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Content archived on 2024-06-18

Integrated large infrastructures for astroparticle science

Final Report Summary - ILIAS (Integrated Large Infrastructures for Astroparticle Science)

There are four major running Deep Underground Laboratories in Europe and 2 major Gravitational Waves installations. The goal of the present integrating activity was to initiate and strengthen coordination between these infrastructures for a better service to users, promote integration of communities involved, in particular for larger scale projects, develop techniques that would allow next generation investigations and facilitate, promote and organise access to Deep Underground labs to enlarged community.

The project aimed to bring together Europe's leading Astroparticle-Physics infrastructures i.e.:
- Deep-Underground Laboratories (from 1000 m to 1700 m deep): The search of such rare processes as Double-Beta Decay and Dark Matter involves the detection of very weak signals. Underground laboratories provide the conditions needed for such low-background experiments, i.e. a deep underground site to avoid cosmic radiation and the provision of the most advanced technologies to deal with all sources of background and pushing them to their lowest level.
- Gravitational-Wave observatories: There exist two types of GW detectors: resonant detectors and laser interferometers, with km-scale interferometers currently entering into operation.

Within ILIAS, a rapid increase of users was foreseen; these would benefit from dedicated experimental underground areas, ultra-low background instrumentation, cryogenic installations, computing networks and many other technical facilities. To this end, ILIAS coordinated the operations via 1 Transnational Access activity, 3 Network activities (improvement of performance, direct dark-matter detection, and double-ß decay) and 2 Joint Research activities (low-background and double-ß decay new techniques).

The network N2 - Deep Underground Science Labolatories (DUSL) was set up as a core component of ILIAS, to act as a focus for the first formal cooperation and communication between the four deep laboratories of Europe, the Boulby facility (UK), LNGS Gran Sasso (Italy), LSC Canfranc (Spain) and LSM Frejus (France). To provide a clear pivot for this new cross-laboratory interaction, N2 was assigned three work packages, with clear annual deliverables totalling over 50 items, with remit to work together on: performance improvements, possible extensions of the deep underground laboratories and scientific coordination (WP1); safety problems and accident prevention in the underground sites (WP2); and public communication (WP3).

One of the activities carried out in ILIAS was the identification and quantification of the different background components at the four European underground laboratories (LNGS, LSC, LSM and Boulby). A complete survey of previous measurements, complemented with new measurements was carried out at the different labs, and the results collected in a database which was made available to the whole community. These data would be of great importance in the design and choice of location for new experiments requiring a certain maximum level of background. In such an experiment, some aspects were crucial, such as shielding and the selection of materials of the appropriate radiopurity.

In order to help future experiments with the selection of materials, collaboration within ILIAS made possible a collection of new and old data on radioactive contamination and cosmogenic activation of materials used in different experiments, which was made available to the community as a free-access database.

The main goal of the N3 network (Direct Dark Matter Detection (DMB)) was to reach convergence in the assessment of the different detector concepts (cryogenic, liquid noble gases, conventional, potential new types) for a large-scale direct dark matter search project. Considerable progress was achieved in this respect. In particular, two main techniques were identified as priorities for future direct detection dark matter experiments, namely liquid/gas noble targets and cryogenic detectors.

The network achieved important progress on simulations, shielding strategy and material purity requirements. In particular, the main reference Monte Carlo simulation codes were extensively tested and benchmarked, with exchange of software libraries between the network participants, This led to agreement on simulation codes to be used, and recommendations for the shielding strategies. In particular, two alternative solutions (20-25 cm of lead complemented by 50-60 cm of polyethylene, or 3 m of water) were defined as the two recommended lines of shielding. Also, a list of the main radiopure materials, such as copper and acrylic, was defined, which could be used without additional shielding in the detector construction. The network also studied the constraints on the amount and nature of materials with higher concentrations of radio-isotopes.

The overall objective of the N4 network was to coordinate the European double beta decay community, enhancing thus the ability of the proponents to produce proposals for the next generation experiments, beyond the current above cited experiments. The network activities were based on three working groups dedicated to the following topics:
(i) Coordination of the double beta decay searches;
(ii) Enrichment of pure isotopes; and
(iii) Nuclear matrix elements.

The purpose of JRA2: Integrated Double Beta Decay (IDEA) was to set the bases for future underground searches for 0?ßß with a substantial improvement of the present discovery potential.

A next-generation sensitive DBD search needed three basic ingredients:
i) a large amount of candidate isotopes;
ii) a detector technology tailored to the most promising candidates;
iii) a deep knowledge and control of the background sources.

IDEA was successful under two aspects: from one side, it enabled substantial progresses in most of the technologies crucial for 0nbb; on the other hand, it contributed to the formation of a really unified 0?ßß European community, facilitating the exchange of ideas, people and technological solutions to common problems. It would not be surprising if the IDEA experience would work as an incubator for new sensitive approaches to the study of a process which was fundamental for the comprehension of the elementary constituents of matter and the structure of the Universe.

The N5: Gravitational Wave antenna (GWA) network focused the 5 years activity on three major subjects: commissioning of the current gravitational wave interferometric detectors, developing of common data analysis methodology and harmonisation of the upgrade strategies in Europe and in the world.

The joint research activity on gravitational waves (JRA3), dealt with the Study of Thermal noise REduction in Gravitational Antennas (STREGA). It brought together scientists from various European laboratories dealing with experimental topics that seemed apparently very far and uncorrelated, but that all shared the same common target: fighting thermal noise, one of the fundamental limiting causes for sensitivity of all detectors.

One of the most important achievements of this program of activities was the completion and first test of a complete 1:1 scale prototype of a cryogenic interferometer payload, i.e. the large (30 cm diameter) end mirror and the complex system of suspensions needed to isolate it from external vibrations while allowing fine positioning for optical alignment. The challenge of providing a thermal path suitable to cool the masses involved down to 5 K, while barring all mechanical paths to vibrations was successfully met.

The ENTApP (European Network of Theoretical Astroparticle Physics) activity covered the theoretical aspects of ILIAS science and thus comprised theoretical work on the neutrino-less double beta decay, on dark matter and on gravitational waves. Specialized meetings on each of these topics were held to assemble the relevant theory experts and the intersections between these different theory activities were discussed in common annual meetings.

The main focus of this working group was the detailed prediction of the gravitational wave signals from these sources. A major achievement was that for the first time reliable waveforms for merging black holes were produced by techniques of numerical relativity. Although gravitational waves were not yet detected directly, this would play an important role in extracting gravitational wave signals from the detector signals which were always noise dominated and thus required precise general knowledge of the signal searched for. Core collapse supernovae are complicated physical systems which can emit gravitational waves from the collapse, subsequent oscillations and dynamical instabilities, and even from anisotropic emission of neutrinos which provided a link to the activities on the physics and astrophysics of neutrinos of WG1. Significant progress was made by the European groups involved in ILIAS in modelling these processes. Isolated neutron stars can emit gravitational waves by free precession, small mountains on the surface of these compact stars, and accretion. For the first time, data from the gravitational wave detectors were used to derive upper limits on the deformations of isolated neutron stars. This provided valuable information on the physics of neutron stars such as the nuclear equation of state.

The aim of the Transnational access to the Deep Underground laboratories (TA-DUSL) activity within ILIAS was to coordinate the access of external users to the deep underground laboratories in the EU and to provide free-of-charge access to their scientific infrastructures, with full scientific, technical and technological support.

The projects supported within TA-DUSL were related to geophysics / seismology (survey and time variability of Rn emanation from rocks, Rn concentration in groundwater) and climatology (correlation of aerosol in the atmosphere with the level of ionising radiation). The latter has a potential impact on atmospheric physics (e.g. cloud formation, climate changes studies), and possibly public / environmental health (effect of aerosol on human beings through inhalation).