The Identification of Dark Matter

Preface.

CONTENTS.

Observational cosmology experienced a dramatic paradigm shift about six years ago. The measurements of magnitude vs redshift of very distant type Ia supernovae indicated that the expansion rate of the universe is increasing. The acceleration of the universe requires the existence of a ‘dark energy’ component that overcomes the gravitational self-attraction of matter, such as the vacuum energy density associated with the cosmological constant (Λ). Understanding the nature of dark energy, weather constant or dynamical, is among the most fundamental questions in contemporary science. Some of the most critical systematic effects involved in the use of Type Ia supernovae as distance indicators are discussed.

A supersymmetric hybrid potential model with low energy supersymmetry breaking scale (M_S ~ 1 − 10Tev) is presented for both dark matter and dark energy. Cold dark matter is associated with a light modulus field (~ 10 − 100Mev) undergoing coherent oscillations around a saddle point false vacuum with the presently observed energy density (ρ₀ ~ 10⁻¹²eV⁴). The latter is generated by its coupling to a light dark energy scalar field (~ 10⁻¹⁸eV) which is trapped at the origin (“locked quintessence”). Through naturally attained initial conditions the model is consistent with cosmic coincidence reproducing LCDM cosmology. An exit from the cosmic acceleration phase is estimated to occur within some eight Hubble times.

Until the advent of XMM-Newton, the cluster soft excess (CSE) was the subject of some controversy due to both data analysis issues and uncertainties with the soft excess emission mechanism. XMM-Newton observations have finally laid to rest any doubts as to the existence of the CSE and have also given tantalising clues as to the nature of its emission mechanism. Here we report on the analysis of XMM-Newton observations of a number of CSE clusters in an attempt to improve the analysis and understanding of the CSE. Included as part of the study is an analysis of the effects of background subtraction, which calls to question the integrity of the claimed O VII line discovery, though not the soft excess itself. We also give details of both thermal and non-thermal fits to the CSE cluster Abell 3112.

We present the first results of the Ω project, a large XMM program devoted to observe distant SHARC clusters. For the first time a measurement of the L – T evolution with XMM has been obtained. We found clear evidence for a positive evolution of the L – T relation, in agreement with previous analysis based on ASCA and Chandra observations. Its cosmological implication is also discussed based on a new analysis of the modeling of different X-ray surveys : EMSS, RDCS, MACS, SHARC, 160 deg². It is found that a high matter density model fits remarkably well all these surveys while concordance models produce far more faint clusters than observed counts, independently of the local amplitude σ₈, provide that the local abundance of clusters is actually matched, in agreement with independent previous analyzes following the same strategy. This apparent severe failure of the concordance model could be the indication of a deviation from the expected scaling of the M – T relation with redshift. However, no signature of such possibility is found in existing data. We conclude that a self consistent represen- tation of clusters abundance evolution can be obtained only in an Einstein-de Sitter universe.

Dark energy might have an influence on the formation of non–linear structures during the cosmic history. For example, in models in which dark energy couples to dark matter, it will be non–homogeneous and might have some influence on the collapse of a dark matter overdensity. We use the spherical collapse model to estimate how much influence dark energy might have.

We consider classical and quantum dynamics of a free particle in de Sitter's space-times with different topologies to see what happens to space-time singularities of removable type in quantum theory. Our results indicate that taking account of global properties of space-time enables quantization of particle dynamics in all considered cases. We expect that understanding of the nature of curvature singularities may bring some new ideas concerning the nature of the dark energy.

A non geometric cosmology is presented, based on logic of observability, where logical categories of our perception set frontiers to comprehensibility. The Big-Bang singularity finds here a substitute (comparable to a “quantum jump”): a logical process (tied to self-referent and divisible totality) by which information emerges, focalizes on events and recycles, providing a transition from incoherence to causal coherence. This jump manufactures causal order and space-time localization, as exact solutions to Einstein’s equation, where the last step of the process disentangles complex Riemann spheres into real null-cones (a geometric overturning imposed by self-reference, reminding us of our ability to project the cosmos within our mental sphere). Concepts such as antimatter and dark energy (dual entities tied to bifurcations or broken symmetries, and their compensation), are presented as hidden in the virtual potentialities, while irreversible time appears with the recycling of information and related flow. Logical bifurcations (such as the “part-totality” category, a quantum of information which owes its recycling to non localizable logical separations, as anticipated by unstability or horizon dependence of the quantum vacuum) induce broken symmetries, at the (complex or real) geometric level [eg. the antiselfdual complex non linear graviton solutions, which break duality symmetry, provide a model for (hidden) anti-matter, itself compensated with dark-energy, and providing, with space-time localization, the radiative gravitational energy (Bondi flux and related bifurcations of the peeling off type), as well as mass of isolated bodies]. These bifurcations are compensated by inertial effects (non geometric precursors of the Coriolis forces) able to explain (on logical grounds) the cosmic expansion (a repulsion?) and critical equilibrium of the cosmic tissue. Space-time environment, itself, emerges through the jump, as a censor to totality, a screen to incoherence (as anticipated by black-hole event horizons, cosmic censors able to shelter causal geometry). In analogy with black-hole singularities, the Big-Bang can be viewed as a geometric hint that a transition from incoherence to (causal space-time) localization and related coherence (comprehensibility), is taking place (space-time demolition, a reverse process towards incoherence or information recycling, is expected in the vicinity of singularities, as hinted by black-holes and related “time-machines”). A theory of the emergence of perception (and life?), in connection with observability and the function of partition (able to screen totality), is on its way [interface incoherence-coherence, sleeping and awaking states of localization, horizons of perception etc, are anticipated by black-hole event horizons, beyond which a non causal, dimensionless incoherent regime or memorization process, presents itself with the loss of localization, suggesting a unifying regime (ultimate energies?) hidden in cosmic potentialities]. The decoherence process presented here, suggests an ultimate interaction, expression of the logical relation of subsystems to totality, and to be identified to the flow of information or its recycling through cosmic jump (this is anticipated by the dissipation of distance or hierarchies on null-cones, themselves recycled with information and events). The geometric projection of this unified irreversible dynamics is expressed by unified Yang-Mills field equations (coupled to Einsteinian gravity). An ultimate form of action (“set”-volumes of information) presents itself, whose extrema can be achieved through extremal transfer of information and related partition of cells of information (thus anticipating the mitosis of living cells, possibly triggered at the non localizable level, as imposed by the logical regime of cosmic decoherence: participating subsystems ?). The matching of the objective and subjective facets of (information and) decoherences is perceived as contact with a reality.

This paper presents a brief review of the evidence for dark matter in the Universe on the scales of galaxies. In the interests of critically and objectively testing the dark matter paradigm on these scales, this evidence is weighed against that from the only other game in town, modified Newtonian dynamics. The verdict is not as clear cut as one might have hoped.

The notion that dark halos are composed of exotic elementary particles grew out of the exchange of ideas between particle theory and cosmology. Direct detection of these particles requires further input from the field of Galactic dynamics. I will explore this connection and also describe a new set of self-consistent, multi-component models for disk galaxies.

The dark matter problem will be solved only when all of the dark matter is accounted for. Although wimps may be discovered in direct detection experiments soon, we will not know what fraction of the dark matter halo they compose until we measure their local density. In this talk, I will offer a novel method to determine the mass of a wimp from direct detection experiments alone using kinematical consistency constraints. I will then describe a general method to estimate the local density of wimps using both dark matter detection and hadron collider data when it becomes available. These results were obtained in collaboration with Gordon Kane at the University of Michigan.

The late infall of cold dark matter onto an isolated galaxy, such as our own, produces discrete flows and caustics in its halo. The set of caustics includes simple fold catastrophes located on topological spheres surrounding the galaxy, and a series of caustic rings in or near the galactic plane. The caustic rings are closed tubes whose cross-section is an elliptic umbilic catastrophe. The self-similar model of galactic halo formation predicts that the caustic ring radii a_n follow the approximate law a_n ~ 1/n. In a study of 32 extended and well-measured external galactic rotation curves evidence was found for this law. Also, the locations of ten sharp rises in the rotation curve of the Milky Way fit the prediction of the self-similar model at the 3% level. Moreover, a triangular feature in the IRAS map of the Galactic plane is consistent with the imprint of a ring caustic upon the baryonic matter. These observations imply that the dark matter in our neighborhood is dominated by a single flow. Estimates of that flow's density and velocity vector are given.

We study the cosmological origin of small-scale DM clumps with mass ≲ 10³M_☉ in the hierarchical scenario with most conservative assumption of adiabatic gaussian fluctuations. The main included effect (tidal interaction) results in the formation of large core in the center of a clump and in tidal destruction of large fraction of the clumps. The mass distribution of clumps has a cutoff at M_min due to diffusion of DM particles out of a fluctuation and free streaming at later stage. M_min is a model dependent quantity. In the case the neutralino, considered as a pure bino, is a DM particle, M_min ~ 10⁻⁸M_☉. The enhancement of annihilation signal due to DM clumpiness in the Galactic halo, valid for arbitrary DM particles, is calculated. For observationally preferable value of index or primeval fluctuation spectrum n_p ≈ 1, the enhancement of an annihilation signal is described by a factor 2 – 5 depending on the density profile in a clump.

Knowledge of the distribution of dark-matter in our Galaxy plays a crucial role in the interpretation of dark-matter detection experiments. I will argue here that probably the best way of constraining the properties of the dark-matter halo is through astrophysical observations. These provide constraints on the spatial structure (density profile, shape, local density), on the velocity distribution function and on the presence of substructure (streams or lumps of dark-matter).

A panoramic survey of M31's outer regions using the Isaac Newton Telescope Wide Field Camera has revealed a substantial and surprising amount of stellar substructure in the halo of this spiral galaxy, some of which can be used to probe the dark matter distribution of the halo. In particular, a giant stellar stream is observed to extend over a radial range of some 120 kpc from the centre of M31. Combining this with radial velocity data, taken with Keck/DEIMOS, allows for numerical modelling of the orbit of the stream and directly measures, for the first time, the mass of a giant galaxy's halo out to large galactocentric radius. The dynamical mass of M31 within the volume probed by the stream is 7.5 – 15 × 10¹¹ M_☉, and a halo of mass < 5 × 10¹¹ M_☉ is ruled out at the 99% confidence level. A complimentary study of M31's satellite galaxies reveals that their distribution is extremely assymetric, and that the gross assymetry correlates strongly with the position of the Milky Way. The causes of such a distribution, and the consequences for the usage of the satellites as tracers of the dynamical mass of M31, are discussed.

In this proceeding, we review three recent results. First, we show that halos formed in simulations with gas cooling are significantly rounder than halos formed in dissipationless N-body simulations. The increase in principle axis ratios is ~ 0.2 – 0.4 in the inner halo and remains significant at large radii. Second, we discuss the CDM substructure crisis and demonstrate the sensitivity of the crisis to the spectrum of primordial density fluctuations on small scales. Third, we assess the ability of experiments like VERITAS and GLAST to detect γ-rays from neutralino dark matter annihilation in dark subhalos about the MW.

We show that collisional damping and free-streaming of cold dark matter (CDM) induce a sharp cut-off in the CDM power spectrum at about 10⁻⁶M_☉, which sets the typical scale for the first CDM haloes in the hierarchical picture of structure formation. We present a WMAP normalized primordial power spectrum, which could serve as an input for high resolution CDM simulations. The smallest inhomogeneities typically enter the non-linear regime at a redshift of about 60.

The status of the constrained minimal supersymmetric standard model (CMSSM) will be discussed in light of our current understanding of the relic density after WMAP. A global likelihood analysis of the model is performed. Also considered are models which relax and further constrain the CMSSM. Prospects for dark matter detection in colliders and cryogenic detectors will be briefly discussed.

Recent searches for supersymmetric partners of the Standard Model particles at the LEP and Tevatron colliders are presented. In all search analyses the data are found to agree well with the Standard Model background expectation and no evidence for contributions from supersymmetry is found. The data are thus used to constrain the SUSY parameter space. The focus in this report is on analyses taht are sensitive to the lightest supersymmetric particle.

When the mSUGRA framework is extended to allow complex soft terms the phases can induce large changes in the SUSY threshold correction to the b quark mass and affect the neutralino relic density predictions of the model as well as the SUSY contribution to the BR(b → sγ). We present some specific models with large SUSY phases which can accommodate the fermion electric dipole moment constraints and a neutralino relic density within the WMAP bounds. Finally, we discuss the possibility of asymptotic Yukawa unification in these kind of models.

The direct detection of neutralino dark matter in general supergravity theories with non-universal soft scalar and gaugino masses is reviewed. In particular, the neutralino-proton cross section is computed and compared with the sensitivities of dark matter detectors, taking into account the most recent experimental and astrophysical constraints, as well as those coming from charge and colour breaking minima. Gaugino and scalar non-universalities provide a large flexibility in the neutralino sector, and neutralinos close to the present detection limits are possible with a wide range of masses, from over 400 GeV to almost 10 GeV.

This article reviews the life and death of a scientific theory.

The location and of missing baryonic matter is discussed. Most baryons may lie just outside visible galaxies in the form of a cool or warm gas. Within the Milky Way, the major problem is understanding the dynamics associated with the central bar and non-circular orbits which affect the mesurements in the cusp region. Further out, dense molecular clouds may hold significant baryonic mass.

In this paper we review the evidence for dark matter in the form of compact bodies. This comes largely from the analysis of quasar light curves, where the failure to observe time dilation, the statistical symmetry of the variations, the near achromatic changes in brightness and the cusp like nature of many of the variations all point to a microlensing origin. In addition, where microlensing is observed in gravitationally lensed quasar sytems it is not clear that the variations can be accounted for by the microlensing of stars.

The high sensitivity of upcoming space-based gravitational wave detectors suggests the possibility that if halo dark matter were composed of primordial black holes (PBHs) with mass between 10¹⁶ g and 10²⁰ g, the gravitational interaction with detector test masses will lead to a detectable pulse-like signal during the fly-by. For an improved version of the Laser Interferometer Space Antenna with a reduced acceleration noise at the low-end of its frequency spectrum, we find an event rate, with signal-to-noise ratios greater than 5, of ~ a few per decade involving black holes of mass ~ 10¹⁷ g. The detection rate improves significantly for second generation space based interferometers that are currently envisioned, though these events must be distinguished from those involving perturbations due to near-Earth asteroids. While the presence of primordial black holes below a mass of ~ 10¹⁶ g is now constrained based on the radiation released during their evaporation, the gravitational wave detectors will extend the study of PBHs to a several orders of magnitude higher masses.

The Galactic Center measurements of stellar orbits and strongly variable NIR and X-ray emission from Sagittarius A* at the center of the Milky Way have provided the strongest evidence so far that the dark mass concentrations seen in many galactic nuclei are most likely super massive black holes. As proven by the Keplerian orbits of several of the high velocity stars within the central arcsecond at the position of the compact radio source SgrA* the Galactic Center harbors a ~3.5×10⁶M_☉ massive black hole. Simultaneous NIR/X-ray observations of SgrA* in 2003/2004 have revealed first insights into the emission mechanisms of both the powerful near-infrared flares and the ‘quiescent’ emission from within a few 10 - 100 Schwarzschild radii of the super-massive black hole at the center of the Milky Way. The central source shows synchronous NIR/X-ray flare variations and indications of quasi-periodicity within the NIR flares. In addition the detection of a stellar cusp give evidence for the presence of a spherical potential which is neither Keplerian nor harmonic. In such a potential orbits will precess resulting in rosetta shaped trajectories on the sky and the assumption of non-Keplerian orbits is a more physical approach. It is also the only approach through which cusp mass information can be obtained via stellar dynamics of the cusp members. First results of modeling such a system are now available as well.

The nature and the location of the lenses discovered in the microlensing surveys done so far towards the LMC remain unclear. Motivated by these questions we computed the optical depth for the different intervening populations and the number of expected events for self-lensing, using a recently drawn coherent picture of the geometrical structure and dynamics of the LMC disk. The most plausible solution is that the events observed so far are due to lenses belonging to different intervening populations: low mass stars in the LMC, in the thick disk, in the spheroid and some true MACHOs in the halo of the Milky Way and the LMC itself. We report also on recent results of microlensing searches in direction of the M31 galaxy, by using the pixel method. The present analysis still does not allow yet to draw sharp conclusions on the MACHO content of the M31 galaxy.

Microlensed double-image quasars have sent a consistent message that the baryonic dark matter consists of a dark population of free-roaming planet mass objects. This population has long been predicted to have formed at the time of recombination, 300,000 years after the Big Bang, when the primordial plasma changed to neutral atoms with an attendant large increase in viscosity of the primordial matter. Following a very brief review of the observational basis for this conclusion and some alternative explanations, we review some probable effects of this population. After the particles formed by the usual gravitational condensation - void separation process, they collapsed on a 100 million year Kelvin-Helmholz time scale, and started their inevitable cooling process. Although not yet satisfactorily modeled, this process should have caused significant evaporation of primordial gas and taken them through the condensation and freezing points of hydrogen on their way to the 2.73 K temperature of the present universe. At the 20 K freezing point they should have frozen from the outside in, creating tremendous crushing central pressures that would have easily produced the rocky cores of planets and Kuiper-Oort cloud objects mysteriously over-abundant in the present solar system. The mystery of how did the universe become re-ionized by a Pop III that should have been seen at redshifts 6 to 8, now under scrutiny from direct spectroscopic observation, is cleanly side-stepped. Probably 99% of the baryonic matter in the universe was sequestered away in the dark matter bodies and does not need to be re-ionized for the universe to have its present transparency in the far ultraviolet. And the Dark Energy mystery will evaporate when it is understood how this population reduces the transparency of the universe. It is probably not a coincidence that the “self replenishing dust” model that explains the HST supernova brightness deficits closely matches the known dependence of extinction from L_y – α clouds upon redshift. If these mysterious clouds, that should have diffused away on a short time scale, are reforming from slow evaporation of the planet-mass population, they should produce spherical lenses that refract light out of the supernova images to produce a grey reduction of the transparency of the universe.

DAMA is an observatory for rare processes based on the development and use of various kinds of radiopure scintillators; it is operative deep underground at the Gran Sasso National Laboratory of the I.N.F.N. Several low background set-ups have been realized and many rare processes have been investigated. In particular, the DAMA/NaI set-up (≃ 100 kg highly radiopure NaI(Tl)) has effectively investigated the model-independent annual modulation signature, obtaining from the data of seven annual cycles (total exposure of 107731 kg × day) a 6.3 σ C.L. model-independent evidence for the presence of a Dark Matter particle component in the galactic halo. Moreover, some of the many possible corollary model-dependent quests for the candidate particle have also been investigated. At present, the second generation DAMA/LIBRA set-up (≃ 250 kg highly radiopure NaI(Tl)) is in operation deep underground.

The Cryogenic Dark Matter Search (CDMS) Collaboration reports the first results from operations at the Soudan Underground Laboratory. Six cryogenic ZIP detectors were operated to obtain, after analysis cuts, a 19.4 kg-d Ge exposure during the last few months of 2003. A blind analysis yielded no candidate WIMP (Weakly Interacting Massive Particles) interaction events, leading to 90% confidence level upper limits for spin-independent WIMP-nucleon cross section of 4×10⁻⁴³ cm² for a 60 GeV/c² WIMP assuming a standard halo model. This limit places significant bounds on SUSY parameter space. The CDMS collaboration has a second, more extensive data set from 12 detectors under analysis and 18 additional detectors nearing completion for installation into Soudan during Fall 2004. Running during 2005 is expected to yield ~1000 kg-d Ge exposure before analysis cuts.

The EDELWEISS experiment is a Direct Dark Matter Search using 320 g heat-and-ionization Ge cryogenic detectors. The final results obtained by the EDELWEISS-I stage corresponding to a total of 62 kg.day are presented. The status of EDELWEISS-II, involving in a first phase ~ 10 kg of detectors and aiming to gain two orders of magnitude in sensitivity, is also described.

We present first competitive results on WIMP dark matter using the phonon-light-detection technique. A particularly strong limit for WIMPs with coherent scattering results from selecting a region of the phonon-light plane corresponding to tungsten recoils. The observed count rate in the neutron band is compatible with the rate expected from neutron background. CRESST is presently being upgraded with a 66 channel SQUID readout system, a neutron shield and a muon veto system. This results in a significant improvement in sensitivity.

First preliminary results from the Zeplin I WIMP dark matter detector are presented. They are based on the measurements of scintillation pulse shapes in liquid xenon target with 3.2 kg fiducial mass. The detector was located in the Boulby Underground Laboratory (North Yorkshire, UK) at a depth of 2800 m w. e. The data collected dirung 91.5 days did not reveal the presence of second population of events faster than expected from gamma-induced electron recoils. Based on these results new limits were set on the spin-independent WIMP-nucleon and spin-dependent WIMP-neutron cross-sections.

The NAIAD experiment (NaI Advanced Detector) for WIMP dark matter searches at the Boulby Underground Laboratory (North Yorkshire, UK) ran from 2000 until 2003. We present the results of the analysis of 44.9 kg×years of data collected with 2 encapsulated and 4 unencapsulated NaI(Tl) crystals.

SIMPLE is an experimental search for evidence of spin-dependent dark matter, based on superheated droplet detectors using C₂ClF₅. We report preliminary results of a 0.6 kgdy exposure of five one liter devices, each containing ~10 g active mass, in the 1500 mwe LSBB (Rustrel, France). In combination with improvements in detector sensitivity, the results exclude a WIMP–proton interaction above 5 pb at M_χ = 50 GeV/c².

The Korea Invisible Mass Search(KIMS) collaboration has developed low background CsI(Tℓ) detectors and constructed a new experimental hall in the 700 m deep underground facility in Yangyang, Korea. Successful reduction of the internal background of CsI(Tℓ) crystal has been realized. We constructed a new shield composed of 60 tons of pure materials and the muon detector with full coverage of solid angle. In this letter, the preliminary results of WIMP search using CsI(Tℓ) crystal detector and the construction of new underground laboratory will be presented.

The DRIFT experiment is the first directionally sensitive dark matter search. The design is based on a gaseous time projection chamber and employs carbon disulphide gas at low pressure. DRIFT-I was installed in the underground laboratory at Boulby mine in 2001 and has acquired more than 1500 hours of data. The second generation detector, DRIFT-II, is undergoing initial testing and will be installed in the new experimental hall at Boulby early in 2005.

The XMASS project utilizes ultrapure liquid xenon and aims to detect pp and ⁷Be solar neutrinos by means of ν + e scattering. It requires low background and a low threshold which will also enable us to search for dark matter in the galactic halo. By using a prototype detector, we have confirmed its feasibility to realize low background and low threshold. We have estimated the sensitivity of an 800 kg liquid xenon detector for a dark matter search experiment based on the experimental results.

We describe the ZEPLIN II (30-kg) and ZEPLIN III (7-kg) discriminating dark matter detector using two-phase xenon designed for direct detection of cold dark matter in the form of Weakly Interacting Massive Particles. These two detectors are currently being commissioned. Both detector will begin operation in the Boulby Mine, UK in 2005. ZEPLIN II & III are capable of discriminating between nuclear recoils and background events and have a design reach up to two orders of magnitude beyond current limits. These two detectors will also serve as a step in the development program for a next-generation ton-scale detector.

The XENON experiment aims at the direct detection of dark matter in the form of WIMPs (Weakly Interacting Massive Particles) via their elastic scattering off Xenon nuclei. With a fiducial mass of 1000 kg of liquid xenon, a sufficiently low threshold of 16 keV recoil energy and an un-rejected background rate of 10 events per year, XENON would be sensitive to a WIMP-nucleon interaction cross section of ~ 10⁻⁴⁶cm², for WIMPs with masses above 50 GeV. A 1 tonne scale experiment (XENON1T) would be realized with an array of ten identical 100 kg detector modules (XENON100). The detectors are time projection chambers operated in dual (liquid/gas) phase, to detect simultaneously the ionization, through secondary scintillation in the gas, and primary scintillation in the liquid produced by low energy recoils. The distinct ratio of primary to secondary scintillation for nuclear recoils from WIMPs (or neutrons), and for electron recoils from background, is key to the event-by-event discrimination capability of XENON. A 3kg dual phase detector with light readout provided by an array of 7 photomultipliers is currently being tested, along with other prototypes dedicated to various measurements relevant to the XENON program. We present some of the results obtained to-date and briefly discuss the next step in the phased approach to the XENON experiment, i.e. the development and underground deployment of a 10 kg detector (XENON10) during 2005.

Some engineering issues relevant to tonne scale liquid xenon based detectors for weakly interacting dark matter particles (WIMPs) are discussed. The vessel design chosen for this study is a pure copper vessel containing 250 kg of liquid and vapour phase xenon at a maximum pressure of 4 atmospheres. Finite element modelling tools are used to calculate the mass and dimensions of the vessel. The physical size of a passive, room temperature gas dump for such a detector is estimated.

The status and prospects of the ANAIS experiment (Annual Modulation with NaI's) at the Canfranc Underground Laboratory are presented. After a prototype stage with a single NaI crystal (10.7 kg), which resulted in an average of 1.2 counts/(keV kg day) in the 4-10 keV range after an exposure of 2069.85 kg day, the whole experiment has been designed to accommodate up to 10 crystals (more than 100 kg of NaI). Several R&D works are in progress to reduce both energy threshold and background and are presented here.

Current spin-dependent WIMP searches are analyzed within the model-independent framework of Tovey et al., which itself is extended to the case of positive signal experiments. The results indicate the need of combining experiments with different neutron–to–proton group spin ratios in order to obtain, for a given WIMP mass, reduced allowed areas in the spin-dependent WIMP–proton, WIMP–neutron cross section plane. In the sample survey presented here, and in the case of null signal experiments, these derive from NAIAD and ZEPLIN I, yielding, for a WIMP mass of 50 GeV, σ_n ≤ 0.18, σ_p ≤ 0.7 pb; confirmation of the DAMA/NaI results would imply σ_n ≤ 0.17, 0.01 ≤ σ_p ≤ 0.29 pb.

Weakly Interacting Massive Particle (WIMP) direct detection strategies and data analyses are often based on the simplifying assumption of a standard spherical, isotropic halo model, but observations and numerical simulations indicate that galaxy halos are in fact triaxial and anisotropic and contain substructure. The annual modulation of the event rate (due to the motion of the Earth) provides a potential WIMP ‘smoking gun’, however this signal depends sensitively on the local WIMP velocity distribution. I briefly review observations and numerical simulations of the stucture of dark matter halos and the construction of halo models. I then discuss the effect of two specific models (with parameters chosen to reproduce the properties of observed and simulated halos) on exclusions limits and the annual modulation signal. Exclusion limits undergo a relatively small (halo model and experiment dependent) change of shape. The phase and amplitude of the annual modulation signal can change significantly, however. Finally I discuss the possibility that the dark matter distribution is not completely smooth on the very small (sub-mpc) scales probed by WIMP direct detection.

Since the expected rates for neutralino-nucleus scattering are expected to be small, one should exploit all the characteristic signatures of this reaction. Such are: (i) In the standard recoil measurements the modulation of the event rate due to the Earth's motion. (ii) In directional recoil experiments the correlation of the event rate with the sun's motion. One now has both modulation, which is much larger and depends not only on time, but on the direction of observation as well, and a large forward-backward asymmetry. (iii) In non recoil experiments gamma rays following the decay of excited states populated during the Nucleus-LSP collision. Branching ratios of about 6 percent are possible.

We examine whether the annual modulation found by the DAMA dark matter experiment can be explained by WIMPs with spin-dependent couplings, in light of null results from several other direct and indirect detection experiments. We find that, for WIMP masses above 18 GeV and below 5 GeV, no region of this spin-dependent parameter space is compatible with DAMA and all other experiments. For masses in the range (5-18) GeV, we find acceptable regions of parameter space, including ones in which the WIMP-neutron coupling is comparable to the WIMP-proton coupling.

We address the direct detection of neutralino dark matter in the framework of the Next-to-Minimal Supersymmetric Standard Model. We conduct a detailed analysis of the parameter space, taking into account all the available constraints from LEPII, and compute the neutralino-nucleon cross section. We find that sizable values for the detection cross section, within the reach of dark matter detectors, are attainable in this framework, and are associated with the exchange of very light Higgses, , the latter exhibiting a significant singlet composition.

The direction dependence of the event rate in WIMP direct detection experiments provides a powerful tool for distinguishing WIMP events from potential backgrounds. We consider a variety of non-parametric statistical tests to examine the number of events required to distinguish a WIMP signal from an isotropic background, taking into account uncertainties in the reconstruction of the nuclear recoil direction and different models for the Milky Way halo.

We calculate the flow's velocity and density on Earth for a cold flow of dark matter. The main sources of the modulation, including the Sun's and the Earth's gravity, the orbital and rotational motions of the Earth are analyzed. The expected signal modulation in axion and (non-directional) WIMP detectors is derived, and the DAMA result is discussed.

The mass number dependence of the WIMP–nucleus scattering offers a method for identifying a true WIMP signal over a neutron background. In this paper we present a study on using a combination of ZnWO₄ and CaWO₄ absorbers to exploit this materials signature for WIMP detection. We show that already modest exposure in the region of 5 kg years should allow the detection of WIMP interaction for cross sections smaller than current experimental sensitivities. The combination of these two tungstates could form the basis of the first multi-target detector capable of WIMP identification through materials signature.

The first four naked high purity Germanium detectors (10 kg) were installed successfully in liquid nitrogen in the GENIUS-Test-Facility (GENIUS-TF) in the GRAN SASSO Underground Laboratory on May 5, 2003. This is the first time ever that this novel technique aiming at extreme background reduction in search for rare decays is going to be tested underground. First results on the background are presented. The GENIUS-TF experiment, aims to search for the annual modulation of the Dark Matter signal using 40 kg of naked-Ge detectors in liquid nitrogen. It should be able to confirm the DAMA result within two or three years of measuring time.

HDMS (Heidelberg Dark Matter Search) is the only experiment worldwide, operating an enriched ⁷³Ge detector and is looking for spin-dependent WIMP-neutron interactions. Results for the measurement Febr. 2001 - July 2003 are presented. They improve the best existing present limits for low WIMP masses.

The WARP programme for dark matter search with a double phase argon detector is presented. In such a detector both excitation and ionization produced by an impinging particle are evaluated by the contemporary measurement of primary scintillation and secondary (proportional) light signal, this latter being produced by extracting and accelerating ionization electrons in the gas phase. The proposed technique, verified on a 2.3 liters prototype, could be used to efficiently discriminate nuclear recoils, induced by WIMP's interactions, and measure their energy spectrum. An overview of the 2.3 liters results and of the proposed 100 liters detector is shown.

The capabilities and reach of the first phase of COUPP (the Chicago Observatory for Underground Particle Physics) are described. During this first phase of the experiment a 2 kg CF₃I bubble chamber sensitive to WIMPs will be operated at the ~300 m.w.e. of the Minos-near gallery at FNAL. Prospects for larger devices are briefly discussed.

The project of a micro-TPC matrix of cells of 3He for direct detection of non-baryonic dark matter is presented. The privileged properties of 3He for this detection are highlighted. The double detection: ionization – projection of tracks is explained and its rejection evaluated. The specific capabilities of this project with respect to other experiments are mentioned and its complementarities concerning the supersymmetric phenomenology explicitly showed.

We describe our project of applying superfluid ³He as an extremely sensitive detector for the search of Dark Matter. Different prototypes of this detector have been developed and used in our Grenoble facility, demonstrating a real potential of ³He as a sensitive medium with unique properties for direct detection of non-baryonic dark matter. The new project will associate the efforts of the ultra-low temperature laboratories of Grenoble, Helsinki and Kyoto, with theoretical support from groups in Moscow and Grenoble.

NEWAGE (NEw generation WIMP search with an Advanced Gaseous tracking dEvice) is an experiment seeking for the WIMPs with a gaseous micro time projection chamber(μ-TPC). We have developed a prototype μ-TPC with an original two-dimensional imaging detector, or the μ-PIC and investigated its performance as a WIMP detector.

We have carried out the dark matter search with a 116g direction-sensitive stilbene crystal in Kamioka Observatory. With the crystal fixed to the earth, we searched the modulation of the light output. No modulation signal was found due to the small size of the detector crystal and the higher background rate yet to be eliminated. However, it demonstrated the effectiveness of the method of direction sensitive search for the dark matter with an implementation of the anisotropic organic scintillation crystal.

The performance of a scintillating sapphire bolometer has been estimated and its suitability for dark matter detection has been studied. Characterization of the detectors to be used in the ROSEBUD (Rare Objects SEarch with Bolometers UndergrounD) experiment has shown high discrimination power (electron versus nuclear recoils) down to about 10-15 keV. The light-heat anticorrelation observed in the γ events is used to improve significantly the energy resolution and the particle discrimination threshold. Prospects for future runs at the Canfranc Underground Laboratory, planned for the coming months, are also presented.

Searches for weakly interacting massive particle(WIMP) is being carried out at the underground laboratory, Yangyang, Korea. Characteristics and internal background of CsI(Tℓ) crystal have been investigated. In our extensive R&D, we developed a technique to reduce internal background in the CsI(Tℓ) crystal. With the latest CsI(Tℓ) crystal, we have achieved 6 counts/keV/kg/day level of background. Further reduction of internal background is foreseen with the CsI powder lately produced.

Scintillation in liquid rare gases, Ar and Xe is discussed in relation with WIMP detectors. Although the model is approximate, it shows good agreement with neutron scattering experiments. The RC/γ ratio in liquid Ne is also estimated. A simple way to estimate the RC/γ ratios in organic and inorganic scintillators is proposed and demonstrated for CsI(Tl) crystal.

Eleven developmental 128mm hemispherical quartz photomultipliers were cooled to liquid xenon temperatures, to determine their response (combination of photo-cathode quantum efficiency and dynode gain) as a function of temperature. The responses were measured at two wavelengths of light; 460 and 370nm. The tests were performed using light sources at varying distance from the photo-cathode, to investigate the effect of resistivity changes on tube response. Single electron noise was also studied as a function of temperature. The equipment used is described in detail and results are presented.

If the DM consists of elementary Planckian black holes, their number (and flux) should be fairly low. If, however, they carry an electric charge corresponding to their mass (up to Ze ≈ 10e), such DArk Electric Matter Objects, daemons, should interact strongly with matter. They should be slowed down somewhat when crossing celestial bodies, build up in them, and in multiple systems, in close lying orbits too (e.g., in Earth-crossing orbits). Capture, say, of a Fe nucleus by a negative daemon releases >100 MeV of energy, i.e., cause ejection of ~10 nucleons. The detector consisting of two ZnS(Ag) scintillation screens stacked one upon the other (four modules 0.25 m² each) detects at CL > 99% events with a time shift corresponding to velocities V ~ 30-5 km/s (in both down- and upward crossings). Such velocities are typical for objects trapped into helio- and geocentric orbits (with the latter crossing the Earth's surface to become finally confined to its interior). Of particular significance (> 3σ) is a group with V ≈ 10-15 km/s, which is characteristic of objects falling from near-Earth almost circular heliocentric orbits. Their flux is >10⁻⁹ cm⁻²s⁻¹ and varies with P = 0.5 year.

Hypothetical axion-like particles with a two-photon interaction would be produced in the Sun by the Primakoff process. In a laboratory magnetic field (“axion helioscope”) they would be transformed into X-rays with energies of a few keV. Using a decommissioned LHC test magnet, CAST has been running for about 6 months during 2003. The first results from the analysis of these data are presented here. No signal above background was observed, implying an upper limit to the axion-photon coupling g_aγ < 1.16 × 10⁻¹⁰ GeV⁻¹ at 95% CL for m_a ≲ 0.02 eV. This limit is comparable to the limit from stellar energy-loss arguments and considerably more restrictive than any previous experiment in this axion mass range.

Microscopic processes in the quantum vacuum, such as photon-photon scattering and the Primakoff effect, where light, neutral, scalar/pseudoscalar particles are produced from a two-photon vertex, could give rise, in the presence of an external magnetic field, to macroscopically observable optical phenomena, such as vacuum birefringence and dichroism. Such particles are candidate constituents of the Cold Dark Matter. The PVLAS collaboration is operating a high-sensitivity (~10⁻⁷ 1/√Hz) optical ellipsometer capable of detecting very small changes in the light polarisation state induced by a strong transverse magnetic field on a linearly polarised laser beam. This ellipsometer is capable of measuring vacuum birefringences and dichroisms, in an independent way, down to levels below 10⁻⁸ rad, for about one hour of data taking time. Preliminary results, involving the observation of candidate signals in vacuum, will be discussed.

The Axion Dark Matter Experiment (ADMX) at Lawrence Livermore National Laboratory has been searching for dark-matter axions using the Sikivie microwave cavity technique. Axions are light pseudoscalar particles which arise from the Peccei-Quinn solution to the Strong-CP problem. The ADMX collaboration includes LLNL, the University of Florida, the National Radio Astronomy Observatory, and the University of California at Berkeley.

Laboratori Nazionali del Gran Sasso (LNGS) is actually the largest deep underground laboratory in the world completely devoted to fundamental science. In this talk I give a review of the main characteristics of the infrascructure and of the past and ongoing scientific activities. LNGS is taking part in the EU initiative ILIAS (Integrated Large Infrastructures for Astroparticle Physics). Within ILIAS LNGS is collaborating with the other three european deep underground sites: Laboratoire Soterrain de Modane (France), Laboratorio Subterraneo de Canfranc (Spain), and Boulby Mine Underground Laboratory (UK).

The “Laboratoire Souterrain de modane”, with a rock coverage of 4800 mwe, is one of the deepest underground laboratory in the world. It is currently sheltering experiments dedicated to fundamental research in physics and low radioactivity measurements applied to many fields. In this paper, the main characteristics, activities and performances of the lab are given together with a brief history. Short, medium and long term projects are sketched. More informations can be found on dedicated web sites.

A brief history of the Canfranc Underground Laboratory is presented together with its current status. The description of a new, enlarged underground facility with a main experimental hall of 40 × 15 × 11 m³ and a total surface of about 1, 500 m² at a depth of 2,450 m.w.e. is outlined as well.

The Boulby Mine is situated near Whitby in the north-east of England. Since 1990 it has been the site of experimental underground science studies, and is currently the home of the UK Dark Matter Collaboration. The physical properties of the mine relevant to low background measurements such as infrastructure and background radiation levels will be discussed.

An International facility for Underground Science is under construction at Sudbury in Canada. The facility will expand the existing SNO experiment to allow several concurrent experiments to be carried out. All of the space will be established as a connected clean room at a depth of 2000 m (6000 MWE). Proposals for projects that would exploit this low background environment are welcome at any time.

Four sets of the IGEX-DM low energy data, obtained with different neutron-shielding conditions, have been compared to simulations to quantify the neutron populations from different sources: the flux of neutrons coming from the radioactivity of the surrounding rock, (3.82 ± 0.44) × 10⁻⁶ cm⁻²s⁻¹, the flux of muon-induced neutrons in the rock, (1.73 ± 0.22(stat)±0.69(syst))×10⁻⁹ cm⁻²s⁻¹ and the rate of neutron production by muons in the lead shielding, (4.8 ± 0.6(stat)±1.9(syst))×10⁻⁹ cm⁻³s⁻¹. It can be concluded that a suitable neutron shielding practically eliminates the main contribution (rock radioactivity neutrons) to the IGEX background at the present level of sensitivity, while the remaining neutron populations (muon-induced neutrons in the rock or in the shielding) are below the present background level thanks to the veto system. These neutron studies are extremely useful to understand the effect of neutrons in other current and future experiments at the Canfranc Underground Laboratory.

High energy neutrons, generated as a product of cosmic muon interaction in the rock or in the detector passive material, represent the most dangerous background for a large list of topics like reactor neutrino studies, the search for SN relic neutrinos, solar antineutrinos, etc. ¹ Up to now there are few measurements of the muon-produced neutron flux at large depth underground. Moreover it is difficult to reproduce the measured data with Montecarlo simulation because of the large uncertainties in the neutron production and propagation models. We present here the results of such a measurement with the LVD detector, that is well suited for the detection of neutrons produced by cosmic-ray muons, reporting the neutron flux at various distances from the muon track, for different neutron energies (E > 20 MeV) and as a function of the muon track length in scintillator.

We present results of neutron background studies based on Monte Carlo simulations for the direct dark matter search experiment CRESST II. Simulations suggest that the events measured by CRESST II without any neutron moderator are due to the neutrons induced by the local radioactivity of the rock/concrete surrounding the experimental setup. The contributions of neutrons from other origins and how they would affect CRESST are also discussed.

Neutron background is significant in limiting the sensitivity of dark matter detectors. Presented here are results of simulations performed for a time projection chamber acting as a particle dark matter detector in an underground laboratory. The investigated background includes neutrons from rock and detector components, generated via spontaneous fission and (α,n) reactions, as well as those due to cosmic-ray muons. Also examined are methods of neutron background supression.

For the development and the analysis of high sensitivity dark matter detection experiments, it is important to understand and reduce the background of neutron induced nuclear recoils. For this task, monte–carlo simulations written in GEANT4 are employed to understand the signal due to the neutron background.

The production of high energy neutrons by muons in rock and in shielding materials typically used in direct dark matter search experiments has been simulated using the GEANT4 Monte Carlo toolkit. The results obtained agree within 25 % for different selections of physics models and within a factor of 2 with FLUKA simulations. Therefore we will use it for our simulations to check the relevance of muon-induced backgrounds.

A comparison study of the Monte Carlo codes GEANT4 and FLUKA for simulating neutron production by muons penetrating deep underground has been carried out. GEANT4 was found to generate fewer neutrons at muon energies above ~100 GeV, by at most a factor of 2 in some materials, which we attribute mainly to lower neutron production in hadronic cascades. The muon-induced neutron background expected in a 250 kg liquid xenon WIMP dark matter detector was calculated with the two codes and good agreement was found for the recoil event rates.

Monte Carlo simulations of the veto performance for large-scale liquid xenon dark matter detectors are presented. A number of possible veto configurations are considered with the aim of maximizing the neutron and gamma rejection efficiency. Also discussed are the shielding requirements for reducing the external gamma background.

In underground laboratories, the identification of WIMPs is limited by the ambient neutron background flux. The measurement of this flux is essential for the thorough understanding of detector performance. This paper reviews previous low-background thermal neutron detector systems and proposes a new detector based on lithium salicylate.

For the first time the natural alpha decay of ¹⁸⁰W has been unambiguously detected in a (γ, β and neutron)-free background spectrum. This has been obtained by simultaneously measuring phonon and light signals with CRESST II cryogenic detectors. Results on the radio purity of the detectors and on the measured half-life of ¹⁸⁰W are presented.

There is compelling evidence for the existence of dark matter in the Universe. One of the favourite candidates is a Weakly Interacting Massive Particle (WIMP). We will here focus on indirect ways to search for WIMPs and compare their advantages and disadvantages. As a concrete WIMP example, we will focus on the neutralino that arises in supersymmetric extensions of the standard model.

The EGRET excess in the diffuse galactic gamma ray data above 1 GeV shows all the features expected from Dark Matter WIMP Annihilation: a)it is present and has the same spectrum in all sky directions, not just in the galactic plane. b) The intensity of the excess shows the 1/r² profile expected for a flat rotation curve outside the galactic disc with additionally an interesting substructure in the disc in the form of a doughnut shaped ring at 14 kpc from the centre of the galaxy. At this radius a ring of stars indicates the probable infall of a dwarf galaxy, which can explain the increase in DM density. From the spectral shape of the excess the WIMP mass is estimated to be between 50 and 100 GeV, while from the intensity the halo profile is reconstructed. Given the mass and intensity of the WIMPs the mass of the ring can be calculated, which is shown to explain the peculiar change of slope in the rotation curve at about 11 kpc. These signals of Dark Matter Annihilation are compatible with Supersymmetry and have a statistical significance of more than 10σ in comparison with a fit of the conventional galactic model to the EGRET data. The statistical significance combined with all features mentioned above provide an intriguing hint that the EGRET excess is indeed a signal from Dark Matter Annihilation.

The Alpha Magnetic Spectrometer (AMS-02) is a large acceptance (≈ 0.8m²sr) particle physics detector, planned to perform accurate, long duration measurements of charged cosmic rays (up to the TeV energy range) and gamma rays in space. The detector is approved by NASA to be installed on the International Space Station and is expected to take data for at least 3 years. AMS-02 is designed for superb particle identification, so that it will provide precise spectra for particles and antiparticles and all nuclear isotopes up to Fe. This will allow to constrain the propagation models of our galaxy with unprecedented precision and start to investigate new phenomena, usually not included in such models, like the presence of antimatter in our universe or the production of antimatter and gamma rays by Dark Matter Annihilation. This paper concentrates on the latter topic.

The direct detection of annihilation products in cosmic rays offers an alternative way to search for supersymmetric dark matter particles candidates. The study of the spectrum of gamma-rays, antiprotons and positrons in space has already showed some deviation from the expected signals but with weak statistical evidence. We will review the present situation and the achievable limits with the experiments GLAST and PAMELA.

We are proposing the CALET (CALorimetric Electron Telescope) instrument for the observation of high-energy gamma rays and electrons at the Exposed Facility of the Japanese Experiment Module on the International Space Station. The CALET has a capability to observe gamma rays in 20 MeV - 10 TeV and electrons (+positrons) in 1 GeV - 10 TeV with a high energy resolution of 2 % at 100 GeV, a good angular resolution of 0.06 deg at 100 GeV, and a high proton rejection power of 10⁶. The CALET has the geometrical factor of nearly 1m²sr and three-years observation is expected. The excellent energy resolution of CALET, which is much better than GLAST or air Cherenkov telescopes over 10 GeV, enables us to detect gamma-ray lines in the GeV - TeV region from WIMP dark matter annihilations. In addition, although the CALET cannot separate negative electrons and positrons, the high precise spectrum of electrons(+positrons) enables us to detect distinctive features from WIMP annihilations in the Galactic halo. Thus the CALET has a unique capability to search for WIMP dark matter by the hybrid observation of high-energy gamma rays and electrons.

The ANTARES experiment is being installed in the Mediterranean Sea near Toulon, France, at a depth of 2500 m. The prospects for Dark Matter searches from the Sun, the Earth, the Galactic Centre and the status of the project are discussed.

In this talk, we discuss the potential for the indirect detection of Kaluza-Klein dark matter using neutrino telescopes and cosmic positron experiments. We find that future kilometer-scale neutrino telescopes, such as IceCube, as well as future experiments capable of measuring the cosmic positron spectrum, such as PAMELA and AMS-02, will be quite sensitive to this scenario. Current data from the HEAT experiment can also be explained by the presence of Kaluza-Klein dark matter in the Galactic halo.

Superheavy particles are produced at the end of inflation and could, for a likely set of parameters (e.g. mass M_X ~ 10¹³ GeV and reheating temperature T_R ~ 10⁹ GeV), constitute the main part of dark matter. If they are metastable, their decay products may dominate the ultra-high energy cosmic ray flux above ~ 8 × 10¹⁹ eV. The main signatures of this scenario, galactic anisotropy and photon dominance, should allow the Auger experiment to test this hypothesis conclusively within one year of data taking.

We give a rough estimate on the relative advantage of attempting to detect strange quark nuggets (SQN), with seismometers, on the Moon over Earth (about 50 or more times more detections).

The determination of the absolute neutrino mass scale is of fundamental importance in particle physics and cosmology. Apart from indirect methods (large scale structure formation in cosmology, time-of-flight measurements of Supernova neutrinos, searching for 0νββ decay) there is only one model-independent strategy to address the neutrino mass directly: investigating the kinematics of electrons from β decay. We present an overview of the experimental strategies as well as results from experiments investigating the kinematics of β decay. Activities to reach sub-eV sensitivity in the near future by analysing the electron energy of the ³H β decay near its endpoint are reported.

The Double-Chooz experiment goal is to search for a non-vanishing value of the θ₁₃ neutrino mixing angle. This is the last step to accomplish prior moving towards a new era of precision measurements in the lepton sector. The current best constraint on the third mixing angle comes from the CHOOZ reactor neutrino experiment sin(2θ₁₃)² < 0.2 (90% C.L., . Double-Chooz will explore the range of sin(2θ₁₃)² from 0.2 to 0.03-0.02, within three years of data taking. The improvement of the CHOOZ result requires an increase in the statistics, a reduction of the systematic error below one percent, and a careful control of the backgrounds. Therefore, Double-Chooz will use two identical detectors, one at 150 m and another at 1.05 km distance from the Chooz nuclear cores. In addition, the near detector as a “state of the art” prototype will be used to investigate the potential of neutrinos for monitoring the civil nuclear power plants. The plan is to start operation with two detectors in 2008, and to reach a sensitivity sin²(2θ₁₃) of 0.05 in 2009, and 0.03-0.02 in 2011.

A novel low-energy (a few keV) neutrino-oscillation experiment NOSTOS, combining a strong tritium source and a high pressure spherical TPC detector of 10 m in radius has been recently proposed. The neutrino oscillation of such energies occurs within the detector itself enabling a very precise measurement of the oscillation parameters, and in particular the mixing angle θ₁₃. This detector could also be sensitive to the neutrino magnetic moment and capable of accurately measure the Weinberg angle at very low energy transfer. The same apparatus filled with high pressure Xenon, would exhibit a high sensitivity as a supernova neutrino detector. Results of a first prototype in operation will be shown in this paper.

We recall how flight time effects for neutrinos can be used to determine the acceleration parameter q of cosmology and mention some other ideas suggested by the possibility of looking back to very early times via bursts of weakly interacting particles.

With neutrino oscillations now firmly established, neutrinoless double beta decay assumes great importance since it is one of the most powerful tools to set the neutrino mass absolute scale. The present status of the experimental search for this rare decay is reported and the prospects for next generation experiments are reviewed.

Nuclear double beta decay provides an extraordinarly broad potential to search for beyond-standard-model physics. The occurrence of the neutrinoless decay (0νββ) mode has fundamental consequences: first total lepton number is not conserved, and second, the neutrino is a Majorana particle. Further the effective mass measured allows to put an absolute scale of the neutrino mass spectrum. In addition, double beta experiments yield sharp restrictions also for other beyond standard model physics. These include SUSY models (R-parity breaking and conserving), leptoquarks (leptoquark-Higgs coupling), compositeness, left-right symmetric models (right-handeld W boson mass), test of special relativity and of the equivalence principle in the neutrino sector and others. First evidence for neutrinoless double beta decay was given in 2001, by the HEIDELBERG-MOSCOW experiment. The HEIDELBERG-MOSCOW experiment is the by far most sensitive 0νββ experiment since more than 10 years. It is operating 11 kg of enriched ⁷⁶Ge in the GRAN SASSO Underground Laboratory. The analysis of the data taken from 2 August 1990 - 20 May 2003, is presented here. The collected statistics is 71.7 kg y. The background achieved in the energy region of the Q value for double beta decay is 0.11 events/kg y keV. The two-neutrino accompanied half-life is determined on the basis of more than 100 000 events to be years. The confidence level for the neutrinoless signal has been improved to a 4.2 σ level. The half-life is years. The effective neutrino mass deduced is (0.2 - 0.6) eV (99.73% c.l.), with the consequence that neutrinos have degenerate masses. The sharp boundaries for other beyond SM physics, mentioned above, are comfortably competitive to corresponding results from high-energy accelerators like TEVATRON, HERA, etc.

CUORE will be an observatory for rare events consisting of a tightly packed array of TeO₂ bolometers, with a total mass of ~740 kg, operating in the underground Gran Sasso laboratory. A first step towards CUORE is CUORICINO, a running experiment with 40.7 kg of TeO₂. Present results from CUORICINO for the neutrinoless double beta decay of ¹³⁰Te will be presented here (, 〈m_ν〉 ≤ 0.26-1.4 eV at 90% C.L.). The status of CUORE preparation and its physics potential, including dark matter searches, will be shown.

Studying double beta decay is possibly the best way to determine the absolute mass scale of neutrinos. The EXO experimental program is devoted to the search of neutrinoless double beta decay in ¹³⁶Xe. A sensitivity of order 0.01 eV to the effective neutrino mass is eventually aimed for. This will be achieved by combining a large source mass and state of the art background reduction. This includes an improved event signature, by identifying the daughter ion by laser tagging. A first prototype liquid xenon TPC is being designed, and will be described.

LIST OF PARTICIPANTS.