The possibility that neutrinos may be their own antiparticles, unique among the known fundamental particles, arises from the symmetric theory of fermions proposed by Ettore Majorana in 19371. Given the profound consequences of such Majorana neutrinos, among which is a potential explanation for the matter–antimatter asymmetry of the universe via leptogenesis2, the Majorana nature of neutrinos commands intense experimental scrutiny globally; one of the primary experimental probes is neutrinoless double beta (0νββ) decay. Here we show results from the search for 0νββ decay of 130Te, using the latest advanced cryogenic calorimeters with the CUORE experiment3. CUORE, operating just 10 millikelvin above absolute zero, has pushed the state of the art on three frontiers: the sheer mass held at such ultralow temperatures, operational longevity, and the low levels of ionizing radiation emanating from the cryogenic infrastructure. We find no evidence for 0νββ decay and set a lower bound of the process half-life as 2.2 × 1025 years at a 90 per cent credibility interval. We discuss potential applications of the advances made with CUORE to other fields such as direct dark matter, neutrino and nuclear physics searches and large-scale quantum computing, which can benefit from sustained operation of large payloads in a low-radioactivity, ultralow-temperature cryogenic environment.
It is shown that a Weakly Interacting Massive dark matter Particle (WIMP) interpretation for the positron excess observed in a variety of experiments, HEAT, PAMELA, and AMS-02, is highly constrained by the Fermi/LAT observations of dwarf galaxies. In particular, this paper has focused on the annihilation channels that best fit the current AMS-02 data (Boudaud et al., 2014). The Fermi satellite has surveyed the γ-ray sky, and its observations of dwarf satellites are used to place strong bounds on the annihilation of WIMPs into a variety of channels. For the single channel case, we find that dark matter annihilation into {bb, e + e − , µ-e, or 4-τ } is ruled out as an explanation of the AMS positron excess (here b quarks are a proxy for all quarks, gauge and Higgs bosons). In addition, we find that the Fermi/LAT 2σ upper limits, assuming the best-fit AMS-02 branching ratios, exclude multichannel combinations into bb and leptons. The tension between the results might relax if the branching ratios are allowed to deviate from their best-fit values, though a substantial change would be required. Of all the channels we considered, the only viable channel that survives the Fermi/LAT constraint and produces a good fit to the AMS-02 data is annihilation (via a mediator) to 4-µ, or mainly to 4-µ in the case of multichannel combinations.Weakly Interacting Massive Particles (WIMPS), such as the lightest supersymmetric particles (for reviews, see Refs. [1, 2]), are thought to be the best motivated dark matter (DM) candidates. The particles in consideration are their own antiparticles; thus, they annihilate among themselves in the early universe and naturally provide the correct relic density today to explain the dark matter of the universe. This same annihilation process takes place in the present universe wherever the DM density is sufficiently high and is the basis for DM indirect detection searches. Indirect detection experiments search for the annihilation products of dark matter particles, including electrons and/or positrons, antiprotons, photons, and neutrinos. Promising sites for the observation of dark matter annihilation products include the core of the Sun [3], the Earth [4,5], our Galactic halo [6-9], Galactic center [10], dwarf satellite galaxies [11,12], and from DM substructures [13][14][15][16].Over the past several years, there have been a number of experimental signals which have been interpreted as possible indications of DM. Confirmation that any of these observations are actually due to DM, rather than being a mere experimental artifact or astrophysical background, would likely require more than one experiment to provide complementary information. In this paper, we consider the anomalous features in the spectrum of cosmic ray positrons and electrons reported by , PAMELA [18,19], and the Large Area Telescope of the Fermi Gamma Ray Space Telescope (Fermi/LAT) [20] (as well as in earlier indications from HEAT [21][22][23]). The positron fraction was found to be a steadily increasing function of energy, above...
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