Stochastic excitation of acoustic modes in stars

For more than ten years, solar-like oscillations have been detected and frequencies measured for a growing number of stars with various characteristics (e.g. different evolutionary stages, effective temperatures, gravities, metal abundances ...). Excitation of such oscillations is attributed to turbulent convection and takes place in the uppermost part of the convective envelope. Since the pioneering work of Goldreich & Keely (1977), more sophisticated theoretical models of stochastic excitation were developed, which differ from each other both by the way turbulent convection is modeled and by the assumed sources of excitation. We review here these different models and their underlying approximations and assumptions. We emphasize how the computed mode excitation rates crucially depend on the way turbulent convection is described but also on the stratification and the metal abundance of the upper layers of the star. In turn we will show how the seismic measurements collected so far allow us to infer properties of turbulent convection in stars.Comment: Notes associated with a lecture given during the fall school organized by the CNRS and held in St-Flour (France) 20-24 October 2008 ; 39 pages ; 11 figure

Measurement of the D+ and Ds+ decays into K+K-K+

We present the first clear observation of the doubly Cabibbo suppressed decay D+ --> K-K+K+ and the first observation of the singly Cabibbo suppressed decay Ds+ --> K-K+K+. These signals have been obtained by analyzing the high statistics sample of photoproduced charm particles of the FOCUS(E831) experiment at Fermilab. We measure the following relative branching ratios: Gamma(D+ --> K-K+K+)/Gamma(D+ --> K-pi+pi+) = (9.49 +/- 2.17(statistical) +/- 0.22(systematic))x10^-4 and Gamma(Ds+ --> K-K+K+)/Gamma(Ds+ --> K-K+pi+) = (8.95 +/- 2.12(statistical) +2.24(syst.) -2.31(syst.))x10^-3.Comment: 10 pages, 8 figure

Study of Hadronic Five-Body Decays of Charmed Mesons

We study the decay of D+ and Ds+ mesons into charged five body final states, and report the discovery of the decay mode D+ -> K+K-Pi+Pi+Pi-, as well as measurements of the decay modes D+ -> K-Pi+Pi+Pi+Pi-, Ds+ -> K+K-Pi+Pi+Pi-, Ds+ -> PhiPi+Pi+Pi- and D+/Ds+ -> Pi+Pi+Pi+Pi-Pi-. An analysis of the resonant substructure is also included, with evidence suggesting that both decays proceed primarily through an a1 vector resonance.Comment: 11 pages, 3 figure

New Measurements of the D+ to K* mu nu Form Factor Ratios

Using a large sample of D+ to K- pi+ mu+ nu decays collected by the FOCUS photoproduction experiment at Fermilab, we present new measurements of two semileptonic form factor ratios: rv and r2. We find rv = 1.504 \pm 0.057 \pm 0.039 and r2 = 0.875 \pm 0.049 \pm 0.064. Our form factor results include the effects of the s-wave interference discussed in a previous paper.Comment: 12 pages, 5 figure

The Target Silicon Detector for the FOCUS Spectrometer

We describe a silicon microstrip detector interleaved with segments of a beryllium oxide target which was used in the FOCUS photoproduction experiment at Fermilab. The detector was designed to improve the vertex resolution and to enhance the reconstruction efficiency of short-lived charm particles.Comment: 18 pages, 14 figure

Measurement of the relative branching ratio BR(\Xi_c^+ \to p^+ K^-\pi^+)\BR(\Xi_c^+ \to \Xi^- \pi^+ \pi^+)

We report the observation of the Cabibbo suppressed decay \Xi_c^+ \to p K^-\pi^+ using data collected with the FOCUS spectrometer during the 1996--97 Fermilab fixed target run. We find a \Xi_c^+ signal peak of 202\pm35 events. We have measured the relative branching ratios BR(\Xi^+_c\to p K^-\pi^+)/BR(\Xi^+_c\to\Xi^-\pi^+\pi^+)= 0.234 \pm 0.047 \pm 0.022 and BR(\Xi^+_c\to p \bar{K}^*(892)^0)/BR(\Xi^+_c\to p K^-\pi^+)= 0.54 \pm 0.09 \pm 0.05 .Comment: 9 pages, 4 figure

Observation of a 1750 MeV/c^2 Enhancement in the Diffractive Photoproduction of K^+K^-

Using the FOCUS spectrometer with photon beam energies between 20 and 160 \gev, we confirm the existence of a diffractively photoproduced enhancement in $K^+K^-$ at 1750 \mevcc with nearly 100 times the statistics of previous experiments. Assuming this enhancement to be a single resonance with a Breit-Wigner mass shape, we determine its mass to be $1753.5\pm 1.5\pm 2.3$ \mevcc and its width to be $122.2\pm 6.2\pm 8.0$ \mevcc. We find no corresponding enhancement at 1750 \mevcc in $K^*K$, and again neglecting any possible interference effects we place limits on the ratio $\Gamma (X(1750) \to K^*K)/\Gamma (X(1750) \to K^+K^-)$. Our results are consistent with previous photoproduction experiments, but, because of the much greater statistics, challenge the common interpretation of this enhancement as the $\phi (1680)$ seen in $e^+e^-$ annihilation experiments.Comment: 10 pages, 5 figure

Charm System Tests of CPT and Lorentz Invariance with FOCUS

We have performed a search for CPT violation in neutral charm meson oscillations. While flavor mixing in the charm sector is predicted to be small by the Standard Model, it is still possible to investigate CPT violation through a study of the proper time dependence of a CPT asymmetry in right-sign decay rates for $D^0\to K^-\pi^+$ and \d0b\to K^+\pi^-. This asymmetry is related to the CPT violating complex parameter $\xi$ and the mixing parameters $x$ and $y$: $A_{CPT}\propto{\rm Re} \xi y-{\rm Im} \xi x$ . Our 95% confidence level limit is $-0.0068<{\rm Re} \xi y-{\rm Im} \xi x<0.0234$. Within the framework of the Standard Model Extension incorporating general CPT violation, we also find 95% confidence level limits for the expressions involving coefficients of Lorentz violation of $(-2.8<N(x,y,\delta)(\Delta a_0 + 0.6 \Delta a_Z)<4.8)\times 10^{-16}$ GeV, $(-7.0<N(x,y,\delta)\Delta a_X<3.8)\times 10^{-16}$ GeV, and $(-7.0<N(x,y,\delta)\Delta a_Y<3.8)\times 10^{-16}$ GeV, where $N(x,y,\delta)$ is the factor which incorporates mixing parameters $x$, $y$ and the doubly Cabibbo suppressed to Cabibbo favored relative strong phase $\delta$.Comment: 12 pages 5 figure

Study of the Cabibbo-suppressed decay modes D0-->Pi-pi+ and D0-->K-K+

Using data from the FOCUS (E831) experiment at Fermilab, we present a new measurement for the branching ratios of the Cabibbo-suppressed decay modes D0-->Pi-Pi+ and D0-->K-K+. We measured: Gamma(D0-->K-K+)/Gamma(D0-->Pi-Pi+) = 2.81 +/- 0.10(stat) +/- 0.06(syst), Gamma(D0-->K-K+)/Gamma(D0-->K-Pi+) = 0.0993 +/- 0.0014(stat) +/- 0.0014(syst), and Gamma(D0-->Pi-Pi+)/Gamma(D0-->K-Pi+) = 0.0353 +/- 0.0012 (stat) +/- 0.0006(syst). These values have been combined with other experimental data to extract the ratios of isospin amplitudes and the phase shifts for the D-->KK and D-->PiPi decay channels.Comment: 12 pages, 1 Figure, accepted for publication in Phys.Lett.

Quantum Dimensional Zeeman Effect in the Magneto-optical Absorption Spectrum for Quantum Dot - Impurity Center Systems

Magneto-optical properties of the quantum dot - impurity center (QD-IC) systems synthesized in a transparent dielectric matrix are considered. For the QD one-electron state description the parabolic model of the confinement potential is used. Within the framework of zero-range potential model and the effective mass approach, the light impurity absorption coefficient for the case of transversal polarization with respect to the applied magnetic field direction, with consideration of the QD size dispersion, has been analytically calculated. It is shown that for the case of transversal polarization the light impurity absorption spectrum is characterized by the quantum dimensional Zeeman effect.Comment: 18 pages, 1 figure, PDF fil