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Axions can be considered as good dark matter candidates. The detection of such light particles can be achieved by observing axion-induced atomic excitations. The target is in a magnetic field so that the m-degeneracy is removed, and the energy levels can be suitably adjusted. Using an axion-electron coupling indicated by the limit obtained by the Borexino experiment, which is quite stringent, reasonable axion absorption rates have been obtained for various atomic targets The obtained results depend, of course, on the atom considered through the parameters ϵ (the spin−orbit splitting) as well as δ ( the energy splitting due to the magnetic moment interaction). This assumption allows axion masses in the tens of μeV if the transition occurs between members of the same multiplet, i.e., |J1,M1=−J1⟩→|J1,M1=−J+1⟩,J1≠0, and axion masses in the range 1 meV–1 eV for transitions of the spin−orbit splitting type |J1,M=−J1⟩→|J2,M2=−J1+q⟩,q=−1,0,1, i.e., three types of transition. The axion mass that can be detected is very close to the excitation energy involved, which can vary by adjusting the magnetic field. Furthermore, since the axion is absorbed by the atom, the calculated cross-section exhibits the behavior of a resonance, which can be exploited by experiments to minimize any background events.

A brief discussion of the early history of unconventional uses of Ge detectors is given, followed by a more detailed discussion focusing on their uses for axion searches. The main purpose of this discussion is to explore the possibility of pushing the envelope of sensitivity of solar axion searches with future large Ge detector arrays applied to searches employing coherent Bragg-Primakoff conversion, as well as the axio-electric effect.

Charge conservation and the Pauli exclusion principle result from fundamental symmetries in the standard model of particle physics, and are typically taken as axiomatic. High-precision tests for small violations of these symmetries could point to new physics. Here we consider three models for violation of these processes, which would produce detectable ionization in the high-purity germanium detectors of the M ajorana D emonstrator experiment. Using a 37.5 kg yr exposure, we report a lower limit on the electron mean lifetime, improving the previous best limit for the e → ν e ν e ¯ ν e decay channel by more than an order of magnitude. We also present searches for two types of violation of the Pauli exclusion principle, setting limits on the probability of an electron to be found in a symmetric quantum state. The M ajorana D emonstrator experiment reports searches for the violation of the Pauli exclusion principle and of charge conservation. In the absence of a signal, exclusion limits for these processes are reported.

P-type point contact (PPC) HPGe detectors are a leading technology for rare event searches due to their excellent energy resolution, low thresholds, and multi-site event rejection capabilities. We have characterized a PPC detector’s response to α particles incident on the sensitive passivated and p+ surfaces, a previously poorly-understood source of background. The detector studied is identical to those in the MajoranaDemonstrator experiment, a search for neutrinoless double-beta decay (0νββ) in 76Ge. α decays on most of the passivated surface exhibit significant energy loss due to charge trapping, with waveforms exhibiting a delayed charge recovery (DCR) signature caused by the slow collection of a fraction of the trapped charge. The DCR is found to be complementary to existing methods of α identification, reliably identifying α background events on the passivated surface of the detector. We demonstrate effective rejection of all surface α events (to within statistical uncertainty) with a loss of only 0.2% of bulk events by combining the DCR discriminator with previously-used methods. The DCR discriminator has been used to reduce the background rate in the 0νββ region of interest window by an order of magnitude in the MajoranaDemonstrator and will be used in the upcoming LEGEND-200 experiment.

We report a study of the CUORE sensitivity to neutrinoless double beta ( [Formula omitted]) decay. We used a Bayesian analysis based on a toy Monte Carlo (MC) approach to extract the exclusion sensitivity to the [Formula omitted] decay half-life ( [Formula omitted]) at [Formula omitted] credibility interval (CI) - i.e. the interval containing the true value of [Formula omitted] with [Formula omitted] probability - and the [Formula omitted] discovery sensitivity. We consider various background levels and energy resolutions, and describe the influence of the data division in subsets with different background levels. If the background level and the energy resolution meet the expectation, CUORE will reach a [Formula omitted] CI exclusion sensitivity of [Formula omitted] year with 3 months, and [Formula omitted] year with 5 years of live time. Under the same conditions, the discovery sensitivity after 3 months and 5 years will be [Formula omitted] year and [Formula omitted] year, respectively.

At present, Majorana is a research and development (R&D) project to investigate the feasibility and cost of constructing and operating a one ton 76Ge 0νββ-decay experiment with ∼1000 kg of Ge detectors fabricated from germanium enriched to 86% in 76Ge. The study will include three separate cryostats with various types of detectors: un-segmented, un-segmented point-contact, minimally segmented, and highly segmented. One cryostat will contain at least 30 kg of enriched (preferably point-contact) detectors. The performance of the cryostats and detectors as well as background levels will be investigated. The goal of the demonstrator project is to reach a 3σ discovery sensitivity of ∼ 1026y.

We report on the measurement of the two-neutrino double-beta decay half-life of [Formula omitted]Te with the CUORE-0 detector. From an exposure of 33.4 kg year of TeO [Formula omitted], the half-life is determined to be [Formula omitted] = [8.2 ± 0.2 (stat.) ± 0.6 (syst.)] [Formula omitted] 10 [Formula omitted] year. This result is obtained after a detailed reconstruction of the sources responsible for the CUORE-0 counting rate, with a specific study of those contributing to the [Formula omitted]Te neutrinoless double-beta decay region of interest.

We report on the measurement of the two-neutrino double-beta decay half-life of 130 Te with the CUORE-0 detector. From an exposure of 33.4 kg year of TeO 2 , the half-life is determined to be T 1 / 2 2 ν = [8.2 ± 0.2 (stat.) ± 0.6 (syst.)] × 10 20  year. This result is obtained after a detailed reconstruction of the sources responsible for the CUORE-0 counting rate, with a specific study of those contributing to the 130 Te neutrinoless double-beta decay region of interest.