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.
120605148
Partial-wave analysis of lepton-pair annihilation into two photons
The partial-wave (Jp) composition of the process l+l− → γγ is analyzed in lowest order quantum electrodynamics. The results for low-momentum leptons are as expected, the partial wave with Jp = 0− being dominant. At high energies, the partial wave with Jp = 2+ has the largest single partial cross section. At all energies, it is found that lepton pairs in the triplet state give rise exclusively to positive-parity final states, whereas pairs in the singlet state give rise to negative-parity final states.Some features of the differential cross section are also explained in terms of the spin state of the annihilating lepton pair. Possible implications for e+e− → γγ → hadrons and hadrons are briefly discussed.
123512923
Sequential fragmentation and rate oscillations in exclusive decays
Abstract We consider the decay of heavy quarkonia into two light mesons, and assume that quark-antiquark pairs are created sequentially when the final state is formed. We find quantum oscillations in the decay rate as a function of total energy. These oscillations can explain the energy dependence observed in the πϱ and K ∗ K channels at the J ψ and ψ ′ and predict the behaviour at the heavier Ψ family. In the mechanism we discuss, a given final state is produced only in a narrow range of the possible distances between the initial light quark and light antiquark.
117025439
On the Monopole Model of Form Factors for Heavy Meson Decays
A pole model for the form factors describing heavy to light meson transitions is constructed, and the results compared with the predictions of the heavy quark effective theory (HQET). While most of the HQET-predicted relationships among form factors hold at the maximum value of q{sup 2}, many are violated, suggesting that the simplest version of the pole model of meson form factors should be used with caution, especially when combined with HQET.
119191937
Photoproduction of meson pairs: First measurement of the polarization observable I**s
Abstract The polarization observable I s , a feature exclusive to the acoplanar kinematics of multi-meson final states produced via linearly polarized photons, has been measured for the first time. Results for the reaction γ → p → p π 0 η are presented for incoming photon energies between 970 MeV and 1650 MeV along with the beam asymmetry I c . The comparably large asymmetries demonstrate a high sensitivity of I s to the dynamics of the reaction. The sensitivity of these new polarization observables to the contributing partial waves is demonstrated by fits using the Bonn–Gatchina partial wave analysis.
125011745
Heavy quark effective theory
After a brief introduction, the results of application of the heavy quark effective theory to semileptonic decays of beta mesons are discussed. A nearly-model-independent extraction of {vert_bar}V{sub cb}{vert_bar} from data is described. Application of the effective theory to inclusive semileptonic decays of heavy mesons, in semileptonic decays of heavy baryons, and to the nonleptonic decays of hadrons are outlined. The authors conclude by mentioning other areas of research in this very active field.
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.
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.
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.}
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.
37123844
Systematics of 8Li-induced radioactive beam reactions: E=13-20 MeV.
Elastic and inelastic scattering, one-nucleon transfers [mostly ${(}^{8}$Li, $^{7}\mathrm{Li}$)] and the ${(}^{8}$Li,\ensuremath{\alpha}) fusion-evaporation reaction have been studied on a variety of targets (A=1\char21{}58) at E${(}^{8}$Li)\ensuremath{\approxeq}13\char21{}20 MeV using the University of Michigan\char21{}University of Notre Dame radioactive nuclear beam (RNB) facility. The latter, which produces an energy-resolved (\ensuremath{\sim}500 keV FWHM), focused beam with intensity \ensuremath{\gtrsim}${10}^{6}$ $^{8}\mathrm{Li}$/s, permitted measurements to selected nuclear levels with cross sections down to approximately 1 mb/sr. Based on the systematics of the measured $^{8}\mathrm{Li}$ elastic scattering an appropriate $^{8}\mathrm{Li}$ optical potential was deduced. Large inelastic scattering cross sections (and B[E2\ensuremath{\uparrow}]) are observed for $^{8}\ensuremath{\rightarrow}^{8}$${\mathrm{Li}}_{0.98}^{\mathrm{*}}$. Large cross sections are also observed for the ${(}^{8}$Li${,}^{7}$Li) transfer reaction corresponding to quasielastic (viz., Q\ensuremath{\approxeq}0) neutron transfer to selected high spin excited levels in the residual nucleus. The ${(}^{8}$Li,\ensuremath{\alpha}) fusion-evaporation reaction also appears to be significant and can produce very-high-energy \ensuremath{\alpha} particles, viz., ${\mathit{E}}_{\mathrm{\ensuremath{\alpha}}}$\ensuremath{\gg}${\mathit{E}}_{\mathrm{beam}}$. Although observed using $^{8}\mathrm{Li}$, these features appear to be important for many RNB-induced reactions and they must be considered, for example, in nucleosyntheis calculations involving $^{8}\mathrm{Li}$ and other short-lived radioactive nuclei.