Bulletin of the American Physical Society
APS April Meeting 2010
Volume 55, Number 1
Saturday–Tuesday, February 13–16, 2010; Washington, DC
Session H6: Universality in Few-Fermion Systems |
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Sponsoring Units: GFB DNP Chair: Daniel Phillips, Ohio University Room: Washington 5 |
Sunday, February 14, 2010 10:45AM - 11:21AM |
H6.00001: Universal Three-Body Bound States of Ultracold Fermionic Atoms Invited Speaker: In the early 1970's, Vitaly Efimov predicted that three-body systems with resonant two-body interactions admit an infinite sequence of arbitrarily shallow three-body bound states. The binding energy of these so-called Efimov trimers have a geometric spectrum with an accumulation point at the three- particle scattering threshold. The existence of these universal Efimov trimers is independent of the detailed structure of the two-body interactions and subsequent trimer states in the spectrum exhibit a discrete scaling symmetry with a universal scale factor $\approx 22.7$. I will present experimental evidence for the existence of the ground- and first-excited states of this infinite sequence in a system of ultracold fermionic atoms. Near resonant two-body interactions in our system of ultracold $^6$Li atoms are realized by making use of three overlapping, magnetically-tunable Feshbach scattering resonances. I will describe how our observations of three-body recombination in the ultracold gas allows us to determine the spectrum of the Efimov trimers as well as their lifetime. [Preview Abstract] |
Sunday, February 14, 2010 11:21AM - 11:57AM |
H6.00002: Universal interactions in atomic and low-energy few-nucleon systems Invited Speaker: Atomic systems with large two-body scattering lengths present remarkable similarities with nuclear systems at low energies. In both cases, the system properties are universal, depending mainly on the scattering length, which is much larger than the interparticle separation, and not on the details of the interaction. Therefore, the few-body methods developed to test one system, can be readily applicable to the other system. The study of the atomic systems characterized by large scattering lengths provide an excellent testing ground for few- and many-body methods that can be further applied, with little or no changes, to the description of nuclear systems at low energies. In this talk, I will present an effective-field theory approach to constructing two-body effective interactions in no-core shell model (a method developed for describing nuclear systems) finite spaces, with direct applications to the description of cold atom gases in harmonic traps. In particular, results up to next-to-next-to-leading order for the spectrum of the three-fermion system at unitarity will be presented and shown to agree with know results. Next, I will present the extension to finite values of the scattering length, as well as finite albeit small finite range, of interest for nuclear physics. Finally, I will discuss further application of such an approach to the description of atomic nuclei. [Preview Abstract] |
Sunday, February 14, 2010 11:57AM - 12:33PM |
H6.00003: Large Scattering Lengths, Universality, Correlations and Few-Nucleon Systems Invited Speaker: In a plethora of processes pivotal e.g.~for Big-Bang Nucleo-synthesis BBN, the typical energy scale lies below $10\;\mathrm{MeV}$. Since the scattering lengths between two nucleons are much larger than the typical range of the nucleon-nucleon interaction, Nuclear Physics at these energies is described by the Effective Field Theory of Point-Like Interactions, EFT(PLI), a model-independent theory with systematically improvable, reliable theoretical uncertainties. It helps to provide the bridge from the deceptive simplicity of high-energy QCD, the microscopic theory of strong interactions, to the richness and complexity of few-nucleon physics, and to explain in turn how universal aspects emerge from that complexity. In contradistinction to atomic systems, effective-range contributions have often to be accounted for, as they provide sizable corrections of up to $30\%$. EFT(PLI) is an excellent tool to check data consistencies, to extract nucleon properties by uniquely subtracting nuclear binding effects, and to model-independently predict processes which are experimentally hard to access, e.g.~for BBN and interactions between neutrinos and the lightest nuclei. Furthermore, its model-independent assessment of few-body interactions explains correlations between e.g.~binding energies and scattering lengths, and thus allows to differentiate between observables which are dominated by large scattering lengths from those which are sensitive to the details of the nuclear force. The same concepts apply to halo-nuclei, i.e.~systems which are much larger than its constituents, namely a small core orbited by nucleons. Some of these systems exhibit e.g.~Borromean binding or an Efimov-spectrum. While the nucleon-nucleon scattering lengths cannot be tuned experimentally, there are indications that they are infinite when the pion has about $1.4$ times its physical mass. EFT(PLI) explores whcih impact varying fundamental parameters of QCD has on the nuclear spectrum, and in particular on BBN. This contribution will illustrate the above points, focusing on concrete examples of general relevance. [Preview Abstract] |
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