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 1WA: Workshop: Theory and Computation for Neutrinos and Fundamental Symmetries |
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Chair: Joe Carlson, Los Alamos National Laboratory Room: Sweeney Ballroom A |
Wednesday, October 28, 2015 9:00AM - 9:30AM |
1WA.00001: Coupled-cluster computation of electroweak observables Invited Speaker: Sonia Bacca Recently, coupled-cluster computations were extended to electro-weak observables in light and medium-mass nuclei. In particular, we have reformulated the Lorentz Integral transform method within the coupled-cluster formalism [1] to allow the investigation of break-up observables with the continuum properly taken into account. This new method, dubbed LIT-CC, has permitted ab-initio studies of photodisintegration cross sections in stable nuclei (16O, 40Ca) and Coulomb break-up cross sections in unstable nuclei (22O). Next, we aim at studying Gamow-Teller strengths distribution using this method. I will report on a recent calculation of the total Gamow-Teller strength in the beta decay of 14C, 22O and 24O [2]. We found that two-body currents lead to a quenching of the Ikeda sum rule and it is interesting to see how the strength is distributed. This will be studied using the LIT-CC method. Finally, our long term goal is to tackle neutrino-nucleus interactions using this coupled-cluster theory. Neutrino cross sections and nuclear effects lead to systematic uncertainty in the extraction of oscillation parameters in neutrino experiments. Because detectors include complex nuclei, knowledge of their interactions with neutrinos is required with quantified uncertainties to be used in simulations. The LIT-CC method is well suited to investigate the charge-changing quasi elastic peak in neutrino scattering. While our goal is to tackle the weak response in 16O, I will show some preliminary results on 4He, in particular regarding the Coulomb sum rule. \\[4pt] [1] S. Bacca, N. Barnea, G. Hagen, G. Orlandini and T. Papenbrock, Phys. Rev. Lett. 111, 122502 (2013).\\[0pt] [2] A. Ekstroem, G.R. Jansen, K.A. Wendt, G. Hagen, T. Papenbrock, S. Bacca, B. Carlsson, D. Gazit, Phys. Rev. Lett. 113, 262504 (2014). [Preview Abstract] |
Wednesday, October 28, 2015 9:30AM - 10:00AM |
1WA.00002: Towards More Accurate Double-Beta Matrix Elements Invited Speaker: Jonathan Engel All the methods currently used to calculate the nuclear matrix elements governing neutrinoless double beta decay omit potentially important correlations. I discuss steps --- mostly underway --- to improve the most prominent methods: the shell model, the generator coordinate method, the quasiparticle random phase approximation, and the interacting boson model. I focus particularly on the first two. The shell model is beginning to include effective interactions and operators, constructed non-perturbatively from ab initio calculations, that compensate for the parts of Hilbert space it omits. The generator coordinate method is starting to incorporate important non-shape degrees of freedom as coordinates. Both approaches face computational challenges, but stochastic methods will help us to meet them. [Preview Abstract] |
Wednesday, October 28, 2015 10:00AM - 10:30AM |
1WA.00003: Electromagnetic and neutral-weak response functions of light nuclei Invited Speaker: Alessandro Lovato A major goal of nuclear theory is to understand the strong interaction in nuclei as it manifests itself in terms of two- and many-body forces among the nuclear constituents, the protons and neutrons, and the interactions of these constituents with external electroweak probes via one- and many-body currents. Using imaginary-time projection technique, quantum Monte Carlo allows for solving the time-independent Schr\"{o}dinger equation even for Hamiltonians including highly spin-isospin dependent two- and three- body forces. I will present a recent Green’s function Monte Carlo calculation of the quasi-elastic electroweak response functions in light nuclei, needed to describe electron and neutrino scattering. We found that meson-exchange two-body currents generate excess transverse strength from threshold to the quasielastic to the dip region and beyond. These results challenge the conventional picture of quasi elastic inclusive scattering as being largely dominated by single-nucleon knockout processes. These findings are of particular interest for the interpretation of neutrino oscillation signals. [Preview Abstract] |
Wednesday, October 28, 2015 10:30AM - 11:00AM |
1WA.00004: Coffee Break
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Wednesday, October 28, 2015 11:00AM - 11:30AM |
1WA.00005: Role of nuclear correlations in neutrino interactions with nuclei and nuclear matter. Invited Speaker: Sanjay Reddy Neutrino-nuclear interactions play an important role in astrophysics and in terrestrial neutrino experiments. Correlations and interactions between nucleons influence neutrino-nucleus cross-sections in nuclei for neutrino energies in the range MeV-GeV, and neutrino production and propagation in supernovae and neutron stars. To summarize our current understanding ? survey recent calculations neutrino-nuclear interaction rates and emphasize the role of nucleon-nucleon correlations. I will also discuss some open questions and the need to develop new techniques to extract the nuclear response function using non-perturbative methods that can incorporate both short and long-distance correlations and multi-particle excitations in nuclei and nuclear matter. [Preview Abstract] |
Wednesday, October 28, 2015 11:30AM - 12:00PM |
1WA.00006: Constraining neutrinoless double-beta decay matrix elements Invited Speaker: Javier Menendez Neutrinoless double-beta decay, if detected, would proof the Majorana nature of neutrinos. The decay lifetime is governed by the absolute neutrino masses and the nuclear matrix elements of the transition. Therefore accurate matrix elements are needed to asses the sensitivity of current and future experiments, and to determine the absolute neutrino masses and hierarchy with neutrinoless double-beta decay. However, present nuclear matrix element calculations show significant uncertainties. These affect the nuclear structure description of the mother and daughter nuclei, and also the treatment of the transition operator. In this talk I cover recent progress on neutrinoless double-beta decay nuclear matrix element calculations. On the one hand, I discuss the role of the size of the configuration space and of nuclear structure correlations. By comparing matrix elements obtained with different nuclear structure approaches and interactions, optimal strategies for improving the nuclear structure calculations capturing the most important correlations are identified. On the other hand, I describe first attempts to include two-body currents in the double-beta decay operator. They can be related to the ``quenching'' of the spin-isospin operator empirically found in nuclear structure studies. [Preview Abstract] |
Wednesday, October 28, 2015 12:00PM - 12:30PM |
1WA.00007: Status of Lattice QCD calculations of one and two-nucleon matrix elements Invited Speaker: André Walker-Loud Lattice QCD calculations of basic hadronic quantities are now often performed with systematic control over the physical pion mass, continuum and infinite volume limits. This progress signals a new era in which lattice QCD will be used to compute basic properties of hadrons, nucleons and light nuclei directly from the Standard Model (SM). In particular, we will be able to use lattice QCD, combined with Effective Field Theory, to make quantitative statements about the interaction of SM matter and potential beyond the SM physics ranging from direct dark matter detection to permanent electric dipole moments. I will briefly review the status and challenges of lattice QCD calculations of select one- and two-nucleon matrix elements. These calculations are significantly more challenging than the basic quantities computed with all systematics controlled, but substantial progress is being made. [Preview Abstract] |
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