Bulletin of the American Physical Society
Joint Fall 2010 Meeting of the APS Ohio Section and AAPT Appalachian and Southern Ohio Sections
Volume 55, Number 8
Friday–Saturday, October 8–9, 2010; Marietta, Ohio
Session C4: Nuclear, Atomic, and Molecular Physics |
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Chair: Daniel Philips, Ohio University Room: Rickey Science Center 148 |
Saturday, October 9, 2010 8:00AM - 8:12AM |
C4.00001: Beyond Universality in Three-Body Recombination Chen Ji, Lucas Platter, Daniel Phillips A three-body system interacting through a large two-body scattering length displays universal features known as Efimov physics. This physics manifests itself in interesting dependencies of the loss rates of trapped cold atoms as an applied magnetic field is varied. In particular, the use of Feshbach resonances allows the exploration of these loss rates as the two-body scattering length is varied by orders of magnitude. Particular loss features were recently observed with trapped Lithium-7 atoms by the Bar-Ilan [1] and Rice [2] groups. Effective field theory (EFT) methods have been shown to provide a good description of the positions of these loss features. I will display the EFT predictions in the limit of interactions with zero effective range [3], and then show how to extend those calculations to the case of a finite effective range [4]. \\[4pt] [1] Gross N. {\it et al.} Phys. Rev. Lett., {\bf 103}, 163202 (2009); {\it ibid.}, {\bf 105}, 103203 (2010). \newline [2] Pollack S. E., Dries D. and Hulet R. G., Science, {\bf 326}, 1683 (2009). \newline [3] Braaten E. and Hammer H.-W., Phys. Rept., {\bf 428}, 259 (2006). \newline [4] Ji C., Phillips D., and Platter L., arXiv:1005.1990. [Preview Abstract] |
Saturday, October 9, 2010 8:12AM - 8:24AM |
C4.00002: Potential Model Approaches to the Supernova Equation of State Ken Moore, Madappa Prakash, Constantinos Constantinou We employ the Hamiltonian density constructed in [1] to calculate the equation of state (EOS) relevant for core collapse supernova simulations. Thermodynamic properties (such as the free energy, pressure, and chemical potentials) are calculated as functions of baryon density, proton to baryon ratio and temperature. These properties are then compared with results obtained using traditional Skyrme-like interactions in order to isolate regions of agreement and/or disagreement. For the bulk homogeneous phase, results from analytical expressions are compared with the exact results in the non-degenerate (classical) and degenerate (quantum) cases. Our future plans are to extend our calculations to the subnuclear region in which nuclei are present. Comparisions with the supernova EOS of Lattimer and Swesty [2] will also be performed.\\[4pt] [1] A. Akmal, V. R. Pandharipande and D. J. Ravenhall, Phys. Rev. C. 58, 1804 (1998).\\[0pt] [2] J. M. Lattimer and F. D. Swesty, Nucl. Phys. A., 535 (331) 1991. [Preview Abstract] |
Saturday, October 9, 2010 8:24AM - 8:36AM |
C4.00003: The Supernova Equation of State: Potential vs. Field-Theoretical Approaches Constantinos Constantinou, Ken Moore, Madappa Prakash Simulations of core collapse supernova explosions require the equation of state (EOS) of nucleonic matter for densities up to 4-5 times the nuclear equilibrium density, temperatures up to 50 MeV and proton fractions in the range 0 to 1/2. Here we compare results from two different approaches for the bulk homogeneous phase. In the nonrelativistic approach, we employ the Hamiltonian density constructed in [1] and compare results with those from a field-theoretic approach that includes nonlinear interactions involving $\sigma$, $\omega$, and $\rho$ meson exchanges [2]. For both approaches, we provide analytical expressions for the thermal pressure and energy in the classical and quantum limits. Our next steps are to calculate these EOS's in the presence of nuclei and to perform comparisons with the EOS of Lattimer {\&} Swesty [3].\\[4pt] [1] A. Akmal, V. R. Pandharipande {\&} D. J. Ravenhall, Phys. Rev. C. 58, 1804 (1998).\\[0pt] [2] H. Mueller {\&} B. D. Serot, Nucl. Phys. A., 606 (508) 1996.\\[0pt] [3] J. M. Lattimer {\&} F. D. Swesty, Nucl. Phys. A., 535 (331) 1991. [Preview Abstract] |
Saturday, October 9, 2010 8:36AM - 8:48AM |
C4.00004: Electromagnetic properties of Beryllium-11 in Halo EFT Daniel Phillips, Hans-Werner Hammer We compute properties of ${}^{11}$Be using an effective field theory (EFT) that exploits the separation of scales in this halo system. This nucleus has both a shallow $1/2^+$ {\it and} a shallow $1/2^-$ state. At leading order (LO) in the EFT the theory contains three parameters: the binding energies of these two states, as well as the effective ``range" for p-wave ${}^{10}$Be-neutron scattering. We use data on the $1/2^+$ and $1/2^-$ levels and the ${\rm B(E1)}$ strength of the $1/2^+$ to $1/2^-$ transition in the ${}^{11}$Be nucleus to fix these three parameters. We then compute the dissociation spectrum obtained from Coulomb excitation of the ${}^{11}$Be nucleus into ${}^{10}$Be plus a neutron, and compare to experimental data. At LO this spectrum is a prediction of the EFT. At next-to-leading order (NLO) one additional parameter associated with the $1/2^+$ state arises. This can be adjusted to obtain a good description of the low-energy part of the $d{\rm B(E1)}/dE$ spectrum. We also predict the charge radius of the $1/2^+$ state, which agrees with experiment at the level expected for an NLO calculation. The convergence pattern of the halo EFT is consistent with the nominal expansion parameter in this system. This allows us to extract the s-wave scattering length and effective range and the p-wave scattering volume in the effective-range expansions that parametrize scattering of a neutron from a ${}^{10}$Be nucleus. [Preview Abstract] |
Saturday, October 9, 2010 8:48AM - 9:00AM |
C4.00005: Coulomb Energy of Single-Proton Halo Systems Bijaya Acharya, Daniel Phillips Halo nuclei have unusually large spatial extension because one or more nucleons are weakly bound to a ``core.'' For a single-neutron halo, the behavior of the radial wave function, as well as its dependence on binding energy and angular momentum can be calculated using a square-well as a model for the nuclear potential [1]. This model facilitates predictions for experimental measurements of the radii, photodisintegration cross sections, etc of these halo systems. A similar square-well model can be employed for nuclei which have a single-proton halo, such as ${}^{17}$F [2]. We have used such a model to compute the Coulomb energies of halo systems. We have done this both to all orders in the Coulomb potential, and in Born approximation. The dependence of the Coulomb energy on the ``halo parameter,'' i.e. the ratio of the range of the nuclear potential to the size of the system, has been examined. This allows us to determine the range of this parameter where the Born approximation is an accurate way to compute the Coulomb energy in halo nuclei. [Preview Abstract] |
Saturday, October 9, 2010 9:00AM - 9:12AM |
C4.00006: Nuclear electromagnetic currents from chiral EFT Stefan K\"olling, Evgeny Epelbaum, Hermann Krebs, Ulf-G. Mei{\ss}ner Using the method of unitary transformation in combination with chiral effective field theory we derive the pion exchange contributions to the two-nucleon electromagnetic current. A formal definition of the current operator in this scheme and the power counting is presented. We discuss the implications of additional unitary transformations that have to be present to ensure the renormalizability of the one-pion exchange current. Further, we give explicit and compact results for the current in coordinate-space. [Preview Abstract] |
Saturday, October 9, 2010 9:12AM - 9:24AM |
C4.00007: Electromagnetic properties of heavy deformed nuclei in an algebraic model Gabriela Popa Calculations of electromagnetic properties of heavy deformed nuclei are presented. An algebraic model is used in a series of heavy deformed nuclei, governed by an overarching symmetry. The models treats protons and neutrons in the valence shells as fermions. The hamiltonian contains two parts, first is made of SU(3) generators, and the second one is the proton and neutron pairing interaction. Low energy spectra and electromagnetic transitions are compared to the experimental data. [Preview Abstract] |
Saturday, October 9, 2010 9:24AM - 9:36AM |
C4.00008: Comparison of Viscosities from the Chapman -- Enskog {\&} Relaxation Time Methods Anton Wiranata, Madappa Prakash Viscosity to entropy ratios of hadrons and the quark-gluon system control the elliptic flow observed in relativistic heavy-ion collisions. Here we establish the extent to which results from different approximation schemes for shear viscosities agree (or disagree) by choosing classic examples in which the elastic scattering cross sections are specified. The two different approximation schemes chosen are the Chapman-Enskog [1] and the Relaxation Time [2] methods. These test studies are performed for (i) a hard sphere gas ($\sigma = a^2/(4\pi$), where $a$ is the hard sphere radius), (ii) the Maxwell gas ($\sigma = m\Gamma(\theta)/2g$) with $m$ being the mass of the particles, $\Gamma(\theta$) is an arbitrary function of $\theta$, and \textbf{g} is the relative velocity), (iii) chiral pions ($\sigma = 5s/(48\pi f^4_{\pi}$), where $s$ is the squared c.m. energy and $f_{\pi}$ is the pion-decay constant, and (iv) massive pions (here $\sigma(\theta)$ is taken from experiments). Where possible, analytical results are obtained in either the non-relativistic or extremely relativistic cases. \\[4pt] [1] M. Prakash, et. al, Physics Report 227, 6 (1993) 321 -- 366. \\[0pt] [2] P. Chakraborty and J. I. Kapusta, arxiv:1006.0257v1 (2010). [Preview Abstract] |
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