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The long-standing model-independent annual modulation effect measured by DAMA Collaboration is examined in the context of asymmetric mirror dark matter, assuming that dark atoms interact with target nuclei in the detector via kinetic mixing between mirror and ordinary photons, both being massless. The relevant ranges for the kinetic mixing parameter are obtained taking into account various existing uncertainties in nuclear and particle physics quantities as well as characteristic density and velocity distributions of dark matter in different halo models.

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 (i.e. adding a further 0.17 ton × yr exposure) are presented. The DAMA/LIBRA–phase1 data give evidence 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, at 7.5 σ C.L. Including also the first generation DAMA/NaI experiment (cumulative exposure 1.33 ton × yr, corresponding to 14 annual cycles), the C.L. is 9.3 σ and 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.

The DAMA experiment using ultra low background NaI(Tl) crystal scintillators has measured an annual modulation effect in the keV region which satisfies all the peculiarities of an effect induced by Dark Matter particles. In this paper we analyze this annual modulation effect in terms of mirror Dark Matter, an exact duplicate of ordinary matter from parallel hidden sector, which chemical composition is dominated by mirror helium while it can also contain significant fractions of heavier elements as Carbon and Oxygen. Dark mirror atoms are considered to interact with the target nuclei in the detector via Rutherford-like scattering induced by kinetic mixing between mirror and ordinary photons, both being massless. In the present analysis we consider various possible scenarios for the mirror matter chemical composition. For all the scenarios, the relevant ranges for the kinetic mixing parameter have been obtained taking also into account various existing uncertainties in nuclear and particle physics quantities.

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.

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.

The channeling effect of low energy ions along the crystallographic axes and planes of NaI(Tl) crystals is discussed in the framework of corollary investigations on WIMP dark matter candidates. In fact, the modeling of this existing effect implies a more complex evaluation of the luminosity yield for low energy recoiling Na and I ions. In the present paper related phenomenological arguments are developed and possible implications are discussed at some extent.

The long-standing model-independent annual modulation measured by DAMA at Gran Sasso Laboratory with different experimental configurations is summarized. The full exposure is 2.86 ton × yr over 22 annual cycles. DAMA/LIBRA–phase2 set-up, ≃ 250 kg highly radio-pure NaI(Tl), confirms the evidence of a signal that meets all the requirements of the model independent Dark Matter annual modulation signature at high confidence level. The new configuration, DAMA/LIBRA–phase2–empowered, has been taking data with lower energy threshold until fall 2024, as stated in the primordial plans of the collaboration; few details are highlighted.

The existence of Dark Matter particles as a significant portion of the Universe’s total mass is suggested by theoretical reasoning at the galactic and larger scales as well as experimental data. This motivates the DAMA experiment’s efforts to investigate the presence of the Dark Matter particles in the galactic halo by utilizing a model-independent signature with an extremely radio-pure set-up underground. The long-standing, model-independent annual modulation effect at Gran Sasso seen by DAMA with several experimental set-ups is summarized in this paper, along with its perspectives. DAMA/LIBRA-phase2 set-up, ≃ 250 kg highly radio-pure NaI(Tl) further confirms the evidence of a signal that meets all the requirements of the model independent Dark Matter annual modulation signature at high C.L.; the combined exposure of DAMA/NaI and DAMA/LIBRA is 2.86 ton × yr over 22 independent annual cycles. The experiment is currently collecting data in the DAMA/LIBRA–phase2 empowered configuration with an even lower software energy threshold.

In the anisotropic scintillators the light output and the pulse shape for heavy particles ( p , α , nuclear recoils) depend on the direction with respect to the crystal axes; the response to γ / β radiation is isotropic instead. This feature offers the possibility to study the directionality approach, which is applicable in the particular case of those Dark Matter candidate particles inducing just nuclear recoils. Among the anisotropic scintillators, the ZnWO 4 has unique features, which make it an excellent candidate for this type of research, and there is still plenty of room for the improvement of its performances. In this paper the possibility of a low background pioneer experiment (named ADAMO—Anisotropic detectors for DArk Matter Observation) to exploit deep underground the directionality approach by using anisotropic ZnWO 4 scintillators is discussed.

In the present paper the results obtained in the investigation of possible diurnal effects for low-energy single-hit scintillation events of DAMA/LIBRA-phase1 (1.04 ton × year exposure) have been analysed in terms of an effect expected in case of dark matter (DM) candidates inducing nuclear recoils and having high cross-section with ordinary matter, which implies low DM local density in order to fulfill the DAMA/LIBRA DM annual modulation results. This effect is due to the different Earth depths crossed by those DM candidates during the sidereal day.