Search

Experimental observations and theoretical arguments at Galaxy and larger scales suggested that a large fraction of the universe is composed by Dark Matter particles. This motivated the DAMA experimental efforts to investigate the presence of such particles in the galactic halo by exploiting a model-independent signature and very highly radiopure set-ups deep underground. Here, a review of the model-independent positive results, obtained by the DAMA set-ups at the Gran Sasso National Laboratory of the INFN, and some of the implications will be given.

A search for the β+β+, β+/EC, and EC/EC decays of 106Cd was performed at the Modane Underground Laboratory (France) located at a depth of 4800 m w.e. using a TGV-2 multidetector germanium spectrometer. A preliminary evaluation is performed of the experimental data accumulated during the measurements (12 900 h) of ∼13.6 g of 106Cd (with an enrichment of 75%) and the spectrometer background without samples and with samples of natural Cd. New limits (at a 90% confidence level) of half-lives are obtained: T 1/2 ⩾ 1.7 × 1020 yr and T 1/2 ⩾ 1.6 × 1020 yr for the 0νEC/EC resonant decay of 106Cd to the 2741 keV and 2718 keV excited states of the daughter nucleus 106Pd and T 1/2 ⩾ 4.2 × 1020 yr for the 2νEC/EC decay to the ground state of 106Pd (0+ → 0+, g.s.). The limits for other branches of the double beta decay of 106Cd with transitions to the ground and excited states of 106Pd are improved.

The double-electron capture and the electron capture with positron emission in 168Yb have been investigated for the first time at the STELLA facility of the Gran Sasso underground laboratory (Italy) measuring 371 g of highly purified ytterbium oxide placed on the end-cap of a 465 cm3 ultra-low-background high purity Germanium detector (HPGe). No gamma associated to double beta processes in 168Yb have been observed after 2074 h of data taking. This has allowed setting the half-life limits on the level of lim ⁡ T 1 / 2 ∼ 10 14 – 10 18 yr at 90% C.L. Particularly, a lower half-life limit on a possible resonant neutrinoless double-electron capture in 168Yb to the ( 2 ) − 1403.7 keV excited state of 168Er is set as T 1 / 2 ≥ 1.9 × 10 18 yr at 90% C.L. Half-life limits T 1 / 2 2 ν ( 0 ν ) ≥ 4.5 ( 4.3 ) × 10 16 yr were set on the 2 ν ( 0 ν ) 2 β − decay of 176Yb to the 2 + 84.3 keV first excited level of 176Hf.

The half-life of $^{212}$Po was measured with the highest up-to-date accuracy as $T_{1/2}=295.1(4)$ ns by using thorium-loaded liquid scintillator., Comment: 28 pages, 13 figures, 4 tables

Double-beta processes in $^{184}$Os and $^{192}$Os were searched for over 15851 h at the Gran Sasso National Laboratory (LNGS) of the I.N.F.N. by using a 118 g ultra-pure osmium sample installed on the endcap of a 112 cm$^3$ ultra-low-background broad-energy germanium detector. New limits on double-electron capture and electron capture with positron emission in $^{184}$Os were set at the level of $\lim T_{1/2} \sim 10^{16}-10^{17}$ yr. In particular the $2\nu$2K and $2\nu$KL decays of $^{184}$Os to the ground state of $^{184}$W are restricted as $T_{1/2}\geq3.0\times 10^{16}$ yr and $T_{1/2}\geq2.0\times 10^{16}$ yr, respectively. A lower limit on the half-life for the double-beta decay of $^{192}$Os to the first excited level of $^{192}$Pt was set as $\lim T_{1/2}=2.0\times 10^{20}$ yr at 90\% C.L., Comment: 22 pages, 9 figures, 2 tables

Residual radioactive contaminants of a caesium hafnium chloride (Cs$_2$HfCl$_6$) crystal scintillator have been measured in a low background setup at the Gran Sasso National Laboratory of the INFN, Italy. The total alpha activity of the detector is at the level of 7.8(3) mBq/kg. The results of direct studies of the $\alpha$ decay of naturally occurring Hf isotopes that have been performed using the "source=detector" approach are presented. In 2848 h of data taking, the $\alpha$ decay of $^{174}$Hf was observed with T$_{1/2} = (7.0\pm1.2)\times10^{16} $ y., Comment: Accepted for publication in Nuclear Physics, Section A

The first results obtained by the DAMA/LIBRA–phase2 experiment with the data collected deep underground at the Gran Sasso National Laboratory over 6 independent annual cycles (corresponding to a total exposure of 1.13 ton × yr) are presented. The DAMA/LIBRA–phase2 apparatus, about 250 kg highly radio-pure NaI(Tl), profits of a second generation high quantum efficiency photomultipliers and of new electronics; in the new configuration the software energy threshold is at 1 keV. The DAMA/LIBRA–phase2 data confirm the evidence of a signal that meets all the requirements of the model independent Dark Matter annual modulation signature, at 9.5 σ C.L. in the energy region (1-6) keV. In the energy region between 2 and 6 keV, where data are also available from DAMA/NaI and DAMA/LIBRA–phase1 the achieved C.L. for the full exposure (2.46 ton × yr) is 12.9 σ.

A Barium Tungstate single crystal (BaWO 4 ) was produced using the low thermal gradient Czochralski technique. In this paper the results concerning its light emission and radioactive contaminants are presented. The aim of this work is to investigate the possibility to realize BaWO 4 crystals with suitably features to study the double beta decay of 130 Ba and 132 Ba isotopes by the “source=detector” approach. The results show the limitations of a BaWO 4 crystal as a scintillator and give some idea on how to overcome them in order to take profit from the potentiality of this single crystal.

Precise measurement of half-life of $^{212}$Po (one of the daughter nuclides in radioactive chain of $^{232}$Th) was realized by means of liquid scintillator based on toluene doped by complex of thorium and trioctylphosphine oxide with concentration of Th $\sim0.1$ mass %. Fast photomultiplier tube and high frequency oscilloscope were used to acquire the scintillation signals waveforms. The algorithms were developed to find pairs of $^{212}$Bi beta-decays and subsequent $^{212}$Po alpha-decays, to calculate time differences between the events in the pair, and to build $^{212}$Bi beta-decay and $^{212}$Po alpha-decay energy spectra. Preliminary the $^{212}$Po half-life is $T_{1/2} = (294.8 \pm 1.9)$ ns. The experiment is in progress aiming at reduction of the statistical and systematic uncertainties., 7 pages, in Ukrainian, 7 figures

The double beta decay of 150Nd to the first excited 0+ level of 150Sm (Eexc = 740.5 keV) was investigated with the help of the ultra-low-background setup consisting of four HP Ge (high-purity germanium) detectors (≃225 cm3 volume each one) at the Gran Sasso underground laboratory of INFN (Italy). A highly purified 2.381-kg sample of neodymium oxide (Nd2O3) was used as a source of γ quanta expected in the decays. Gamma quanta with energies 334.0 keV and 406.5 keV emitted after deexcitation of the 01+ 740.5 keV excited level of 150Sm are observed in the coincidence spectra accumulated over 16375 h. The half-life relatively to the two neutrino double beta decay 150Nd → 150Sm(01+) is measured as T1/2 = [4.7+4.1-1.9(stat)±0.5(syst)]×1019 y, in agreement with results of previous experiments.

Anisotropic scintillators can offer a unique possibility to exploit the so-called directionality approach in order to investigate the presence of those Dark Matter (DM) candidates inducing nuclear recoils. In fact, their use can overcome the difficulty of detecting extremely short nuclear recoil traces. In this paper we present recent measurements performed on the anisotropic response of a ZnWO$_4$ crystal scintillator to nuclear recoils, in the framework of the ADAMO project. The anisotropic features of the ZnWO$_4$ crystal scintillators were initially measured with $\alpha$ particles; those results have been also confirmed by the additional measurements presented here. The experimental nuclear recoil data were obtained by using a neutron generator at ENEA-CASACCIA and neutron detectors to tag the scattered neutrons; in particular, the quenching factor values for nuclear recoils along different crystallographic axes have been determined for three different neutron scattering angles (i.e. nuclear recoils energies). From these measurements, the anisotropy of the light response for nuclear recoils in the ZnWO$_4$ crystal scintillator has been determined at 5.4 standard deviations., Comment: 22 pages; 12 figures. In press on Eur. Phys. J. A

The first direct search for the double electron capture ($2\epsilon$) and the electron capture with positron emission ($\epsilon\beta^+$) in $^{144}$Sm to the ground state and to the excited levels of $^{144}$Nd was realized by measuring - over 1899 h - a 342 g sample of highly purified samarium oxide (Sm$_2$O$_3$) with the ultra-low background HP-Ge $\gamma$ spectrometer GeCris (465 cm$^3$) at the STELLA facility of the Gran Sasso National Laboratory (LNGS). No effect was observed and half-life limits were estimated at the level of $T_{1/2} \sim (0.1-1.3) \times 10^{20}$ yr (90% C.L.). Moreover, for the first time half-life limits of the double beta ($2\beta^-$) decay of $^{154}$Sm to several excited levels of $^{154}$Gd have been set; they are at the level of $T_{1/2} \sim (0.06-8) \times 10^{20}$ yr (90% C.L.)., Comment: 20 pages, 7 figures and 4 tables

Several of the many proposed Dark Matter candidate particles, already investigated with lower exposure and a higher software energy threshold, are further analyzed including the first DAMA/LIBRA--phase2 data release, with an exposure of 1.13 ton $\times$ yr and a lower software energy threshold (1 keV). The cumulative exposure above 2 keV considering also DAMA/NaI and DAMA/LIBRA--phase1 results is now 2.46 ton $\times$ yr. The analysis permits to constraint the parameters' space of the considered candidates restricting their values -- with respect to previous analyses -- thanks to the increase of the exposure and to the lower energy threshold., 48 pages, 33 figures; in press on Nucl. Phys. At. Energy (2019)

The DAMA/LIBRA experiment, consisting of about 250 kg of highly radio-pure NaI(Tl) target, is running deep underground at the Gran Sasso National Laboratory (LNGS) of the I.N.F.N.; its main aim is the investigation of Dark Matter (DM) particles in the Galactic halo by means of the model independent DM annual modulation signature. In this paper we briefly summarize the results obtained in its first phase of measurements (DAMA/LIBRA–phase1) lasted for 7 annual cycles with a total exposure of 1.04 ton x year . The DAMA/LIBRA–phase1 and the former DAMA/NaI data (cumulative exposure 1.33 ton x year, corresponding to 14 annual cycles) give evidence at 9.3 σ C.L. for the presence of DM particles in the galactic halo. No systematic or side reaction able to mimic the exploited DM signature has been found or suggested by anyone over more than a decade. At fall 2010 a relevant upgrade of the experiment has been performed: all the PMTs have been replaced by new ones having higher quantum efficiency. After some optimization periods, a new phase of measurement, DAMA/LIBRA–phase2, has began in this new configuration with increased sensitivity. Some of the perspectives of the presently running DAMA/LIBRA–phase2 are mentioned.

The first DAMA/LIBRA–phase2 model-independent results (exposure: [Formula: see text], and software energy threshold at 1 keV). They further confirm — with high confidence level — the evidence already observed by DAMA/NaI and DAMA/LIBRA–phase1 on the basis of the exploited model-independent dark matter (DM) annual modulation signature. The total exposure of the three experiments above the 2 keV software energy threshold is [Formula: see text]. Here, several DM candidate particles and related scenarios are analyzed including the latest results. Thanks to the increased exposure and to the lower software energy threshold, corollary model-dependent analyses permit to significantly restrict the allowed regions for the parameters spaces of various dark matter candidates and astrophysical, particle and nuclear physics scenarios.

Experimental observations and theoretical arguments at galactic and larger scales pointed out that a large fraction of the Universe is composed of Dark Matter (DM) particles. This has motivated the pioneer DAMA experimental efforts to investigate the presence of such particles in the galactic halo, by exploiting a model independent signature and very highly radio-pure apparatus in deep underground. In this paper, after a short introductory part, the long-standing model-independent annual modulation effect measured by DAMA Collaboration, with various experimental configurations, is examined. In the energy region between 2 and 6 keV, the data from DAMA/NaI, DAMA/LIBRA-phase1 and DAMA/LIBRA-phase2 (full exposure: 2.46 ton × yr) confirm the evidence of a signal that meets all the several specific requirements of the exploited model independent DM annual modulation signature, at 12.9 σ C.L. The DAMA/LIBRA-phase2 configuration, profiting from new high quantum efficiency photomultipliers, new electronics and other improvements with respect to DAMA/LIBRA-phase1, has also allowed the confirmation of such an evidence down to a software energy threshold of 1 keV. The complexity and the uncertainties of corollary model dependent quests for the DM candidate particle(s) and related scenarios are also addressed at some extent and several of the many possibilities are examined. The efforts towards the new phase3 of the experiment are summarized, showing the strategies and the results obtained with the present developments.

The first model independent results obtained by the DAMA/LIBRA-phase2 experiment are presented. The data have been collected over 6 annual cycles corresponding to a total exposure of 1.13 ton $\times$ yr, deep underground at the Gran Sasso National Laboratory (LNGS) of the I.N.F.N. The DAMA/LIBRA-phase2 apparatus, $\simeq$ 250 kg highly radio-pure NaI(Tl), profits from a second generation high quantum efficiency photomultipliers and of new electronics with respect to DAMA/LIBRA-phase1. The improved experimental configuration has also allowed to lower the software energy threshold. New data analysis strategies are presented. The DAMA/LIBRA-phase2 data confirm the evidence of a signal that meets all the requirements of the model independent Dark Matter (DM) annual modulation signature, at 9.5 $\sigma$ C.L. in the energy region (1-6) keV. In the energy region between 2 and 6 keV, where data are also available from DAMA/NaI and DAMA/LIBRA-phase1 (exposure $1.33$ ton $\times$ yr, collected over 14 annual cycles), the achieved C.L. for the full exposure (2.46 ton $\times$ yr) is 12.9 $\sigma$; the modulation amplitude of the single-hit scintillation events is: $(0.0103 \pm 0.0008)$ cpd/kg/keV, the measured phase is $(145 \pm 5)$ days and the measured period is $(0.999 \pm 0.001)$ yr, all these values are well in agreement with those expected for DM particles. No systematics or side reaction able to mimic the exploited DM signature (i.e. to account for the whole measured modulation amplitude and to simultaneously satisfy all the requirements of the signature), has been found or suggested by anyone throughout some decades thus far., Comment: 28 pages, 17 figures, 5 tables. In press on Journal Nucl. Phys. and Atomic Energy. arXiv admin note: substantial text overlap with arXiv:1308.5109, arXiv:1002.1028, arXiv:1306.1411

An attempt to study the feasibility of a new experiment to search for double beta decay in $^{112}$Sn and $^{124}$Sn was carried out by using ultra-low background HPGe detector (244 cm$^{3}$) inside the Gran Sasso National Laboratory (LNGS) of the INFN (Italy). A small sample of natural Sn was examined for 2367.5 h. The radioactive contamination of the sample has been estimated. The data has also been considered to calculate the present sensitivity for the proposed search; half-life limits $\sim$ $10^{17} - 10^{18}$ years for $\beta^{+}$EC and EC-EC processes in $^{112}$Sn and $\sim$ $10^{18}$ years for $\beta^{-}\beta^{-}$ transition in $^{124}$Sn were measured. In the last section of the paper the enhancement of the sensitivity for a proposed experiment with larger mass to reach theoretically estimated values of half-lives is discussed., Comment: 20 pages, 11 figures, 4 tables, accepted for publication in NIMA (in press)

The DAMA project has obtained many competitive or new results in the search for various rare nuclear processes. Most of them have been obtained with the help of many different high purity crystal scintillators which have been measured in the low-background DAMA set-ups located in the Gran Sasso underground laboratory of INFN In this paper, the main results will be summarized.

A search for double electron capture ($2\varepsilon$), electron capture with positron emission ($\varepsilon\beta^+$), and double positron emission $2\beta^+$) in $^{136}$Ce and $^{138}$Ce was realized with a 465 cm$^3$ ultra-low background HP Ge $\gamma$ spectrometer over 2299 h at the Gran Sasso underground laboratory. A 627 g sample of cerium oxide deeply purified by liquid-liquid extraction method was used as a source of $\gamma$ quanta expected in double $\beta$ decay of the cerium isotopes. New improved half-life limits were set on different modes and channels of double $\beta$ decay of $^{136}$Ce and $^{138}$Ce at the level of $T_{1/2}>10^{17}-10^{18}$ yr.

Search for double $\beta$ decay of $^{136}$Ce and $^{138}$Ce was realized with 732 g of deeply purified cerium oxide sample measured over 1900 h with the help of an ultra-low background HPGe $\gamma$ detector with a volume of 465 cm$^3$ at the STELLA facility of the Gran Sasso National Laboratories of the INFN (Italy). New improved half-life limits on double beta processes in the cerium isotopes were set at the level of $\lim T_{1/2}\sim 10^{17}-10^{18}$~yr; many of them are even two orders of magnitude larger than the best previous results., Comment: 21 pages, 6 figures, 3 tables; version accepted for publication on Nucl. Phys. A

The DAMA/LIBRA experiment, running at the Gran Sasso National Laboratory of the INFN, has a sensitive mass of about 250 kg highly radiopure Nal(Tl). It is mainly devoted to the investigation of Dark Matter (DM) particles in the Galactic halo by exploiting the model independent DM annual modulation signature. The present DAMA/LIBRA experiment and the former DAMA/NaI one (the first generation experiment having an exposed mass of about 100 kg) have released so far results corresponding to a total exposure of 1.17 ton x year over 13 annual cycles. They provide a model independent evidence of the presence of DM particles in the galactic halo at 8.9 sigma C.L. After the upgrade at fall 2010 when all the PMTs have been replaced with new ones having higher quantum efficiency, the feasibility to decrease the software energy threshold has been demonstrated and the set-up is running in this new configuration, named DAMA/LIBRA-phase2. The perspectives of DAMAILIBRA-phase2 will be shortly summarized. (C) 2013 Elsevier B.V. All rights reserved.

The presence of Dark Matter (DM) particles in the galactic halo can be unambiguously pointed out in a model-independent way by exploiting the DM annual modulation signature with an apparatus of specific features placed deep underground. At present DAMA/LIBRA is running at the Gran Sasso National Laboratory of the I.N.F.N. and has presented so far the results obtained with the data collected in the first six annual cycles (exposure 0.87 ton × yr). When including the exposure of the former DAMA/NaI experiment (0.29 ton × yr), the total exposure is 1.17 ton × yr for 13 annual cycles, a value order of magnitude larger than those typically released in the field. These DAMA/LIBRA data have further confirmed the model-independent evidence of the presence of Dark Matter particles in the galactic halo on the basis of the exploited DM signature (8.9 σ C.L. for the cumulative exposure).

The radioactive contamination of ZnWO4 crystal scintillators has been measured deep underground at the Gran Sasso National Laboratory (LNGS) of the INFN in Italy with a total exposure 3197 kg x h. Monte Carlo simulation, time-amplitude and pulse-shape analyses of the data have been applied to estimate the radioactive contamination of the ZnWO4 samples. One of the ZnWO4 crystals has also been tested by ultra-low background gamma spectrometry. The radioactive contaminations of the ZnWO4 samples do not exceed 0.002 -- 0.8 mBq/kg (depending on the radionuclide), the total alpha activity is in the range: 0.2 - 2 mBq/kg. Particular radioactivity, beta active 65Zn and alpha active 180W, has been detected. The effect of the re-crystallization on the radiopurity of the ZnWO4 crystal has been studied. The radioactive contamination of samples of the ceramic details of the set-ups used in the crystals growth has been checked by low background gamma spectrometry. A project scheme on further improvement of the radiopurity level of the ZnWO4 crystal scintillators is briefly addressed., Comment: 15 pages, 8 figures, 6 tables, submitted for publication

A sample of 100MoO3 powder with molybdenum enriched in 100Mo to 99.5% and mass of 1199 g was measured for 18120 h in a low-background set-up with 4 HP Ge detectors ( ≃ 225 cm 3 volume each one) deep underground (3600 m w.e.) at the Laboratori Nazionali del Gran Sasso of the INFN (Italy). The two γ quanta of 540 keV and of 591 keV emitted in the deexcitation process after a 2 β 2 ν decay of 100Mo to the 0 1 + excited level of 100Ru ( E exc = 1131 keV ) are observed in the accumulated data both in coincidence and in the 1-dimensional sum spectrum. The measured half life is: T 1 / 2 = 6.9 − 0.8 + 1.0 ( stat. ) ± 0.7 ( syst. ) × 10 20 yr , well in agreement with positive results obtained in previous experiments. Moreover, the limit on charge non-conserving β decay of 100Mo is also set: τ CNC > 4.5 × 10 19 yr at 90% C.L.; it corresponds to the limit on CNC admixture in weak currents: ϵ ν 2 2.9 × 10 − 21 .

In this paper the performances and the potential of applications of a CeCl 3 scintillator are investigated. In particular, the light response, the energy resolution, the α / β light ratio, the α / β discrimination capability and the main radioactive contaminants have been studied. All the measured features put forward the CeCl 3 scintillator as an interesting detector medium for several possible applications in the field of Nuclear and Particle Physics and, potentially, of Medical Imaging.

Arguments on the investigation of the DarkMatter particles in the galactic halo are addressed. Recent results obtained by exploiting the annual modulation signature are summarized and the perspectives are discussed.

A small CeCl 3 crystal (6.9 g) was measured deep underground (3600 m w.e.) at the Gran Sasso National Laboratories of the INFN (Italy) with a low background HP Ge detector (244 cm 3 ) during 1280 h. The crystal is not polluted by 232 Th, 40 K, 60 Co, 137 Cs (limits were set on the activity at a level of 0.05–1 Bq/kg), but contains radioactive 138 La (0.68 Bq/kg) and, probably, is polluted by 235 U and 238 U (0.3–0.7 Bq/kg). The half life limits for different double β processes in 136 Ce and in 138 Ce were set in the range of ( 1 – 6 ) × 10 15 yr . In particular, the 2 e captures in 136 Ce to various excited levels of 136 Ba were considered for the first time. The limits for the resonant neutrinoless transitions to the 2392.1 keV and 2399.9 keV levels of 136 Ba are: T 1 / 2 > 2.4 × 10 15 yr and T 1 / 2 > 4.1 × 10 15 yr at 90% C.L., respectively.

The $\simeq$ 250 kg highly radiopure NaI(Tl) DAMA/LIBRA apparatus, running at the Gran Sasso National Laboratory (LNGS) of the I.N.F.N., is described., Comment: 37 pages, 27 figures

The search for double-β processes in 108Cd and 114Cd was realized by using data of the low-background experiment with the CdWO4 crystal scintillator at the Gran Sasso National Laboratories of the INFN. New improved half-life limits on double-beta processes were established, in particular T 1/2 0ν2ɛ( ^108Cd ) ≥ 1.0(2.7)×1018 yr, T 1/2 2ν2β( ^114Cd ) ≥ 1.3(2.1)×1018 yr, and T 1/2 0ν2β( ^114Cd ) ≥ 1.1(2.5)×1021 yr at 90(68)% C.L.

As low as possible radioactive contamination of a detector plays a crucial role to improve sensitivity of a double beta decay experiment. The radioactive contamination of a sample of $^{116}$CdWO$_4$ crystal scintillator by thorium was reduced by a factor $\approx 10$, down to the level 0.01 mBq/kg ($^{228}$Th), by exploiting the recrystallization procedure. The total alpha activity of uranium and thorium daughters was reduced by a factor $\approx 3$, down to 1.6 mBq/kg. No change in the specific activity (the total $\alpha$ activity and $^{228}$Th) was observed in a sample of ZnWO$_4$ crystal produced by recrystallization after removing $\approx 0.4$ mm surface layer of the crystal., Comment: 14 pages, 5 figures and 2 tables

Two important parts of the DAMA/LIBRA setup are the calibration system and the monitoring/alarm system. The calibration system allows to perform detector calibrations without changing the running condition of the experiment; the monitoring/alarm system allows to record several parameters to control the running status and its stability.In this paper, we will describe the two system reporting some related obtained results.

The [Formula: see text] 250 kg highly radiopure NaI(Tl) DAMA/LIBRA apparatus, presently running at the Gran Sasso National Laboratory (LNGS) of the I.N.F.N. is described.

The effect pointed out by A. B. Migdal in the 40'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., 14 pages, 6 figures, 2 tables, Int. J. Mod. Phys. A (in publication)

The DAMA/NaI experiment (≃ 100 kg highly radiopure NaI(Tl)) at the Gran Sasso National Laboratory of the I.N.F.N. had the unique feature to effectively investigate the presence of Dark Matter particle in the galactic halo by exploiting the model independent annual modulation signature. With a total exposure of more than 10 5 kg × day, collected over seven annual cycles, it has pointed out at 6.3 σ C.L. an effect which satisfies all the many peculiarities of the signature. Neither systematics nor side reactions able to account for the observed effect were found. No experiment whose result can be directly compared in a model independent way with the experimental one of DAMA/NaI is available so far. Several (but still few with respect to the possibilities) corollary model dependent quests for the candidate particle have also been carried out. At present the second generation DAMA/LIBRA set-up (≃ 250 kg highly radiopure NaI(Tl)) is in operation. Positive model dependent hints have also been pointed out by indirect searches for Dark Matter particles in space experiments and are not in contradiction with DAMA/NaI. Thus, the ongoing of model independent experiment deep underground and the new space experiments foreseen in incoming years will certainly further increase our knowledge of the field.

Some extensions of the Standard Model provide Dark Matter candidate particles which can have a dominant coupling with the lepton sector of the ordinary matter. Thus, such Dark Matter candidate particles ($\chi^{0}$) can be directly detected only through their interaction with electrons in the detectors of a suitable experiment, while they are lost by experiments based on the rejection of the electromagnetic component of the experimental counting rate. These candidates can also offer a possible source of the 511 keV photons observed from the galactic bulge. In this paper this scenario is investigated. Some theoretical arguments are developed and related phenomenological aspects are discussed. Allowed intervals and regions for the characteristic phenomenological parameters of the considered model and of the possible mediator of the interaction are also derived considering the DAMA/NaI data., Comment: 16 pages, 6 figures. Accepted for publication in PRD. One typo corrected

A search for the double beta decay of zinc and tungsten isotopes has been performed with the help of radiopure ZnWO4 crystal scintillators (0.1-0.7 kg) at the Gran Sasso National Laboratories of the INFN. The total exposure of the low background measurements is 0.529 kg yr. New improved half-life limits on the double beta decay modes of 64Zn, 70Zn, 180W, and 186W have been established at the level of 10^{18}-10^{21} yr. In particular, limits on double electron capture and electron capture with positron emission in 64Zn have been set: T_{1/2}(2\nu 2K) > 1.1 10^{19} yr, T_{1/2} (0\nu 2\epsilon) > 3.2 10^{20} yr, T_{1/2} (2\nu \epsilon \beta^+) > 9.4 10^{20} yr, and T_{1/2} (0\nu \epsilon \beta^+) > 8.5 10^{20} yr, all at 90% C.L. Resonant neutrinoless double electron capture in 180W has been restricted on the level of T_{1/2} (0\nu 2\epsilon) > 1.3 10^{18} yr. A new half-life limit on alpha transition of 183W to the metastable excited level 1/2^- 375 keV of 179Hf has been established: T_{1/2} > 6.7 10^{20} yr., Comment: This is an author-created, un-copyedited version of an article published in J. Phys. G: Nucl. Part. Phys. IOP Publishing Ltd is not responsible for any errors or omissions in this version of the manuscript or any version derived from it. The definitive publisher authenticated version is available online at doi: 10.1088/0954-3899/38/11/115107

The results obtained with the total exposure of 1.04 ton x yr collected by DAMA/LrBRA-phase1 deep underground at the Gran Sasso National Laboratory (LNGS) of the I.N.F.N. during 7 annual cycles are summarized. The DAMA/LLBRA-phase1 and the former DAMA/NaI data (cumulative exposure 1.33 ton x yr, corresponding to 14 annual cycles) give evidence at 9.3 sigma C.L. for the presence of Dark Matter (DM) particles in the galactic halo, on the basis of the exploited model independent DM annual modulation signature by using highly radio-pure NaI(T1) target. The modulation amplitude of the single-hit events in the (2-6) keV energy interval is: (0.0112 +/- 0.0012) cpd/kg/keV; the measured phase is (144 +/- 7) days and the measured period is (0.998 +/- 0.002) yr, values well in agreement with those expected for DM particles. No systematic or side reaction able to mimic the exploited DM signature has been found or suggested by anyone over more than a decade. Some of the perspectives of the presently running DAMA/LIBRA-phase2 are outlined.

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 set-up. 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 6.3 sigma 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., Comment: 23 pages, 6 figures, 1 table, Int. J. Mod. Phys. A (in press)

After a short introduction on the low background liquid xenon DAMA set-up (DAMA/LXe) and its main previous results, we discuss the search for the nucleon, di-nucleon and tri-nucleon decays into invisible channels (disappearance or decay to neutrinos, Majorons, etc.) in the 136Xe isotope. The obtained limits (90% C.L.) on the lifetimes are: τ n > 3.3 · 1023 yr, τ p > 4.5 · 1023 yr, τ np > 3.2 · 1023 yr, τ pp > 1.9 · 1024 yr, τ nnp > 1.4 · 1022 yr, τ npp > 2.7 · 1022 yr and τ ppp > 3.6 · 1022 yr. In particular, the tri-nucleon decay into invisible channels is investigated here for the first time.

The DAMA/LIBRA experiment, running at LNGS, has a sensitive mass of about 250 kg highly radiopure NaI(TI) and it is mainly devoted to the investigation of Dark Matter (DM) particles in the Galactic halo by exploiting the model independent DM annual modulation signature. The present DAMA/LIBRA experiment and the former DAMA/NaI one have released so far results corresponding to a total exposure of 1.17 ton x yr over 13 annual cycles. They provide a model independent evidence of the presence of DM particles in the galactic halo at 8.9 sigma C.L. (C) 2011 Elsevier B.V. All rights reserved.

The DAMA/LIBRA–phase1 and the former DAMA/NaI data (cumulative exposure 1.33 ton [Formula: see text] yr, corresponding to 14 annual cycles) give evidence at 9.3[Formula: see text] C.L. for the presence of Dark Matter (DM) particles in the galactic halo, on the basis of the exploited model independent DM annual modulation signature by using highly radio-pure NaI(Tl) target. Results and comparisons will be shortly recalled. Recent analyses on possible diurnal effects and on the Earth shadowing effect (the latter holds only for some DM candidates) will be mentioned. The analysis of the time distribution of the low-energy single-hit events in DAMA/LIBRA–phase1 is reported for the first time. Finally, some perspectives of the presently running DAMA/LIBRA–phase2 will be mentioned.

This paper shortly summarizes the results obtained with the total exposure of 1.04 ton × yr collected by DAMA/LIBRA-phase1 deep underground at the Gran Sasso National Laboratory (LNGS) of the I.N.F.N. during 7 annual cycles. The DAMA/LIBRA-phase1 and the former DAMA/NaI data (cumulative exposure 1.33 ton × yr, corresponding to 14 annual cycles) give evidence at 9.3 σ C.L. for the presence of Dark Matter (DM) particles in the galactic halo, on the basis of the exploited model independent DM annual modulation signature by using highly radio-pure NaI(Tl) target. The modulation amplitude of the single-hit events in the (2–6) keV energy interval is: (0.0112 ± 0.0012) cpd/kg/keV; the measured phase is (144 ± 7) days and the measured period is (0.998 ± 0.002) yr, values well in agreement with those expected for DM particles. No systematic or side reaction able to mimic the exploited DM signature has been found or suggested by anyone over more than a decade. Some of the perspectives of the presently running DAMA/LIBRA-phase2 are outlined.

A new investigation of Pp decay modes in Xe-134 and in Xe-136 is presented. The data have been collected deep underground at the Gran Sasso National Laboratory of the INFN over a period of 8823.54 hours with the similar or equal to 6.5 kg DAMA liquid xenon pure scintillator, filled by Kr-free xenon containing 17.1 % of Xe-134 and 68.8% of Xe-136. New limits are set for various decay modes. (C) 2002 Elsevier Science B.V. All rights reserved.

The coincidence technique can offer a useful way to investigate β and ββ decay processes in 48 Ca. In this paper the results of a preliminary experimental search are presented. In particular, here the first experimental limit on the half life of the ββ 2 ν (0 + –2 + ) decay of 48 Ca has been obtained; it is T 1/2 >1.2×10 18 y (90% C.L.).

The main features of the low background DAMA pure liquid xenon scintillator set-up running deep underground in the Gran Sasso National Laboratory of the INFN are described. (C) 2002 Elsevier Science B.V. All rights reserved.

New results have been obtained by investigating the neutrinoless ββ decay in 134 Xe deep underground at the Gran Sasso National Laboratory of INFN by means of the ≃6.5 kg liquid xenon setup of the DAMA experiment. New limits on the half-lives of the β − β − 0 ν (0 + →0 + ) and β − β − 0 ν (0 + →2 + ) decay modes have been obtained. They are: T 1/2 >5.8×10 22 yr (90% C.L.) and T 1/2 >2.6×10 22 yr (90% C.L.), respectively. The T 1/2 limit for β − β − 0 ν (0 + →0 + ) process is about three orders of magnitude higher than the one previously available, while the T 1/2 limit for β − β − 0 ν (0 + →2 + ) has been set for the first time.

The radioactive contamination of a BaF$_2$ scintillation crystal with mass of 1.714 kg was measured over 101 hours in the low-background DAMA/R&D set-up deep underground (3600 m w.e.) at the Gran Sasso National Laboratories of INFN (LNGS, Italy). The half-life of $^{212}$Po (present in the crystal scintillator due to contamination by radium) was measured as $T_{1/2}(^{212}$Po) = 298.8$\pm$0.8(stat.)$\pm$1.4(syst.) ns by analysis of the events' pulse profiles. The $^{222}$Rn nuclide is known as 100% decaying via emission of $\alpha$ particle with $T_{1/2}$ = 3.82 d; however, its $\beta$ decay is also energetically allowed with $Q_\beta = 24\pm21$ keV. Search for decay chains of events with specific pulse shapes characteristic for $\alpha$ or for $\beta/\gamma$ signals and with known energies and time differences allowed us to set, for the first time, the limit on the branching ratio of $^{222}$Rn relatively to $\beta$ decay as $B_\beta < 0.13$% at 90% C.L. (equivalent to limit on partial half-life $T_{1/2}^\beta > 8.0$ y). Half-life limits of $^{212}$Pb, $^{222}$Rn and $^{226}$Ra relatively to $2\beta$ decays are also improved in comparison with the earlier results., Comment: 10 pages, 9 figures, 2 tables

The radiopurity of a lithium molybdate ( Li 2 MoO 4 ) single crystal, a potential detector for the search for the neutrinoless double beta decay of 100 Mo, was studied deep underground at the Laboratori Nazionali del Gran Sasso (LNGS) (Italy). Data were collected with a crystal sample with a mass of 33.95 g, using a high purity germanium (HPGe) detector with a total measurement time of 1240.3 h. With the exception of slight pollution with 40 K ( ( 170 ± 80 ) mBq / kg ), no other radioactive contaminants were found; the derived upper limits are: 20 mBq / kg for 238 U chain, 30 mBq / kg for 232 Th chain, 4 mBq / kg for 137 Cs and 8 mBq / kg for 60 Co.