Search

We report a study on the background of the Advanced Molybdenum-Based Rare process Experiment (AMoRE), a search for neutrinoless double beta decay (\znbb) of $^{100}$Mo. The pilot stage of the experiment was conducted using $\sim$1.9 kg of \CAMOO~ crystals at the Yangyang Underground Laboratory, South Korea, from 2015 to 2018. We compared the measured $\beta/\gamma$ energy spectra in three experimental configurations with the results of Monte Carlo simulations and identified the background sources in each configuration. We replaced several detector components and enhanced the neutron shielding to lower the background level between configurations. A limit on the half-life of $0\nu\beta\beta$ decay of $^{100}$Mo was found at $T_{1/2}^{0\nu} \ge 3.0\times 10^{23}$ years at 90\% confidence level, based on the measured background and its modeling. Further reduction of the background rate in the AMoRE-I and AMoRE-II are discussed.

The construction of a butt-end multicell matrix proportional counter (MMPC) is presented in the work. Each cell is a butt-end proportional counter with a 5 mm cathode diameter and 0.8 mm circular anode diameter. In the example of the $3\times3$ matrix, it is shown that the gas multiplication of the central cell depends on the potentials at the anodes of the peripheral cells, the drift electrode, the forming rings, and the surrounding metal parts of the structure. The amplitude characteristics were measured when the MMPC was filled with mixtures of 96.3\% Ar + 3.7\% Xe and 90\% Ar + 10\% CH$_4$ at pressures of 620 Torr and 62 Torr. The calibration was carried out with $\alpha$-particles and $\gamma$-quanta from a $^{238}$Pu source. For photons with energies of 7.5 keV, a resolution of 26\% was obtained. It is shown that, based on MMPC, it is possible to fabricate recording surfaces of arbitrary configuration., Comment: 7 pages, 4 figures

Results of a comparative analysis of the $^{214}$Po ($T_{1/2}= 163.47\pm0.03$ $\mu$s), $^{213}$Po ($T_{1/2}=3.705 \pm 0.001$ $\mu$s) and $^{212}$Po ($T_{1/2}=294.09\pm0.07$ ns) half-life annular variation parameters are presented. It is shown that two independent sequential sets of the $^{214}$Po $\tau$-values $(\tau\equiv T_{1/2})$ obtained in the spaced laboratories can be described by sinusoidal functions. The sinusoid curve with amplitude $A=(5.0 \pm1.5) \cdot 10^{-4}$, period $\omega=(365\pm 8)$ days, and phase $\phi=(170 \pm 7)$ days approximates the set of $^{214}$Po $\tau$ values obtained at BNO INR RAS during the $\sim$973 days starting on January 4, 2012. The function approximates a set of $\tau$-values with a time duration of $\sim1460$ days obtained at the KhNU has an amplitude $A=(4.9\pm1.8)\cdot10^{-4}$, a period $\omega= (377\pm13)$ days and a phase $\phi=(77\pm10)$ days. The $^{213}$Po $\tau$-value set with a time duration of $\sim1700$ days can be described by a sinusoidal function with an amplitude $A=(3.9\pm1.2)\cdot10^{-4}$, a period $\omega= (370\pm13)$ days and a phase $\phi=(130\pm9)$ days. The $^{212}$Po $\tau$-value set with a time duration of $\sim670$ days can be described by a sinusoidal function with an amplitude $A=(7.5\pm1.6)\cdot10^{-4}$, a period $\omega= (375\pm13)$ days and a phase $\phi=(40\pm10)$ days., Comment: 6 pages, 5 figures, Prepared for the proceedings of The 5th International Conference on Particle Physics and Astrophysics (ICPPA-2020)

The Advanced Molybdenum-based Rare process Experiment (AMoRE) aims to search for neutrinoless double beta decay (0$\nu\beta\beta$) of $^{100}$Mo with $\sim$100 kg of $^{100}$Mo-enriched molybdenum embedded in cryogenic detectors with a dual heat and light readout. At the current, pilot stage of the AMoRE project we employ six calcium molybdate crystals with a total mass of 1.9 kg, produced from $^{48}$Ca-depleted calcium and $^{100}$Mo-enriched molybdenum ($^{48\textrm{depl}}$Ca$^{100}$MoO$_4$). The simultaneous detection of heat(phonon) and scintillation (photon) signals is realized with high resolution metallic magnetic calorimeter sensors that operate at milli-Kelvin temperatures. This stage of the project is carried out in the Yangyang underground laboratory at a depth of 700 m. We report first results from the AMoRE-Pilot $0\nu\beta\beta$ search with a 111 kg$\cdot$d live exposure of $^{48\textrm{depl}}$Ca$^{100}$MoO$_4$ crystals. No evidence for $0\nu\beta\beta$ decay of $^{100}$Mo is found, and a upper limit is set for the half-life of 0$\nu\beta\beta$ of $^{100}$Mo of $T^{0\nu}_{1/2} > 9.5\times10^{22}$ y at 90% C.L.. This limit corresponds to an effective Majorana neutrino mass limit in the range $\langle m_{\beta\beta}\rangle\le(1.2-2.1)$ eV.

A search for resonant absorption of the solar axion by $^{83}\rm{Kr}$ nuclei was performed using the proportional counter installed inside the low-background setup at the Baksan Neutrino Observatory. The obtained model independent upper limit on the combination of isoscalar and isovector axion-nucleon couplings $|g_3-g_0|\leq 8.4\times 10^{-7}$ allowed us to set the new upper limit on the hadronic axion mass of $m_{A}\leq 65$ eV (95\% C.L.) with the generally accepted values $S$=0.5 and $z$=0.56., Comment: 4 pages, 2 figures, Proceedings of the 13th Patras Workshop on Axions, WIMPs and WISP, May 15th to 19th 2017, Thessaloniki, Greece

A series of measurements has been started where the ¹⁴C concentration is determined from several liquid scintillator samples. A dedicated setup has been designed and constructed with the aim of measuring concentrations smaller than 10−18. Measurements take place in two underground laboratories: in the Baksan Neutrino Observatory, Russia, and in the new Callio Lab in the Pyhäsalmi mine, Finland. Low-energy neutrino detection with a liquid scintillator requires that the intrinsic ¹⁴C concentration in the liquid is extremely low. In the Borexino CTF detector the concentration of 2 × 10−18 has been achieved being the lowest value ever measured. In principle, the older the oil or gas source that the liquid scintillator is derived from and the deeper it situates, the smaller the ¹⁴C concentration is supposed to be. This, however, is not generally the case and the concentration is probably due to the U and Th content of the local environment.

A search for resonant absorption of the solar axion by $^{83}\rm{Kr}$ nuclei was performed using the proportional counter installed inside the low-background setup at the Baksan Neutrino Observatory. The obtained model independent upper limit on the combination of isoscalar and isovector axion-nucleon couplings $|g_3-g_0|\leq 8.4\times 10^{-7}$ allowed us to set the new upper limit on the hadronic axion mass of $m_{A}\leq 65$ eV (95\% C.L.) with the generally accepted values $S$=0.5 and $z$=0.56., Comment: 4 pages, 2 figures, Proceedings of the 13th Patras Workshop on Axions, WIMPs and WISP, May 15th to 19th 2017, Thessaloniki, Greece

The main background hindering low-energy (≲ 200 keV) neutrino measurements with liquid scintillators comes from the minute remanence of the cosmogenic ¹⁴C (T₁/₂ ≃ 5700 a) present in the organic oil constituting the bulk of the scintillator. The β-decay endpoint energy of ¹⁴C is quite low, Q = 156 keV, and the counting rate from ¹⁴C is often reduced by threshold settings. However, too high concentration of ¹⁴C may results in pile-up pulses. For example, in the Borexino detector at Gran Sasso, Italy, being the most sensitive neutrino detector, the trigger rate is largely dominated by the ¹⁴C isotope [1] with the concentration of 2 × 10⁻¹⁸ [2] It is the lowest ¹⁴C concentration value ever measured. There are only a few results available on the ¹⁴C concentration. In addition to the one in Ref. [2] there are three other measurements reported in Refs. [3, 4, 5]. Obviously ¹⁴C cannot be removed from liquid scintillators by chemical methods, or by other methods in large quantities (liters). In principle, the older is the oil or gas source that the liquid scintillator is made of and the deeper it situates, the smaller the ¹⁴C concentration should be. This, however, is not generally the case and it is believed that the ratio depends on the activity (U and Th content) in the environment of the source. We are performing a series of measurements where the ¹⁴C concentration will be measured from several liquid scintillator samples. They need low-background environment and are taking place in two deep underground laboratories: in the new CallioLab laboratory in the Pyhäsalmi mine, Finland, and at the Baksan Neutrino Observatory, Russia, in order to reduce and better understand the systematical uncertainties. Preliminary results will be presented.

The matrices formed of silicon photomultipliers (SiPMs) are very promising photosensors for the scintillation detectors. The use of SiPM matrices with appropriate optical collector gives, in principle, a possibility to do a snapshot of glowing track of charged particle traversing a scintillator. The prototype of such scintillation detector is under development now in INR RAS. The preliminary results of characterization study of the matrix ArrayC-60035-64P-PCB (SensL company) for the prototype of such detector are presented., Comment: Poster contribution to the International Conference on New Photo-detectors (July 6-9, 2015, Moscow, Troitsk, Russia), to be published in PoS (PhotoDet2015)

The brief description of installation TAU-2 intended for long-term monitoring of the half-life value $\tau$ ($\tau_{1/2}$) of the $^{214}$Po is presented. The methods of measurement and processing of collected data are reported. The results of analysis of time series values $\tau$ with different time step are presented. Total of measurement time was equal to 590 days. Averaged value of the $^{214}$Po half-life was obtained $\tau=163.46\pm0.04$ $\mu$s. The annual variation with an amplitude $A=(8.9\pm2.3)\cdot10^{-4}$, solar-daily variation with an amplitude $A_{So}=(7.5\pm1.2)\cdot10^{-4}$, lunar-daily variation with an amplitude $A_L=(6.9\pm2.0)\cdot10^{-4}$ and sidereal-daily variation with an amplitude $A_S=(7.2\pm1.2)\cdot10^{-4}$ were found in a series of $\tau$ values. The maximal values of amplitude are observed at the moments when the projections of the installation Earth location velocity vectors toward the source of possible variation achieve its maximal magnitudes., Comment: Talk at The International Workshop on Prospects of Particle Physics: "Neutrino Physics and Astrophysics" February 1 - Ferbuary 8, 2015, Valday,Russia, 7 pages, 12 figure (to be published in PEPAN)

A search for resonant absorption of the solar axion by $^{83}\rm{Kr}$ nuclei was performed using the proportional counter installed inside the low-background setup at the Baksan Neutrino Observatory. The obtained model independent upper limit on the combination of isoscalar and isovector axion-nucleon couplings $|g_3-g_0|\leq 1.69\times 10^{-6}$ allowed us to set the new upper limit on the hadronic axion mass of $m_{A}\leq 130$ eV (95\% C.L.) with the generally accepted values $S$=0.5 and $z$=0.56., Comment: 5 pages, 2 figures, Proceedings of the 10th Patras Workshop on Axions, WIMPs and WISP 29 June - 4 July 2014, CERN, Geneva, Switzerland

A search for resonant absorption of the solar axion by $^{83}\rm{Kr}$ nuclei was performed using the proportional counter installed inside the low-background setup at the Baksan Neutrino Observatory. The obtained model independent upper limit on the combination of isoscalar and isovector axion-nucleon couplings $|g_3-g_0|\leq 1.69\times 10^{-6}$ allowed us to set the new upper limit on the hadronic axion mass of $m_{A}\leq 130$ eV (95\% C.L.) with the generally accepted values $S$=0.5 and $z$=0.56., Comment: 5 pages, 2 figures, Proceedings of the 10th Patras Workshop on Axions, WIMPs and WISP 29 June - 4 July 2014, CERN, Geneva, Switzerland

In order to detect low-energy neutrinos, for example the solar neutrinos from the ppchain (with the maximum neutrino energy of approximately 400 keV) requires that the intrinsic ¹⁴C content in a liquid scintillator is at extremely low level. In the Borexino detector, a 300-ton liquid scintillation detector at Gran Sasso, Italy, the ratio of ¹⁴C to ¹²C of approximately 2 × 10⁻¹⁸ has been achieved. It is the lowest value ever measured. The detector situates underground at the depth of 3200 mwe (1200 m). ¹⁴C cannot be removed from liquid scintillators by chemical methods, or by other methods in large quantities (liters). In principle, the older is the oil or gas source that the liquid scintillator is made of and the deeper it situates, the smaller should be the ¹⁴C-to-¹²C ratio. This, however, is not generally the case, and the ratio depends on the activity (U and Th content) in the environment of the source. We have started a series of measurements where the ¹⁴C-to-¹²C ratio will be measured from liquid scintillator samples. The measurements take place in two underground laboratories: in the Pyhäsalmi mine, Finland, at the depth of 4000 mwe (1400 meters) and at the Baksan Underground Laboratory, Russia at 4800 mwe, for reducing and better understanding systematical uncertainties. There will be about ten samples with the known origin, each of them 2 litres. The liquid scintillator vessel, light quides and low-active PMTs will be shielded with thick layers copper and lead. Nitrogen flow is used to reduce the radon background. The aim is to measure ratios smaller than 10⁻¹⁸, if such samples exists. One measurement takes several weeks.

A search for resonant absorption of the solar axion by $^{83}\rm{Kr}$ nuclei was performed using the proportional counter installed inside the low-background setup at the Baksan Neutrino Observatory. The obtained model independent upper limit on the combination of isoscalar and isovector axion-nucleon couplings $|g_3-g_0|\leq 1.69\times 10^{-6}$ allowed us to set the new upper limit on the hadronic axion mass of $m_{A}\leq 130$ eV (95\% C.L.) with the generally accepted values $S$=0.5 and $z$=0.56., Comment: 5 pages, 2 figures, Proceedings of the 10th Patras Workshop on Axions, WIMPs and WISP 29 June - 4 July 2014, CERN, Geneva, Switzerland

The matrices formed of silicon photomultipliers (SiPMs) are very promising photosensors for the scintillation detectors. The use of SiPM matrices with appropriate optical collector gives, in principle, a possibility to do a snapshot of glowing track of charged particle traversing a scintillator. The prototype of such scintillation detector is under development now in INR RAS. The preliminary results of characterization study of the matrix ArrayC-60035-64P-PCB (SensL company) for the prototype of such detector are presented., Comment: Poster contribution to the International Conference on New Photo-detectors (July 6-9, 2015, Moscow, Troitsk, Russia), to be published in PoS (PhotoDet2015)

The brief description of installation TAU-2 intended for long-term monitoring of the half-life value $\tau$ ($\tau_{1/2}$) of the $^{214}$Po is presented. The methods of measurement and processing of collected data are reported. The results of analysis of time series values $\tau$ with different time step are presented. Total of measurement time was equal to 590 days. Averaged value of the $^{214}$Po half-life was obtained $\tau=163.46\pm0.04$ $\mu$s. The annual variation with an amplitude $A=(8.9\pm2.3)\cdot10^{-4}$, solar-daily variation with an amplitude $A_{So}=(7.5\pm1.2)\cdot10^{-4}$, lunar-daily variation with an amplitude $A_L=(6.9\pm2.0)\cdot10^{-4}$ and sidereal-daily variation with an amplitude $A_S=(7.2\pm1.2)\cdot10^{-4}$ were found in a series of $\tau$ values. The maximal values of amplitude are observed at the moments when the projections of the installation Earth location velocity vectors toward the source of possible variation achieve its maximal magnitudes., Comment: Talk at The International Workshop on Prospects of Particle Physics: "Neutrino Physics and Astrophysics" February 1 - Ferbuary 8, 2015, Valday,Russia, 7 pages, 12 figure (to be published in PEPAN)

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 \mohundred. 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 \Mo[100]-enriched and \Ca[48]-depleted calcium molybdate ($\mathrm{^{48depl}Ca^{100}MoO_4}$) crystals that are located in a deep underground laboratory in Korea. The \mohundred nuclide was chosen for this \zeronubb decay search because of its high $Q$-value and favorable nuclear matrix element. Tests have demonstrated that \camo crystals produce the brightest scintillation light among all of the molybdate crystals, both at room and at cryogenic temperatures. $\mathrm{^{48depl}Ca^{100}MoO_4}$ 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 \mohundred 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 $\mathrm{^{48depl}Ca^{100}MoO_4}$ crystals operating for three years., Comment: 93 pages