Atomic Alchemy

We consider the transitions between electromagnetic bound states, such as the exclusive weak decay of a muonic atom into an electronic atom: $(\mu^- Z) \to (e^- Z) {\bar \nu_e }\nu_\mu .$ We show that relativistic effects in the atomic wavefunctions are crucial for determining the rate. In the case of heavy atoms, the exclusive channel branching ratios exceed $10^{-6},$ possibly bringing the study of these rare decays within experimental reach. Such processes thus provide a detailed laboratory for studying the high momentum tail of wavefunctions in atomic physics; in addition, they provide a simple toy model for investigating analogous exclusive heavy hadronic decays in quantum chromodynamics such as $B \to \pi e \nu.$Comment: 16 pages and 5 Figures, SLAC-PUB-648

Photoluminescence and photoluminescence excitation studies of lateral size effects in Zn_{1-x}Mn_xSe/ZnSe quantum disc samples of different radii

Quantum disc structures (with diameters of 200 nm and 100 nm) were prepared from a Zn_{0.72}Mn_{0.28}Se/ZnSe single quantum well structure by electron beam lithography followed by an etching procedure which combined dry and wet etching techniques. The quantum disc structures and the parent structure were studied by photoluminescence and photoluminescence excitation spectroscopy. For the light-hole excitons in the quantum well region, shifts of the energy positions are observed following fabrication of the discs, confirming that strain relaxation occurs in the pillars. The light-hole exciton lines also sharpen following disc fabrication: this is due to an interplay between strain effects (related to dislocations) and the lateral size of the discs. A further consequence of the small lateral sizes of the discs is that the intensity of the donor-bound exciton emission from the disc is found to decrease with the disc radius. These size-related effects occur before the disc radius is reduced to dimensions necessary for lateral quantum confinement to occur but will remain important when the discs are made small enough to be considered as quantum dots.Comment: LaTeX2e, 13 pages, 6 figures (epsfig

Test of a Density-Dependent Effective Interaction Using In-Plane 28-Si(p,p')28-Si Polarization Transfer Measurements

This research was sponsored by the National Science Foundation Grant NSF PHY-931478

Investigation of the Effective NN Interaction Through 28-Si(p,p')28-Si Polarization Transfer

This research was sponsored by the National Science Foundation Grant NSF PHY-931478

Evidence for Fragmentation of "Stretched" 6- Strength in 28-Si(p,p')28-Si

This research was sponsored by the National Science Foundation Grant NSF PHY-931478

Observation of the Charge Symmetry Breaking d + d -> 4He + pi0 Reaction Near Threshold

We report the first observation of the charge symmetry breaking d + d -> 4He + pi0 reaction near threshold at the Indiana University Cyclotron Facility. Kinematic reconstruction permitted the separation of 4He + pi0 events from double radiative capture 4He + gamma + gamma events. We measured total cross sections for neutron pion production of 12.7 +- 2.2 pb at 228.5 MeV and 15.1 +- 3.1 pb at 231.8 MeV. The uncertainty is dominated by statistical errors.Comment: 7 pages, 2 figures, plain Te

Photoproduction of Positive Mesons from Hydrogen: Results

The center-of-mass differential cross section for photoproduction of positive pions from hydrogen has been measured by the methods described in the two previous abstracts, in the angular range 40° to 150°, for photons from 220 to 475 Mev. (Photon energies refer to the Laboratory System.) Results obtained by the two methods are in essential agreement. At 90°, dσ/dω has a maximum of 2.7 X 10^(-29) cm^2/sterad near 280 Mev and falls by a factor 5 at 450 Mev. The maximum in the excitation curve is even more pronounced at larger angles, but less pronounced at smaller ones. At 40° (c.m.) the peak occurs near 350 Mev and at 450 Mev the cross section has decreased only to 0.7 the, peak value. Angular distributions in the center-of-mass system show a marked assymetry about 90°, which changes character from low energy to high. Below 325 Mev, there ii a backward maximum, whereas above 375 Mev, there is a forward maximum. The total cross section reaches a maximum near 290 Mev and decreases by about a factor 3 at 450 Mev. The results below 300 Mev agree with the data already reported from Berkeley and Cornell

Measurements of the Spin Observables D_NN' and P in the Inelastic Proton Scattering from 12-C and 16-O at 200 MeV

This research was sponsored by the National Science Foundation Grant NSF PHY-931478

Comparison of Zn_{1-x}Mn_xTe/ZnTe multiple-quantum wells and quantum dots by below-bandgap photomodulated reflectivity

Large-area high density patterns of quantum dots with a diameter of 200 nm have been prepared from a series of four Zn_{0.93}Mn_{0.07}Te/ZnTe multiple quantum well structures of different well width (4 nm, 6 nm, 8 nm and 10 nm) by electron beam lithography followed by Ar+ ion beam etching. Below-bandgap photomodulated reflectivity spectra of the quantum dot samples and the parent heterostructures were then recorded at 10 K and the spectra were fitted to extract the linewidths and the energy positions of the excitonic transitions in each sample. The fitted results are compared to calculations of the transition energies in which the different strain states in the samples are taken into account. We show that the main effect of the nanofabrication process is a change in the strain state of the quantum dot samples compared to the parent heterostructures. The quantum dot pillars turn out to be freestanding, whereas the heterostructures are in a good approximation strained to the ZnTe lattice constant. The lateral size of the dots is such that extra confinement effects are not expected or observed.Comment: 23 pages, LaTeX2e (amsmath, epsfig), 7 EPS figure