Technical Design Report for the AMoRE $0νββ$ Decay Search Experiment

Abstract

The AMoRE (Advanced Mo-based Rare process Experiment) project is a series of experiments that use advanced cryogenic techniques to search for the neutrinoless double-beta decay of 100 Mo. The work is being carried out by an international collaboration of researchers from eight countries. These searches involve high precision measurements of radiation-induced temperature changes and scintillation light produced in ultra-pure 100 Mo-enriched and 48 Ca-depleted calcium molybdate ( 48depl Ca 100 MoO 4 ) crystals that are located in a deep underground laboratory in Korea. The 100 Mo nuclide was chosen for this 0νββ decay search because of its high Q-value and favorable nuclear matrix element. Tests have demonstrated that CaMoO 4 crystals produce the brightest scintillation light among all of the molybdate crystals, both at room and at cryogenic temperatures. 48depl Ca 100 MoO 4 crystals are being operated at milli-Kelvin temperatures and read out via specially developed metallic-magnetic-calorimeter (MMC) temperature sensors that have excellent energy resolution and relatively fast response times. The excellent energy resolution provides good discrimination of signal from backgrounds, and the fast response time is important for minimizing the irreducible background caused by random coincidence of two-neutrino double-beta decay events of 100 Mo nuclei. Comparisons of the scintillating-light and phonon yields and pulse shape discrimination of the phonon signals will be used to provide redundant rejection of alpha-ray-induced backgrounds. An effective Majorana neutrino mass sensitivity that reaches the expected range of the inverted neutrino mass hierarchy, i.e., 20-50 meV, could be achieved with a 200 kg array of 48depl Ca 100 MoO 4 crystals operating for three years.

Neutron and muon-induced background studies for the AMoRE double-beta decay experiment

“…The simulation results with configuration 1 for the single-hit event rate in the (2)(3)(4)(5)(6)(7)(8) MeV energy region at the six energy binnings are shown in red in Fig 9.…”

“…The second phase of the AMoRE project (AMoRE-II) is being planned to operate at the YEMI underground laboratory (YEMI), located at Handuk, an active iron mine in the region of Mt. Yemi, South Korea [2]. The AMoRE-II experiment will use a ∼200 kg array of molybdate crystals with the aim of achieving the zerobackground level of <10 −5 counts/(keV•kg•yr) (ckky) in the region of interest (ROI), 3.034±0.010 MeV.…”

Charge-to-heat transducers exploiting the Neganov-Trofimov-Luke effect for light detection in rare-event searches

“…In spite of 10 14 -10 16 yr half-live of these rare beta decays, the induced counting rate and subsequently the probability of pile-ups in macro-bolometers containing these nuclides can be rather high, which strongly affects the precision of the spectrum reconstruction. Instead of using the macro-bolometer to trace 3 No light is expected for the interaction of alpha particles from natural radioactivity because of four orders of magnitude higher energy threshold required for the associated light emission (∼ 50 keV and ∼ 400 MeV respectively for TeO 2 ).…”

“…Bolometric light detectors are nowadays employed in several cryogenic experiments searching for rare events, as direct detection of dark matter (CRESST [1], COSINUS [2]) and searches for neutrinoless double-beta decay (AMoRE [3], LUCIFER/CUPID-0 [4], LUMINEU [5] and its follow-up CUPID-Mo [6]). They are coupled to the main scintillating crystals which contain the nuclear targets for the dark-matter particles or the nuclei that can undergo neutrinoless double-beta decay.…”

Neutron background measurement for rare event search experiments in the YangYang underground laboratory

“…In another tunnel space (A5) in the YangYang Pumped Storage Power station, several hundred meters away and at a similar depth, two laboratories were built in 2014. They were intended for a dark matter search experiment called COSINE [4], and a search for neutrinoless double beta decay, the Advanced Mo-based Rare process Experiment (AMoRE) [5,6].…”