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.
23690451
Systematics of inclusive pion double charge exchange in the delta resonance region.
A systematic study of inclusive pion double charge exchange is reported for nuclei between A=16 and A=208. The doubly differential cross sections for the A(${\mathrm{\ensuremath{\pi}}}^{+}$,${\mathrm{\ensuremath{\pi}}}^{\mathrm{\ensuremath{-}}}$) and A(${\mathrm{\ensuremath{\pi}}}^{\mathrm{\ensuremath{-}}}$,${\mathrm{\ensuremath{\pi}}}^{+}$) reactions in $^{16}\mathrm{O}$, $^{40}\mathrm{Ca}$, $^{103}\mathrm{Rh}$, and $^{208}\mathrm{Pb}$ were measured at incident energies between 120 and 270 MeV at three to five outgoing pion angles. Pion spectra were measured over the energy range from 10 MeV to the kinematic limit for double charge exchange. Integrating these spectra over outgoing pion energy generated angular distributions, and subsequently integrating these angular distributions generated total reaction cross sections. The shapes of the measured spectra are compared with those determined by the distribution of events in four-body phase space and with those predicted by a model in which the pion undergoes two sequential single charge exchanges on nucleons in a Fermi gas. The cross sections are compared with predictions of cascade calculations in which more than two interactions, including pion absorption and scattering without charge exchange, may occur.
121478239
Breakup of B-8 at sub-Coulomb energies
125276782
Search for isovector giant monopole resonances via the Sn-124(He-3,tn) reaction
The (He-3,t) reaction on Sn-124 at E(He-3)=199 MeV and the subsequent decay by neutron emission at backward angles were studied in an attempt to distinguish isovector monopole strength (spin-flip and non-spin-flip) at excitation energies above 25 MeV from the nonresonant continuum. The present approach is based on the assumption that a large fraction of the contributions to the continuum result from quasifree processes and breakup-pickup processes which leave the nucleus in low-lying excited states below the threshold for neutron emission. It was found, however, that even at high "apparent" excitation energies (above 30 MeV) the branching ratio for decay by neutrons was as high as similar to 50%, indicating that a large part of the nonresonant continuum may not be due to quasifree processes involving valence neutrons only. No evidence for monopole strength at high excitation energies was found, although the experiment had sufficient sensitivity and accuracy to detect isovector monopole strength based on theoretical predictions calculated in the framework of normal-mode collective excitations and the distorted-wave Born approximation.
125696689
High-resolution study of Gamow-Teller transitions via the Fe-54(He-3, t)Co-54 reaction
28323397
Very-high-energy light charged-particle production near 0 degrees in heavy-ion collisions, 9 <= E/A <= 40 MeV.
Very energetic light ions (primarily protons and alphas) with energies often approaching the full beam energy have been observed at or near {theta}=0{degree} in heavy-ion collisions, {ital Z}=8 to 28, {ital E}/{ital A}{dot =}9 to 40 MeV/nucleon from Ta and, in selected cases, Cu targets. Analysis of spectral shapes and angular distributions using a standard moving source model requires that the source velocity approaches the beam velocity as {theta}{r arrow}0{degree} and that the spectral slope parameters and apparent source temperatures be increased. Large values for the latter ({ital T}{sub {ital S}}{r arrow}16 MeV), which are typically twice as large as those deduced from complex fragment emission, are often required to fit the alpha particle spectra {theta}=0{degree}. Massive cluster transfer and other quasitransfer mechanisms may provide an alternative model for the generation of the {ital E}{r arrow}{ital E}{sub beam} alpha particles and other light fragments.
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.
32389654
Dynamical chiral symmetry breaking and confinement with an infrared-vanishing gluon propagator?
We have studied a model Dyson-Schwinger equation for the quark propagator, constructed using an Ansatz for the gluon propagator of the form D(q) {approximately} q{sup 2}/[(q{sup 2}){sup 2} + b{sup 4}] and two Ansatze for the quark-gluon vertex: the minimal Ball-Chiu and the modified form suggested by Curtis and Pennington. The aim was to determine whether such a form of the gluon propagator, which was suggested by a number of authors and which recent lattice simulations of QCD suggest may be plausible, can support dynamical chiral symmetry breaking and ensure quark confinement. The form of the gluon propagator at small space-like momenta is crucial to the nature of the strong interaction spectrum but is presently unknown and information gathered in such studies is invaluable in supporting or invalidating given hypotheses. It was found that there is a critical value of b = b{sub c} such that the model does not support dynamical chiral symmetry breaking for b > b{sub c}. Further, it was shown that this form of gluon propagator cannot confine quarks. As a consequence this form represents a physically unreasonable model. In addition, these results formed the basis for an invited presentation at a workshop on quantum infraredmore » physics and will be published in the proceedings.« less
26570396
Measurement of the inclusive semielectronic D0 branching fraction.
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.
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.}