A Measurement of n(g->cc) using D* Mesons

At LEP I charm quarks are mainly produced directly from the Z decay or via the decay of bottom hadrons. A third source is a primary quark radiating a hard gluon which then splits into a ccbar pair. This process is predicted to occur in approximately 1.5% of all hadronic Z decays. The data collected with the ALEPH detector from 1991 to 1995 have been investigated to look for this process. Charm quarks are tagged by reconstructing D*+- mesons via their decay D*+ -> D0 pi+ -> K- pi+ pi+. D*'s from gluon splitting are mostly found in a high--mass hemisphere. Fitting the hemisphere mass distribution for events with reconstructed D*'s, the contribution of g -> D* is extracted. The average multiplicity n(g->cc) of charm quark pairs from gluon splitting in hadronic Z decays is measured

Measurement of the 40Ca(3He,t)40Sc reaction

Levels in [Formula Presented] below 2.5 MeV excitation energy have been populated in a high-resolution study of the [Formula Presented] reaction. Three new states have been observed at energies [Formula Presented] 1871, and 1925 keV. Correspondence of the observed [Formula Presented] levels with known [Formula Presented] states in [Formula Presented] and [Formula Presented] are based on predictions provided by the isobaric multiplet mass equation. Our results confirm recently estimated stellar reaction rates for proton capture on [Formula Presented]

Investigation of the23Na(p, γ)24Mg and 23Na(p, α)20Ne reactions via (3He,d) spectroscopy

States near the 23Na+p threshold in 24Mg were investigated using the 23Na(3He,d)24Mg reaction over the angular range of 5° ≤ θlab ≤ 35° at E(3He)=20 MeV. Spectroscopic factors were extracted for states corresponding to resonances in the 23Na(p, γ) 24Mg and 23Na(p, α)20Ne reactions. We find that one state, corresponding to a previously unobserved resonance at Ec.m.= 138 keV, may make a significant contribution to the rates of both reactions at low temperatures. Another state, corresponding to a possible resonance at Ec.m.=37 keV may make a small contribution to the 23Na(p, α)20Ne reaction. New rates for the 23Na(p, γ)24Mg and 23Na(p, α) 20Ne reactions are presented and the astrophysical implications are discussed

Investigation of the 22Ne(p,y)23Na reaction via a (3He,d) spectroscopy

States near the [Formula Presented] threshold in [Formula Presented] were investigated using the [Formula Presented] reaction over the angular range of [Formula Presented] at [Formula Presented] Spectroscopic factors were extracted for states corresponding to resonances in the [Formula Presented] reaction. Two previously suggested resonances at [Formula Presented] and 100 keV were not observed at any angle. A new rate for the [Formula Presented] reaction has been calculated and its implications are discussed

14N(3He,d)15O as a probe of direct capture in the 14N(p,γ)15O reaction

Spectroscopic factors and asymptotic normalization coefficients (ANCs) have been determined for bound states in 15O using the 14N(3He,d)15O reaction. These results are used to calculate the astrophysical S factor for direct capture in the 14N(p, γ)13O reaction. We also discuss how uncertainties in optical-model parameters influence both the spectroscopic factors and the ANCs, and the effect that this has on the predicted direct-capture reaction rate

The Generalized Gell-Mann--Low Theorem for Relativistic Bound States

The recently established generalized Gell-Mann--Low theorem is applied in lowest perturbative order to bound-state calculations in a simple scalar field theory with cubic couplings. The approach via the generalized Gell-Mann--Low Theorem retains, while being fully relativistic, many of the desirable features of the quantum mechanical approaches to bound states. In particular, no abnormal or unphysical solutions are found in the model under consideration. Both the non-relativistic and one-body limits are straightforward and consistent. The results for the spectrum are compared to those of the Bethe-Salpeter equation (in the ladder approximation) and related equations.Comment: 24 pages, 6 pspicture diagrams, 4 postscript figure

Evolution and Nucleosynthesis of Massive Stars and Related Nuclear Uncertainties

Properties of atomic nuclei important for the prediction of astrophysical reaction rates are reviewed. In the first part, a recent simulation of evolution and nucleosynthesis of stars between 15 and 25 solar masses is presented. This study is used to illustrate the required nuclear input as well as to give examples of the sensitivity to certain rates. The second part focusses on the prediction of nuclear rates in the statistical model (Hauser-Feshbach) and direct capture (DWBA). Some of the important ingredients are addressed. Discussed in more detail are approaches to predict level densities, parity distributions, and optical alpha+nucleus potentials.Comment: Invited talk at 17th Int. Nucl. Phys. Conf. of the EPS "Nuclear Physics in Astrophysics", Debrecen, Hungary, 2002 (new version: fixed typo in alpha potential parameters; note: the parameters are incorrect in the NPA paper