Bulletin of the American Physical Society
19th Annual Meeting of the APS Northwest Section
Volume 63, Number 6
Thursday–Saturday, May 31–June 2 2018; Tacoma, Washington
Session F4: Nuclear Physics |
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Chair: Francesca Sammarruca, University of Idaho Room: Thompson Hall 395 |
Saturday, June 2, 2018 1:30PM - 2:00PM |
F4.00001: Pions and the Proton Sea Invited Speaker: Mary Alberg Light quark sea asymmetry, an excess of dbar quarks over ubar quarks in the proton, has been confirmed by deep inelastic scattering and Drell-Yan experiments. However, no satisfactory theoretical explanation has been proposed for the momentum dependence of the ratio dbar/ubar. New measurements of the ratio have been made by the SeaQuest experiment, and we await final results of their analysis. The pion plays an important role in nuclear physics, as the mediator of the long-range nucleon force, and as the representative of dynamical symmetry breaking. A pion cloud provides a natural explanation of the proton sea asymmetry. We make precise predictions, based on the pion cloud idea, for the final results of the SeaQuest experiment. We use light cone perturbation theory and experimental constraints on a chiral Lagrangian so that the relevant Fock-space components of the nucleon wave function are computed with reasonable accuracy. We compare our results to existing experimental information from experiment E866, and make predictions, including uncertainties, for future experimental measurements. The SeaQuest results will either confirm or rule out the idea that the pion cloud is the origin of the proton's light quark sea asymmetry.\\ \\In collaboration with Gerald A. Miller, University of Washington [Preview Abstract] |
Saturday, June 2, 2018 2:00PM - 2:30PM |
F4.00002: Jet energy loss in heavy ion collisions Invited Speaker: Yacine Mehtar-Tani The phenomenon of jet quenching in ultra-relativistic heavy ion collisions reveals the effect of substantial final state interactions that cause QCD jets to lose energy to the quark-gluon plasma (QGP), mainly by induced gluon radiation. In standard analytic approaches to energy loss, jets are approximated by single partons and thus higher-order effects in the strong coupling constant are neglected. This may prove insufficient to reliably extract QGP properties at high pT, where a significant jet suppression was recently reported by the ATLAS collaboration in PbPb collisions at the LHC. In this work we explore higher-order contributions to the inclusive jet spectrum which may be sizable owing to the fact that the probability for a highly virtual parton to split in the medium increases with the jet pT. As the effective number of jet constituents increases, jets are expected to lose more energy than a single color charge. This translates into a logarithmic enhancement of higher-orders in the perturbative series that need to be resummed. As a result we obtain a Sudakov-like suppression factor which we investigate in the leading logarithmic approximation. We note, however, that the phase space for higher-order corrections is mitigated by coherence effects that relate to the fact that, below a characteristic angular scale, the medium does not resolve the inner jet structure. In this case, the jet lose energy coherently as a single color charge, namely, the primary parton. [Preview Abstract] |
Saturday, June 2, 2018 2:30PM - 2:42PM |
F4.00003: The Nucleon-Nucleon Interaction in Chiral Effective Field Theory up to 6th Order (N5LO) Yevgen Nosyk, Ruprecht Machleidt We will discuss the basics of Chiral Effective Field Theory for the nucleon-nucleon interaction and present recent results developed within this framework. While attempts to solve the equations of Quantum Chromodynamics (QCD) numerically in the low energy limit are increasingly successful ("lattice QCD"), Chiral Effective Field Theory (ChEFT) remains a potent alternative method for deriving nuclear forces. We will present the NN potential at N4LO, which shows excellent agreement with experimental data in all partial waves and can be applied further in nuclear structure calculations. Since a modified power counting scheme is used for the N4LO potential, full NN potentials at NLO, NNLO and N3LO are also recalculated using the modified scheme. This allows for systematic estimations of truncation errors when applying potentials to calculations of nuclear structure and reactions. We will also present calculations of dominant pion exchange contributions to nucleon-nucleon scattering at 6th order (N5LO). The latter contributions further improve the agreement with experiment and also turn out to be smaller compared to N4LO, thus showing a trend towards convergence. [Preview Abstract] |
Saturday, June 2, 2018 2:42PM - 2:54PM |
F4.00004: Understanding a Key Nuclear Explosion Signature through the Noble Gas Migration Experiment Brian Milbrath Radionuclide detections are often considered to be the key ``proof'' that a nuclear explosion has occurred. Chemically inert noble gases are the radionuclides most likely to escape from an underground nuclear explosion. As part of a multidisciplinary study noble gases, and stable tracer gases were injected into a historical nuclear explosion test chimney in July of 2016. The radioactive gases were Ar-37 and Xe-127, and the stables gases were SF6, C8F8. Subsequent sampling from the cavity/chimney complex, several deep (\textasciitilde 160 meter) segmented bore holes and near surface sampling points have given quantitative results with respect to subsurface plume migration and evolving concentrations over a period of one year due to atmospheric barometric changes. It took several months before the radioactive gases were detected at the surface. Analysis of the datasets obtained thus far have revealed that the stable and radioactive gases migrate through the subsurface at different rates and the radioactive gases appear to migrate at the same speed. Sampling measurements also showed significant quantities of Ar-39 still remained from the initial nuclear explosion and that it was a strong interference for Ar-37 measurements. [Preview Abstract] |
Saturday, June 2, 2018 2:54PM - 3:06PM |
F4.00005: Black hole-neutron star post-merger evolution using viscous relativistic hydrodynamics Milad Haddadi The post-merger evolution of black hole-neutron star and neutron star-neutron star systems is driven by magnetohydrodynamic turbulence. ~Such multiscale problems are very costly to simulate. ~One approach is to use artificially large seed magnetic fields to resolve the magnetorotational instability. ~Another is to add some model of subgrid-scale effects, with subgrid angular momentum transport often being modeled as a shear viscosity. ~We simulate the disk from a black hole-neutron star model in both ways and compare results. ~We present a new implementation of the relativistic Navier-Stokes equations in the Spectral Einstein Code, with accompanying star and accretion torus tests. ~For the post-merger system, we analyze the combination of shocks and turbulent/viscous dissipation acting to heat the disk in the early post-merger phase. [Preview Abstract] |
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