Narrow Results

Some extensions of the Standard Model provide Dark Matter candidate particles with sub-GeV mass. These Light Dark Matter particles have been considered for example in Warm Dark Matter scenarios (e.g. the keV scale sterile neutrino, axino or gravitino). Moreover, MeV scale DM candidates have been proposed in supersymmetric models and as source of the 511 keV line from the Galactic center. In this paper the possibility of direct detection of a Light Dark Matter candidate is investigated considering the inelastic scattering processes on the electron or on the nucleus targets. Some theoretical arguments are developed and related phenomenological aspects are discussed. Allowed volumes and regions for the characteristic phenomenological parameters of the considered scenarios are derived from the DAMA/NaI annual modulation data.

In this paper another class of Dark Matter candidate particles — the pseudoscalar and scalar light bosonic candidates — is discussed. Particular care is devoted to the study of the processes for their detection (which only involves electrons and photons/X-rays) in a suitable underground experimental setup. For this purpose the needed calculations are developed and various related aspects and phenomenologies are discussed. In particular, it is shown that — in addition to the WIMP cases already discussed elsewhere — there is also possibility for a bosonic candidate to account for the 6.3σ C.L. model independent evidence for the presence of a particle DM component in the galactic halo observed by DAMA/NaI. Allowed regions in these scenarios are presented also paying particular care on the cosmological interest of the bosonic candidate.

The effect pointed out by A. B. Migdal in 1940's (hereafter named Migdal effect) has so far been usually neglected in the direct searches for WIMP Dark Matter candidates. This effect consists in the ionization and the excitation of bound atomic electrons induced by the recoiling atomic nucleus. In the present paper the related theoretical arguments are developed and some consequences of the proper accounting for this effect are discussed by some examples of practical interest.

The Gran Sasso National Laboratories (LNGS) of the National Institute of Nuclear Physics (INFN) are equipped with an underground ultra-low background facility namely the SubTErranean Low Level Assay (STELLA), which is in first line dedicated to material screening for the fundamental physics experiments installed in the underground laboratories. The high level of performance of the ultra-low-level detector systems allows for detecting extremely low radioactivity levels in materials down to the $\mu \mathrm{\text{Bq}}\cdot {\mathrm{\text{kg}}}^{-1}$ level. The installations and experimental setups using ultra-low background techniques will be described shortly, and an example of material screening will be discussed.

The DAMA/NaI experiment (≃100 kg highly radiopure NaI(Tl)) was proposed, designed and realized to effectively investigate in a model-independent way the presence of a Dark Matter particle component in the galactic halo by exploiting the annual modulation signature. With a total exposure of 107731 kg · day, collected over seven annual cycles deep underground at the Gran Sasso National Laboratory of the I.N.F.N., it has pointed out — at 6.3σC.L. — an effect which satisfies all the peculiarities of the signature and neither systematic effects nor side reactions able to mimic the signature were found. Moreover, several (but still few with respect to the possibilities) corollary model dependent quests for the candidate particle have been carried out. In this paper the obtained results are summarized and some perspectives are discussed at some extent.

The DAMA project is an observatory for rare processes operating deep underground at the Gran Sasso National Laboratory of the I.N.F.N. In particular, the main apparatus DAMA/LIBRA is mainly dedicated to the investigation of the presence of Dark Matter (DM) particles in the galactic halo by exploiting the model independent DM annual modulation signature. The present DAMA/LIBRA and the former DAMA/NaI (exposed masses: ≃ 250 kg and ≃ 100 kg of highly radiopure NaI(Tl), respectively) experiments have released so far a total exposure of 1.17 ton × yr, collected over 13 annual cycles. They have obtained a positive model independent result for the presence of DM particles in the galactic halo at 8.9σ C.L. Some of the obtained results are shortly summarized and future perspectives mentioned.

The exceptional sensitivity and high resolution of high purity germanium detectors in gamma-ray spectrometry and their use in underground laboratories has increasing application because of the important science and technology that they allow to be studied. In fundamental physics their application is focussed on rare phenomena, e.g. double beta decay, rare nuclear decays and Dark Matter search. In the past years there has been a growing number of underground measurements also in other fields such as environmental monitoring, surveillance of nuclear activities, benchmarking of other physical techniques, Life Science and material selection for equipment which require materials with extremely low levels of radioactivity. This report describes the state of the art in underground gamma-ray spectrometry with high purity germanium detectors. Various applications in underground laboratories are presented.

The DAMA/NaI experiment (≃ 100 kg highly radiopure NaI(Tl)) at the Gran Sasso National Laboratory of the I.N.F.N. has pointed out - by a model independent approach - the presence of Dark Matter particles in the galactic halo at 6.3 σ C.L. with an exposure larger than 10⁵kg × day collected over seven annual cycles. Several corollary model dependent quests for the candidate particle have also been carried out; others (of the many possible) are in progress. At present the second generation DAMA/LIBRA set-up (≃ 250 kg highly radiopure NaI(Tl)) is in data taking deep underground. A 3-rd generation R&D towards a possible 1 ton set-up, we proposed in 1996, is also in progress. Many searches for other rare processes have been and are under investigation as well.

The liquid Xenon set-up of the DAMA project (DAMA/LXe) is a low background experiment located deep underground at LNGS. It is in operation since time and has been uograded several times. It can be filled with Kr-free Xenon enriched either in ¹²⁹Xe at 99.5% or in ¹³⁶Xe at 68.8%. This set-up has already given several competitive results investigating various kinds of rare processes. In this paper we shortly remind the main recent results on Dark Matter, double beta decay, charge non-conserving processes, nucleon, di-nucleon and tri-nucleon decay.

The DAMA/NaI experiment (≃ 100 kg highly radiopure NaI(Tl)) at the Gran Sasso National Laboratory of the I.N.F.N, uniquely investigated the presence of Dark Matter particles in the galactic halo. An exposure of more than 10⁵kg × day, collected over seven annual cycles, has pointed out at 6.3 σ C.L. an effect which satisfies all the peculiarities of the model independent annual modulation signature. Several corollary model dependent quests for the candidate particle have also been carried out; others (of the many possible) are in progress. The second generation DAMA/LIBRA set-up (≃ 250 kg highly radiopure NaI(Tl)) is in data taking deep underground.

Arguments on the investigation of the Dark Matter particles in the galactic halo are addressed. Recent results obtained by the DAMA/LIBRA set-up – exploiting the model independent annual modulation signature for Dark Matter (DM) particles – are shortly summarized. In fact, the DAMA project is an observatory for rare processes and it is operative deep underground at the Gran Sasso National Laboratory of the I.N.F.N. Its main apparatus is at present the DAMA/LIBRA set-up, consisting of ≃ 250 kg highly radiopure NaI(Tl) detectors. Its first results confirm those obtained by the former DAMA/NaI, supporting the evidence for Dark Matter presence in the galactic halo at 8.2 σ C.L.; in addition, the cumulative data satisfy all the many peculiarities of the DM annual modulation signature. Future perspectives are also addressed.

With the present technology the only reliable signature able to point out, in a model independent way, the presence of Dark Matter (DM) particles in the galactic halo and sensitive to wide ranges both of DM candidates and of interaction types, is the DM annual modulation signature. This investigation is explored with suitable features by DAMA experiments. In particular, the first DAMA/LIBRA results confirm the evidence for the presence of DM particles in the galactic halo, as pointed out by the former DAMA/NaI set-up; cumulatively the data support such evidence at 8.2 σ C.L. and satisfy all the many peculiarities of the DM annual modulation signature. No systematics or side reactions able to account for the measured modulation amplitude and to contemporaneously satisfy all the requirements of the signature have been found or suggested by anyone over more than a decade. Moreover, no other experiment exists, whose result can be directly compared in a model-independent way with those of the DAMA experiments. Future perspectives are briefly addressed.

EDELWEISS-2 is a Ge-bolometer experiment searching for WIMP dark matter and located in the underground laboratory, Laboratoire Souterrain de Modane (LSM, France). The collaboration uses new cryogenic detectors with an improved background rejection (interleaved electrode design and continues further developments. An operation of ten 400-g bolometers at LSM together with an active muon veto shielding has been achieved. Results based on a total effective exposure of 384 kgd obtained in 2009/2010 have been published recently. A cross-section for spin-independent scattering of WIMPs on the nucleon of 4.4·10⁻⁸ pb is excluded at 90%CL for a WIMP mass of 85 GeV. This bolometer data and the latest measurements with 800-g detectors are presented. Further plans of the collaboration to reach sensitivity of 5 · 10⁻⁹pb and for a next generation experiment, EURECA, are discussed.

Recently enlarged, the Canfranc Underground laboratory hosts a multidisciplinary scientific program, with a focus on rare event physics. Up to now, seven experiments have been approved and are being installed at the new facilities. We present the main research activity that our group is developing in the underground facilities: ANAIS, an experiment that will look for dark matter annual modulation with 250 kg of NaI(Tl) scintillators.