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Exploiting Universality in Atoms with Large Scattering Lengths

Description: The focus of this research project was atoms with scattering lengths that are large compared to the range of their interactions and which therefore exhibit universal behavior at sufficiently low energies. Recent dramatic advances in cooling atoms and in manipulating their scattering lengths have made this phenomenon of practical importance for controlling ultracold atoms and molecules. This research project was aimed at developing a systematically improvable method for calculating few-body observables for atoms with large scattering lengths starting from the universal results as a first approximation. Significant progress towards this goal was made during the five years of the project.
Date: May 31, 2012
Creator: Braaten, Eric
Partner: UNT Libraries Government Documents Department

Lattice calculation of I=2 pion scattering length

Description: We present results for the I=2 pion scattering length calculated using staggered fermions in the quenched approximation. The calculation uses the finite volume dependence of the energy of a two pion state. We find good agreement with current algebra predictions for scattering of Goldstone pions, and reasonable agreement for the non-Goldstine pions.
Date: January 1, 1992
Creator: Kilcup, Gregory; Gupta, Rajan & Sharpe, Stephen
Partner: UNT Libraries Government Documents Department

Measurement of porosity in a composite high explosive as a function of pressing conditions by ultra-small-angle neutron scattering with contrast variation

Description: We have used ultra-small-angle neutron scattering (USANS) with contrast variation to measure the porosity (voids and binder-filled regions) in a composite high explosive, PBX 9501, formulated with a deuterated binder. Little is known about the microstructure of pressed PBX 9501 parts and thus how it is affected by processing. Here, we explore the effect of varying the pressing intensity on the PBX 9501 microstructure. Disk-shaped samples of PBX 9501 were die-pressed with applied pressures ranging between 10,000 and 29,000 psi at 90 C. Five samples were prepared at each pressure that differed in the fraction of deuterated binder, facilitating variation of the neutron scattering length density contrast ({Delta}{rho}) and thus, the resolution of microstructural details. The sample composition was determined by calculation of the Porod Invariant as a function of {Delta}{rho} and compared with compositional estimates obtained from the bulk sample density. Structural modeling of the USANS data, at different levels of contrast, assuming both spherical and cylindrical morphologies, allowed the mean size and size distribution of voids and binder-filled regions to be determined. A decrease in the mean diameter of binder-filled regions was found with increasing pressing intensity, while the mean void diameter showed no significant change.
Date: January 1, 2009
Creator: Mang, Joseph Thomas; Hjelm, Rex P & Francois, Elizabeth G
Partner: UNT Libraries Government Documents Department

Meson-Baryon Scattering Lengths from Mixed-Action Lattice QCD

Description: The {pi}{sup +}{Sigma}{sup +}, {pi}{sup +}{Xi}{sup 0}, K{sup +}p, K{sup +}n, {bar K}{sup 0}{Sigma}{sup +}, and {bar K}{sup 0}{Xi}{sup 0} scattering lengths are calculated in mixed-action Lattice QCD with domain-wall valence quarks on the asqtad-improved coarse MILC configurations at four light-quark masses, and at two light-quark masses on the fine MILC configurations. Heavy Baryon Chiral Perturbation Theory with two and three flavors of light quarks is used to perform the chiral extrapolations. We find no convergence for the kaon-baryon processes in the three-flavor chiral expansion. Using the two-flavor chiral expansion, we find a{sub {pi}{sup +}{Sigma}{sup +}} = -0.197 {+-} 0.017 fm, and a{sub {pi}{sup +}{Xi}{sup 0}} = -0.098 {+-} 0.017 fm, where the comprehensive error includes statistical and systematic uncertainties.
Date: June 30, 2009
Creator: Beane, S; Detmold, W; Luu, T; Orginos, K; Parreno, A; Torok, A et al.
Partner: UNT Libraries Government Documents Department

Scattering length measurements from radiative pion capture and neutron-deuteron breakup

Description: The neutron-neutron and neutron-proton {sup 1}S{sub 0} scattering lengths a{sub nn} and a{sub np}, respectively, were determined simultaneously from the neutron-deuteron breakup reaction. Their comparison with the recommended values obtained from two body reactions gives a measure of the importance of three-nucleon force effects in the three-nucleon continuum. In order to check on the result obtained for a{sub nn} from the two-body {pi}{sup {minus}}-d capture reaction, a new measurement was performed at LANL. Preliminary results of the three experiments are given.
Date: July 1, 1997
Creator: Gibson, B. F.; Tornow, W. & Carman, T. S.
Partner: UNT Libraries Government Documents Department

A PROPOSAL TO MEASURE THE CROSS SECTION OF THE SPACE STAR IN NEUTRON-DEUTERON BREAKUP IN A RECOIL GEOMETRY SETUP

Description: Nucleon-deuteron (Nd) breakup is an important tool for obtaining a better understanding of three-nucleon (3N) dynamics and for developing meson exchange descriptions of nuclear systems. The kinematics of the nd breakup reaction enable observables to be studied in a variety of exit-channel configurations that show sensitivity to realistic nucleon-nucleon (NN) potential models and three-nucleon force (3NF) models. Rigorous 3N calculations give very good descriptions of most 3N reaction data. However, there are still some serious discrepancies between data and theory. The largest discrepancy observed between theory and data for nd breakup is for the cross section for the space-star configuration. This discrepancy is known as the “Space star Anomaly”. Several experimental groups have obtained results consistent with the “Space Star Anomaly”, but it is important to note that they all used essentially the same experimental setup and so their experimental results are subject to the same systematic errors. We propose to measure the space-star cross-section at the Triangle Universities Nuclear Laboratory (TUNL) using an experimental technique that is significantly different from the one used in previous breakup experiments. This technique has been used by a research group from the University of Bonn to measure the neutron-neutron scattering length. There are three possible scenarios for the outcome of this work: 1) the new data are consistent with previous measurements; 2) the new data are not in agreement with previous measurements, but are in agreement with theory; and 3) the new data are not in agreement with either theory or previous measurements. Any one of the three scenarios will provide valuable insight on the Space Star Anomaly.
Date: September 30, 2009
Creator: III, Benjamin J. Crowe
Partner: UNT Libraries Government Documents Department

Resonant Soft X-Ray Contrast Variation Methods as Composition-Specific Probes of Thin Polymer Film Structure

Description: We have developed complementary soft x-ray scattering and reflectometry techniques that allow for the morphological analysis of thin polymer films without resorting to chemical modification or isotopic 2 labeling. With these techniques, we achieve significant, x-ray energy-dependent contrast between carbon atoms in different chemical environments using soft x-ray resonance at the carbon edge. Because carbon-containing samples absorb strongly in this region, the scattering length density depends on both the real and imaginary parts of the atomic scattering factors. Using a model polymer film of poly(styrene-b-methyl methacrylate), we show that the soft x-ray reflectivity data is much more sensitive to these atomic scattering factors than the soft x-ray scattering data. Nevertheless, fits to both types of data yield useful morphological details on the polymer?slamellar structure that are consistent with each other and with literature values.
Date: April 4, 2008
Creator: Welch, Cynthia; Welch, Cynthia F.; Hjelm, Rex P.; Mang, Joseph T.; Hawley, Marilyn E.; Wrobleski, Debra A. et al.
Partner: UNT Libraries Government Documents Department

Chemical Depth Profiling from Neutron Reflectometry

Description: The material profile of a thin film can be analyzed by placing the film on a substrate and by sending a neutron beam onto it at various angles of incidence. Technically, the scattering length density of the film needs to be determined as a function of depth. A reflectometer is used to measure the amount of reflection (reflectivity) as a function of the angle of incidence. Mathematically, this is equivalent to sending the neutron beam onto the film at every energy but at a fixed angle of incidence. The film profile needs to be recovered from the measured reflectivity data. Unfortunately, the unique recovery is impossible, and many distinct unrelated profiles may correspond to the same reflectivity data. In our DOE/EPSCoR sponsored research, we have developed an analytical method to uniquely recover the profile of a thin film from the measured reflectivity data. We have shown that by taking reflectivity measurements with two different substrates, one can uniquely determine the film profile. Previously, it was known that one could uniquely recover the profile by taking reflectivity measurements with three different substrates, and our findings indicate that the same goal can be accomplished by using fewer measurements. At Mississippi State University we started an informal weekly seminar (called ''the reflectometry meeting'') at to attract various undergraduate and graduate students into the field. There were about 3 undergraduate students, 6 graduate students, and 2 faculty members attending these seminars. The PI has collaborated with Dr. Norm Berk at National Institute of Standards and Technology (NIST) on various aspects of neutron reflectometry, from which various interesting problems of theoretical and practical importance have arisen. One of these problems is closely related to the important mathematical problem known as analytic extrapolation. Under appropriate conditions (known to hold in neutron reflectometry), the reflection data taken ...
Date: March 21, 2006
Creator: Aktosun, Tuncay
Partner: UNT Libraries Government Documents Department

Determination of the S-Wave Pi Pi Scattering Lengths From a Study of K - to Pi - Pi0 Pi0 Decays

Description: We report the results from a study of the full sample of {approx}6.031 x 10{sup 7} K{sup {+-}} {yields} {pi}{sup {+-}}{pi}{sup 0}{pi}{sup 0} decays recorded by the NA48/2 experiment at the CERN SPS. As first observed in this experiment, the {pi}{sup 0}{pi}{sup 0} invariant mass (M{sub 00}) distribution shows a cusp-like anomaly in the region around M{sub 00} = 2m{sub +}, where m{sub +} is the charged pion mass. This anomaly has been interpreted as an effect due mainly to the final state charge exchange scattering process {pi}{sup +}{pi}{sup -} {yields} {pi}{sup 0}{pi}{sup 0} in K{sup {+-}} {yields} {pi}{sup {+-}}{pi}{sup +}{pi}{sup -} decay. Fits to the M{sub 00} distribution using two different theoretical formulations provide the presently most precise determination of a{sub 0} - a{sub 2}, the difference between the {pi}{pi} S-wave scattering lengths in the isospin I = 0 and I = 2 states. Higher-order {pi}{pi} rescattering terms, included in the two formulations, allow also an independent, though less precise, determination of a{sub 2}.
Date: March 29, 2012
Creator: Batley, J. R.; Culling, A. J.; Kalmus, G.; Lazzeroni, C.; Munday, D. J.; Slater, M. W. et al.
Partner: UNT Libraries Government Documents Department

High statistics analysis using anisotropic clover lattices: (III) Baryon-baryon interactions

Description: Low-energy baryon-baryon interactions are calculated in a high-statistics lattice QCD study on a single ensemble of anisotropic clover gauge-field configurations at a pion mass of m{sub {pi}} {approx} 390 MeV, a spatial volume of L{sup 3} {approx} (2.5 fm){sup 3}, and a spatial lattice spacing of b {approx} 0.123 fm. Luescher's method is used to extract nucleon-nucleon, hyperon-nucleon and hyperon-hyperon scattering phase shifts at one momentum from the one- and two-baryon ground-state energies in the lattice volume. The isospin-3/2 N{Sigma} interactions are found to be highly spin-dependent, and the interaction in the {sup 3}S{sub 1} channel is found to be strong. In contrast, the N{Lambda} interactions are found to be spin-independent, within the uncertainties of the calculation, consistent with the absence of one-pion-exchange. The only channel for which a negative energy-shift is found is {Lambda}{Lambda}, indicating that the {Lambda}{Lambda} interaction is attractive, as anticipated from model-dependent discussions regarding the H-dibaryon. The NN scattering lengths are found to be small, clearly indicating the absence of any fine-tuning in the NN-sector at this pion mass. This is consistent with our previous Lattice QCD calculation of NN interactions. The behavior of the signal-to-noise ratio in the baryon-baryon correlation functions, and in the ratio of correlation functions that yields the ground-state energy splitting is explored. In particular, focus is placed on the window of time slices for which the signal-to-noise ratio does not degrade exponentially, as this provides the opportunity to extract quantitative information about multi-baryon systems.
Date: January 19, 2010
Creator: Beane, S; Detmold, W; Lin, H; Luu, T; Orginos, K; Savage, M et al.
Partner: UNT Libraries Government Documents Department

The structure of fillers, polymers and their interfaces in polymer composites using neutron scattering methods

Description: The neutron scattering methods, small-angle neutron scattering and neutron reflectometry, provide information on the structure of polymer composite materials that is not available from other structural probes. The unique capabilities of these methods derive from three factors. First, the length scales probed correspond to polymer conformation, molecular and domain scales and to the characteristic sizes of many fillers. Second, neutrons are able to penetrate relatively thick samples, allowing bulk samples to be measured, and enabling buried interfaces to be studied. This characteristic also allows for the construction of special sample containment needed for studying materials under stress, extremes in pressure and temperature, etc. Third, neutrons readily distinguish between different light elements, and between different isotopes of the same element. The ability to distinguish between hydrogen and deuterium is particularly important in this regard. New ways of exploiting the capabilities of neutrons are opening up with the development of improved sources and instruments in the US and elsewhere. In this talk the author will discuss the basic concepts that give rise to the unique capabilities of neutron scattering, giving several examples of the uses of neutron scattering techniques in the study of polymer composites. The examples will include the morphology of fillers, polymer binders and matrices, interfaces and defect structures.
Date: December 1, 1998
Creator: Hjelm, R.P.
Partner: UNT Libraries Government Documents Department

Minimal relativistic three particle equations

Description: A relativistic, 3-particle equation with minimal 2-body input has unique solutions for bound states, and exhibits the Efimov effect (that there is an infinite accumulation of 3-particle bound states as the scattering length between the pairs increases without bound). The theory is Lorentz invariant and unitary. The physical input (for the three equal mass case) is in one parameter ..mu.., the mass of the 2-body bound (or virtual) states. The Efimov effect for the nonrelativistic theory occurs for (absolute value a/R) ..-->.. infinity, where a is the scattering length and R an effective range parameter, whereas in this theory the behavior is for ..mu.. ..-->.. 2m, where m is the mass of any one of the three particles.
Date: May 1, 1980
Creator: Lindesay, J.V. & Noyes, H.P.
Partner: UNT Libraries Government Documents Department

Few-body hypernuclear constraints

Description: Since the discovery of the first hyperfragment in a balloon flown emulsion stack some two score years ago, physicists have worked to understand how the addition of the strangeness degree of freedom alters the picture of nuclei and the baryon-baryon force. Because the {Lambda} and {Sigma} masses differ markedly from that of the proton and neutron, SU (3) symmetry is broken. How it is broken is a question of importance to the fundamental understanding of the baryon-baryon interaction. New dynamical symmetries, forbidden by the Pauli principle in conventional nuclei, appear. Three-body forces play a more significant role. A binding anomaly in A {equals} 5 as well as a possible spin inversion between ground and excited states in A {equals} 4 appear. Surprisingly narrow structure near the threshold for {Sigma} production has been reported in the {sup 4}He (K{sup {minus}}, {pi}{sup {minus}}) spectrum while no corresponding structure is observed in the companion {sup 4}He(K{sup {minus}}, {pi}{sup +}) spectrum; this has been interpreted as evidence for a {sub {Sigma}}{sup 4}He bound state. Finally, the reported observation of {Lambda}{Lambda}-hypernuclei, in particular {sub {Lambda}{Lambda}}{sup 6}He, bears directly upon the possibilities for the prediction of a bound H particle--the S {equals} {minus}2 dibaryon. Although it is not feasible to invert the analysis and determine the interaction from the data on few-body systems, it is possible to utilize these data to constrain the models, provided one is careful. The author will explore briefly the constraints which the few-body data impose and the level of understanding that has been achieved.
Date: December 31, 1993
Creator: Gibson, B. F.
Partner: UNT Libraries Government Documents Department

Theories of the eta-meson-nucleus interaction

Description: It is sown that the pion-nucleon elastic scattering, eta-nucleon scattering length and the cross sections for pion-induced eta production on a nucleon satisfy a set of consistency relations. These relations are used to examine the {eta}N scattering lengths given by the various models. The nature of the threshold {eta}N interaction is discussed and recent advancements in {eta}N interaction is discussed and recent advancements in {eta}-nucleus reaction theory are reviewed.
Date: August 1, 1994
Creator: Liu, L. C.
Partner: UNT Libraries Government Documents Department

Pion nucleon interaction at low energy

Description: A theory of the ..pi..N interaction at low energy is described. An analogy is made with an unusual approach to potential scattering theory. Phase shifts, cross sections, and scattering amplitudes and lengths are calculated. 28 references. (JFP)
Date: March 1, 1979
Creator: Banerjee, M.K.
Partner: UNT Libraries Government Documents Department

Experiments on eta-meson production

Description: Following a review of some highlights of eta-meson characteristics, the status of eta-meson production experiments is reviewed. The physics motivations and first results of two LAMPF experiments on (..pi..,eta) reactions are discussed. Possible future experiments are also discussed. 42 refs., 12 figs., 4 tabs.
Date: January 1, 1985
Creator: Peng, J.C.
Partner: UNT Libraries Government Documents Department

Bayesian spectral analysis of reflectivity data

Description: The analysis of neutron and x-ray reflectivity data to obtain scattering-length density profiles is akin to the notorious phaseless Fourier problem, well-known in many fields such as crystallography. Current methods of analysis culminate in the refinement of a few parameters of a functional model, and are often preceded by a long and laborious process of trial-and-error. A discussion of the use of maximum entropy for obtaining free-form'' solutions of the density profile, as an alternative to the trial-and-error phase when a functional model is not available, and the suggestion for a novel experimental procedure designed to alleviate the ambiguity problems inherent in traditional reflectivity measurements, are given in Sivia et al. (1990). In this paper we consider the Bayesian spectral analysis approach, which is appropriate for optimising the parameters of a simple (but adequate) type of model when the number of parameters is not known. 8 refs., 3 figs.
Date: January 1, 1990
Creator: Sivia, D.S.; Hamilton, W.A. & Smith, G.S.
Partner: UNT Libraries Government Documents Department