Bulletin of the American Physical Society
4th Joint Meeting of the APS Division of Nuclear Physics and the Physical Society of Japan
Volume 59, Number 10
Tuesday–Saturday, October 7–11, 2014; Waikoloa, Hawaii
Session CM: Mini-Symposium on Double Beta Decay and Dark Matter I |
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Chair: Nicolai Tolich, University of Washington Room: Kona 5 |
Wednesday, October 8, 2014 7:00PM - 7:30PM |
CM.00001: Neutrino physics and double-beta decay: what can we learn and how Invited Speaker: Mihai Horoi Nutrinoless double-beta decay, if observed, would signal physics beyond the Standard Model that would be discovered at energies significantly lower than those at which the relevant degrees of freedom can be excited. Therefore, it could be difficult to use the neutrinoless double-beta decay observations to distinguish between several beyond Standard Model competing mechanisms that were propose to explain this process (see e.g. Phys. Rev. C 87, 014320 (2013)). Accurate nuclear structure calculation of the nuclear matrix elements (NME) necessary to analyze the decay rates could be helpful to narrow down the list of competing mechanisms, and to better identify the more exotic properties of the neutrinos. In my talk I will analyze the status of the NME shell model calculations, and their relevance for discriminating the possible competing mechanisms to the neutrinoless double-beta decay process. [Preview Abstract] |
Wednesday, October 8, 2014 7:30PM - 7:45PM |
CM.00002: Effect of QRPA correlations on nuclear matrix element of neutrinoless double-beta decay through overlap of QRPA states Jun Terasaki We calculate the nuclear matrix element of the neutrinoless double-beta decay for $^{150}$Nd $\rightarrow$ $^{150}$Sm using quasiparticle random-phase approximation (QRPA) with Skyrme and volume pairing energy density functionals. We calculate the overlap of the QRPA states obtained on the basis of the ground states of the parent and the daughter nuclei using the definition of QRPA ground state as the vacuum to QRPA quasi bosons. More QRPA correlations are included in the nuclear matrix element by this method than usual QRPA approaches. These QRPA correlations have a significant effect to lower the nuclear matrix element through the overlap. This reseach is supported by Grants-in-Aid for Scientific Research (C), 26400265, and HPCI Strategic Program Field 5. The computations were performed using the K computer, AICS, RIKEN (hp120192 and hp120287); Mira, ALCF; T2K-Tsukuba and Coma, CCS, University of Tsukuba; CX400, Information Technology Center, Nagoya University (hp120287); and SR16000, YITP, Kyoto University. [Preview Abstract] |
(Author Not Attending)
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CM.00003: $\beta\beta$-decay nuclear matrix elements and half-life predictions in the interacting boson model with isospin restoration J. Kotila, J. Barea, F. Iachello Recently, we have introduced a method for isospin restoration in the calculation of nuclear matrix elements (NME) for $0\nu\beta\beta$ and $2\nu\beta\beta$ decay within the framework of IBM-2 [1]. With this method, we calculate NME for all processes of interest in $0\nu\beta^-\beta^-$, $2\nu\beta^-\beta^-$, and in $0\nu\beta^+\beta^+$, $0\nu\beta^+ EC^+$, $0\nu ECEC$, $2\nu\beta^+\beta^+$, $2\nu\beta^+EC$, and $2\nu ECEC$. With isospin restoration, we find that the Fermi (F) matrix elements for $2\nu\beta\beta$ vanish, as expected, and those for $0\nu\beta\beta$ are considerably reduced. By combining these matrix elements with recently calculated phase-space factors [2-4] we are able to make our most accurate half-life predictions for all discussed processes.\\[4pt] [1] J.\ Barea, J. Kotila and F.\ Iachello, In preparation.\\[0pt] [2] J. Kotila and F.\ Iachello, Phys. Rev. C \textbf{85}, 034316 (2012).\\[0pt] [3] J. Kotila and F.\ Iachello, Phys. Rev. C \textbf{87}, 024313 (2013).\\[0pt] [4] J. Kotila, J. Barea, and F.\ Iachello, Phys. Rev. C \textbf{89}, 064319 (2014). [Preview Abstract] |
Wednesday, October 8, 2014 8:00PM - 8:15PM |
CM.00004: Large-scale shell model calculations for two-neutrino double-beta decay of 48Ca Yoritaka Iwata, Noritaka Shimizu, Yutaka Utsuno, Michio Honma, Takashi Abe, Takaharu Otsuka Two-neutorino double-beta decay of $^{48}$Ca is studied based on large-scale shell model calculations. According to the experiments by Yako et al., shell model calculations accounting only for one major shell (pf shell) possibly underestimate the Gamow-Teller transition strength from $^{48}$Ca to $^{48}$Sc and that from $^{48}$Sc to $^{48}$Ti. It may imply that the shell model calculations accounting only for pf shell fails to evaluate the contribution of the highly-excited 1$^+$ state of $^{48}$Sc, where the Gamow-Teller transition is the main process of two-neutrino double-beta decay. In this paper, a large-scale shell model calculations including two major shells is carried out. By expanding the model space from pf shell to sdpf shell, the effect due to the excitation of nucleons from sd shell to pf shell is taken into account. In this model space the proton excitation states, which is expected to play an important role in both low and high energy excited states of 48Ca, 48Sc and 48Ti, can appear. Consequently the effect due to the excitation across the two major shells is evaluated as Gamow-Teller transition strength from $^{48}$Ca to $^{48}$Sc, that from $^{48}$Sc to $^{48}$Ti, and two-neutrino double-beta decay matrix element of $^{48}$Ca. [Preview Abstract] |
Wednesday, October 8, 2014 8:15PM - 8:30PM |
CM.00005: Nuclear matrix elements of the double beta decay for mass around 80 Naotaka Yoshinaga, Koji Higashiyama, Eri Teruya In nature there are 30 kinds of nuclei which are expected to have double beta decays. Among them ten nuclei are actually observed for the neutrino double beta decays. Still no observation is made for the neutrinoless double beta decays (0$\nu \beta \beta )$. The 0$\nu \beta \beta $ decay is expected to occur only when neutrinos have masses and they are Majorana particles. In that respect observation of 0$\nu \beta \beta $ is to determine whether neutrinos are Majorana particles or not. In theoretical side in order to estimate the half life of 0$\nu \beta \beta $ determination of the nuclear matrix elements are essential. They were calculated in many theoretical frameworks, but the results are not consistent in various models. In this study we carry out shell model calculations for $^{82}$Se and $^{82}$Kr nuclei. After obtaining the wavefunctions, we calculate the nuclear matrix elements. For comparison we make pair truncated shell model calculations. [Preview Abstract] |
Wednesday, October 8, 2014 8:30PM - 8:45PM |
CM.00006: CANDLES -- Search for Neutrino-less Double Beta Decay of $^{48}$Ca Saori Umehara CANDLES is the project to search for neutrino-less double beta decay (0$\nu\beta\beta$) of $^{48}$Ca. The CANDLES system aims at a high sensitive measurement by a characteristic detector system and $^{48}$Ca enrichment. The system realizes a complete 4$\pi$ active shield by immersing the CaF$_{2}$ scintillators in liquid scintillator. The active shield by the liquid scintillator will effectively reject background events from external origins. On the other band, we have studied $^{48}$Ca enrichment and succeeded in obtaining enriched $^{48}$Ca although it is a small amount. Now we have developed the CANDLES III system, which contained 350 g of $^{48}$Ca without enrichment, at the Kamioka underground laboratory. Two improvements, a light-concentration system and a new DAQ system, were installed for the CANDLES III system. The light-concentration system improved a energy resolution by increasing a PMT photo-coverage by 80\%. The new DAQ system, which is a dead time less system, improved a rejection efficiency for a characteristic background origin. We checked detector performance with the light-concentration system and the new DAQ system. Here we will report the detector performance for background rejection and the expected sensitivity with the two improvements. [Preview Abstract] |
Wednesday, October 8, 2014 8:45PM - 9:00PM |
CM.00007: Search for $0\nu\beta\beta$ with CUORE: Preliminary results from CUORE-0 Jonathan Ouellet The Cryogenic Underground Observatory for Rare Events (CUORE) is a next-generation bolometric detector that will search for neutrinoless double-beta (0$\nu\beta\beta$) decay and other rare processes. It is currently in the advanced stages of construction in the Gran Sasso National Laboratories in Italy. Its predecessor, Cuoricino, set the most stringent limits to date on the 0$\nu\beta\beta$ decay half-life of $^{130}$Te, at $T_{1/2}\geq2.8\times10^{24}$ yr (90\% C.L.). CUORE will have an active mass nearly 19 times larger and an anticipated background about 16 times lower, providing a 1$\sigma$ sensitivity to 0$\nu\beta\beta$ decay half-life of $T_{1/2}\geq1.6\times10^{26}$ yr after 5 years of live time. CUORE is expected to begin taking data in early 2015. CUORE-0, the first stage of CUORE, is currently operating in the former Cuoricino cryostat and has been taking data since March 2013. Here we present early results from CUORE-0 and the implications for CUORE. [Preview Abstract] |
Wednesday, October 8, 2014 9:00PM - 9:15PM |
CM.00008: Overview and Status of the MAJORANA DEMONSTRATOR Susanne Mertens A unique way to explore the nature of the neutrino is the search for neutrinoless double beta decay ($\beta\beta$(0$\nu$)-decay). Observation of $\beta\beta$(0$\nu$)-decay would decisively prove that neutrinos are Majorana particles and that lepton number is violated. The MAJORANA DEMONSTRATOR will perform a search for $\beta\beta$(0$\nu$)-decay in 76Ge. The experiment is currently under construction at the Sanford Underground Laboratory in South Dakota, USA. It will use an array of 40 kg of HPGe detectors, up to 30 kg of which will be enriched to 86\% in 76Ge, surrounded by passive and active shielding. The major goal is to demonstrate a path forward to achieving a background rate at or below 1 cnt/(ROI-t-y) in the 4 keV region of interest (ROI) around the 2039-keV Q-value of the 76Ge $\beta\beta$(0$\nu$)-decay. This is required for the next generation of tonne-scale germanium-based $\beta\beta$(0$\nu$)-decay searches that will probe the neutrino mass scale in the inverted-hierarchy region. This talk will give a general overview of the experiment and its current status. [Preview Abstract] |
Wednesday, October 8, 2014 9:15PM - 9:30PM |
CM.00009: {\sc Majorana Demonstrator}: Prototype Module Commissioning Christopher O'Shaughnessy The {\sc Majorana Demonstrator} is designed to explore the feasibility of operating a tonne-scale search for neutrinoless double beta decay by utilizing germanium detectors enriched in the isotope $^{76}$Ge as both a source and detector. A key goal of the {\sc Demonstrator} is to achieve a background of 3 counts per tonne-year in the region of interest using a compact copper and lead shield. Meeting such a stringent background limit necessitates the custom design of components from materials known to be clean. Most notable are the inner shield, the strings that hold the enriched detectors, and the module cryostats that contain the strings. These are fabricated from ultra-high purity copper that has been electroformed underground. A prototype module with strings of natural Ge detectors has been operated using a cryostat and components fabricated from commercial copper. Here we will highlight the performance of the prototype module and its role in assembly of the ultra-pure modules. [Preview Abstract] |
Wednesday, October 8, 2014 9:30PM - 9:45PM |
CM.00010: Overview of the AMoRE Hong Joo Kim Searching for neutrino-less double beta decay of Mo-100 using a cryogenic technique with Mo-100 enriched and Ca-48 depleted calcium molybdate (CaMoO4) crystal scintillators will be performed by AMoRE (Advanced Mo-based Rare process Experiment) international collaboration. The project aims to build a large-scale multi-detector with 200 kg of CaMoO4 crystals operating in in a deep underground laboratory in Korea for several years. Significant improvement of effective Majorana neutrino mass sensitivity is expected at the level of 20-50 meV covering the inverted hierarchy region. CaMoO4 crystals show the brightest scintillation light among variety of molybdate crystals at room and cryogenic temperatures. The AMoRE will run at milli-Kelvin temperature with CaMoO4 crystals and metallic magnetic calorimeters (MMCs) as a temperature sensor that shows excellent energy resolution. Optimization of scintillation properties of CaMoO4 crystals grown by Czochralski method with different conditions will be shown. The internal background study of large CaMoO4 crystals as well as background reduction methods using GEANT4 simulations will be presented. The current status and future plan of the AMoRE project will be also presented. [Preview Abstract] |
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