Bulletin of the American Physical Society
2017 Fall Meeting of the APS Division of Nuclear Physics
Volume 62, Number 11
Wednesday–Saturday, October 25–28, 2017; Pittsburgh, Pennsylvania
Session PC: Mini-Symposium on Nuclear Matrix Element Calculations for Neutrinoless Double-Beta Decay |
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Chair: John Engel, UNC Chapel Hill Room: Salon 3 |
Saturday, October 28, 2017 10:30AM - 11:06AM |
PC.00001: Effective theory approach to neutrinoless double beta decay Invited Speaker: Vincenzo Cirigliano After a short introduction on neutrinoless double beta decay as probe of lepton number violation, I will discuss an effective field theory approach to the problem. I will begin by classifying the possible sources of lepton number violation in the effective theory that describes new physics beyond the Standard Model. Then, for each major class of operators (including the light Majorana neutrino mass), I will discuss the matching to hadronic and nuclear descriptions, using chiral effective theory as the organizing principle. I will highlight recent progress in this matching and recent results from lattice QCD and few-body calculations. [Preview Abstract] |
Saturday, October 28, 2017 11:06AM - 11:18AM |
PC.00002: First principles calculations of weak decays in atomic nuclei Gaute Hagen This talk reports on recent progress in first principles computations of neutrinoless and two-neutrino double-beta decay in~$^{\mathrm{48}}$Ca, with interactions and currents from chiral effective field theory. Predictions from coupled-cluster and in-medium similarity-renormalization-group calculations agree, and they yield a nuclear matrix element for the neutrinoless double beta decay that is smaller than expected. Calculations of Gamow-Teller decays from~$p$-shell nuclei to tin isotopes reveal that the long-standing problem of the quenching of the axial coupling constant~$g_{\mathrm{A}}~$can be resolved by meson exchange currents and a proper treatment for many-body~correlations. In particular,~meson-exchange currents play a crucial role in the~super-allowed Gamow-Teller decay of~$^{\mathrm{100}}$Sn. [Preview Abstract] |
Saturday, October 28, 2017 11:18AM - 11:30AM |
PC.00003: Ab initio $0\nu\beta\beta$ matrix elements from the valence space IMSRG Ragnar Stroberg, Charlie Payne, Jason Holt Neutrinoless double beta decay poses two main challenges to nuclear theory: (1) The process has not been observed, and so there is no way to experimentally constrain an empirical effective operator for phenomenological approaches, as is done with e.g. the quenching of $g_{A}$ or effective charges for E2 transitions. This may be addressed by deriving the transition operator from chiral effective field theory, however this raises the second issue: (2) Nuclei of interest in searches for neutrinoless double beta decay, such as $^{76}$Ge and $^{136}$Xe, are difficult to treat with the ab initio many-body approaches needed to employ a transition operator derived from chiral effective field theory. I will discuss recent process towards overcoming these two difficulties by using the valence space in-medium similarity renormalization group approach. [Preview Abstract] |
Saturday, October 28, 2017 11:30AM - 11:42AM |
PC.00004: Double beta decay nuclear matrix elements in extended shell model spaces Mihai Horoi In a recent publication (Phys. Rev. C 92, 041301(R) (2015)) we concluded that the shell model double beta decay nuclear matrix elements may be affected to certain degrees by the lack of pairing correlations with orbitals outside the typical shell model spaces. Here we report results of calculations for $^{48}$Ca that includes 21 spherical orbitals for both protons and neutrons. We are using a realistic Hamiltonian inside the $fp$ model space, thus maintaining a good description of the nuclear structure properties of the nuclei of interest. We are only allowing pairing interactions between the $fp$ orbitals and the remaining 17 orbitals, and up to two particle excitations in and out of the $fp$ model space. This approach could be also extended to the case of $^{82}$Se. [Preview Abstract] |
Saturday, October 28, 2017 11:42AM - 11:54AM |
PC.00005: Collective aspects of nuclear structure as a constraint on neutrinoless double-beta decay nuclear matrix element calculations Jack Henderson, James Smallcombe, Adam Garnsworthy, Jenna Smith Large discrepancies are found between calculations of the neutrinoless double-beta decay nuclear matrix element performed in different theoretical frameworks, corresponding to differences of almost order-of-magnitude when translated to deviations in the decay rate. Given this discrepancy, experimental nuclear-structure input is essential to constrain calculations. To date a number of studies have been performed, for example probing nuclear occupancies and Gamow-Teller strengths. Meanwhile, work utilizing beyond mean-field methodologies has demonstrated a significant dependence of the neutrinoless double-beta decay transition strength on the deformation of both the parent and daughter nuclei. That this dependence exists can also be concluded based on simple arguments regarding the geometric overlap of the initial and final states. It is important, therefore, to experimentally verify the nuclides' collective nuclear properties. To that end I will describe a proposed campaign of measurements utilizing well-established nuclear structure techniques such as Coulomb excitation and $E0$ spectroscopy to determine the collective properties of neutrinoless double-beta decay candidates. These measurements can provide both qualitative and quantitative constraints on the nuclear matrix element. [Preview Abstract] |
Saturday, October 28, 2017 11:54AM - 12:06PM |
PC.00006: Neutrinoless double beta decay from lattice QCD Amy Nicholson, Chia Cheng, Evan Berkowitz, Enrico Rinaldi, Andre Walker-Loud, Pavlos Vranas, Thorsten Kurth, M. A. Clark, Nicolas Garron, Brian Tiburzi, Henry Monge-Camacho, David Brantley, Balint Joo Lepton number-violating neutrinoless double beta decay is a natural consequence of Majorana neutrinos and many BSM theories, and, if observed, could potentially explain the observed matter/anti-matter asymmetry in the universe. Several experimental searches for these processes using nuclear sources are planned and/or underway worldwide, and understanding quantitatively how neutrinoless double beta decay would manifest in nuclear environments is key for interpreting any observed signals. While long-range, light neutrino exchange is the most common mechanism studied, short-range interactions involving heavy mediator exchange may also contribute. In this talk I will give an overview of the microscopic observables relevant for experimental searches for neutrinoless double beta decay which may be calculated directly from QCD using lattice methods, and present results for short-range matrix elements contributing to pion exchange diagrams between nucleons. [Preview Abstract] |
Saturday, October 28, 2017 12:06PM - 12:18PM |
PC.00007: Two-body currents in NLDBD matrix elements of light nuclei Saori Pastore We report recent Quantum Monte Carlo calculations of neutrinoless double-beta decay matrix elements in $A=6-10$ nuclei with standard and non-standard two-body current contributions. [Preview Abstract] |
Saturday, October 28, 2017 12:18PM - 12:30PM |
PC.00008: Double-beta decay processes from lattice quantum chromodynamics Zohreh Davoudi, Brian Tiburzi, Michael Wagman, Frank Winter, Emmanuel Chang, William Detmold, Kostas Orginos, Martin Savage, Phiala Shanahan While an observation of neutrinoless double-beta decay in upcoming experiments will establish that the neutrinos are Majorana particles, the underlying new physics responsible for this decay can only be constrained if the theoretical predictions of the rate are substantially refined. This talk demonstrates the roadmap in connecting the underlying high-scale theory to the corresponding nuclear matrix elements, focusing mainly on the nucleonic matrix elements in the simplest extension of Standard Model in which a light Majorana neutrino is mediating the process. The role of lattice QCD and effective field theory in this program, in particular, the prospect of a direct matching of the nn to pp amplitude to lattice QCD will be discussed. As a first step towards this goal, the results of the first lattice QCD calculation of the relevant matrix element for neutrinofull double-beta decay will be presented, albeit with unphysical quark masses, along with important lessons that could impact the calculations of nuclear matrix elements involved in double-beta decays of realistic nuclei. [Preview Abstract] |
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