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Register a new userImproved model-dependent corollary analyses after the first six annual cycles of DAMA/LIBRA-phase2
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R. Bernabei
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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.
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Assuming a standard Maxwellian for the WIMP velocity distribution, we obtain the bounds from null WIMP search results of 59.5 days of COSINE-100 data on the DAMA/LIBRA-phase2 modulation effect within the context of the non-relativistic effective theory of WIMP-nucleus scattering. Here, we systematically assume that one of the effective operators allowed by Galilean invariance dominates in the effective Hamiltonian of a spin-1/2 dark matter (DM) particle. We find that, although DAMA/LIBRA and COSINE-100 use the same sodium-iodide target, the comparison of the two results still depends on the particle-physics model. This is mainly due to two reasons: i) the WIMP signal spectral shape; ii) the expected modulation fractions, when the upper bound on the time-averaged rate in COSINE-100 is converted into a constraint on the annual modulation component in DAMA/LIBRA. We find that the latter effect is the dominant one. For several effective operators the expected modulation fractions are larger than in the standard spin-independent or spin-dependent interaction cases. As a consequence, compatibility between the modulation effect observed in DAMA/LIBRA and the null result from COSINE-100 is still possible for several non-relativistic operators. At low WIMP masses such relatively high values of the modulation fractions arise because COSINE-100 is mainly sensitive to WIMP-sodium scattering events, due to the higher threshold compared to DAMA/LIBRA. A next COSINE analysis is expected to have a full sensitivity for the 5$sigma$ region of DAMA/LIBRA.
Recently, the DAMA/LIBRA collaboration released updated results from their search for the annual modulation signal from Dark Matter (DM) scattering in the detector. Besides approximately doubling the exposure of the DAMA/LIBRA data set, the updated photomultiplier tubes of the experiment allow a lower recoil energy threshold of 1,keV electron equivalent compared to the previous threshold of 2 keV electron equivalent. We study the compatibility of the observed modulation signal with DM scattering. Due to a conspiracy of multiple effects, the new data at low recoil energies is very powerful for testing the DM hypothesis. We find that canonical (isospin conserving) spin-independent DM-nucleon interactions are no longer a good fit to the observed modulation signal in the standard halo model. The canonical spin-independent case is disfavored by the new data, with best fit points of a DM mass of $sim 8,$GeV, disfavored by $5.2,sigma$, or a mass of $sim 54,$GeV, disfavored by $2.5,sigma$. Allowing for isospin violating spin independent interactions, we find a region with a good fit to the data with suppressed effective couplings to iodine for DM masses of $sim 10,$GeV. We also consider spin-dependent DM-nucleon interactions, which yield good fits for similar DM masses of $sim 10,$GeV or $sim 45,$GeV
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 x 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 x yr, corresponding to 13 annual cycles. The data further confirm the model independent evidence of the presence of Dark Matter (DM) particles in the galactic halo on the basis of the DM annual modulation signature (8.9 sigma C.L. 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.
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 $times$ yr 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.
This paper summarizes in a simple and intuitive way why the neutrons, the muons and the solar neutrinos cannot give any significant contribution to the DAMA annual modulation results. A number of these elements have already been presented in individual papers; they are recalled here. Afterwards, few simple considerations are summarized which already demonstrate the incorrectness of the claim reported in PRL 113 (2014) 081302.
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