First Model Independent Results from DAMA/LIBRA–Phase2

Abstract

The first results obtained by the DAMA/LIBRA–phase2 experiment are presented. The data have been collected over six independent annual cycles corresponding to a total exposure of 1.13 ton × year, deep underground at the Gran Sasso National Laboratory. The DAMA/LIBRA–phase2 apparatus, about 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. 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 × year) is 12.9 σ .

Improved model-dependent corollary analyses after the first six annual cycles of DAMA/LIBRA-phase2

“…Comparing the expected modulated signal for this scenario with the experimental result obtained cumulatively by DAMA/NaI, DAMA/LIBRA-phase1 and DAMA/LIBRA-phase2 [3,4,5,6,7], it is possible to determine a 10 σ C.L. allowed volume in the space (m H , ∆, ξσ e m ).…”

“…With regard to the interaction of LDM with target nuclei, the allowed volume in the space (m H , ∆, ξσ nucleus m ) at 10σ from the null hypothesis can be obtained by comparing the expected modulated signal with the experimental results obtained by DAMA/NaI, DAMA/LIBRA-phase1 and DAMA/LIBRA-phase2 [3,4,5,6,7].…”

“…The model-independent results of the first six full annual cycles measured by DAMA/LIBRA-phase2 with software energy threshold lowered down to 1 keV 1 [1,2] have been released [3,4,5,6,7]. On the basis of the exploited Dark Matter (DM) annual modulation signature, the model-independent evidence for the presence of DM particles in the galactic halo has been further confirmed after the previous DAMA/LIBRA-phase1 [8,9,10,11,1,2,12,13,14] and the former DAMA/NaI [15,16]; the cumulative C.L.…”

“…No background of this sort has been found or suggested by anyone over some decades, see Refs. [2,3,4,5,6,7,8,9,10,11,12,13]; in particular, in the latter two references the case of neutrons, muons, and solar neutrinos has further been addressed in details 3 . Noteworthy, as already pointed out in Refs.…”

“…Therefore, the DM annual modulation signature allows one to overcome -in the identification of 2 Throughout this paper ton means metric ton (1000 kg). 3 Concerning recently appeared remarks, let us comment that any hypothetical effect due to environmental Helium diffusion inside the photomultipliers (PMTs) can be excluded, even considering the following simple arguments [7]: i) the PMTs are kept in high purity (HP; 5.5 grade) Nitrogen atmosphere, the gas being continuously flushed through the apparatus ( 250 liters / hour) [8]; thus no Helium accumulation process can take place (typical characteristic time for accumulation of Helium in PMTs through glass -considering the permeability of the materials -is 1 year). An estimate of Helium concentration within the DAMA shield is less than 5 × 10 −11 ppm.…”