New results from DAMA/LIBRA

DAMA/LIBRA is running at the Gran Sasso National Laboratory of the I.N.F.N. Here the results obtained with a further exposure of 0.34 ton × yr are presented. They refer to two further annual cycles collected one before and one after the first DAMA/LIBRA upgrade occurred on September/October 2008. The cumulative exposure with those previously released by the former DAMA/NaI and by DAMA/LIBRA is now 1.17 ton × yr, corresponding to 13 annual cycles. The data further confirm the previous positive results obtained investigating the presence of Dark Matter (DM) particles in the galactic halo by means of the model independent Dark Matter annual modulation signature; the confidence level is now 8.9 σ for the cumulative exposure. In particular, with the cumulative exposure the modulation amplitude of the single-hit events in the (2–6) keV energy interval measured in NaI(Tl) target is (0.0116±0.0013) cpd/kg/keV; the measured phase is (146±7) days and the measured period is (0.999±0.002) yr, values well in agreement with those expected for the DM particles.     

First results from DAMA/LIBRA and the combined results with DAMA/NaI

The highly radiopure ≃ 250 kg NaI(Tl) DAMA/LIBRA set-up is running at the Gran Sasso National Laboratory of the INFN. In this paper the first result obtained by exploiting the model independent annual modulation signature for Dark Matter (DM) particles is presented. It refers to an exposure of 0.53 ton×yr. The collected DAMA/LIBRA data satisfy all the many peculiarities of the DM annual modulation signature. Neither systematic effects nor side reactions able to account for the observed modulation amplitude and to contemporaneously satisfy all the several requirements of this DM signature are available. Considering the former DAMA/NaI and the present DAMA/LIBRA data all together (total exposure 0.82 ton×yr), the presence of Dark Matter particles in the galactic halo is supported, on the basis of the DM annual modulation signature, at 8.2 σ C.L.; in particular, in the energy interval (2–6) keV, the modulation amplitude is (0.0131±0.0016) cpd/kg/keV and the phase and the period are well compatible with June 2 ^nd and one year, respectively.     

Signals from dark Universe: DAMA/LIBRA at LNGS

The DAMA/LIBRA set-up (about 250 kg highly radiopure NaI(Tl) sensitive mass) is running at the Gran Sasso National Laboratory of the INFN. The first DAMA/LIBRA results point out the presence of a dark matter particle component in the galactic halo, as well as the former DAMA/NaI set-up; cumulatively the data support such evidence at 8.2σ CL and satisfy all the peculiarities of the dark matter annual modulation signature.     

Toward extracting $$\gamma $$ from $$B\rightarrow DK$$ without binning

SABRE (Sodium iodide with Active Background REjection) is a direct detection dark matter experiment based on arrays of radio-pure NaI(Tl) crystals. The experiment aims at achieving an ultra-low background rate and its primary goal is to confirm or refute the results from the DAMA/LIBRA experiment. The SABRE Proof-of-Principle phase was carried out in 2020–2021 at the Gran Sasso National Laboratory (LNGS), in Italy. The next phase consists of two full-scale experiments: SABRE South at the Stawell Underground Physics Laboratory, in Australia, and SABRE North at LNGS. This paper focuses on SABRE South and presents a detailed simulation of the detector, which is used to characterise the background for dark matter searches including DAMA/LIBRA-like modulation. We estimate an overall background of 0.72 cpd/kg/\(\hbox {keV}_{\hbox {{ee}}}\) in the energy range 1–6 \(\hbox {keV}_{\hbox {{ee}}}\) primarily due to radioactive contamination in the crystals. Given this level of background and considering that the SABRE South has a target mass of 50 kg, we expect to exclude (confirm) DAMA/LIBRA modulation at \(4~(5)\sigma \) within 2.5 years of data taking.

     

Particle dark matter in the galactic halo

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).     

Results from a low-energy analysis of the CDMS II germanium data

We report results from a reanalysis of data from the Cryogenic Dark Matter Search (CDMS II) experiment at the Soudan Underground Laboratory. Data taken between October 2006 and September 2008 using eight germanium detectors are reanalyzed with a lowered, 2 keV recoil-energy threshold, to give increased sensitivity to interactions from weakly interacting massive particles (WIMPs) with masses below ～10 GeV/c(2). This analysis provides stronger constraints than previous CDMS II results for WIMP masses below 9 GeV/c(2) and excludes parameter space associated with possible low-mass WIMP signals from the DAMA/LIBRA and CoGeNT experiments.     

Particle dark matter: From DAMA/NaI to DAMA/LIBRA

DAMA is an observatory for rare processes and it is operative deep underground at the Gran Sasso National Laboratory of the INFN. Several low background setups have been realized and many rare processes have been investigated. In particular, the DAMA/Nal setup (≃100 kg of highly radiopure NaI(Tl)) has effectively investigated the model-independent annual modulation signature over seven annual cycles (total exposure of 107 731 kg day), obtaining 6.3σ C.L. model-independent evidence for the presence of a dark matter particle component in the galactic halo. Some of the many possible corollary model-dependent quests for the candidate particle have been investigated and others are in progress. At present, the second generation DAMA/LIBRA setup (≃250 kg of highly radiopure NaI(T1)) is in data taking deep underground. The text was submitted by the authors in English.     

Testing a new sterile neutrino dark matter candidate

A new class of sterile neutrino dark matter is suggested by an explanation for time variations in the solar neutrino flux in which coupling of sterile neutrinos to other matter is via a very small flavor off-diagonal transition magnetic moment, TMM. The dark matter sterile neutrino’s decay in the radiative channel then depends on the local magnetic field and the unknown value of the TMM. An interesting application of this model uses the DAMA/LIBRA claimed detection of dark matter (assuming they are observing the electromagnetic signal) to provide the decay rate in the Earth’s field, and hence the TMM value. That version of the model is then examined to see if it can be falsified by cosmic X-ray observations or by other direct detection experiments. Particularly the latter could provide a simple, definitive test of this dark matter candidate, which would bring concordance to these experiments.     

Results from DAMA/LIBRA at Gran Sasso

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. In particular, the DAMA/LIBRA (Large sodium Iodide Bulk for RAre processes) set-up consists of highly radiopure NaI(Tl) detectors for a total sensitive exposed mass of ?250 kg. Recent results, obtained by this set-up by exploiting the model independent annual modulation signature of Dark Matter (DM) particles, have confirmed and improved those obtained by the former DAMA/NaI experiment. A model independent evidence for the presence of Dark Matter particles in the galactic halo is cumulatively obtained at 8.2?σ C.L. No systematics or side reactions able to account for the measured modulation amplitude and to contemporaneously satisfy all the many specific requirements of the signature have been found or suggested by anyone over more than a decade. An example of one of the many possible model dependent corollary quests for the candidate particles and for the related astrophysical, nuclear and particle physics scenarios is presented considering the whole cumulative exposure. Future perspectives are shortly addressed.     

Particle physics implications for CoGeNT, DAMA, and Fermi

Recent results from the CoGeNT Collaboration (as well as the annual modulation reported by DAMA/LIBRA) point toward dark matter with a light (5-10 GeV) mass and a relatively large elastic scattering cross section with nucleons (σ∼¹⁰−40 cm²). In order to possess this cross section, the dark matter must communicate with the Standard Model through mediating particles with small masses and/or large couplings. In this Letter, we explore with a model-independent approach the particle physics scenarios that could potentially accommodate these signals. We also discuss how such models could produce the gamma rays from the Galactic Center observed in the data of the Fermi Gamma-Ray Space Telescope. We find multiple particle physics scenarios in which each of these signals can be accounted for, and in which the dark matter can be produced thermally in the early Universe with an abundance equal to the measured cosmological density.     

Direct dark matter investigation

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.     

Can large scintillators be used for solar-axion searches to test the cosmological axion–photon oscillation proposal?

Solar-axion interaction rates in NaI, CsI and Xe scintillators via the axio-electric effect were calculated. A table is presented with photo-electric and axio-electric cross sections, solar-axion fluxes, and the interaction rates from 2.0 to 10.0 keV. The results imply that annual-modulation data of large NaI and CsI arrays, and large Xe scintillation detectors, might be made sensitive enough to probe coupling to photons at levels required to explain axion–photon oscillation phenomena proposed to explain the survival of high-energy photons traveling cosmological distances. The DAMA/LIBRA data are used to demonstrate the power of the model-independent annual modulation due to the seasonal variation in the earth-sun distance.     

Dark light-Higgs bosons

We study a limit of the nearly Peccei-Quinn-symmetric next-to-minimal supersymmetric standard model possessing novel Higgs and dark matter (DM) properties. In this scenario, there naturally coexist three light singletlike particles: a scalar, a pseudoscalar, and a singlinolike DM candidate, all with masses of order 0.1-10 GeV. The decay of a standard model-like Higgs boson to pairs of the light scalars or pseudoscalars is generically suppressed, avoiding constraints from collider searches for these channels. For a certain parameter window annihilation into the light pseudoscalar and exchange of the light scalar with nucleons allow the singlino to achieve the correct relic density and a large direct-detection cross section consistent with the DM direct-detection experiments, CoGeNT and DAMA/LIBRA, preferred region simultaneously. This parameter space is consistent with experimental constraints from LEP, the Tevatron, Υ, and flavor physics.     

New limits on dark matter from Super-Kamiokande

The signals observed at the direct detection experiments DAMA, CoGeNT and CRESST could be explained by light WIMPs with sizeable spin-independent cross sections with nucleons. The capture and subsequent annihilation of such particles in the Sun would induce neutrino signals in the GeV range which may be observed at Super-Kamiokande. We determine the rate of upward stopping muons and fully contained events at Super-Kamiokande for various possible WIMP annihilation channels. This allows us to provide strong constraints on the cross section of WIMPs with nucleons. We find that the DAMA and CoGeNT signals are inconsistent with standard thermal WIMPs annihilating dominantly into neutrino or tau pairs. We also provide limits for spin-dependent WIMP nucleus scattering for masses up to 80 GeV. These exclude the DAMA favored region if WIMPs annihilate even subdominantly into neutrinos, taus, bottoms or charms.     

Cosmic-ray antiproton constraints on light singlino-like dark matter candidates

The CoGeNT experiment, dedicated to direct detection of dark matter, has recently released excess events that could be interpreted as elastic collisions of ∼10 GeV dark matter particles, which might simultaneously explain the still mysterious DAMA/LIBRA modulation signals, while in conflict with results from other experiments such as CDMS, XENON-100 and SIMPLE. It was shown that 5-15 GeV singlino-like dark matter candidates arising in singlet extensions of minimal supersymmetric scenarios can fit these data; annihilation then mostly proceeds into light singlet-dominated Higgs (pseudo-)scalar fields. We develop an effective Lagrangian approach to confront these models with the existing data on cosmic-ray antiprotons, including the latest PAMELA data. Focusing on a parameter space consistent with the CoGeNT region, we show that the predicted antiproton flux is generically in tension with the data whenever the produced (pseudo-)scalars can decay into quarks energetic enough to produce antiprotons, provided the annihilation S-wave is significant at freeze out in the early universe. In this regime, a bound on the singlino annihilation cross section is obtained, 〈σv〉?¹⁰−26 cm³/s, assuming a dynamically constrained halo density profile with a local value of ρ_⊙=0.4 GeV/cm³. Finally, we provide indications on how PAMELA or AMS-02 could further constrain or detect those configurations producing antiprotons which are not yet excluded.     

Dark forces at the Tevatron

A simple explanation of the W+dijet excess recently reported by the CDF collaboration involves the introduction of a new gauge boson with sizable couplings to quarks, but with no or highly suppressed couplings to leptons. Anomaly-free theories which include such a leptophobic gauge boson must also include additional particle content, which may include a stable and otherwise viable candidate for dark matter. Based on the couplings and mass of the Z^′ required to generate the CDF excess, we predict such a dark matter candidate to possess an elastic scattering cross section with nucleons on the order of σ∼¹⁰−40 cm², providing a natural explanation for the signals reported by the CoGeNT and DAMA/LIBRA collaborations. In this light, CDF may be observing the gauge boson responsible for the force which mediates the interactions between the dark and visible matter of our universe.     

A CoGeNT confirmation of the DAMA signal

The CoGeNT Collaboration has recently reported a rising low energy spectrum in their ultra low noise Germanium detector. This is particularly interesting as the energy range probed by CoGeNT overlaps with the energy region in which DAMA has observed their annual modulation signal. We show that the mirror dark matter candidate can simultaneously explain both the DAMA annual modulation signal and the rising low energy spectrum observed by CoGeNT. This constitutes a model dependent confirmation of the DAMA signal and adds weight to the mirror dark matter paradigm.     

Effect of thallium impurities in the DAMA experiment on the allowed parameter space for inelastic dark matter

The inelastic dark matter scenario was proposed to reconcile the DAMA annual modulation with null results from other experiments. In this scenario, weakly interacting massive particles (WIMPs) scatter into an excited state, split from the ground state by an energy δ comparable to the available kinetic energy of a galactic WIMP. We note that for large splittings δ the dominant scattering at DAMA can occur off of thallium nuclei, with A～205, which are present as a dopant at the 10(-3) level in NaI(Tl) crystals. For a WIMP mass mχ≈100 GeV/c2 and δ≈200 keV, we find a region in δ-mχ-parameter space which is consistent with all experiments. These parameters, in particular, can be probed in experiments with thallium in their targets, such as KIMS, but are inaccessible to lighter target experiments. Depending on the tail of the WIMP velocity distribution, a highly modulated signal may or may not appear at CRESST-II.     

Asymptotically safe phantom cosmology

New lifetime limits on the charge non-conserving (CNC) electron capture with excitation of the 417.9 keV nuclear level in the ¹²⁷I are established by using the coincidence technique. The analysed exposure is 0.87 ton × yr, collected deep underground at the Gran Sasso National Laboratory of the INFN by the highly radiopure DAMA/LIBRA setup (??250 kg of highly radiopure NaI(Tl)). The new limit on the mean life is ??>1.2×10²⁴?yr (90?% C.L.), about one order of magnitude larger than those previously available for CNC electron capture involving nuclear level excitations of ¹²⁷I and of the same order of magnitude than those achieved for analogous processes in ¹²⁹Xe.