Bulletin of the American Physical Society
Spring 2012 Meeting of the APS Ohio-Region Section
Volume 57, Number 4
Friday–Saturday, April 13–14, 2012; Columbus, Ohio
Session F3: Nuclear Physics |
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Chair: Richard Furnstahl, Ohio State University Room: Physics Research Building 4138 |
Saturday, April 14, 2012 8:00AM - 8:12AM |
F3.00001: Proton Halos in Effective Field Theory Bijaya Acharya, Daniel Phillips Single proton halo systems are studied using an effective field theory (EFT) that exploits the separation of scales between the size of the system and the size of the core. The strength of Coulomb interaction between the proton and the core is calculated at leading order (LO) and next-to-leading order (NLO) in the EFT by using the effective range parameters derived from a square well model. The LO and the NLO results are compared to the full result obtained by solving the Schr\"{o}dinger equation for the square well model. This is done both at first order and to all orders in the electromagnetic coupling constant. Calculations of proton halo electromagnetic observables of will be presented. [Preview Abstract] |
Saturday, April 14, 2012 8:12AM - 8:24AM |
F3.00002: Polarization Phenomena in the Reaction $^6$He(p,p)$^6$He Azamat Orazbayev, Stephen Weppner, Charlotte Elster Recently, the polarization in elastic scattering of $^6$He off a polarized proton target was measured at the RIKEN facility. It turns out that calculations of this observable using conventional microscopic optical potentials fail to describe the data. The goal of this work is to improve the microscopic folding optical potential by explicitly taking into account the shell structure of $^6$He. This leads to additional terms containing the full spin-momentum structure of the nucleon-nucleon (NN) t-matrix as well as the shell structure of the valence neutrons. The density matrix of the $^6$He nucleus is obtained by using harmonic oscillator wave functions. Parameters of the wave functions are chosen to fit the experimental value for the charge radius and theoretical estimations for the matter radius of $^6$He. The NN t-matrix is calculated from the CD-Bonn potential. Preliminary results indicate that the polarization is sensitive to the additional terms. The calculations are performed in a recoil free approximation. [Preview Abstract] |
Saturday, April 14, 2012 8:24AM - 8:36AM |
F3.00003: The Supernova Equation of State: Potential vs. Field-Theoretical Approaches Constantinos Constantinou An important ingredient in simulations of core collapse supernova explosions is the equation of state of nucleonic matter for densities extending from $10^{-7}$ fm$^{-3}$ to $1$ fm$^{-3}$, temperatures up to 50 MeV, and proton-to-baryon fraction in the range 0 to 1/2. In this work we study supernova matter using a non-relativistic potential model as well as a relativistic mean-field theoretical one. In the former approach, we employ the Skyrme-like Hamiltonian density of Akmal, Pandharipande, and Ravenhall which takes into account the long scattering lengths of nucleons that determine the low density characteristics. In the latter, we use a Walecka-like Lagrangian density supplemented by non-linear interactions involving $\sigma, \omega$, and $\rho$ meson exchanges, calibrated so that known properties of nuclear matter are reproduced. We focus, initially, on the bulk homogeneous phase and calculate its thermodynamic properties as functions of baryon density, temperature, and proton-to-baryon ratio. The exact results are then compared to approximate ones in the degenerate and non-degenerate limits for which analytical formulae have been derived. Our next step would be to extend our calculations of the state variables to the subnuclear region in which nuclei are present. [Preview Abstract] |
Saturday, April 14, 2012 8:36AM - 8:48AM |
F3.00004: Nuclear Scaling with Low Momentum Interactions E.R. Anderson Nuclear scaling is observed in the ratios of inclusive electron scattering on different nuclei for \(1.5\leq x_{B}\leq2.0\) at large momentum transfer \(Q^{2}\). The ratios depend on the nucleus but are independent of \(Q^{2}\), and have been understood to be a result of strong short-range correlations induced by the nucleon-nucleon interaction. Recent calculations of nuclear structure make use of the similarity renormalization group to soften the nuclear potential through a series of unitary transformations, which suppress these short range correlations.\footnote{E.D. Jurgenson, P. Navr\'atil, and R.J. Furnstahl, Phys. Rev. Lett. \textbf{103}, 082501 (2009).}\(^{,}\)\footnote{E. R. Anderson, S. K. Bogner, R. J. Furnstahl, and R. J. Perry, Phys. Rev. C \textbf{82}, 054001 (2010)} However, we can now understand and calculate this scaling ratio as an effect of low momentum nuclear structure via factorization of operator expectation values. Recent calculations in nuclear matter, and in a Hartree-Fock basis for finite nuclei will be presented. We also apply this framework to an observed correlation with the EMC effect.\footnote{L. B. Weinstein \textit{et al.}, Phys. Rev. Lett. \textbf{106}, 052301 (2011)} [Preview Abstract] |
Saturday, April 14, 2012 8:48AM - 9:00AM |
F3.00005: Universality in SRG Evolved Potentials and the Choice of an Efficient Potential Brian Dainton Two-body nuclear observables can be accurately described using a variety of potentials. Using the similarity renormalization group (SRG), evolved interactions exhibit universality in the low energy regime. One can exploit this universality by choosing a computationally efficient potential. A separable potential from inverse scattering is one such analytically simple potential. With a simple solution to the two-body interaction, one can more efficiently solve few- and many-body problems. [Preview Abstract] |
Saturday, April 14, 2012 9:00AM - 9:12AM |
F3.00006: Making sense of scale- and scheme-dependent observables in low-energy nuclear physics R.J. Furnstahl Nuclear observables such as binding energies and cross sections can be directly measured. Other physically useful quantities, such as spectroscopic factors, are related to measured quantities by convolutions whose decompositions are not unique. I'll discuss some of the implications of such scale- and scheme-dependent observables in the context of renormalization group methods for low-energy nuclear physics. [Preview Abstract] |
Saturday, April 14, 2012 9:12AM - 9:24AM |
F3.00007: Momentum space evolution of chiral three-nucleon forces Kai Hebeler A framework to evolve three-nucleon (3N) forces in a plane-wave basis with the Similarity Renormalization Group (SRG) is presented and applied to consistent interactions derived from chiral effective field theory at next-to-next-to-leading order (N2LO). We demonstrate the unitarity of the SRG transformation, show the decoupling of low and high momenta, and present the first investigation of universality in chiral 3N forces at low resolution scales. The momentum-space-evolved 3N forces are consistent and can be directly combined with the standard SRG-evolved two-nucleon interactions for ab-initio calculations of nuclear structure and reactions. [Preview Abstract] |
Saturday, April 14, 2012 9:24AM - 9:36AM |
F3.00008: In-Medium Similarity Renormalization Group for Finite Nuclei Heiko Hergert The Similarity Renormalization Group (SRG) has emerged as a powerful and versatile tool for many-body physics. So far, its primary application in the framework of the nuclear many-body problem is the derivation of effective interactions from underlying realistic NN (and recently 3N) interactions. A recent development is the In-Medium SRG, where the Hamiltonian is evolved directly in the A-body system (i.e., at finite density). By a suitable choice of generator the ground state is decoupled from particle-hole excitations, and the IMSRG can be considered an Ab Initio technique for solving the many-body problem. The computational effort is comparable to Coupled Cluster approaches, which makes calculations for medium-mass and heavy nuclei feasible. I will give a brief overview of the method, present results for closed-shell nuclei with NN and 3N interactions, and discuss an effort to generalize the IM-SRG formalism for arbitrary reference states, with the aim of extending our calculations to open-shell nuclei. \textbf{References:} K. Tsukiyama, S. Bogner, and A. Schwenk, Phys. Rev. Lett. 106, 222502 (2011) S. Bogner, R. Furnstahl, and A. Schwenk, Prog. Part. Nucl. Phys. 65, 94 (2010) [Preview Abstract] |
Saturday, April 14, 2012 9:36AM - 9:48AM |
F3.00009: Local Projections of Low-Momentum Potentials Kyle Wendt Nuclear interactions evolved via renormalization group methods to lower resolution become increasingly non-local (off-diagonal in coordinate space) as they are softened. This inhibits both the development of intuition about the interactions and their use with some methods for solving the quantum many-body problem. By applying local projections, a softened interaction can be reduced to a local effective interaction plus a non-local residual interaction. At the two-body level, a local projection after similarity renormalization group (SRG) evolution manifests the elimination of short-range repulsive cores and the flow toward universal low-momentum interactions. The SRG residual interaction is found to be relatively weak at low energy, which motivates a perturbative treatment. [Preview Abstract] |
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