22293006
Energy and flux limits of cold-fusion neutrons using a deuterated liquid scintillator.
Deuterated liquid scintillator detectors (NE230), which give excellent {ital n}/{gamma} discrimination and provide a direct measure of the neutron {ital energy} spectrum, have been used to search for 2 to 3 MeV neutrons produced in {ital d}+{ital d} cold fusion. The apparatus consisted of an electrolytic cell using high-efficiency inverted-well geometry. Several samples of annealed Pd wire and a Pd casting (up to 13 g) were studied over a period of several weeks. An upper limit of {le}10{sup {minus}3} fusion ({ital n}/s g) Pd was obtained corresponding to {lt}7{times}10{sup {minus}24} fusion ({ital n}/s) {ital dd} pair in our samples which excludes most of the reported positive results. Several sources of spurious signals, which could closely mimic signals from fusion neutrons, were also observed.
125696689
High-resolution study of Gamow-Teller transitions via the Fe-54(He-3, t)Co-54 reaction
121478239
Breakup of B-8 at sub-Coulomb energies
43243436
Production of an isomeric, excited radioactive nuclear beam.
2502593
Dependence of the cross section for inclusive pion double charge exchange on nuclear mass and charge.
Total reaction cross sections for inclusive pion double charge exchange have been obtained at incident pion energies of 180 and 240 MeV for /sup 4/He, /sup 6.7/Li, /sup 9/Be, /sup 12/C, /sup 16/O, /sup 40/Ca, /sup 103/Rh, and /sup 208/Pb. An explanation of the dependence of these cross sections upon the mass and charge of the target nucleus and the charge of the incident pion is suggested in terms of a phenomenological model in which successive single-charge-exchange processes compete with more probable processes such as quasifree scattering.
19324012
Fragmentation and splitting of Gamow-Teller resonances in Sn(3He,t)Sb charge-exchange reactions, A=112-124.
Fragmentation and splitting of the Gamow-Teller (GT) strength has been observed in a systematic study of the ([sup 3]He,[ital t]) charge-exchange reaction at [ital E]([sup 3]He)=200 MeV over the entire range of stable Sn isotopes. Triton energy spectra were observed with a high-resolution magnetic spectrometer at angles near [theta]=0[degree] where [Delta][ital L]=0 transitions are enhanced. Excitation energies, widths, 0[degree] cross sections, and strengths [ital B](GT) were determined. A theoretically predicted configuration splitting of the main GT component into two components, expected to be dominant near [ital A]=118 at the onset of the filling of the 1[ital h][sub 11/2] neutron orbital, could not be observed. This may be due to the fact that the total widths of the resonances of 5--6 MeV exceed the predicted splitting. A comparison of the 0[degree] cross sections for the transitions to the GT resonances and the isobaric analog states leads to strengths [ital B](GT) for the main Gamow-Teller components of typically 65% of the sum-rule value of 3([ital N][minus][ital Z]). Three to four additional Gamow-Teller fragments were observed in all final nuclei at lower excitation energies. The excellent energy resolution of the experiment made it possible to observe a pronounced fine structure in these low-lyingmore » resonances which is believed to be due to coupling to two-particle--two-hole doorway states. Also seen with all target nuclei was a systematic sequence of strong [ital J][sup [pi]]=1[sup +] states near the ground states in all Sb isotopes ([ital E][sub [ital x]]=0 to 220 keV). In addition, strong [Delta][ital L]=1 resonances were observed in all nuclei at excitation energies of typically 20 MeV. Furthermore, nonresonant background from quasifree charge exchange was observed. An average of [similar to]85% of all excess neutrons seems to contribute to this background in approximate agreement with results from ([ital e],[ital e][prime][ital p]) experiments.« less
7361514
Continuum Study of Deconfinement at Finite Temperature.
Deconfinement and chiral symmetry restoration are explored in a confining, renormalizable, Dyson-Schwinger equation model of two-flavor QCD.An order parameter for deconfinement is introduced and used to establish that, in the chiral limit, deconfinement and chiral symmetry restoration are coincident at {ital T}{sub {ital c}}{approx_equal}150 MeV. The transitions are second order and each has the same critical exponent: {beta}{approx_equal}0.3. The deconfinement transition exhibits sensitivity to the current-quark mass. {ital f}{sub {pi}} and {ital m}{sub {pi}} change by less than 10{percent} for {ital T}{lt}0.7{ital T}{sub {ital c}}; however, as {ital T}{r_arrow}{ital T}{sub {ital c}}, thermal fluctuations cause the pion bound state contribution to the four-point quark-antiquark correlation function to disappear. {copyright} {ital 1996 The American Physical Society.}
11167229
Simple tests of the factorization assumption.
We suggest simple experimental tests to determine whether or not the factorization assumption is valid for the two-body, nonleptonic decays of heavy hadrons, when both daughter hadrons are also heavy.
7502410
Model gluon propagator and pion and rho -meson observables.
A one parameter, model confined-gluon propagator is employed in a phenomenological application of the Dyson-Schwinger and Bethe-Salpeter equations to the calculation of a range of \ensuremath{\pi}- and \ensuremath{\rho}-meson observables. Good agreement is obtained with the data. The calculated quark propagator does not have a singularity on the real-${\mathit{p}}^{2}$ axis. A mass formula for the pion, involving only the vacuum, dressed quark propagator, is presented and shown to provide an accurate estimate of the mass obtained via a direct solution of the Bethe-Salpeter equation. \textcopyright{} 1996 The American Physical Society.
1769931
Soft pion emission in semileptonic B-meson decays.
An analysis of semileptonic decays of B mesons with the emission of a single soft pion is presented in the framework of the heavy-quark limit using an effective Lagrangian which implements chiral and heavy-quark symmetries. The analysis is performed at leading order of the chiral and inverse heavy mass expansions. In addition to the ground state heavy mesons some of their resonances are included. The estimates of the various coupling constants and form factors needed in the analysis are obtained using a chiral quark model. As the main result, a clear indication is found that the 0{sup +} and 1{sup +} resonances substantially affect the decay mode with a D{sup *} in the final state, and a less dramatic effect is also noticed in the D mode. An analysis of the decay spectrum in the D{sup *}-{pi}{sup 2} invariant mass is carried out, showing the main effects of including the resonances. The obtained rates show promising prospects for studies of soft pion emission in semileptonic B-meson decays in a B-meson factory where, module experimental cuts, about 10{sup 5} such decays in the D meson mode and 10{sup 4} in the D{sup *} mode could be observed per year.
11657024
Critical coupling for dynamical chiral-symmetry breaking.
We study chiral-symmetry breaking in a model of quantum chromodynamics (QCD). In our study we make a critical analysis of an approximation that is often used in QCD and other theories to simplify the Schwinger-Dyson equation for the fermion self-energy. Solving the Schwinger-Dyson equation numerically, without employing the approximation, we find that chiral symmetry is restored when the running coupling constant at zero momentum transfer falls below 0.890.