Bulletin of the American Physical Society
2015 Fall Meeting of the APS Division of Nuclear Physics
Volume 60, Number 13
Wednesday–Saturday, October 28–31, 2015; Santa Fe, New Mexico
Session DD: Mini-Symposium on Nuclear Structure Relevant to Neutrinoless Double Beta Decay |
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Chair: Calem Hoffman, Argonne National Laboratory Room: Sweeney Ballroom C |
Thursday, October 29, 2015 10:30AM - 11:06AM |
DD.00001: Nuclear-Structure Data Relevant to Neutinoless-Double-Beta-Decay Matrix Elements Invited Speaker: Benjamin Kay An observation of neutrinoless double beta decay is one of the most exciting prospects in contemporary physics. It follows that calculations of the nuclear matrix elements for this process are of high priority. The change in the wave functions between the initial and final states of the neutrinoless-double-beta-decay candidates $^{76}$Ge$\rightarrow^{76}$Se, $^{100}$Mo$\rightarrow^{100}$Ru, $^{130}$Te$\rightarrow^{130}$Xe, and $^{136}$Xe$\rightarrow^{136}$Ba have been studied with transfer reactions. The data are focused on the change in the occupancies of the valence orbitals in the ground states as two neutrons decay into two protons. The results set a strict constraint on any theoretical calculations describing this rearrangement and thus on the magnitude of the nuclear matrix elements for this process, which currently exhibit uncertainties at the factor of 2-4 level. Prior to these measurements there were limited experimental data were available $A=76$ and 100 systems, and very limited data for the $A=130$ and 136 systems, in a large part due to the gaseous Xe isotopes involved. The uncertainties on most of these data are estimated to range from 0.1-0.3 nucleons. The program started with the $A=76$ system, with subsequent calculations, modified to reproduce the experimental occupancies, exhibiting a significant reduction in the discrepancy between various models. New data are available for the $A=100$, 130, and 136 systems. I review the program, making detailed comparisons between the latest theoretical calculations and the experimental data where available. [Preview Abstract] |
Thursday, October 29, 2015 11:06AM - 11:18AM |
DD.00002: Ground state occupation probabilities of neutrinoless double beta decay candidates Jenni Kotila, Jose Barea A better understanding of nuclear structure can offer important constraints on the calculation of $0\nu\beta\beta$ nuclear matrix elements. A simple way to consider differences between initial and final states of neutrinoless double beta decay candidates is to look at the ground state occupation probabilities of initial and final nuclei. As is well known, microscopic interacting boson model (IBM-2) has found to be very useful in the description of detailed aspects of nuclear structure. In this talk I will present results for ground state occupation probabilities obtained using IBM-2 for several interesting candidates of $0\nu\beta\beta$-decay. Comparison with recent experimental results is also made. [Preview Abstract] |
Thursday, October 29, 2015 11:18AM - 11:30AM |
DD.00003: Neutrino nuclear responses for double beta decays and astro neutrino interactions Hidetoshi Akimune, Hiroyasu Ejiri Neutrino nuclear matrix elements (NMEs), are crucial to extract neutrino properties from double beta decay (DBD) experiments, and to evaluate astro-neutrino nuclear interaction and nucleosynthesis rates. NMEs are very sensitive to nucleon nucleon spin-isospin($\sigma \tau$) and nuclear medium effects. Theoretical calculations for NMEs are very hard. Experimental inputs from charge exchange reactions such as ($^3$He,t) and ($\mu,\nu_{\mu}xn \gamma$) are very important for evaluating $\nu$-weak NMEs for $\beta \beta $ and astro-$\nu$ processes. Gamow-Teller (GT) and spin dipole (SD) NMEs are studied. Note GT is major for 2$\nu \beta \beta $, while SD is one of major components for $0\nu \beta \beta $. The observed NMEs for both GT and SD transitions are found to be reduced by $k_{\sigma \tau} \approx $0.4-0.5 due to the nucleon $\sigma \tau$ correlation and to the one $k_{NM}\approx $0.5-0.6 due to the nuclear medium effects such as nucleon isobar ($\Delta$) that are not explicitly included in the pnQRPA. The nuclear medium effects such as N$\Delta $ correlations are incorporated by using the effective coupling constant $g_A^{eff}$=(0.5-0.6)$\times g_A(free)$ for $ \beta \beta $ and astro-$\nu$ NMEs. [Preview Abstract] |
Thursday, October 29, 2015 11:30AM - 11:42AM |
DD.00004: Disentangling effects of mechanisms that could contribute to the neutrinoless double beta decay Mihai Horoi, Andrei Neacsu Neutrinoless double-beta decay, if observed, would signal physics beyond the Standard Model that could be discovered at energies significantly lower than those at which the relevant degrees of freedom could be excited. Therefore, it could be challenging to further use the neutrinoless double-beta decay observations to distinguish between many beyond Standard Model competing mechanisms to this process. Accurate nuclear structure calculation of the nuclear matrix elements 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. We will present information that one can get from the angular and energy distribution of the emitted electron assuming that the right-handed currents exist. [Preview Abstract] |
Thursday, October 29, 2015 11:42AM - 11:54AM |
DD.00005: Neutrinoless double-beta decay nuclear matrix elements for mass A$\sim$130 Andrei Neacsu, Mihai Horoi Neutrinoless double beta decay is an important process that could, if measured, provide valuable information regarding several neutrino properties and it's nature. Up to date, the most significant uncertainties in the theoretical study of this decay are related to the accuracy of the nuclear matrix elements that appear in the expressions of the lifetimes. We calculate the nuclear matrix elements for 124Sn and 130Te in a shell model approach, using a recently proposed effective Hamiltonian in the jj55 model space. For a better reliability of the nuclear matrix elements results, we investigate the effective Hamiltonian performing calculations of several spectroscopic quantities that are compared to the latest experimental data available, and we also analyze the two-neutrino double beta decay and the neutrinoless double beta decay matrix elements for 136Xe. We report new values of the nuclear matrix elements for 124Sn and 130Te for both light neutrino exchange and heavy neutrino exchange mechanisms, alongside a brief overview of some recent values from the literature. [Preview Abstract] |
Thursday, October 29, 2015 11:54AM - 12:06PM |
DD.00006: New limits for the $2\nu\beta\beta$ decay of $^{96}$Zr to excited nuclear states of $^{96}$Mo Sean Finch, Werner Tornow The final results from our search for the $2\nu\beta\beta$ decay of $^{96}$Zr to excited $0^+$ and $2^+$ states of $^{96}$Mo are presented. Such measurements provide valuable test cases for $2\nu\beta\beta$-decay nuclear matrix element calculations, which in turn are used to tune $0\nu\beta\beta$-decay nuclear matrix element calculations. After undergoing double-$\beta$ decay to an excited state, the excited daughter nucleus decays to the ground state, emitting two coincident $\gamma$ rays. These two $\gamma$ rays are detected in coincidence by two HPGe detectors sandwiching the $^{96}$Zr sample, with a NaI veto in anti-coincidence. This experimental apparatus, located at the Kimballton Underground Research Facility (KURF), has previously measured the $2\nu\beta\beta$ decay of $^{100}$Mo and $^{150}$Nd to excited nuclear states. Experimental limits on the $T_{1/2}$ and corresponding nuclear matrix element are presented for each of these decays. As a byproduct of this experiment, limits were also set on the single-$\beta$ decay of $^{96}$Zr. [Preview Abstract] |
Thursday, October 29, 2015 12:06PM - 12:18PM |
DD.00007: Low-lying levels of $^{76}$Ge, a candidate for neutrinoless double-$\beta$ decay S. Mukhopadhyay The low-spin structure of $^{76}$Ge was studied at the University of Kentucky with the (n,n$'\gamma$) reaction. This nucleus is a parent in double-$\beta$ decay and is also a rare example of a nucleus to exhibit rigid triaxial deformation in the low-lying states. Excitation function measurements performed with neutrons from 1.6 to 3.7 MeV helped determine the threshold for the $\gamma$ rays and hence their placement in the level scheme. Lifetimes, spins,multipolarities, and branching ratios were obtained from angular distributions measured at neutron energies of 3.0 and 3.5 MeV. New levels identified around 2 MeV will give insight to the nuclear structure aspects of $^{76}$Ge. It is also important to identify any $\gamma$ rays around 2039 keV, as the experimental signature for neutrinoless double-$\beta$ decay is a weak peak at this energy. In a recent study with 4.9-MeV neutrons, a reported 2039-keV $\gamma$ ray from the 3952-keV level was not observed. However, definitely a new level at 3147 keV with 2584- and 2038-keV $\gamma$ rays to the $2^+_1$ and $2^+_2$ states, respectively was established. These findings indicate that backgrounds in the search for the neutrinoless double-$\beta$ decay of $^{76}$Ge may be more complex. [Preview Abstract] |
Thursday, October 29, 2015 12:18PM - 12:30PM |
DD.00008: Precise Penning trap measurements of double $\beta $-decay Q-values M. Redshaw, M. Brodeur, G. Bollen, S. Bustabad, M. Eibach, K. Gulyuz, C. Izzo, D.L. Lincoln, S.J. Novario, R. Ringle, R. Sandler, S. Schwarz, A.A. Valverde The double $\beta $-decay ($\beta \beta $-decay) Q-value, defined as the mass difference between parent and daughter atoms, is an important parameter for both two-neutrino $\beta \beta $-decay (2$\nu \beta \beta$) and neutrinoless $\beta \beta $-decay (0$\nu \beta \beta$) experiments. The Q-value enters into the calculation of the phase space factors, which relate the measured $\beta \beta $-decay half-life to the nuclear matrix element and, in the case of 0$\nu \beta \beta $, the effective Majorana mass of the neutrino. In addition, the Q-value defines the total kinetic energy of the two electrons emitted in 0$\nu \beta \beta $, corresponding to the location of the single peak that is the sought after signature of 0$\nu \beta \beta $. Hence, it is essential to have a precise and accurate Q-value determination. Over the last decade, the Penning trap mass spectrometry community has made a significant effort to provide precise $\beta \beta $-decay Q-value determinations. Here we report on recent measurements with the Low Energy Beam and Ion Trap (LEBIT) facility at the National Superconducting Cyclotron Laboratory (NSCL) of the $^{48}$Ca, $^{82}$Se, and $^{96}$Zr Q-values. These measurements complete the determination of $\beta \beta $-decay Q-values for the 11 ``best'' candidates (those with Q \textgreater 2 MeV). We also report on a measurement of the $^{78}$Kr double electron capture (2EC) Q-value and discuss ongoing Penning trap measurements relating to $\beta \beta $-decay and 2EC. [Preview Abstract] |
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