton decay & neutrino astrophysics *TopicsGLACIER(100 kt)

LENA(50 kt)

MEMPHYS(500 kt)

5 × 1034
11 × 1034

4 × 1034

15 × 1034
2.5 × 1034

~ 38,500
1.6 × 104 (νe)
2.2 × 104
0.8 × 103 (e)-~16,000
1.3×104 (anti-νe)
1.0×103
6.2×102 (e)2.6×103 (p)~250,000
2.5 × 105 (anti-νe)
1.3 × 103 (e)-~50/30~30/5~60/50(1 module with Gd)

Solar neutrinos# events, 1 year

8
B ES : 3.0 × 104
Abs:
1.0 × 105

Be: 3.6×106
pep: 1.0×105
8
B: 2.9×104

Atmospheric ν# events, 1 year

11 × 103

5 × 103

5 × 104

Below threshold

1.5×103

Below thresholdproton decay,
sensitivity(10 years)
e+ π0
anti-ν K+(**)
SN at 10 kpc,
# events
CC
NC
ES
Elastic scatt. p
Diffuse SN#Signal/Background
events (5 years)

Geo-neutrinos# events, 1 year

A next generation underground observatory/observatories will be global in nature and follow
worldwide coordination and cost sharing. LAGUNA,
a common design study within the 7th European
Framework Program (FP7), has been underway since2008. It started by assessing the feasibility of sevenpre-selected large European underground sites inFinland (Pyhäsalmi, up to 4 km m.w.e. depth) France(Frejus, 4.8 km m.w.e.), Italy (Umbria, 1.5 m.w.e.)7

B ES: 1.2 × 105

8Poland (Sieroszowice, 2.4 km m.w.e.), Romania(Slanic, 0.6.km m.w.e.), Spain (Canfranc, 2.1 km
m.w.e.), United Kingdom (Boulby, 2.8 km m.w.e.)
to host one or more instrumented tanks filled withliquids (water, liquid scintillator, or liquid argon).
The LAGUNA design study was focused on theunderground cavern infrastructure, tank design andliquid procurement, at the expense of a sufficiently_____________________* some numbers strongly depend on model assumptions and give a qualitative rather than an exact quantitative comparison.
** this channel is particularly prominent in SUSY theories. Indications for SUSY at the LHC would boost its importance.

37
detailed detector design allowing a full relative costing Due to the high cost and long development time
exercise of the various options. The main findings of necessary to realize this program, the committee
the design study are that:recommends that it be pursued in a global context.
It is also recommended that programs with anda) all seven sites appear technically and environ- without a new neutrino beam are considered in ordermentally feasible, though not all sites are interesting to preserve possible scienctific opportunities.
for all detector options,
In the context of long-baseline measurements ofb) it appears feasible to excavate the desired neutrino oscillations, of the detection of supernova
underground caverns and infrastructures, to build the burst neutrinos and of the search for proton decay, wenecessary tanks underground, and to fill them with the also mention a further infill of the DeepCore detector
liquids,
nested in IceCube at the South Pole. A moderate infill of
15-20 strings would result in a threshold of ~1 GeV andc) the cost of the excavation, although significant, is might allow to measure matter oscillation effects that are
not the dominant cost of the project.
sensitive to the neutrino mass hierarchy. A massive infill
Studies indicate that some European options offer of 50-100 strings might lead to a 20 Megaton detector
potential physics and/or technical advantages that need sensitive to supernova bursts from much beyond ourto be specially and carefully confronted with other own galaxy and possibly even to proton decay. The
options worldwide. The physics goals play a dominant committee encourages the ongoing Monte-Carlorole in selecting the site.
studies and related photo-sensor developments.
In order to proceed with the project, a better understandingof the costs of the full detector design and construction
including their instrumentation for the three detector
options is essential. This design study is therefore thenext logical step beyond the very successful LAGUNA
design study. After the completion of this phase (called
LAGUNA-LBNO – from Long Baseline Neutrino
Observation since it will also focus to neutrino beam
options), all objective technical and costing information
should be available. The prospects for LAGUNA-LBNO
have increased the interest in the project compared to
LAGUNA, which now includes members from Denmark,Finland France, Italy, Germany, Greece, Poland Romania,
Spain, Switzerland United Kingdom, Russia and Japan,
as well as CERN. This situation could naturally lead to a
preparatory phase.

Neutrino astronomy would benefit from themeasurements of nuclear cross-sections of astrophysicalinterest using underground nuclear accelerators. We
recommend therefore supporting the update of
the ongoing programs with LUNA and follow-up
projects at higher energy.
The interpretation of current and future long baseline
experiments depends highly on the detailed knowledgeof neutrino-nucleus interactions. Hence, the committee
encourages more dedicated theoretical work in thisfield.

Several anomalies in the neutrino sector and incosmology have been noted over the last 15 years andgenerated increased interest in sterile neutrinos as apossible explanation. This makes new experimental
Recommendations: LAGUNA is the European campaigns necessary, with the goal to either falsify
effort to develop neutrino detectors on the the anomalies or indeed discover physics beyond“Megaton scale” both for accelerator-based and the Standard Model.
astroparticle neutrino measurements. The scientificgoals are both broad and ambitious. The LAGUNA The ambitious activities discussed in this and thesite study is almost completed, showing that there previous sections should be paired with an increased
are possible sites in Europe that could host such theoretical effort on predictions in these fields. (Seeexperiments. The committee recommends that the Section 5).
study is pursued with LAGUNA-LBNO focusing
on detector designs, in order to lead to a better
understanding of the costs of the various detector
technology options and on the prospects for a newlong baseline neutrino beam from CERN.

38
4. Dark Energy &Gravitational Waves
4.1 Dark Energy
The expansion of the Universe ought to be slowing
down due to the collective mutual gravitational
attraction of matter. However in 1998, observationsof very distant supernova explosions (of type Ia)
led to the conclusion that the expansion has been
accelerating during the recent evolution of the
Universe. The mechanism responsible for thisacceleration has been named “Dark Energy” (DE) –it behaves like Einstein’s Cosmological Constant i.e.
has negative pressure, and appears to make up about¾ of the energy density of the Universe. The Nobel
prize for physics in 2011 has just been awarded for thismomentous discovery, yet it is acknowledged that it
has no physical explanation. Clearly, establishing thenature of DE and its place in the general theoreticalscheme of physics is a research priority of the highest
order. Today, basic questions about DE remainunanswered, for instance:- Does dark energy really exist or is it an artefact ofinterpreting the observations in the framework of
an idealised (perfectly homogeneous) cosmologicalmodel?
- Is the DE density in the universe really constantin time (as is expected for Einstein’s Cosmological
Constant)?
- If so, is this vacuum energy? Then how does one
compute this vacuum energy in the context of atheory unifying gravitation and the quantum theoryof fundamental interactions (the Standard Model orits extensions)? This is especially problematic since
the naïve expectation is that the energy scale of thevacuum energy is the Fermi scale (~102 GeV) or even
the Planck scale (~1019 GeV), rather than ~10-12 GeV
as inferred from the cosmological data – this is thenotorious as yet unsolved Cosmological Constantproblem.
- If not, how did the evolution of DE impact on thehistory of the Universe?

a scale factor a(t) (linked to the red shift via a(t)= 1/(1+z), a(t0) normalized to 1 at present time t0) that
describes the variation of distances in the expanding
Universe as a function of time, and a growth ofstructure parameter g(t) that describes deviations froman average density.
There are two basic “kinematical” approaches used
for measuring a(t):Supernovae: the experimental programme consistsof discovering large numbers of Type 1a supernovae
at different redshifts, and measuring their apparent
luminosities and redshifts. Their intrinsic brightness
can be deduced from the data to within ±15%, so theratio of apparent to intrinsic luminosity allows an
estimate of the distance and therefore the time of theevent in the framework of an assumed cosmologicalmodel, e.g. the standard homogeneous FriedmannRobertson-Walker cosmology. Since a(t) can be
deduced from the red shift one can plot a(t) vs t andmeasure the acceleration of the expansion rate of the
Universe (a(t) >0).
Baryon Acoustic Oscillations (BAO): The early
universe was a radiation-dominated hot plasma, andtiny statistical density fluctuations of overdensity
propagated as acoustic pressure waves with apredictable velocity of v=c/√3, where c is the velocity
of light. At decoupling (when the radiation ceased tointeract with matter) the waves stalled. The time ofdecoupling has been measured in Cosmic Microwave
Background experiments to be 379,000±8,000 yr, so
the scale at which the waves stalled can be estimatedto be Rs = 147±2 Mpc, serving as a “standard ruler”
imprinted on the galaxy distribution. This standard
size Rs subtends an angular size Δϑ to an observer on
Earth. The BAO method consists of measuring theposition and red shift of tens of millions of galaxies;
the angular distances between all pairs of galaxies at agiven red shift exhibit an excess at the size Δϑ of the“standard ruler”. From this measurement the angularsize distance DA can be inferred (DA = Rs /Δϑ). Since
this “apparent” angular distance (which varies with
redshift) depends on the expansion history (again, in
the framework of an assumed cosmological model),it measures indirectly the cosmological parametersand provides information about the nature of DE.

However these data can also be matched in alternative
cosmological models (e.g. the Lemaitre-TolmanBondi inhomogeneous cosmology) without requiringdark energy. Hence it is essential to find convincing
dynamical effects of dark energy. Two other experimental
The scientific investigation of DE centres around two methods measure both kinematical effects and theory
time-dependent properties of the evolving Universe: related parameters through the measurement of g(t):- Does the existence of DE necessitate the introductionof a new particle-type field, or a revision of the theoryof General Relativity, or both?

39
Weak Lensing: Light from distant galaxies is deflectedby intervening concentrations of mass, an effect known
as gravitational lensing. In weak lensing the effect is notstrong enough to produce separated images of distantobjects, but merely distorts (shears) the image of the
distant objects. This shear map can be constructed fromobservations of the shapes and red shifts of large numbersof galaxies, and provides a sensitive measurement of
the intervening mass distribution. Measuring the mass
distributions at a variety of redshifts (times) gives ameasurement of g(t).
Galaxy Clustering:Due to the attractive
gravitational forces between them, galaxies form
clusters. The presence of Dark Energy, with its
repulsive gravitational effects, slows down thisprocess. Thus, measurements of the number density,
red shifts, and mass distribution of observed clusters
provide another measure of g(t). These studies often
use the Sunyaev–Zel’dovich (SZ) effect to measure
the angular position of the clusters. The SZ effectis a slight distortion of the CMB spectrum in the
direction of the cluster, caused by the interactionsof electrons of the gas in the cluster with the CMB
photons. The effect is independent of redshift andthus the SZ information has to be combined with z
measurements provided by an independent survey.
An example of this complementarity is the foreseencollaboration between the South Pole Telescope (aSZ survey) and DES (a photometric redshift survey;
see below). Another important test of DE is the‘late integrated Sachs-Wolfe (ISW) effect’, which
generates a secondary anisotropy in the CMB onlarge angular scales when DE comes to dominate.
This is because the negative pressure of DE then halts
structure formation through gravitational collapse
so that the blueshift/redshift experienced by CMB
photons when they pass through galaxy clusters (orvoids) do not cancel. Accordingly the CMB should
appear slightly hotter in the directions where there ismore structure, and slightly cooler where there is lessstructure. To detect the ISW effect requires crosscorrelating galaxy maps with maps of the CMB.
If dark energy is regarded as a relativistic “fluid”, anattempt can be made to determine the relationshipbetween its density ρ and pressure p. The relationw = p / ρ is called the “equation of state” of dark energy
and contains important information about its nature;
it is often parameterised as w = w0 + wa (1 – a), where
w0 is the constant term and wa characterizes its timedependence. If dark energy coincides with vacuum
energy i.e. appears as a cosmological constant, then w0 =-1 and wa = 0. Thus measuring these quantities provides atest of the relationship of dark energy to vacuum energy,
or any alternative theory driving time dependence.

The progress of the quality of the Dark Energy
measurements is usually characterized by a Figure of
Merit (FOM) defined as the reciprocal of the errors
i.e. the area of the error ellipse in the equation ofstate parameters w0 and wa.
- The completed or underway ground based experiments
are expected to yield a FOM of about 10.
- The projects in preparation are expected to produce a
FOM in the vicinity of 50 to 100, in the next 5 years
or so.
- The proposed future projects are estimated to
produce a FOM of the order of 1,000 in the next
decade.
These four experimental approaches have different
strengths and weaknesses. A strong research
program on DE needs experiments using all of theseapproaches since a) their systematic uncertainties
are very different and a combination of results isrequired to reach reliable conclusions, b) the different
methods exhibit different correlations between thecosmological parameters and the combined data canbe used to increase the measurement precision, andc) a comparison of the results of the measurementsof the growth of the scale factor a(t) with the growthof structure g(t) provides an important check on
General Relativity (GR).
The role of astroparticle physics. The
methodology used for dark energy studies is that of
traditional astronomy, e.g. large surveys, photometry,
spectroscopic methods, etc. Nevertheless, particle
physicists were involved in DE investigations fromthe very beginning, motivated by its unquestionable
theoretical importance, and also by the relevance of
certain methodologies of particle physics (large arraysof sensors, importance of very precise calibrations,end-to-end simulations, large data sets). It has therefore
become a field where the convergence of the two
disciplines has provided a strong innovation factor.
Need for space missions? All of the projects
that have been completed, are underway or are inpreparation are using ground-based facilities, except
for the projects using the Hubble Space Telescope.
The generally accepted rule is that anything that canpossibly be done from the ground should be done
there because the costs associated with space-based
efforts are very high.
The motivation to do space-based DE experiments isdriven by the desire to trace the expansion history of
the universe further back in time. In most models of
DE, the dark energy component begins to dominate40
over non-relativistic matter at z~1. At these redshifts,
the bulk of the light from the objects of interest isredshifted into the infrared (IR). The Earth generates
IR backgrounds in ground-based experiments thatare difficult to overcome. In contrast, space is cold,
with IR backgrounds 4-5 orders of magnitude lower,
making the required high redshift measurements
possible. In addition, the much better resolution andthe stable observing conditions due to the absenceof the atmosphere allow for much smaller systematic
uncertainties, which will be crucial for the next
generation of precision measurements. For thesereasons, space is advantageous. This should however
be put in balance with the cost of space missions andthe time needed to prepare one (usually 10 years ormore). It is worth noting also that space missions inthis field require complementary ground observations
because of the need for a lot of photometry.
Among the projects completed or on-going ) in which
the astroparticle community participates, one may
cite SN Factory, SuperNova Legacy Survey (SNLS),
Canada France Hawaii Legacy Survey (CFHLS),
Baryon Oscillation Spectroscopic Survey (BOSS,
part of the Sloan Survey). Among the proposed future
projects, some are focussed on astronomical issues,
but would contribute to DE studies in any case. One
may cite: Pan-STARRS-4, a combination of fourlarge optical/near-IR survey telescopes to be sited on
Mauna Kea in Hawaii; the Square Kilometre Array(SKA), a proposed radio telescope with a collecting
area of order 1 km2 capable of operating at a wide
range of frequencies and angular resolutions; IXO,
a large X-ray space observatory; the Extremely Large
Telescope (ELT), a 30 m-class telescope with optical/
near-infrared capabilities. In space, the James Webb
Space Telescope (JWST), a 6.5 m deployable spacetelescope, would be useful for many types of darkenergy studies including supernovae, clustering, andweak lensing at high redshift.

The scientific objective of DES is to measure theDE equation of state parameter, w, with four
complementary techniques (redshift distribution
and clustering evolution of galaxy clusters, weakgravitational lensing on large scales, evolution oflarge-scale structure including baryon acoustic
oscillations and Type Ia supernova distances). To
achieve these goals, DES will operate DECam for 525
nights over 5 years (roughly 30% of the observingtime) beginning in FY12 and carry out two surveys:
a wide-area survey of ~300 million galaxies over 5000
square degrees and a time-domain survey over tens ofsquare degrees to discover and measure light curves forseveral thousand supernovae. The precision achieved
should result in an improvement of a factor of 4-5 in
the figure of merit (presently around 10, as discussed
above). Since clusters and weak lensing are sensitive
to the growth of structure, while BAO and SNe aresensitive to expansion history, the combination ofprobes will constrain modified gravity theories, inwhich the relation between perturbation growth andexpansion history is altered from General Relativity.
DES has assembled an international collaborationof 120 scientists, including groups from UK (opticalcorrector), Spain (camera electronics) and Germany(data reduction). In addition to the DOE and NSF
in the USA, the European funding agencies involved
are the UK Science & Technology Facilities Council,
the UK Science Research Infrastructure Fund, theAstronomy & Astrophysics program of the Ministryof Science & Innovation in Spain, and the German
Science Foundation’s Excellence Cluster “Origin and
Structure of the Universe”.

During 2011, construction of DECam will becompleted in stages, and components will be installedon the telescope. Commissioning was carried out at
the end of 2011, followed by early science operations.
Normal survey operations will commence mid-2012
and are expected to continue through 2017. The total
In the following paragrpahs, details are provided for estimated cost of DES is 45 M$ (with a European
the most important future projects in which Europe share amounting to 5 M€).
is (or may be) a stakeholder.
LSST, the Large Synoptic Survey Telescopeenvisions a newly constructed 8.4m ground based
telescope and a 3 Gigapixel CCD camera combined
Description of present and proposed future with rapid slewing and readout enable imaging of
projects
the entire seasonally available sky (20,000 square
degrees) every three clear nights in six colours. The
The Dark Energy Survey (DES) Collaboration is images may be examined individually for transienta project to build, install and operate a new 519 phenomena such as supernovae, or summed tomegapixel CCD camera (the Dark Energy Camera) produce deep images suitable for cosmic shear andto be mounted at the prime focus of the Blanco galaxy-cluster surveys. Coverage from 320-1,080
4m telescope at the Cerro Tololo Inter-American nm will allow LSST to push ground-based CCD
Observatory (CTIO) located in La Serena, Chile. observing to its limits for dark energy studies and41
a wide range of astrophysical investigations, from consists of three major components: (i) an opticalnear-Earth asteroids to high-redshift gamma-ray corrector that provides a 3 degree diameter field ofbursts.
view at the Mayall prime focus; (ii) a focal planewith 5,000 fibers, each controlled by an independent
LSST will discover and measure the shapes and robotic actuator; (iii) ten identical spectrographs,
photometric redshifts of over 3 billion galaxies in each viewing 500 fibers and covering the wave-length
the redshift range 0.5 < z < 3, and use this data to range from 460 to 1040 nm with a resolution of R
measure cosmic shear. The LSST galaxy data will = λ / Δλ = 3000 - 4800. In addition, the BigBOSS
also be used to execute the BAO probe using the project includes a data pipeline and archive to makephoto-z technique. LSST imaging will discover processed spectra and redshifts available to theenormous numbers of Type Ia supernovae. As community.
there is no spectroscopic component to the LSST
program, precision redshifts and spectral diagnostics BigBOSS will survey a comoving volume that iswill require other resources. LSST light curves for 10 times larger than that covered by BOSS, theSNe (~30,000 per year) will be of high quality. This experiment at the 2.5 m Sloan telescope in New
data set will enable detailed studies of SN diversity, Mexico, and will measure redshifts for almost 20
which will be of value to other dedicated SN studies million galaxies (fifteen times more than BOSS).
using spectroscopy or imaging. The overall figure of The BigBOSS targets are luminous red galaxies
merit is expected to be some 10 times larger than for (LRGs) and emission line galaxies (ELGs), both
DES.
selected from current and planned imaging. LRGs
are observed up to a redshift z=0.9 while ELGs
The LSST data set will permit real-time investigations are detected up to z=1.7 through detection of thefor studying variable objects. In time-domain bright [OII] emission line doublet at a rest framestudies, LSST’s specific goals include mapping of wavelength of 3727 Angstroms. BigBOSS will morenear-Earth objects, supernovas, gamma-ray bursts, than double the BAO FOM over the combined
variable stars, and high-energy transients. Its archival power of all predecessor experiments, achieving an
science will include mapping the Milky Way and the accuracy on the angular diameter distance of 0.4%
distant universe, creating an accurate photometric for 0.5 < z < 1.0 and 0.6% for 1.0 < z < 1.7. In
and astrometric data set, studying stellar kinematics a multiyear survey a sample of 30x106 galaxies will
and performing a census of the solar neighbourhood. be observed out to z~2. In addition, a large number
Another goal of interest for the high energy (600,000) of quasars with redshift z>2.2 will be
community is the determination of the sum of observed and used as backlights for intervening large
neutrino masses.
scale structure as revealed in the absorption featuresin the Lyman-alpha forest.
The LSST project involves a large collaboration ofscientists - both astroparticle and astro-physicists. The The BigBOSS collaboration includes consortiums
instrument and data processing plans are advanced - from France and the UK, and there are somethe primary/tertiary and secondary mirrors have been collaborating institutions in Spain. The French
cast and a Chilean site selected – using private and will be responsible for the spectrograph design andpreliminary agency funding. The estimated cost is fabrication, the UK group has expertise in the design
465 M$, with operation costs of 42M$/yr. The bulk and fabrication of large optical elements, and theof the funds for construction and 10-yr operations Spanish group has experience in focal plane design
are sought from NSF, DOE, international research and fabrication.
agencies and private donors. In Europe, only the
French community is involved in this project at this The Subaru Measurement of Images and Redshifts
point but there are discussions in other countries for (SuMIRe) survey is being designed for the Subaru
further involvement. First light is expected in 2020, 8-m telescope at Mauna Kea. It would have a fieldwith science runs starting in 2022 for 10 years.
of view of about 1.5 degrees, and the capability tosimultaneously obtain spectra for about 20,000
objects/night. A redshift range of 0.6 < z < 1.7 forSpectrographic surveys:
emission-line galaxies will be targeted, and 2.3 < z< 3.3 for Lyman-break galaxies. Its primary goal is
BigBOSS is a proposed ground based spectroscopic to measure BAO, as well as to measure thousands of
Baryon Acoustic Oscillation experiment to be SNe Ia.
installed on the 4 m Mayall telescope at Kitt PeakNational Observatory. The BigBOSS instrument Discussions are being held presently to join efforts42
with the US-led WFMOS (Wide-Field Multi-Object
Spectrograph) collaboration, which did not receive
approval to be placed at the focal plane of the
GEMINI telescope. The cost estimate from WFMOS
is 68.5M$, 16.5M$ being already available throughJapanese funding. Discussions are being held with
US, Brazilian and European groups to complete thefunding.
Space missions:WFIRST first appeared in the report of the US
Decadal survey in summer 2010. WFIRST is a
1.5-meter telescope that will orbit the second
Lagrange point (L2), 1.5 million km from Earth,providing a wide-field-of-view near-infrared imaging
and low-resolution spectroscopy observatory. It
will image the sky at near-infrared wavelengths andperform low-resolution infrared spectroscopy. The
mission concept is inspired from the one of the JDEM
(Joint Dark Energy Mission) proposed earlier.

WFIRST will address two of the most fundamental
questions in astrophysics: Why is the expansion
rate of the universe accelerating and are there othersolar systems like ours, with planets like Earth? In
addition, WFIRST’s surveys will address issues
central to understanding how galaxies, stars andblack holes evolve. To measure the properties ofdark energy, WFIRST will employ three different
techniques: it will image about 2 billion galaxies andcarry out a detailed study of weak lensing that will
provide distance and rate-of-growth information; it
will measure spectra of about 200 million galaxies in
EUCLID’s main goals are:order to monitor distances and expansion rate using- Measuring the DE equation of state parameters baryon acoustic oscillations; and finally, it will detect
w0 and wa, respectively, using both expansion history about 2,000 distant supernova explosions, which canand structure growth (the figure of merit should be used to measure distances.
reach 1,500 for the Euclid-Planck combination).
The Decadal Survey estimated the cost of WFIRST- Measuring the growth factor exponent γ (where to be around 1.6 B$, with a time from project
growth of structure rate g(t) a(t)γ ) with a precision start to launch of 82 months and recommendedof 2%, enabling to distinguish the predictions of a prompt start (2013). Given the delays in the
General Relativity from modified-gravity theories
JWST program, NASA responded by delaying
WFIRST and recommending in the meantime a- Testing the Cold Dark Matter paradigm for structure junior participation (20%) to the ESA-led EUCLID
formation, and measuring the sum of neutrino mission which, however, was not considered timely
masses to better than 0.04 eV when combined with by the US community.
Planck.
EUCLID is a European project led by ESA to study
DE using weak lensing and BAO. The baseline
payload consists of a Korsch telescope with a primary
mirror of 1.2 m diameter designed to provide a large
field of view (0.5 deg2) to an imaging instrumentwith a visible channel, a NIR imaging channel anda NIR spectroscopic channel. The first two support
the weak lensing probe, whereas the third is designed
to perform the wide spectroscopic galaxy survey.

Combined with the Planck data, this should lead to an Setting priorities
improvement by a factor of 20 in the determinationof the cosmological parameters compared to Planck The projects described above do not need to beprioritised by this Committee. First, one may note thatalone.
the leadership of all ground projects lies outside Europe.
EUCLID is currently one of the 3 M missions Second, the timing and funding status of these projects
planned for 2019-20, a downward selection step is different: DES is funded and will be the main project
to only two missions occurring in 2011. Its cost is of the years 2012-2016; LSST was recognized by theevaluated at 500 M€ plus some 200 M€ paid by US Decadal Survey as the top priority among the large
member states for the scientific payload (and 170M$ ground projects and will thus be a priority of NSF and
for NASA, who is a junior partner at the 20% level). DOE in the coming years. BigBOSS and SuMIRe have
It should be noted that there will be significant a different funding status: the first one has just started
need for ground-based photometry (agreement with applying for funds, whereas the second one is searching
Pan-STARRS and DES, and potentially with LSST). funds to complement those that it already has. It is
EUCLID has just been approved by ESA for launch unclear what will be the future of either project, but
it is clear that a significant European participation to
in 2019, with a 5-year nominal lifetime.
either of them would enhance their chances.

43
As for the space projects, Euclid, the mission with
European leadership will most probably be the firstmission ready for launch at the end of the decade. We
should know within a few months whether WFIRST
is indeed postponed because of the important cost
overrun of JWST. If it is so, WFIRST might be therelevant space mission of the 2020 decade in case adeparture from a cosmological constant is detected on
the ground or in space. It should also be stressed thatthe hardware cost of space missions is entirely coveredby space agencies (by ESA or the European national
agencies). Research agencies only contribute to R&D
as well as personnel costs.
Recommendation for Dark Energy projects: The
SAC welcomes the participation of the European
astroparticle physics community in experimentsin this field. This community should ensure thatit can participate in the harvest of results fromthe presently planned ground-based projects andshould also exploit the unique chance for leadershipin space with the ESA-led EUCLID mission.

4.2 Gravitational Waves

gamma-ray bursts? What are the conditions in thedense central cores of galactic nuclei dominated bymassive black holes? Where and when do massive
black holes form, and what role do they play in theformation of galaxies? What happens when a massive
star collapses? How do compact binary stars formand evolve, and what has been their effect on starformation rates?
Gravitational waves should propagate essentiallyun-attenuated across a wide range of frequencies, from
10-17 Hz for ripples in the cosmological backgroundassociated with inflation, up to 103 Hz when neutronstars or black holes are born in supernova explosions,and even 1010 Hz for cosmological backgrounds
associated with phase transitions at the grand unified
scale. GW sources of great astrophysical interest exist
within this range, including black hole and neutronstar interactions and coalescences, ultra-compact
binary stars and rotating asymmetric neutron stars
such as pulsars. Because of the very weak nature ofgravity, detection is most likely for radiation emitted
by astrophysical systems in which very large masses
undergo strong accelerations.
Earth-based
detectors

andhigherfrequency

Gravitational Wave (GW) science is on the verge ofdirect observation3 of the waves predicted by Einstein’s The search for gravitational waves began in the 1960s,
General Theory of Relativity, thus inaugurating the using large instrumented masses that were expected
new field of Gravitational Wave Astronomy.
to vibrate in an observable way due to the passage
of a gravitational wave. The last decades have seen
Gravitational wave detectors will study sources a shift in the dominant technology to long baselinecharacterised by extreme physical conditions: strong laser interferometry. The first generations of large
non-linear gravity and relativistic motions, very high gravitational wave interferometers have been and are
densities, temperatures and magnetic fields. In the being operated. These ground-based km-scale laser
coming decades, arrays of ground-and space-based driven interferometers of the Michelson type, andinstruments could observe the gravitational wave sky. their advanced upgraded versions, will be critical inThis new window into the cosmos has the potential establishing the field of gravitational wave astronomy
to truly revolutionize the understanding of the through the detection of high luminosity gravitational
Universe. Below are just some of the key scientific wave sources such as the merger of binary neutron
questions to which answers will be sought:stars and black holes.
- fundamental physics: What are the properties ofgravitational waves? Is General Relativity still valid
under strong-gravity conditions? Are nature’s black
holes the black holes of General Relativity? How
does matter behave under extremes of density andpressure?
- cosmology: What is the history of the accelerating
expansion of the Universe? Were there phasetransitions in the early Universe?
- astrophysics: How abundant are stellar-mass
black holes? What is the mechanism that generates

In the U.S., the Laser Interferometer Gravitationalwave Observatory (LIGO) consists of three multikilometre scale interferometers, two in Hanford,____________________
3
Gravitational waves have yet to be observed directly, but strong indirect evidence
was obtained in 1974 by R. Hulse and J. Taylor. They measured a decline in theorbital energy of a binary pulsar, presumably due to intense gravitational radiation.
For this ingenious work, they were awarded the Nobel Prize in 1993.

44
Washington, and one in Livingston, Louisiana. In
Europe, Virgo is a multi-kilometre scale interferometer
located near Pisa, Italy, and GEO600, a 600-m
interferometer, is located near Hannover, Germany.
The TAMA detector near Tokyo is 300 m in size,
whereas CLIO, an advanced 100-m interferometerin the Kamioka mine, has recently demonstrated
interferometry with cryogenic mirrors. In orderto make the most out of the presently available
detectors, the GW community has now established aclosely connected network between the gravitational
wave antennas in Europe and in the U.S.A, withcoordinated data-taking, immediate sharing of dataand co-signature of publications.

extraction of information from the network ofground based advanced detectors existing then, orfrom space or astronomical observations, the aim
would be to move to third generation detectors,
probing Gpc scales and cosmological distances, thus
fully realizing the gravitational wave astronomy
potential.
Successful deployment of third generation,
underground gravitational wave observatories would
require development of a number of new technologies
by the gravitational wave community. Many of
the necessary R&D programs are undertaken ina limited number of places, but with a growing
level of coordination and communication. The
proposed Einstein Telescope (ET) is an advanced
concept for a wide band underground observatory
with significantly improved sensitivity over that ofplanned advanced detectors, especially in the low
frequency range.

Major upgrades of LIGO (Advanced LIGO), Virgo(Advanced Virgo) and GEO600 (GEO HF) havebeen started and will be completed in the next five
years. It is expected that the first direct observationof gravitational waves will be made in the next few
years by this international network of 2nd generation
detectors.
The ET conceptual design study, funded by theEuropean Union, demonstrated the feasibility of a
The next step would be to pinpoint the sources on the 3rd-generation GW observatory, with a significantly
sky and to extract all the information about each source’s higher sensitivity, especially below 10 Hz, due to an
behaviour encoded in the gravitational wave signal. underground location. The ET cost estimates are
To carry this out, a true global array of gravitational strongly depending on the site location and on the soil
wave antennae separated by inter-continental distances characteristics, but the rough estimation performed
would be required. Such a network would improve in the ET design study confirmed the feasibility ofsource location to or below that needed for wide-field the ET infrastructure at costs of the order of 800 M€.
electromagnetic telescope to be able to perform effective The realization of third-generation antennas would
follow-up and can result in better sky coverage and be triggered by the first detection of GWs expected
improved signal to noise ratio.
around 2017-2018, and scientific data would start
being available in the second half of the 2020s.
In the medium term this would be achieved byadding further detectors with appropriately chosen The ET project has as its goal the realisation of aintercontinental baselines and orientations to Research Infrastructure, (in the meaning adopted by
maximize the ability to extract source information. the European Commission of an infrastructure that
The most advanced plans along these lines are with will allow European scientists to «use» a «facility»)
the Japanese Large-scale Cryogenic Gravitational- with a lifetime of decades, allowing forefront
wave Telescope (LCGT), recently approved in order astrophysics, fundamental physics and astronomy
to participate in the first direct observation, and the to be carried out, via the study of gravitational
Australian International Gravitational Observatory radiation from astrophysical sources. The concept is(AIGO). Further, possibilities for a detector in India to realize first the required site infrastructure, then
(INDIGO) are also being studied.
to implement the detector hardware. This modus
The state of the art detectors can currently detect operandi is not uncommon; in fact the LCGT projecta ripple of space with 10-22 relative sensitivity, able in Japan is currently readying an underground site
to monitor cataclysmic mergers or explosions up to and a first-stage room temperature detector, with
20-25 Mpc away. The next generation would reach cryogenics to be implemented subsequently.
sensitivities of 10-23, able to monitor cataclysmic
mergers or explosions up to 250 Mpc away. The The creation of the ET observatory in a manner
network of detectors exhibiting this sensitivity consistent and integrated with the capabilities of the(2nd generation or advanced concept) would be in European scientific field currently engaged in theprinciple able to observe gravitational wave signals installation and commissioning of Advanced GW
at a monthly or even weekly rate from compact detectors is possible via the specific nature of the ET
coalescing binaries. Following first detection and project.

45
The focus for the first 6-7 years (2015-2022) is on
the infrastructure: (1) underground site, (2) vacuum
infrastructure and (3) cryogenic facilities.
The engineers involved in (1) are to a large extent
from a different manpower pool than the scientists
involved in advanced detectors. Underground facility
specialists will be required, working on the technicaldesign of the infrastructure 2014-2017, and then on
the excavation activities (2018-2022).
The engineers and the scientists involved in (2)and (3) are involved at the periphery of efforts for
Advanced detectors and mainly in the early years (toimplement the needed additional vacuum chambers
and cryo-traps). The timing is thus compatible(-2014 for advanced detectors; 2015-20 design ofET vacuum facilities; 2021-23 vacuum & cryogenic
plant installation. Larger manpower dedicated to ET
in terms of interferometer experts, will be needed
only starting from around 2018. However thiscore team of physicists will be active throughout
the period 2011-18, with an emphasis able to shiftsmoothly onto relevant hardware and commissioning
efforts via the philosophy outlined above, of an
infrastructure designed to stand for decades housing
hardware which progressively evolves toward a design
achieving the ET sensitivity goal.
The program timing could be considered as being
close to optimal in the sense that the expertise
gained in the construction and commissioning of theadvanced detectors can smoothly be steered towards
ET and without a large gap in between where key
skills might be lost.To enable this program, support
for the key R&D activities is needed in the next
7-10 years to develop the technologies that are notshared with advanced detectors, like cryogenic optics
and mechanics, new lasers, gravity gradient noise
suppression. Cryogenic issues, for example, show
important common points between ET and LCGT(For this reason a 4-year scientist exchange program
between the two projects has been proposed andpositively evaluated by the European Commission,under FP7-People (IRSES): ELiTES. It should be
operative from March 2012.

Space-based detectors
LISA, a space-based interferometer would open the
low-frequency gravitational wave window from 0.1
mHz to 0.1 Hz. The scientific objectives of space-based
and ground-based instruments are complementaryin the same way that optical and x-ray astronomy
are complementary and have provided information
about different types of astrophysical objects
and phenomena. LISA is the gravitational wave
community’s priority for a space-based mission, withan earliest launch in the early 2020s, provided thatthe technology precursor mission LISA Pathfinder,
to be launched in 2014, would fulfil its technologicalgoals.
The original LISA project involved an equal sharebetween ESA and NASA. The present financial
situation of NASA prompted ESA to consider areduced mission in a Europe-only context. The new
LISA mission is now being considered in the context
of the “Cosmic Vision”, with a cap cost of around 1.2
billion Euro and an estimated launch date around2022. Decisions to go ahead with phase-A studies
will be made in this context for all large missions
under consideration by ESA in February 2012, witha final selection in 2014.
The scientific programme of the new LISA mission
retains much of the original mission. LISA willrecord the inspirals and mergers of binary systems
or supermassive black holes, the most powerfultransformations of energy in the Universe. It will
map isolated black holes with high precision,
measuring their mass and the three components of
their spin. It will directly observe how massive black
holes form, grow and interact over the entire historyof galaxy formation. Finally, LISA will study in detailthousands of compact binary stars in our Galaxy,providing a new window onto matter at extreme
conditions.

The portion of the gravitational wave spectrum
lying between the LISA band and that probed
by ground-based interferometers also holds great
potential, including observation of coalescences ofintermediate black hole binaries and some of the
These measurements on the ground and underground deepest searches for stochastic backgrounds. The
could be complemented by very long baseline DECI-hertz Interferometer Gravitational wave
(5 million km) space interferometers as is the case Observatory (DECIGO) is a space gravitationalwith the proposed mission LISA, the Laser Interfe- wave antenna proposed in Japan, aiming for launchrometric Space Antenna.
several years after LISA. In the longer time frame,
the Big Bang Observer is targeted at detecting thegravitational waves produced in the big bang andother phenomena in the early Universe.

46
We finally note that there is also a growing effort
to utilize radio astronomy for the detection ofgravitational waves in the nano-hertz frequency
band with the formation of the International Pulsar
Timing Array (IPTA) collaboration. There are
currently projects in North America (NANOGrav),
Australia (Parkes Pulsar Timing Array) and theEuropean Pulsar Timing Array having or requesting
access to the world largest radio telescopes. Search for
primordial gravitational waves is also included in thescientific program of CMB detectors like the Plancksatellite through the measurement of polarization
anisotropies of the cosmic microwave background.
Recommendations for gravitational waves:
The committee recommends the move of theinternational gravitational wave community
towards a single worldwide network of groundinterferometers which will allow better coverageand better pointing capabilities. This also goesin the direction of increasing the community
worldwide.
At a time of down selection of the large mission of
the ESA Cosmic Vision program, the community
renews its strong support of the LISA program
which will open the scientifically challenging
domain of low frequency (10-4Hz, 10-1Hz)
gravitational wave astronomy, as well as advanceour knowledge of fundamental physics.
The committee acknowledges the progress of theEinstein Telescope Design Study, supports a newproposal for coordination actions for ET and
encourages ASPERA/ApPEC to take steps for a
future inclusion of ET into the ESFRI list.
The committee supports an enhancement of the
R&D effort in order to accompany the developmentof the second generation network and to prepare
for the third generation (ET). For this purpose,
we propose an ASPERA call for R&D.

47
5. Transversal activities

data requires Grid- and Cloud-type solutions, as docomputer simulations, for instance of extensive air
The activities addressed in this section are of importance showers or of cataclysmic cosmic events. We welcome
to all of the subfields described in the previous the ASPERA common calls for joint funding ofsections. The importance of theoretical studies has research and development. These calls also stimulate
been mentioned occasionally and is highlighted here cooperation with industry, which has been and will be aagain with respect to all subfields.
strong element in developing cutting-edge technology
and for transferring innovative developments to
Theorypractice. We suggest that about 20-25% of astroparticle
funding should be reserved for small initiatives, R&D
Even more than for experimental astroparticle physics, and small-scale participation in experiments withthe distinctions between particle physics, cosmology non-European leadership.
and astrophysics have been blurred for theory. Theory
often motivates experimental projects, links distinct
sub-fields of astroparticle physics, and is indispensablefor the interpretation of experimental results. In parallel Relation to other fields of science
with the ambitious plans for the next-generation
astroparticle experiments in Europe, the associated Our research is primarily directed to basic questions oftheoretical activities – apart from project-specific particle physics, astrophysics and cosmology, but has
analysis and computing activities – need stronger relations to other fields of science through advanced
support and coordination. Predictions for specific dark technologies and infrastructures. Numerous examples
matter candidates, calculation of proton-decay rates, have been impressively presented at the December
assessment of the uncertainties in predictive theories, 2010 Workshop “From the Geosphere to the Cosmos”
an improved understanding of supernova neutrino in Paris. They range from marine sciences, early
emission and the diffuse flux of supernova neutrinos, earth quake warning, climate and weather studies
continued research in solar physics, updated studies and glaciology to the application of high technology
of atmospheric neutrinos and relevant cosmic-ray developed for basic science in medicine, biology andphysics, charm production in atmospheric neutrinos, other sciences. We encourage our colleagues to seek thegeological and geophysical aspects of geo-neutrinos cooperation with communities from applied sciences,– all these activities are of vital relevance for the big not only for the benefit of the results in applied science,experiments that are going to be built and to the but also to broaden the scientific community behindability to answer big questions in cosmology, particle the huge-scale projects of astroparticle physics.
physics and astronomy. As examples for the need ofcoherent actions, which we already highlighted in the2008 roadmap, the assessment and reduction of the Education and Outreach
uncertainty of nuclear matrix elements for double-beta
decay experiments, the interpretation of cosmological The questions of astroparticle physics address very
data and their relevance for dark matter and dark energy, fundamental questions, like the origin and nature of
the modelling of high-energy processes in violent matter, energy and the Universe. They challenge theenvironments and the connection of the activities in imagination and curiosity of a broad audience. The
our field with the exciting prospects of particle physics cutting-edge technology and the sometimes remote,in the LHC era, should all be mentioned.
exotic locations add another factor of fascination. This
makes astroparticle physics an ideal tool to get laymen
interested in basic science. For the same reasons, anResearch and Development
increasing number of young researchers with brilliant
new ideas are motivated to join the field. The number
Technological innovation has been a prerequisite for of university positions on astroparticle physics has been
the enormous progress made over the last two decades continuously increasing over the last decade, reflecting
and has enabled maturity in most fields of astroparticle not only the growing importance of the field, but also aphysics. The astroparticle programme calls for better growing pool of excellent young researchers challenged
and cheaper solutions for all of the ubiquitous detectors by its questions. The support of activities in educationand materials for astroparticle physics. Electronics and outreach are therefore of growing importance forand data acquisition are challenged by the need to society and for the future of basic research.
instrument huge areas or volumes with sophisticated,
often autonomous sensors. On the computing side,
the treatment of large amounts of experimental

48
AppendicesA.1
Charge to the Science Advisory Committee
Terms of reference of the Scientific Advisory
Committee- address issues of critical R&D in view of the large
projects of the roadmap and issues of procurement(from photomultipliers to rare isotopes)- identify the major milestones and decision turning
points with respect to the maturity of technologies
and/or expected scientific results.
- discuss the site issues and the constraints they impose
on the timescale- take a critical look on budget and calendar claims
The main task of the Peer Review Committee concerning the large projects(2006-2009) that prepared the Strategy for Astroparticle
Physics in Europe was to:- take into account international developments andrepresent the European scientific community opinion- identify the major questions of the fieldin the global coordination process happening in thecontext of the Global Science Forum working group- demonstrate its unity despite the diversity of infras- of the OECD on Astroparticle Physics. In particular,
tructures deployed,address the issue of what is the minimal numberof large projects of the same sub-domain that are- identify the major infrastructures that the were scientifically justified on a global scale? Conversely,
necessary for the advancement of the field,
are there projects whose scale demands interregional/
global coordination and/or cooperation and what
- give a semi-realistic budgetary and human resources actions should be taken in this context?
plan.
Concerning the last point, it was of course not possible For the ApPEC Steering Committee and ASPERA
to go through an exhaustive examination of the claims Joint Secretariat:of calendar, the resources needed etc. Nevertheless anaposteriori renormalisation was applied to enforce
adequacy between traditional funding of the field and Stavros Katsanevas
project demands. This gave the well known budget
calendar with a 50% integrated increase over the next
10 years when compared to a flat projection of the2007 expenses.
Since the publication of the European Strategy, andsometimes because of it, many new developments
happened, technical design studies are published or
are in progress, new scientific results, international
roadmaps (especially in the US) are coming along,
first decisions of funding are taken and also agency
meetings are about to start.
The terms of reference of this Scientific Advisory
Committee, which will work for a year (till spring2011) will be:- update the roadmap with new, more detailed
information on the projects (essentially the Magnificent
Seven)- include considerations on dark energy, space projects
and promising R&D

49
A.2
The 2008 ASPERA Roadmap

The Roadmap also supported Earth and space based
missions to explore dark energy, the concept of acooperative network of deep underground laboratories,
common calls for innovative technologies in the fieldof astroparticle physics, efforts to intensify the synergy
with environmental sciences and the formation of aEuropean Centre for Astroparticle Theory.

In the previous ASPERA roadmap from autumn
2008, seven types of strategic projects were defined
which later were christened “The Magnificent Seven”.
Starting from the initial cost and profiles supplied byWith phased time profiles, that Roadmap Committee
the experiments, the 2008 Roadmap Committee had
proposed:looked at possibilities for phasing and cost reduction byinter-continental cooperation. It defined milestones to· Cosmic rays: A large array for the detection of decide which experimental method in any of the sectors
charged cosmic rays in the northern hemisphere “dark matter search”, “double beta decay experiments”
and “large multi-purpose detector underground”(Auger North)should get priority or how competing methods might
be combined. Cost reductions appeared possible in all· Gamma rays: A large array of Cherenkov Telescopes fields. For some projects a rich scientific harvest would
for detection of cosmic high energy gamma-rays be guaranteed even with slightly reduced capabilities.
For others, any compromise in capabilities would(CTA)
jeopardise the success (for instance the observationof point sources in the case of KM3NeT or Auger· High energy neutrinos: A cubic kilometre-scale North). The committee assumed that not all of theneutrino telescope in the Mediterranean (KM3NeT) available budget should be spent on the flagshipprojects, but 15-20% should be reserved for small
initiatives, participation in overseas experiments with· Dark matter search: Ton-scale detectors which non-European dominance, and R&D. The committee
probe a large part of the parameter space of Minimal found that the plans fitted into a scheme where theSupersymmetric Models (i.e. reach a sensitivity range funding for investment had to increase by 70% (orextra 350 M€) over the traditional funding (500 M€)
of 10-44 cm for the spin-independent cross section)
integrated over the next 7 years. The estimated increasein the sum for personnel costs was much smaller.
· Neutrino-less double beta decay: A ton-scaledetector for the determination of the fundamental
nature and mass of neutrinos with the goal to test
inverted hierarchy scenarios.
· Proton decay and low-energy neutrino
astrophysics: A Megaton-scale detector for the searchfor proton decay, for neutrino astrophysics and for theinvestigation of neutrino properties· Gravitational waves: A third-generation undergroundgravitational antenna (E.T.)

50
A.3
From 2008 to 2011
We were – and continue to be! – convinced that theprospects of astroparticle physics merit a factor of
2 increase in budgets over the next decade. On theother hand we are aware that funding realities in mostcountries have become more challenging. An aggressive“factor-2 pressure” appears presently to be beyond
realistic expectations. Instead, we propose to proceedwith the most advanced projects as fast as possible andto exploit their discovery potential. Their expectedsuccesses will then hopefully translate into additional
momentum for the remaining priority projects.
The SAC is also aware, that research priorities will
differ from country to country, depending, e.g., on
their local infrastructures, or on their traditions andhistorically grown strengths in particular fields. The
SAC ranks scientific arguments highest but at the sametime keeps in mind that there are also historical andpolitical aspects. We are careful not to define priorities
in such a way that they might limit the phase spaceof national funding agencies for substantial, positive
funding decisions, once such possibilities for a certain
project may appear on a national level.
We emphasize the strong progress at several fronts
during the last 2.5 years. To mention a few:
- Cosmic rays: The AMS detector has been launched in
May 2011. Several successors of KASCADE-Grande
have been completed in 2010 (Tunka-133, IceTop)or are being installed as low-energy extensions of the
Pierre Auger Observatory. A small but significant
anisotropy of TeV cosmic rays on large and medium
angular scales, reported earlier by the Tibet air
shower array, Super-Kamiokande and the Milagro
experiment, was confirmed by ARGO/YBJ in 2008and by IceCube in 2009. TRACER has provided
boron-to-carbon measurements up to almost 1014
eV. The Pierre Auger Collaboration firmly establishedthe high-energy depression of the flux spectrum
and obtained interesting results on the compositionat the highest energies. On the negative side, twohigh-ranked US committees did not prioritize Auger
North, therefore US funding agencies will not givefunding to the Colorado site. As a consequence, a
new proposal for a next generation observatory withconsiderably enlarged area is envisaged. This requires
3-5 years of preparation.

- Gamma rays: A huge number of new sources havebeen detected by H.E.S.S., MAGIC and VERITAS.
MAGIC-II started stereoscopic operation. The CTA
collaboration has formed and meanwhile includes
all relevant players in the world. The project made it
to the ESFRI list, and the construction of prototype
telescopes has started. Construction of the wide angle
detector HAWC in Mexico (US/Mexico) has started.
China is planning a new high altitude air shower
array (LHAASO).
- High energy neutrinos: IceCube with its low-energy
extension was completed in December 2010 andshows excellent performance. The KM3NeT
technical proposal has been finalized.
- Dark Matter: The experiments XENON100,
EDELWEISS and CDMS have improved thesensitivity of dark matter searches with a gradient
which eventually appears to be as steep as optimistic
extrapolations ten years ago suggested. Constructionof a 1ton XENON detector is under preparation.
EDELWEISS and its US counterpart CDMS haveadvanced to common publications and discuss othermeasures of convergence (common procurement
and compatibility of cryostats for exchange and/or
merging of detector elements). The DAMA/LIBRA
experiment continues data taking with a lower
threshold and confirms an annual modulation of thesignal. Hints for such a modulation area also reported
from the American CoGENT experiment.
- Neutrino-less Double Beta Decay: The first detectorof the new generation double beta experiments,
GERDA, is in its commissioning phase. CUORE-0,
the first CUORE tower, will be assembled and cooled
down in 2011.
- Low energy neutrino astronomy: BOREXINO
in the Gran Sasso Laboratory LNGS shows excellent
performance and has detected not only solar
neutrinos but also geo-neutrinos, with a much smaller
background from reactor neutrinos than KamLAND(Japan). The ICARUS detector in LNGS eventually
started full operation and proves the feasibility ofoperating large liquid argon detectors underground.
The E7 design study LAGUNA is completed and thefollow-up study LAGUNA-LBNO was positively
evaluated.
- Gravitational Waves: Advanced VIRGO and Advanced
LIGO perform as a single antenna. Their advanced phasehas been approved. The E7 Design Study ET has been
completed. There is now a worldwide effort to develop
an array of ground interferometers (Europe, US, Asia
and Australia) demonstrated by the GWIC roadmap.

51- Dark Energy: The project Supernova Legacy
Survey has published results that give currently themost precise determinations of the parameters of
the equation of state of dark energy. With the ESA
mission Euclid, Europe is now taking the lead for the
study of dark energy from space.

52
A.4

Earth-bound gamma astronomy: The Cherenkov
Telescope Array, CTA, is the clear worldwide
Compilation of detailed recommendations priority project of VHE gamma-ray astrophysics.
from the individual chapters
We recommend to design and to prototype CTA,
to select site(s), and to proceed towards start of
deployment in 2014. We strongly recommend
We summarize in the following the recommendation that the various funding agencies work together
given in sections 2-4.
to secure the required funds for the construction
and operation of CTA. The current IACTs should
Galactic Cosmic Rays: We reiterate the suggestion continue to take data until CTA has superiorof the 2007 roadmap, that efforts be directed to sensitivity and sky coverage.
achieve an overlap between present direct andair-shower detection methods in order to get a High-energy neutrino astronomy: IceCube isbetter understanding on the mass composition now providing data with unprecedented quality
and spectral hardening of cosmic rays. This goal and statistics. The European partners should be
may be pursued with large-aperture, long duration supported in order to ensure the appropriate
flight missions above the atmosphere (balloons/ scientific return. There is a strong scientific casesatellites) and by ground detectors with adequate for a neutrino detector in the Northern hemisphere,
particle identification at the highest altitudes with a substantially larger sensitivity than IceCube.
(100 TeV-PeV). The existing experiments IceTop, Resources for a Mediterranean detector should
TUNKA-133 and the low-energy Auger extensions be pooled in a single optimized design for a large(AMIGA/HEAT/AERA) should be exploited. We research infrastructure. The KM3NeT collaborationencourage the further development of MHz radio is encouraged to present a technical proposal
wave detection of air showers, e.g. at the large matching these requirements and in particularfacilities Auger (AERA) and LOFAR, as well as at take final site and design decisions that would
the South Pole and the Tunka site. There should enable start of construction in 2014.. The IceCube
be close cooperation with the particle physics and KM3NeT collaborations are encouraged tocommunity, in particular with respect to LHC strengthen cooperation, with the vision to form a
results. An array at the highest possible altitude is future Global Neutrino Observatory.
desirable to determine the chemical compositionin the energy range overlapping with balloon Ultra-high energy cosmic neutrinos: Given the recent
experiments (10 TeV – PeV). At present, the planned indirect constraints from Fermi on the cosmogenic
LHAASO experiment in China seems to come closest neutrino flux at 109-1011 GeV, it seems clear that
detectors of many tens of cubic kilometres will beto this requirement.
necessary to record more than a handful of neutrinos
Cosmic rays at highest energies: We reiterate the from GZK interactions. We encourage R&D efforts
definition of a substantially enlarged ground-based towards this goal.
observatory as the priority project of high-energy
cosmic ray physics – wherever it will be deployed. Dark matter search:
We encourage the community to work towards a) The committee strongly supports improving
a global common path for such a substantially the DAMA/LIBRA experiment in terms of a lower
enlarged observatory including the development threshold and a lower background, with the goal toof new detection technologies. We recommend that better understand the observed modulation signal.
European groups play a significant role in preparing A fully independent experiment based on the samea proposal for the next generation experiment, and or on a similar technology would be crucial toafter its approval, make a significant contribution cross-check the DAMA/LIBRA effect.
to construction and operation. We also support
European participation in JEM-EUSO with its b) The last two-three years saw a dramatic progressnovel technology. We encourage cross coordination of the liquid-xenon based technology for the direct
between these two approaches .
detection of WIMPs. The 100 kg scale has beenrealised with a low background level and the 1-ton
Space based gamma astronomy: The committee scale is currently being planned. On this basis, therecognizes the scientific importance of a mission committee recommends that DARWIN, a program
to cover the energy range of 1-30 MeV and of the to further extend the target mass of noble liquids
LOFT X-ray mission.
to several tons, is pursued and supported. The

53
choice in favour of a double-target option should
be taken after a clear experimental confirmationthat a liquid argon target is competitive with liquid
xenon in terms of rejection efficiency, backgroundand operation reliability.
c) The bolometric techniques have remainedcompetitive with the noble liquid approach in termsof sensitivity to WIMP interactions. The resultsof the EDELWEISS collaboration showed a clear
technological advancement with germanium detectors
regarding the rejection of surface beta background,which was the main limitation in the “ionisation+heat”
option. The CRESST experiment showed the powerof identifying nuclear recoils from light and heavy
nuclei using CaWO4 The committee recommends
therefore supporting the development of themulti-target approach EURECA, an apparatus
capable of housing 1 ton of bolometric sensitive
mass, and the ongoing cooperation with the CDMS
follow-up projects. This facility is complementary
to the solution provided by noble liquids, and isversatile enough to provide a multi-target approach(including low Z targets tailored to test the low-mass
WIMP region) and to possibly house other rare
event searches based on the bolometric technology.
d) The committee endorses an expansion of theexperiment SIMPLE with a lower backgroundlevel in order to further increase its sensitivity tospin-dependent interactions. This search can be donein synergy with the possibilities provided by xenon(about 50% nuclei have half integer spin) and by thebolometric approach which offers the chance to study
different odd-A target nuclei.
e) The committee recommends supporting the
R&D activities related to the directional detectionof WIMPs, in particular aiming at a substantial
background reduction, as this may become
essential to confirm the galactic dark matter originof the signal in case of a positive signal from thehigh-density target detectors.
f ) Axions: The committee supports the continuationof the corresponding programs.
Direct measurement of the neutrino mass: The
KATRIN beta spectrometer is expected to provide uniqueresults on the direct measurement of the neutrino mass
starting from 2013, testing the degenerate mass region
at the 0.2 eV level. At the moment, no other technology
seems to be really in competition. Since with KATRIN
the maximum feasible size seems to have been reached,
no larger electrostatic spectrometer is currently being
planned, but improvements with respect to resolution

and other parameters are conceivable.. On the other
hand the bolometric approach followed in MARE ismodular and can in principle be extended arbitrarily.
Therefore, we recommend the continuation of R&D
activities on the bolometric approach, regarding
both 187Re (beta decay) and 163Ho (electron capture)sources.
Neutrino-less double beta decay: The European
detectors GERDA and CUORE will explore in thenext years the degenerate region of the neutrino masspattern. CUORE will probe also part of the mass
range predicted by neutrino oscillation experiments
for the case of the inverted mass hierarchy. In case of
discovery at the degenerate mass level, there is a clear
path for “precision measurements”, with possible
evidence in three different nuclei and with the unique
opportunity provided by SuperNEMO to investigate
the leading DBD mechanism. The committee
recommends therefore a prompt realization of theSuperNEMO demonstrator. Whereas GERDA,
CUORE and SuperNEMO rely on the long-term
experience with precursors and extensively validated
techniques, NEXT is a comparatively new approach, witha steep time gradient, combining construction of a full
detector with basic R&D. The committee encourages
the collaboration to demonstrate all aspects of thetechnology and move ahead toward NEXT-100. The
community is working to improve the sensitivity withthe aim to fully cover the inverted hierarchy region,a crucial element for the determination of the neutrinomass hierarchy in synergy with the next stages of theneutrino oscillation program. The general requirement
for this task is 1 ton of isotope and a background at
the level or below 1 count/(y ton-isotope) in theregion of interest. This challenging objective canbe accomplished either by the technologies of theexperiments running or in construction (this option
would provide the advantage of a phased approach)or by new promising technologies which are currently
under study (LUCIFER, COBRA pixel detectors,
pulse shape discrimination in bolometer experiments,
argon instrumentation in GERDA, Cherenkov lightin TeO2). The committee recommends that these
options are pursued at the R&D level in view of a
final assessment of the most effective approaches
for the 1 ton scale. As the required financial
resources are substantial for ton scale experiments,
the committee endorses their realisation in theframework of worldwide collaborations. This
would allow the investigation of more than one
double beta isotope, which is essential to provide
an unambiguous signature of neutrino-less double
beta decay and to determine the effective Majorana
mass. The committee notes progress in the calculationof the nuclear matrix elements for 0νββ decay, with

54
clear signs of convergence and with a validation of the
traditional methods through a new approach. The
committee confirms therefore the importance ofcontinuing this fruitful program, which is based on
both theoretical and experimental investigations.
Extension of the Modane Underground Laboratory:
The recommended projects such as EURECA andDARWIN for dark matter and SuperNEMO for ββdecay need new available space, if possible at a deepsite. There is a unique opportunity to extend thepresent underground laboratory of Modane -LSMby taking advantage of the excavation of the safety
tunnel of the Frejus road tunnel, now started ayear ago. This new laboratory of 60,000 m3 would
be able to host recommended projects. LSM has
the greatest depth of the present undergroundlaboratories in Europe. The committee therefore
strongly recommends the timely support for thisinfrastructure. Such a laboratory - of the size of one
Gran Sasso hall with 6 times lower muon flux, in
operation by 2014 - would enhance the complementarity of the European Deep Undergroundlaboratories.
Present experiments on reactor & low energy natural
neutrinos and long baseline oscillations experiments:
The BOREXINO collaboration is to be congratulated
for measuring solar and geo-neutrinos. The committee
strongly endorses further support this scientificprogram, which is now unique in the world.
The Double Chooz Far Detector has recently started
operation and will measure electron neutrino
disappearance with provide data on θ13 vastly improved
from the original CHOOZ experiment. To achieve
full sensitivity and to be competitive with otherexperiments worldwide, it is critical that the Near
Detector be completed as soon as possible. Knowledgeof θ13 is important to define the path to the discovery of
CP violation in the leptonic sector. It will shed light on
the expected flavor composition of neutrinos emitted
by supernova core collapses. It is recommended that
the LNGS program with OPERA and ICARUS becontinued as planned in order to obtain a moresignificant evidence for tau appearance.
Towards a detector for neutrino astrophysics andproton decay search on the Megaton-scale: LAGUNA
is the European effort to develop megaton neutrino
detectors both for accelerator-based and astroparticle
neutrino measurements. The scientific goals areboth broad and ambitious. The LAGUNA site study
is almost completed, showing that there are possible
sites in Europe that could host such experiments. The
committee recommends that the study be pursued
with LAGUNA-LBNO focusing on detector designs

to lead to a better understanding of the costs ofthe various detector technology options and on theprospects for a new long baseline neutrino beam from
CERN. In addition, due to the high cost and longdevelopment time necessary to realize this program,the committee recommends that it be pursued in a
global context. In addition, it is recommended that
programs with and without a new neutrino beam
are considered, in order to preserve possible science
opportunities. Neutrino astronomy would benefit
from the measurements of nuclear cross-sections ofastrophysical interest using underground nuclear
accelerators. We recommend therefore supporting
the update of the ongoing programs with LUNA
and follow-up projects at higher energy in this field.
The interpretation of current and future long baseline
experiments depends highly on the detailed knowledgeof neutrino-nucleus interactions. Hence, the committee
encourages more dedicated theoretical work inthis field. We also encourage studies to investigate
to which extend parts of the LAGUNA program(supernova neutrinos, oscillation physics, proton
decay) can be addressed by an IceCube low-energy
extension. Several anomalies in the neutrino sector andin cosmology have triggered increased interest in sterile
neutrinos as a possible explanation. This makes newexperimental campaigns necessary, with the goal toeither falsify the anomalies or indeed discover physics
beyond the Standard Model.
Dark Energy projects: We welcome theparticipation of the European astroparticle physics
community in experiments in this field. This
community should make sure that it can participate
in the harvest of results from the presently planned
ground projects and should, on the other hand takethe unique chance for leadership in space with the
ESA-led Euclid mission.
Gravitational waves:a) The committee commends the move of theinternational gravitational wave community towards
a single worldwide network of ground interferometers which will allow better coverage and better
pointing capabilities. This also goes in the directionof increasing the community worldwide.
b) At a time of down selection of the large missionof the ESA Cosmic Vision program, the community
renews its strong support of the LISA program which
will open the scientifically challenging domain of
low frequency (10-4Hz,10-1Hz) gravitational wave
astronomy, as well as advance our knowledge offundamental physics.
c) The committee acknowledges the progress of

55
the Einstein Telescope Design Study, supports a
new proposal for coordination actions for ET, andencourages ASPERA/ApPEC to take steps for a
future inclusion of ET into the ESFRI list.
d) The committee supports an enhancement of the
R&D effort in order to accompany the developmentof the second generation network and to prepare
for the third generation (ET). For this purpose, we
propose an ASPERA call for R&D.

56
A.5
Experiment Overview
Underlined experiments have major contribution of full ASPERA members
Boldfaced experiments cost > 20M€.

The High Energy Universe:
Low & Medium
energy CR+ Gamma Rays		Ultra High-energy
CR

Data Taking

ATIC (balloon)
CREAM (balloon)
TRACER (balloon)
Pamela (space)
Tunka-133
ARGO-YBJ
Tibet ASγ
Gamma
GrapesAMS (space)

Telescope Array
Yakutsk
Pierre Auger Obs

WhippleH.E.S.S.
MAGIC
VERITASCANGAROO
ARGO-YBJAGILE (space)
Fermi (space)

Baikal NT200+
ANTARES
IceCube
ANITAConstruction

Tunka-upgrade
Tibet ASγ

TUS (space)
Auger enhancements(HEAT, AMIGA,
AERA)

Tibet ASγSCORE@Tunka
HAWC

NuMoon as part of
LOFAR*

Prototypes orplannedPEBS (balloon)
GAPS (balloon)
DbarSUSY (balloon)
CALET (space)
NUCLEON (space)
LHAASO

Tunka-RadioRASTA
Follow up to Auger
TA enhancements
JEM-EUSO (space)
LORD (space)

MACE
CTA
HiSCORE
Gamma-400 (space)
LHAASO

Baikal-GVD
KM3NeT
DeepCore+
ARIANNA
ARA* experiment with a different primary focus

Gamma Rays

High-energy
Neutrino

57

Neutrino-less Double Beta Decay:
Calorimetric
Bolometer

Calorimetric
Semiconductor

Calorimetricliquid/gas/solid

Tracking gas
TPC

Commissioning

CUORE-0Gerda-I

EXO-200---

Construction

CUORE

Gerda-II

SNO+

SuperNEMO

Majorana
demonstrator

Kamland-Zen

demonstrator

COBRA

CANDLESDCBA

PANDA-X

MOON

R&D

LUCIFER
AMoRE

NEXT
PlannedCUORE Phase-II

GerdaIII/XMASS-10t

Majorana

EXO

SuperNEMO

58
Dark Matter:
Data taking

Scintillation orionisation

BolometricLiquid Xe

Liquid Ar

DAMA/LIBRA

CDMS-IIXENON-100

WARP-140KIMS

EDELWEISSZEPLIN-III

COUPP

CRESSTXMASS-100

PICASSOROSEBUDSIMPLE
COGENTDAMICTEXONO
Construction

ANAIS

EDELWEISS-III

LUX

Super-CDMS @SoudanDarkSide
MiniCLEAN
ARDM
DEAP 3.6 ton

Advancedplanning

Texono-CDEX

R&D or Planning

LIBRA 1ton

XENON1ton
PANDA-X

EURECA

LZS-3.5ton

MAX/ArDARWIN/Xe

WARP1ton

SuperCDMS @MAX/XeDARWIN/Ar

SNOLAB

LZD

CLEAN

CINDMSXMASS-10ton
GEODM

Gaseous detectors, R&D phase: MIMAC, DRIFT, NEWAGE

59

Large underground detectors for neutrino astrophysics, proton
decay & Low energy neutrino astro- & LBL physic, proton decays:

Data taking

Water
Cherenkov

LiquidScintillator

Liquid Argon

Sandwich
Tracking

SuperKamiokande

KamLANDICARUS

OPERA

Borexino

ArgoNEUT

MINOS

LVD

T2K

BUST (Baksan)
DoubleChooz

Construction

Daya-Bay

NOVA

RENO
SNO+

R&D planned

HyperKamiokande

LENA

LBNE @ DUSELMEMPHYSIn Russia, the SAGE radiochemical experiment continues to take data.

Modular
T2K Argon
GLACIER
Argon @ DUSEL

INO

60
Gravitational Waves
Data taking/G1

Ground interferometricantennas

Pulsar timing and spaceantennas

VIRGO

IPTA

LIGO
GEO
TAMA

Construction

aLIGO

LISA Pathfinder

advVIRGOGEO-HF
LCGT
CLIO

R&D

AIGO
INDIGO

Planned

LISA

61

Dark Energy:
Supernova

Weak lensing

Baryon Acoustic Glaxy clustering
Oscillation

CofA

CTIO

SCP

COSMOS

SPT

SNLS

CFHLS

ACT

ESSENCEDLS

XCS

Completed

HST

LOFAR

RCS2

or

SDSS II

KIDS

Underway

CofA SPDEEP2

SDSS/BOSSPISCOSnfactory
CSP
KAIT
PanSTARRS1

In
Preparation

LRSC

DES

HETDEXSky Mapper

KDS

BOSS

CIX

ALPACA
ODI
Proposed

WFIRST

PanSTARRS4

Big BOSS

10 XbRayEUCLIDSuMIReNASA MEM

LSST

Constellation X

SKA

CCAT

© ASPERA - November 2011www.aspera-eu.org