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
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.
121478239
Breakup of B-8 at sub-Coulomb energies
125696689
High-resolution study of Gamow-Teller transitions via the Fe-54(He-3, t)Co-54 reaction
12221906
Measurements of discrete nuclear reactions induced by a radioactive 8Li beam.
Energy- and angle-resolved nuclear reactions, primarily one-nucleon stripping, have been observed for targets of CD{sub 2}, Be, and C, using a radioactive {sup 8}Li beam ({ital T}{sub 1/2}=842 ms) at {ital E}=14.3 MeV. The ({sup 8}Li,{sup 7}Li) neutron transfer reaction populating discrete final states was identified and angular distributions were obtained. This direct-reaction channel has large cross sections (10--100 mb/sr) due, in part, to the unique nuclear properties of {sup 8}Li. Implications for astrophysical abundances of Li isotopes may be significant.
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.
41501121
Can four-quark states be easily detected in baryon-antibaryon scattering?
We attempt to explain the experimental sparsity of diquonia candidates given the theoretical abundance of such states. We do this by investigating the lowest-order contributions of such states as intermediates in {ital p{bar p}} scattering into exclusive baryon-antibaryon final states. We find that the contributions depend on the partial widths for the meson-meson decays of the diquonia, and that resonant effects can be easily made to disappear. We conclude that if the meson-meson widths of diquonia are larger than about 50 MeV, most of these states will be extremely difficult to observe in {ital p{bar p}} scattering, for instance. We note that diquonia may offer a convenient means of describing some aspects of the dynamics of baryon-antibaryon scattering.
23671598
N pi decays of baryons in a relativized model.
We calculate the [ital N][pi] decay amplitudes of baryon resonances in a semirelativistic version of the [sup 3][ital P][sub 0] model of hadron decays. We use relativized wave functions for the baryons and mesons, and include an intuitive modification of the usual [sup 3][ital P][sub 0] model. Our results are in reasonable agreement with the reported amplitudes for [ital all] known nonstrange resonances, and confirm a proposed solution to the mystery of the missing'' states.
8084451
Renormalization and chiral symmetry breaking in quenched QED in arbitrary covariant gauges.
We extend a previous Landau-gauge study of subtractive renormalization of the fermion propagator Dyson-Schwinger equation in strong-coupling, quenched four-dimensional QED to {ital arbitrary} covariant gauges. We use the fermion-photon proper vertex proposed by Curtis and Pennington with an additional correction term included to compensate for the small gauge dependence induced by the ultraviolet regulator. We discuss the chiral limit and the onset of dynamical chiral symmetry breaking in the presence of nonperturbative renormalization. We extract the critical coupling in several different gauges and find evidence of a small residual gauge dependence in this quantity. {copyright} {ital 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.