New functional material: spark plasma sintered Si/SiO2 nanoparticles - fabrication and properties.

A bulk nanostructured material based on oxidized silicon nanopowder was fabricated using a spark plasma sintering technique. Structural investigations revealed that this material has the composition of ∼14 nm core Si granules inside an SiO2 shell. Photoluminescence measurements have shown that the emission spectra lie in the energy range of 0.6-1.1 eV, which is not typical of the emissions of the Si/SiO2 nanostructures reported in numerous papers. This result can be explained by the formation of energy states in the bandgap and the participation of these states in both electronic transport and photoluminescence emission. Annealing of the sample leads to a decrease in defect density, which in turn leads to quenching of the 0.6-1.1 eV photoluminescence. In this case ∼1.13 eV inter-band transitions in the Si core start to play a dominant role in radiative recombination. Thus, the possibility of controlling the photoluminescence emission over a broad wavelength range was demonstrated.

Direct measurements of Ab and Ac using vertex and kaon charge tags at the SLAC detector.

Exploiting the manipulation of the SLAC Linear Collider electron-beam polarization, we present precise direct measurements of the parity-violation parameters A(c) and A(b) in the Z-boson-c-quark and Z-boson-b-quark coupling. Quark-antiquark discrimination is accomplished via a unique algorithm that takes advantage of the precise SLAC Large Detector charge coupled device vertex detector, employing the net charge of displaced vertices as well as the charge of kaons that emanate from those vertices. From the 1996-1998 sample of 400 000 Z decays, produced with an average beam polarization of 73.4%, we find A(c)=0.673+/-0.029(stat)+/-0.023(syst) and A(b)=0.919+/-0.018(stat)+/-0.017(syst).

Improved direct measurement of the parity-violation parameter Ab using a mass tag and momentum-weighted track charge.

We present an improved direct measurement of the parity-violation parameter A(b) in the Z boson-b-quark coupling using a self-calibrating track-charge technique applied to a sample enriched in Z-->bb events via the topological reconstruction of the B hadron mass. Manipulation of the Stanford Linear Collider electron-beam polarization permits the measurement of A(b) to be made independently of other Z-pole coupling parameters. From the 1996-1998 sample of 400,000 hadronic Z decays, produced with an average beam polarization of 73.4%, we find A(b)=0.906+/-0.022(stat)+/-0.023(syst).

Improved direct measurement of A(b) and A(c) at the Z(0) pole using a lepton tag.

The parity violation parameters A(b) and A(c) of the Zb(b) and Zc(c) couplings have been measured directly, using the polar angle dependence of the polarized cross sections at the Z(0) pole. Bottom and charmed hadrons were tagged via their semileptonic decays. Both the electron and muon analyses take advantage of new multivariate techniques to increase the analyzing power. Based on the 1993-1998 SLD sample of 550,000 Z(0) decays produced with highly polarized electron beams, we measure A(b) = 0.919+/-0.030(stat)+/-0.024(syst), and A(c) = 0.583+/-0.055(stat)+/-0.055(syst).

First symmetry tests in polarized Z0 decays to bbg.

We have made the first direct symmetry tests in the decays of polarized Z0 bosons into fully identified bbg states, collected in the SLD experiment at SLAC. We searched for evidence of parity violation at the bbg vertex by studying the asymmetries in the b-quark polar- and azimuthal-angle distributions, and for evidence of T-odd, CP-even or CP-odd, final-state interactions by measuring angular correlations between the three-jet plane and the Z0 polarization. We found results consistent with standard model expectations and set 95% C. limits on anomalous contributions.

Improved direct measurement of leptonic coupling asymmetries with polarized Z bosons.

We present final measurements of the Z boson-lepton coupling asymmetry parameters A(e), A(mu), and A(tau) with the complete sample of polarized Z bosons collected by the SLD detector at the SLAC Linear Collider. From the left-right production and decay polar angle asymmetries in leptonic Z decays we measure A(e) = 0.1544+/-0.0060, A(mu) = 0.142+/-0.015, and A(tau) = 0.136+/-0.015. Combined with our left-right asymmetry measured from hadronic decays, we find A(e) = 0.1516+/-0.0021. Assuming lepton universality, we obtain a combined effective weak mixing angle of sin (2)theta(eff)(W) = 0.230 98+/-0.000 26.

High-precision measurement of the left-right Z Boson cross-section asymmetry.

We present a measurement of the left-right cross-section asymmetry ( A(LR)) for Z boson production by e(+)e(-) collisions. The measurement includes the final data taken with the SLD detector at the SLAC Linear Collider during the period 1996-1998. Using a sample of 383 487 Z decays collected during the 1996-1998 runs we measure the pole value of the asymmetry, A(0)(LR), to be 0.150 56+/-0.002 39 which is equivalent to an effective weak mixing angle of sin (2)straight theta(eff)(W) = 0.231 07+/-0.000 30. Our result for the complete 1992-1998 data set comprising approximately 537 000 Z decays is sin (2)straight theta(eff)(W) = 0.230 97+/-0.000 27.