Search for the rare leptonic decay B+-->mu(+)nu(mu)

We have performed a search for the rare leptonic decay B+-->mu(+)nu(mu) with data collected at the Upsilon(4S) resonance by the BABAR experiment at the PEP-II storage ring. In a sample of 88.4 x 10(6) BB pairs, we find no significant evidence for a signal and set an upper limit on the branching fraction B(B+-->my(+)nu(my))< 6.6 x 10(-6) at the 90% confidence level.     

Electron-induced neutron knockout from 4He

The differential cross section for electron-induced neutron knockout in the reaction 4He(e,e(')n)(3)He has been measured for the first time with a statistical accuracy of 11%. The experiment was performed in quasielastic kinematics at a momentum transfer of 300 MeV/c and in the missing-momentum range of 25-70 MeV/c. The comparison of the data with theoretical calculations shows an impressive increase of the cross section resulting from final state interaction effects. Specifically, the p-n charge-exchange process dominates the cross section in this kinematical regime.     

Adsorption of selenium wires in silicalite-1 zeolite: a first order transition in a microporous system

A tight binding grand canonical Monte Carlo simulation of the adsorption of selenium in silicalite-1 zeolite is presented. The calculated adsorption-desorption isotherms exhibit characteristic features of a first order transition, unexpected for adsorption in a microporous system with pore size of the order of 0.5 to 0.6 nm. We analyze this behavior as a result of the favored twofold coordinated chain structure of selenium that grows inside the complex three-dimensional microchannel network of silicalite. This analysis is confirmed by simpler calculations of a lattice gas-type model.     

Electrostatic tuning of the hole density in NdBa2Cu3O(7-delta) films and its effect on the Hall response

We have used the ferroelectric field effect in heterostructures based on superconducting NdBa2-Cu(3)O(7-delta) and ferroelectric Pb(Zr0.2Ti0.8)O3 to electrostatically modulate in a reversible and nonvolatile fashion the hole carrier density of the superconducting layer. Reversing the ferroelectric polarization induces a constant relative change in the resistivity and Hall constant of 9% and 6%, respectively, at all temperatures above the superconducting transition. The cotangent of the Hall angle displays a T2 dependence with a slope that increases as the carrier density is reduced.     

Optically driven spin memory in n-doped InAs-GaAs quantum dots

We show that the spin state of the resident electron in an n-doped self-assembled InAs-GaAs quantum dot can be written and read using nonresonant, circularly polarized optical pumping. A simple theoretical model is presented and accounts for the remarkable dynamics producing counterpolarized photoluminescence.     

Measurement of the CP asymmetry amplitude sin2beta with B0 mesons

We present results on time-dependent CP asymmetries in neutral B decays to several CP eigenstates. The measurements use a data sample of about 88 x 10(6) Upsilon(4S)-->B(-)B decays collected between 1999 and 2002 with the BABAR detector at the PEP-II asymmetric-energy B factory at SLAC. We study events in which one neutral B meson is fully reconstructed in a final state containing a charmonium meson and the other B meson is determined to be either a B(0) or B(-0) from its decay products. The amplitude of the CP asymmetry, which in the standard model is proportional to sin2beta, is derived from the decay-time distributions in such events. We measure sin2beta=0.741+/-0.067(stat)+/-0.034(syst) and |lambda|=0.948+/-0.051(stat)+/-0.030(syst). The magnitude of lambda is consistent with unity, in agreement with the standard model expectation of no direct CP violation in these modes.     

Molecular dynamics simulations for CO2 spectra. II. The far infrared collision-induced absorption band

Classical molecular dynamics simulations have been carried out for gaseous CO(2) starting from various anisotropic intermolecular potential energy surfaces. Through calculations for a large number of molecules treated as rigid rotors, the time evolution of the interaction-induced electric dipole vector is obtained and the Laplace transform of its autocorrelation function gives the collision-induced absorption rototranslational spectrum. The results are successfully compared with those of previous similar calculations before studies of the influences of the intermolecular potential and induced-dipole components are made. The calculated spectra show a significant sensitivity to anisotropic forces consistently with previous analyses limited to the spectral moments. The present results also demonstrate the importance of vibrational and back-induction contributions to the induced dipole. Comparisons between measured far infrared (0-250 cm(-1)) spectra at different temperatures and results calculated without the use of any adjustable parameter are made. When the best and more complete input data are used, the quality of our predictions is similar to that obtained by Gruszka et al. [Mol. Phys. 93, 1007 (1998)] after the introduction of ad hoc short-range overlap contributions. Our results thus largely obviate the need for such contributions the magnitudes of which remain questioned. Nevertheless, problems remain since, whereas good agreements with measurements are obtained above 50 cm(-1), the calculations significantly underestimate the absorption below, a problem which is discussed in terms of various possible error sources.     

Molecular dynamics simulations for CO2 spectra. III. Permanent and collision-induced tensors contributions to light absorption and scattering

Classical molecular dynamics simulations have been performed for gaseous CO(2) starting from an accurate anisotropic intermolecular potential. Through calculations of the evolutions of the positions and orientations of a large number of molecules, the time evolutions of the permanent and collision-induced electric dipole vector and polarizability tensor are obtained. These are computed from knowledge of static molecular parameters taking only the leading induction terms into account. The Laplace transforms of the auto-correlation functions of these tensors then directly yield the light absorption and scattering spectra. These predictions are, to our knowledge, the first in which the contributions of permanent and collision-induced tensors are simultaneously taken into account for gaseous CO(2), without any adjusted parameter. Comparisons between computations and measurements are made for absorption in the region of the ν(3) infrared band and for depolarized Rayleigh scattering in the roto-translational band. They demonstrate the quality of the model over spectral ranges from the band center to the far wings where the spectrum varies by several orders of magnitude. The contributions of the permanent and interaction-induced (dipole and polarizability) tensors are analyzed for the first time, through the purely permanent (allowed), purely induced, and cross permanent∕induced components of the spectra. It is shown that, while the purely induced contribution is negligible when compared to the collision-broadened allowed component, the cross term due to interferences between permanent and induced tensors significantly participates to the wings of the bands. This successfully clarifies the long lasting, confusing situation for the mechanisms governing the wings of the CO(2) spectra considered in this work.     

Unusual Formation of Acetylenic Sugar from the Cyanohydrins of 1,2 : 3, 4-Di-O-Isopropylidene-α-D-galacto-hexodialdo-1,5-pyranose

Reaction of methanesulfonate esters 73a and 3b with sodium azide in N, N-dimethylforaamide gave 6, 7-dideoxy-1,2:3,4-di-O-isopropylidene-α-D-galacto-6-heptyno-1,5-pyranose 5. The latter was identified by IR, NMR and mass spectrometry. A pathway for the unusual formation of an alkyne is proposed.