Bulletin of the American Physical Society
2005 7th Annual Meeting of the Northwest Section
Friday–Saturday, May 13–14, 2005; Victoria, BC, Canada
Session G4: Nuclear |
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Chair: John McDonald, University of Alberta Room: MacLaurin D114 |
Saturday, May 14, 2005 2:00PM - 2:36PM |
G4.00001: The Eot-Wash Axion Search Invited Speaker: In the nearly 25 years since it was first proposed, the axion remains the preferred solution to the strong CP problem and a promising dark matter candidate. Although the mass of the axion is now limited to be greater than 1~$\mu$eV by the known flat geometry of the universe and less than 1000~$\mu$eV by the neutrino flux from SN1987A, between these limits the existence of the axion is unconstrained. The Eot-Wash group at the University of Washington has embarked on a new experiment to look for a macroscopic parity and time violating force mediated by virtual axions with a mass in the neighborhood of 200~$\mu$eV. By using the torsion pendulum technique, (and assuming that magnetic systematic errors can be mitigated), we hope to be able to improve on the present limits of such a force by nearly 18 orders of magnitude. This presentation will detail our experimental method and progress to date. [Preview Abstract] |
Saturday, May 14, 2005 2:36PM - 3:12PM |
G4.00002: Probing the Weak Interaction Spacetime Structure with Muon Decay Invited Speaker: Muon decay provides an excellent place to study the structure of the weak interaction. Since it is a purely leptonic process, many uncertainties deriving from the internal structure of the particles involved or from other interactions are reduced. TWIST measures with high precision the momentum and angular dependence of positrons emitted from the decay of polarized positive muons. I will describe the apparatus, some of the novel analysis techniques that we have employed, and our future goals. New results for the muon decay parameters $\rho$\ and $\delta$\ will be presented, together with their implications regarding the spacetime symmetries of the weak interaction. References: J.M. Musser {\it et al}, Phys. Rev. Lett. 94, 101805 (2005), A. Gaponenko {\it et al}, Phys. Rev. D. (Rapid Communications) 71 (2005). [Preview Abstract] |
Saturday, May 14, 2005 3:12PM - 3:37PM |
G4.00003: COFFEE BREAK
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Saturday, May 14, 2005 3:37PM - 4:13PM |
G4.00004: Radiative Capture for Astrophysical Process Invited Speaker: Radiative capture reactions are important in a number of astrophysical processes. Formost among these is the proton radiative capture on $^7$Be. This reaction produces the $^8$B whose decay produces most of the neutrinos seen in water base solar neutrino detectors. Concentrating on this reaction we explore the properties of radiative capture and the analytic structure of the amlitudes. The presence of a sub-threshold pole constrains the range of validity of polynomial fits to the astrophysical S-factor for any radiative capture. [Preview Abstract] |
Saturday, May 14, 2005 4:13PM - 4:25PM |
G4.00005: Microscopic calculations in isospin-asymmetric nuclear matter Francesca Sammarruca, Plamen Krastev, Wilson Barredo A topic of contemporary interest in nuclear physics is the investigation of the effective nucleon-nucleon interaction in a dense hadronic environment. In particular, inclusion of isospin asymmetry is of great interest at this time because of the opportunity to study collisions of neutron-rich nuclei at RIA energies. Based on our previous calculations of the equation of state for neutron-rich matter, we will present microscopic predictions of the (isoscalar and isovector) single-nucleon potentials and two-body cross sections in the isospin-asymmetric nuclear medium. Both are crucial input for isospin-dependent transport model simulations of heavy ion collisions. [Preview Abstract] |
Saturday, May 14, 2005 4:25PM - 4:37PM |
G4.00006: Coupling single particle states to phonons in a microscopical framework Carlo Barbieri The coupling of single particles to collective excitations can be approached microscopically by applying the Faddeev equations technique to quasiparticles. In this formalism, particle-hole and particle-particle~(hole-hole) phonons are treated at the RPA level and beyond. This talk will consider applications in nuclear physics (mostly for the nucleus of O-16) and briefly summarize results obtained for the strength function, one- and two-nucleon knock out and density of states. A recent development considers nucleon-nucleus scattering at astrophysical energies. [Preview Abstract] |
Saturday, May 14, 2005 4:37PM - 4:49PM |
G4.00007: Neutron Capture Cross Sections of Tin Isotopes Jeremy Sylvester, Kenneth Krane Tin has more stable isotopes than any other element, and thus naturally occurring elemental tin provides the opportunity to measure the neutron capture cross sections of several isotopes. Following irradiation of metallic foil samples of tin in our nuclear reactor, we have observed the radioactive decays of the isotopes of tin with mass numbers 113, 117, 123, and 125. In some cases we observed the decays of the ground state and the isomeric state, and thus we were able to deduce separate cross sections for the production of both. By using thermal column and cadmium-shielded core irradiation facilities, we determined both the thermal (2200 m/s) cross section and the average resonance integral. Comparison was made with materials of known thermal and resonance cross sections that served as flux monitors, including Au, Co, Fe, Zn, and Zr. [Preview Abstract] |
Saturday, May 14, 2005 4:49PM - 5:01PM |
G4.00008: Effective Field Theory Approach to Two- and Many-Body Forces Ruprecht Machleidt The past has seen many attempts to derive the nuclear force. The recently developed effective field theory approach to nuclear forces is superior to all earlier attempts. It represents a scheme that has an intimate relationship with QCD and allows to calculate nuclear forces to any desired accuracy. Moreover, nuclear two- and many-body forces are generated on the same footing. In my contribution, I will summarize the current status in the field. [Preview Abstract] |
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