Search

A search for dark matter was conducted by looking for an annual modulation signal due to the Earth's rotation around the Sun using XMASS, a single phase liquid xenon detector. The data used for this analysis was 359.2 live days times 832 kg of exposure accumulated between November 2013 and March 2015. When we assume Weakly Interacting Massive Particle (WIMP) dark matter elastically scattering on the target nuclei, the exclusion upper limit of the WIMP–nucleon cross section 4.3×10−41 cm2 at 8 GeV/c$^{2}$ was obtained and we exclude almost all the DAMA/LIBRA allowed region in the 6 to 16 GeV/c$^{2}$ range at ∼10$^{−40}$ cm$^{2}$. The result of a simple modulation analysis, without assuming any specific dark matter model but including electron/γ events, showed a slight negative amplitude. The p-values obtained with two independent analyses are 0.014 and 0.068 for null hypothesis, respectively. We obtained 90% C.L. upper bounds that can be used to test various models. This is the first extensive annual modulation search probing this region with an exposure comparable to DAMA/LIBRA.

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 At fall 2010 a relevant upgrade of the experiment has been performed: all the PMTs have been replaced by new ones having higher quantum efficiency.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 XENON Collaboration is searching for Dark Matter interactions in a liquid xenon target. The XENON100 detector, a dual phase xenon Time Projection Chamber employing 161 kg of liquid xenon, started the first science run at the Laboratori Nazionali del Gran Sasso in Italy in 2009. It provided limits on the spin-independent and spin-dependent interaction cross sections of Weakly Interacting Massive Particles (WIMPs), and the couplings of solar axions and galactic axion-like particles. We present these results and the status of the successor experiment, XENON1T. The new detector, currently under construction and starting data taking in 2015, will employ 3.3 tons of liquid xenon, reaching a sensitivity to spin-independent WIMP-nucleon cross section of the order of 10 − 47 cm 2 .

Dark matter detectors built primarily to probe elastic scattering of WIMPs on nuclei are also precise probes of light, weakly coupled particles that may be absorbed by the detector material. In this paper, we derive constraints on the minimal model of dark matter comprised of long-lived vector states V (dark photons) in the 0.01-100 keV mass range. The absence of an ionization signal in direct detection experiments such as XENON10 and XENON100 places a very strong constraint on the dark photon mixing angle, down to $O(10^{-15})$, assuming that dark photons comprise the dominant fraction of dark matter. This sensitivity to dark photon dark matter exceeds the indirect bounds derived from stellar energy loss considerations over a significant fraction of the available mass range. We also revisit indirect constraints from $V\to 3\gamma$ decay and show that limits from modifications to the cosmological ionization history are comparable to the updated limits from the diffuse gamma-ray flux., Comment: 10 pages, 4 figures; numerical bug in J-factor corrected; main results unchanged

We report the first results of DarkSide-50, a direct search for dark matter operating in the underground Laboratori Nazionali del Gran Sasso (LNGS) and searching for the rare nuclear recoils possibly induced by weakly interacting massive particles (WIMPs). The dark matter detector is a Liquid Argon Time Projection Chamber with a (46.4+-0.7) kg active mass, operated inside a 30 t organic liquid scintillator neutron veto, which is in turn installed at the center of a 1 kt water Cherenkov veto for the residual flux of cosmic rays. We report here the null results of a dark matter search for a (1422+-67) kg d exposure with an atmospheric argon fill. This is the most sensitive dark matter search performed with an argon target, corresponding to a 90% CL upper limit on the WIMP-nucleon spin-independent cross section of 6.1x10^-44 cm^2 for a WIMP mass of 100 GeV/c^2., 26 pages, 7 figures; updated figures and references, notably Fig. 7 has updated CDMSII curve; fixed typos; clarified some language and figures; updated references

We study in detail sub-GeV dark matter scattering off electrons in xenon, including the expected electron recoil spectra and annual modulation spectra. We derive improved constraints using low-energy XENON10 and XENON100 ionization-only data. For XENON10, in addition to including electron-recoil data corresponding to about $1-3$ electrons, we include for the first time events with $\gtrsim 4$ electrons. Assuming the scattering is momentum independent, this strengthens a previous cross-section bound by almost an order of magnitude for dark matter masses above 50 MeV. The available XENON100 data corresponds to events with $\gtrsim 4$ electrons, and leads to a constraint that is comparable to the XENON10 bound above 50 MeV. We demonstrate that a search for an annual modulation signal in upcoming xenon experiments (XENON1T, XENONnT, LZ) could substantially improve the above bounds even in the presence of large backgrounds. We also emphasize that in simple benchmark models of sub-GeV dark matter, the dark matter-electron scattering rate can be as high as one event every ten (two) seconds in the XENON1T (XENONnT or LZ) experiments, without being in conflict with any other known experimental bounds. While there are several sources of backgrounds that can produce single- or few-electron events, a large event rate can be consistent with a dark matter signal and should not be simply written off as purely a detector curiosity. This fact motivates a detailed analysis of the ionization-only ("S2-only") data, taking into account the expected annual modulation spectrum of the signal rate, as well as the DM-induced electron-recoil spectra, which are another powerful discriminant between signal and background., Comment: 5 pages + 4 pages appendices/references, 10 figures

Application of NaI(Tl) detectors in the search for galactic dark matter particles through their elastic scattering off the target nuclei is well motivated because of the long standing DAMA/LIBRA highly significant positive result on annual modulation, still requiring confirmation. For such a goal, it is mandatory to reach very low threshold in energy (at or below the keV level), very low radioactive background (at a few counts/keV/kg/day), and high detection mass (at or above the 100 kg scale). One of the most relevant technical issues is the optimization of the crystal intrinsic scintillation light yield and the efficiency of the light collecting system for large mass crystals. In the frame of the ANAIS (Annual modulation with NaI Scintillators) dark matter search project large NaI(Tl) crystals from different providers coupled to two photomultiplier tubes (PMTs) have been tested at the Canfranc Underground Laboratory. In this paper we present the estimates of the NaI(Tl) scintillation light collected using full-absorption peaks at very low energy from external and internal sources emitting gammas/electrons, and single-photoelectron events populations selected by using very low energy pulses tails. Outstanding scintillation light collection at the level of 15 photoelectrons/keV can be reported for the final design and provider chosen for ANAIS detectors. Taking into account the quantum efficiency of the PMT units used, the intrinsic scintillation light yield in these NaI(Tl) crystals is above 40 photons/keV for energy depositions in the range from 3 up to 25 keV. This very high light output of ANAIS crystals allows triggering below 1 keV, which is very important in order to increase the sensitivity in the direct detection of dark matter., This work has been financially supported by the Spanish Ministerio de Economía y Competitividad and the European Regional Development Fund (MINECO-FEDER) under grants No. FPA2011-23749 and FPA2014-55986-P, the Consolider-Ingenio 2010 Programme under grants MULTIDARK CSD2009-00064 and CPAN CSD2007-00042 and the Gobierno de Aragón and the European Social Fund (Group in Nuclear and Astroparticle Physics). P. Villar was supported by the MINECO Subprograma de Formación de Personal Investigador.

SABRE (Sodium-iodide with Active Background REjection) is a new NaI(Tl) experiment designed to search for galactic Dark Matter through the annual modulation signature. SABRE will consist of highly pure NaI(Tl) crystals operated in an active liquid scintillator veto. The SABRE experiment will follow a two-phase approach. In the first phase, one high-purity NaI(Tl) crystal will be operated at LNGS in an active liquid scintillator veto with the goal of demonstrating backgrounds low enough for a sensitive test of the DAMA/LIBRA result. An unprecedented radio-purity for both the NaI powder and the crystal growth will be needed to achieve this goal. The second phase will consist in building two high-purity NaI(Tl) detector arrays, with a total mass of about 50 kg each, located at LNGS and in the Stawell Gold Mine in Australia. The operation of twin full-scale experiments in both the northern and the southern hemispheres will strengthen the reliability of the result against any possible seasonal systematic effect.

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.

Experimental efforts and theoretical developments support that most of the Universe is dark and a large fraction of it should be made of relic particles; many possibilities are open on their nature and interaction types. This motivates experimental efforts to investigate the direct detection of these particles with various techniques. In particular, experiments offering a model independent signature for the presence of Dark Matter (DM) particles in the Galactic halo are mandatory. In this paper some general arguments will be summarized and particular care will be given to the results obtained by the DAMA/LIBRA experiment (sensitive mass: ∼250 kg) at the Gran Sasso National Laboratory of the I.N.F.N. by exploiting the model independent DM annual modulation signature with higly radiopure NaI(Tl) target-detectors. Cumulatively with the former DAMA/NaI (sensitive mass: ∼100 kg) an exposure of 1.17 ton yr, collected over 13 annual cycles, has been released so far; a model independent evidence of the presence of DM particles in the galactic halo is supported at 8.9 ρ confidence level (C.L.). In addition, experimental and theoretical uncertainties and their implications in the interpretation and comparison of different kinds of results will be shortly addressed. Some perspectives will be mentioned.

The CTA will mean a significant increase of the potential for dark matter detection, compared to present-day detectors like MAGIC, HESS and VERITAS. In particular, if – as it might be indicated from early LHC results – the dark matter sector is heavy, perhaps in the TeV mass range, imaging air Cherenkov arrays have a good opportunity to detect γ -rays from dark matter annihilation in the galactic halo, the galactic center, dwarf galaxies, or galaxy clusters. A review of the present situation is given and a few of the “miracles” that may enhance chances for detection in CTA are discussed, such as Sommerfeld enhancement and internal bremsstrahlung radiation. A few templates for dark matter are studied, and the importance of the acceptance of the detector at low energies is pointed out. Finally, the idea of a complement to CTA in the form of a high-altitude, low energy threshold dedicated dark matter array, DMA, is discussed.

We study the capture of galactic dark matter particles in the Solar System produced by rotation of Jupiter. It is shown that the capture cross section is much larger than the area of Jupiter orbit being inversely diverging at small particle energy. We show that the dynamics of captured particles is chaotic and is well described by a simple symplectic dark map. This dark map description allows to simulate the scattering and dynamics of $10^{14}$ dark matter particles during the life time of the Solar System and to determine dark matter density profile as a function of distance from the Sun. The mass of captured dark matter in the radius of Neptune orbit is estimated to be $2 \cdot 10^{15} g$. The radial density of captured dark matter is found to be approximately constant behind Jupiter orbit being similar to the density profile found in galaxies., Comment: Accepted in MNRAS Letters, 5 pages, 5 figures

In order to observe annihilation and decay of dark matter, several types of potential sources should be considered. Some sources, such as dwarf galaxies, are expected to have very low astrophysical backgrounds but fairly small dark matter densities. Other sources, like the Galactic center, are expected to have larger densities of dark matter but also have more complicated backgrounds from other astrophysical sources. To search for signatures of dark matter, the large field-of-view of the HAWC detector, covering 2 sr at a time, especially enables searches from sources of dark matter annihilation and decay, which are extended over several degrees on the sky. With a sensitivity over 2/3 of the sky, HAWC has the ability to probe a large fraction of the sky for the signals of TeV-mass dark matter. In particular, HAWC should be the most sensitive experiment to signals coming from dark matter with masses greater than 10-100 TeV. We present the HAWC sensitivity to annihilating and decaying dark matter signals for several likely sources of these signals.

Dark matter may interact with the Standard Model through the kinetic mixing of dark photons, A′, with Standard Model photons. Such dark matter will accumulate in the Sun and annihilate into dark photons. The dark photons may then leave the Sun and decay into pairs of charged Standard Model particles that can be detected by the Alpha Magnetic Spectrometer (AMS). The directionality of this “dark sunshine” is distinct from all astrophysical backgrounds, providing an opportunity for unambiguous dark matter discovery by AMS. We perform a complete analysis of this scenario including Sommerfeld enhancements of dark matter annihilation and the effect of the Sun’s magnetic field on the signal, and we define a set of cuts to optimize the signal probability. With the three years of data already collected, AMS may discover dark matter with mass 1 TeV≲mX≲10 TeV, dark photon masses mA′∼O(100) MeV, and kinetic mixing parameters 10-11≲ϵ≲10-8. The proposed search extends beyond existing beam dump and supernova bounds, and it is complementary to direct detection, probing the same region of parameter space.

We explore the stopping effect that results from interactions between dark matter and nuclei as the dark matter particles travel undergound towards the detector. Although this effect is negligible for heavy dark matter particles, there is parameter phase space where the underground interactions of the dark matter particles with the nuclei can create observable differences in the spectrum. Dark matter particles that arrive on the detector from below can have less energy from the ones arriving from above. These differences can be potentially detectable by upcoming directional detectors. This can unveil a large amount of information regarding the type and strength of interactions between nuclei and light dark matter candidates., 9 pages, 5 figures

If dark matter is composed of weakly interacting particles, Earth’s orbital motion induces a small annual variation in the rate at which these particles interact in a terrestrial detector. The DAMA collaboration has identified at a 9.3σ confidence level (CL) such an annual modulation in their event rate over two detector iterations, DAMA/NaI and DAMA/LIBRA, each with about 7 years of observations. We examine the nature of this modulation signal and find the modulation amplitude for the two detectors is inconsistent at the 3σ CL over 2–6 keVee. Such a time-dependence in the modulation amplitude is unexpected behavior for a dark matter signal, at least for dark matter halo morphologies consistent with the DAMA signal. We also find unusual behavior over the 5–6 keVee energy range that might indicate problems with the data.

Most of the Universe is Dark and a large fraction of it should be made of relic particles; many possibilities are open on their nature and interaction types. Thus, their investigation is an outstanding issue in the field; for this purpose experiments offering a model independent signature for the presence of Dark Matter (DM) particles in the Galactic halo are mandatory. In this paper the DAMA/LIBRA results are described. In particular, the DAMA/LIBRA experiment is mainly devoted to the investigation of 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 provide a model independent evidence of the presence of DM particles in the galactic halo at 8.9 σ C.L.. Future perspectives are mentioned.

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

Dark matter particles can be captured by the sun with rates that depend on the dark matter mass and the DM-nucleon cross section. However, for masses below $\sim 3.3$ GeV, the captured dark matter particles evaporate, leading to an equilibrium where the rate of captured particles is equal to the rate of evaporating ones. Unlike dark matter particles from the halo, the evaporating dark matter particles have velocities that are not limited to values below the escape velocity of the galaxy. Despite the fact that high velocities are exponentially suppressed, I demonstrate here that current underground detectors have the possibility to probe/constrain low dark matter parameter space by (not)-observing the high energy tail of the evaporating dark matter particles from the sun. I also show that the functional form of the differential rate of counts with respect to the recoil energy in earth based detectors can identify precisely the mass and the cross section of the dark matter particle in this case., Comment: 5 pages, 1 figure

Searches for dark matter scattering off nuclei are typically compared assuming that the dark matter's spin-independent couplings are identical for protons and neutrons. This assumption is neither innocuous nor well motivated. We consider isospin-violating dark matter (IVDM) with one extra parameter, the ratio of neutron to proton couplings, and include the isotope distribution for each detector. For a single choice of the coupling ratio, the DAMA and CoGeNT signals are consistent with each other and with current XENON constraints, and they unambiguously predict near future signals at XENON and CRESST. We provide a quark-level realization of IVDM as WIMPless dark matter that is consistent with all collider and low-energy bounds., Comment: 5 pages; v2: added references and fixed figures for Mac users; v3: published version; v4: fixed erroneous Ar values in table I

The excess in cosmic-ray positrons and electrons observed by PAMELA, ATIC, PPB-BET and Fermi can be explained by dark matter decay or annihilation. On the other hand, the negative results from CDMS II and XENON direct detections of dark matter put an upper limit on the elastic-scattering cross section between dark matter and nucleon. We adopted model-independent approaches to study dark matter in cosmic-ray electrons, gamma-ray, relic density, direct detection experiments and LHC. We studied the distribution of the cosmic-ray electron flux observed at the Earth and found that it can reflect the initial energy spectrum of electrons generated from dark matter decay or annihilation even after propagation. We also derive constraints on the decay rate of dark matter into various two-body final states using Fermi and HESS gamma-ray data. We found that the μ+μ- or τ+τ- final state is favored in order to simultaneously explain electron excess and meet all gamma-ray constraints. Finally, we examined various tree-level induced operators of dimension six and constrain them using the current experimental data, including the WMAP data of the relic abundance and CDMS II direct detection of the spin-independent scattering. The implication of LHC search is also explored.

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).

We compute the primordial mirror helium He′ mass fraction emerging from Big Bang nucleosynthesis in the mirror sector of particles in the presence of kinetic mixing between photons and mirror photons. We explore the kinetic mixing parameter ( e ) values relevant for cosmology and which are also currently probed by the dark matter direct detection experiments. In particular, we find that for e ∼ 10 − 9 , as suggested by the DAMA/Libra and other experiments, a large HeO mass fraction ( Y He ′ ≈ 90 % ) is produced. Such a large value of the primordial He′ mass fraction will have important implications for the mirror dark matter interpretation of the direct detection experiments, as well as for the study of mirror star formation and evolution.

Detailed Monte Carlo simulations of the expected radioactive background rates and spectra in NaI crystals are presented. The obtained spectra are then compared to those measured in the DAMA/NaI and DAMA/LIBRA experiments. The simulations can be made consistent with the measured DAMA spectrum only by assuming higher than reported concentrations of some isotopes and even so leave very little room for the dark matter signal. We conclude that any interpretation of the annual modulation of the event rate observed by DAMA as a dark matter signal, should include full consideration of the background spectrum. This would significantly restrict the range of dark matter models capable of explaining the modulation effect., 17 pages, 6 figures

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

Neutron background for the high-sensitivity dark matter experiments is discussed. Neutron production via spontaneous fission and ( α , n) reactions from U and Th and by cosmic-ray muons is considered.

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.

Gamma-rays induced by annihilation or decay of dark matter can be its smoking gun signature. In particular, gamma-rays generated by internal bremsstrahlung of Majorana and real scalar dark matter is promising since it can be a leading emission of sharp gamma-rays. However in the case of Majorana dark matter, its cross section for internal bremsstrahlung cannot be large enough to be observed by future gamma-ray experiments if the observed relic density is assumed to be thermally produced. In this paper, we introduce some degenerate particles with Majorana dark matter, and show they lead enhancement of the cross section. As a result, increase of about one order of magnitude for the cross section is possible without conflict with the observed relic density, and it would be tested by the future gamma-ray experiments such as GAMMA-400 and Cherenkov Telescope Array (CTA). In addition, the constraints of perturbativity, positron observation by the AMS experiment and direct search for dark matter are discussed., 13 pages, 4 figures, version to appear in Physics Letters B

New results are reported from the operation of the PICO-60 dark matter detector, a bubble chamber filled with 52 kg of C_{3}F_{8} located in the SNOLAB underground laboratory. As in previous PICO bubble chambers, PICO-60 C_{3}F_{8} exhibits excellent electron recoil and alpha decay rejection, and the observed multiple-scattering neutron rate indicates a single-scatter neutron background of less than one event per month. A blind analysis of an efficiency-corrected 1167-kg day exposure at a 3.3-keV thermodynamic threshold reveals no single-scattering nuclear recoil candidates, consistent with the predicted background. These results set the most stringent direct-detection constraint to date on the weakly interacting massive particle (WIMP)-proton spin-dependent cross section at 3.4×10^{-41} cm^{2} for a 30-GeV c^{-2} WIMP, more than 1 order of magnitude improvement from previous PICO results.

Among the direct search experiments for weakly interacting massive particle (WIMP) dark matter, the DAMA experiment observed an annual modulation signal interpreted as WIMP interactions with a significance of 9.2 σ . Recently, Jonathan Davis claimed that the DAMA modulation may be interpreted on the basis of the neutron scattering events induced by the muons and neutrinos together. We tried to simulate the neutron backgrounds at the Gran Sasso and Yangyang laboratory with and without the polyethylene shielding to quantify the effects of the ambient neutrons on the direct detection experiments based on the crystals.

The DAMA/LIBRA experiment (about 250 kg of highly radiopure NaI(Tl)) is in operation at the Gran Sasso National Laboratory of the INFN. The main aim of the experiment is to further investigate the Dark Matter (DM) particles in the Galactic halo by exploiting the model independent DM annual modulation signature. At the time of this Workshop, the DAMA/LIBRA experiment and the former DAMA/NaI one (the first generation ex- periment having an exposed mass of about 100 kg) have released results corresponding to a total exposure of 1.17 ton × yr over 13 annual cycles; they have provided a model independent evidence of the presence of DM particles in the galactic halo at 8.9 σ C.L.. The results of a further annual cycle, concluding the DAMA/LIBRA–phase1, have been released after this Workshop and are not included here. 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 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.

We study a Dirac dark matter particle interacting with ordinary matter via the exchange of a light pseudoscalar, and analyze its impact on both direct and indirect detection experiments. We show that this candidate can accommodate the long-standing DAMA modulated signal and yet be compatible with all exclusion limits at 99(S)% C.L. This result holds for natural choices of the pseudoscalar-quark couplings (e.g., flavor universal), which give rise to a significant enhancement of the dark matter-proton coupling with respect to the coupling to neutrons. We also find that this candidate can accommodate the observed 1-3 GeV gamma-ray excess at the Galactic center and at the same time have the correct relic density today. The model could be tested with measurements of rare meson decays, flavor changing processes, and searches for axionlike particles with mass in the MeV range.

An annihilation signal of dark matter is searched for from the central region of the Milky Way. Data acquired in dedicated ON/OFF observations of the Galactic center region with H.E.S.S. are analyzed for this purpose. No significant signal is found in a total of $\sim 9$ h of ON/OFF observations. Upper limits on the velocity averaged cross section, $$, for the annihilation of dark matter particles with masses in the range of $\sim 300$ GeV to $\sim 10$ TeV are derived. In contrast to previous constraints derived from observations of the Galactic center region, the constraints that are derived here apply also under the assumption of a central core of constant dark matter density around the center of the Galaxy. Values of $$ that are larger than $3\cdot 10^{-24}\:\mathrm{cm^3/s}$ are excluded for dark matter particles with masses between $\sim 1$ and $\sim 4$ TeV at 95% CL if the radius of the central dark matter density core does not exceed $500$ pc. This is the strongest constraint that is derived on $$ for annihilating TeV mass dark matter without the assumption of a centrally cusped dark matter density distribution in the search region., Comment: Accepted for publication by Physical Review Letters, contact authors: Ullrich Schwanke (schwanke@physik.hu-berlin.de, Humboldt Universitaet zu Berlin, Berlin) and Gerrit Spengler (gerrit.spengler@fysik.su.se, Oscar Klein Centre for Cosmoparticle Physics, Stockholm)

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.

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 annually modulating $\sim$ keV scintillations observed in the DAMA/NaI and DAMA/Libra experiments might be due to dark matter - electron scattering. Such an explanation is now favoured given the stringent constraints on nuclear recoil rates obtained by LUX, SuperCDMS and other experiments. We suggest that multi-component dark matter models featuring light dark matter particles of mass $\sim$ MeV can potentially explain the data. A specific example, kinetically mixed mirror dark matter, is shown to have the right broad properties to consistently explain the experiments via dark matter - electron scattering. If this is the explanation of the annual modulation signal found in the DAMA experiments then a sidereal diurnal modulation signal is also anticipated. We point out that the data from the DAMA experiments show a diurnal variation at around 2.3$\sigma$ C.L. with phase consistent with that expected. This electron scattering interpretation of the DAMA experiments can potentially be probed in large xenon experiments (LUX, XENON1T,...), as well as in low threshold experiments (CoGeNT, CDEX, C4, ...) by searching for annually and diurnally modulated electron recoils., Comment: About 10 pages, matches published version

Direct searches for low mass dark matter particles via scattering off target nuclei require detection of recoiling atoms with energies of ~1 keV or less. The amount of electronic excitation produced by such atoms is quenched relative to a recoiling electron of the same energy. The Lindhard model of this quenching, as originally formulated, remains widely used after more than 50 years. The present work shows that for very small energies, a simplifying approximation of that model must be removed. Implications for the sensitivity of direct detection experiments are discussed., 6 pages, 5 figures

We explore detection prospects of a non-standard dark sector in the context of boosted dark matter. We focus on a scenario with two dark matter particles of a large mass difference, where the heavier candidate is secluded and interacts with the standard model particles only at loops, escaping existing direct and indirect detection bounds. Yet its pair annihilation in the galactic center or in the Sun may produce boosted stable particles, which could be detected as visible Cherenkov light in large volume neutrino detectors. In such models with multiple candidates, self-interaction of dark matter particles is naturally utilized in the {\it assisted freeze-out} mechanism and is corroborated by various cosmological studies such as N-body simulations of structure formation, observations of dwarf galaxies, and the small scale problem. We show that self-interaction of the secluded (heavier) dark matter greatly enhances the capture rate in the Sun and results in promising signals at current and future experiments. We perform a detailed analysis of the boosted dark matter events for Super-Kamiokande, Hyper-Kamiokande and PINGU, including notable effects such as evaporation due to self-interaction and energy loss in the Sun., 24 pages, 8 figures; discussion on the boosted DM flux from the Earth, references added, typos corrected; published in PLB

After the installation of the first four naked high purity Germanium detectors in liquid nitrogen in the GRAN SASSO Underground Laboratory in the GENIUS-Test-Facility (GENIUS-TF-I) on May 5, 2003, an improved setup GENIUS-TF-II with now six detectors (15 kg), has been installed on October 14, 2004. This is the only setup existing worldwide until now (April 2005) which applies this novel technique aiming at extreme background reduction in search for rare decays underground. The GENIUS-TF experiment, aims to search for the annual modulation of the Dark Matter signal. The HDMS (Heidelberg Dark Matter Search experiment) 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.

A stream of dark matter associated with the Sagittarius dwarf galaxy may be passing by the solar system. In direct searches for weakly interacting dark matter particles (WIMPs) in the stream provide a characteristic signature in the recoil spectrum of target nuclei, namely a new yearly modulation limited to low energy recoils. The maximum recoil energy due to stream WIMPs, and thus the proportion of high energy and low energy recoils, are modulated during the year, in a pattern that would be difficult to attribute to laboratory effects. As such, this new pattern may provide an intrinsic way of ascertaining the WIMP nature of a dark matter signal.

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.

In this paper, the model independent annual modulation effect observed by DAMA during four independent experiments of one annual cycle each (57986 kg $\times$ day total statistics) is analysed in terms of a particle dark matter candidate which can only inelastically scatter by making a transition to a slightly heavier state, as previously suggested in the literature.

The DAMA/LIBRA experiment searches for evidence of Dark Matter scattering off nuclei. Data from DAMA show 9.2 sigma evidence for an annual modulation, consistent with Dark Matter having a cross section around 2x10^(-40) cm^2. However this is excluded by other Direct Detection experiments. We propose an alternative source of annual modulation in the form of neutrons, which have been liberated from material surrounding the detector by a combination of 8B solar neutrinos and atmospheric muons. The phase of the muon modulation lags 30 days behind the data, however we show that adding the modulated neutrino component shifts the phase of the combined signal forward. In addition we estimate that neutrinos and muons need around 1000 m^3 of scattering material in order to generate enough neutrons to constitute the signal. With current data our model gives as good a fit as Dark Matter and we discuss prospects for future experiments to discriminate between the two., v2: Matches version published in PRL. Includes a new figure. 5 pages, 4 figures

We present new constraints on sub-GeV dark matter and dark photons from the electron beam-dump experiment E137 conducted at SLAC in 1980-1982. Dark matter interacting with electrons (e.g., via a dark photon) could have been produced in the electron-target collisions and scattered off electrons in the E137 detector, producing the striking, zero-background signature of a high-energy electromagnetic shower that points back to the beam dump. E137 probes new and significant ranges of parameter space, and constrains the well-motivated possibility that invisibly decaying dark photons can explain the $\sim 3.6 \sigma$ discrepancy between the measured and SM value of the muon anomalous magnetic moment. It also restricts the parameter space in which the relic density of dark matter in these models is obtained from thermal freeze-out. E137 also convincingly demonstrates that (cosmic) backgrounds can be controlled and thus serves as a powerful proof-of-principle for future beam-dump searches for sub-GeV dark matter scattering off electrons in the detector., Comment: 5 pages + references , 2 figures. v2: Fig. 2 now contains all constraints from visible A' searches; note added

Recently, the CDMS/Si experiment has observed a low energy excess of events in their dark matter search. In light of this new result we update the mirror dark matter explanation of the direction detection experiments. We find that the DAMA, CoGeNT, CRESST-II and CDMS/Si data can be simultaneously explained by halo $\sim Fe'$ interactions provided that $v_{rot} \approx 200$ km/s. Other parameter space is also possible. Forthcoming experiments, including CDMSlite, CDEX, COUPP, LUX, C-4,... should be able to further scrutinize mirror dark matter and closely related hidden sector models in the near future., Comment: 10 pages, matches published version

We present a search for low-mass ($\leq 20 GeV/c^{2}$) weakly interacting massive particles(WIMPs), strong candidates of dark matter particles,using the low-background CsI(Tl) detector array of the Korea Invisible Mass Search (KIMS) experiment. With a total data exposure of 24,324.3kg$\cdot$days,we search for WIMP interaction signals produced by nuclei recoiling from WIMP-nuclear elastic scattering with visible energies between 2 and 4keV. The observed energy distribution of candidate events is consistent with null signals, and upper limits of the WIMP-proton spin-independent interaction are set with a 90% confidence level. The observed limit rejects most of the low mass region of parameter space favored by the DAMA annual modulation signal., Comment: 6pages, 5 figures

We look at two improvements related to the DAMA/LIBRA dark matter detector. We show how using a more optimized binning scheme of the current data can lead to significantly tighter contraints on the compatible regions of the WIMP parameter space. In addition, the PMT’s of the detector were upgraded in 2010, allowing the low energy threshold to be lowered from 2 keVee to 1 keVee. We examine the implications for the dark matter interpretion of the DAMA modulation with data in this new energy region. Specifically, we focus on how well the degeneracy between the low mass and high mass regions can be removed by this new data. We find that the lower threshold data should rule out one of the two mass ranges in the spin-independent case at a minimum of the 2.6σ level in the worst case scenario.

Among the direct search experiments for WIMP dark matter, the DAMA experiment observed an annual modulation signal interpreted as WIMP interactions with 9.2$\sigma$ significance. However, this result is contradictory with other direct search experiments reporting null signals in the same parameter space allowed by the DAMA observation, necessitating clarification of the origin of the modulation signal observed using the NaI(Tl) crystals of the DAMA experiment independently. Here, we report the first results of NaI(Tl) crystal measurement at the Yangyang Underground Laboratory to grow ultra-low-background NaI(Tl) crystal detectors., Comment: 12 pages, 16 figures