The NLO QCD Corrections to BcB_c Meson Production in Z0Z^0 Decays

The decay width of $Z^0$ to $B_c$ meson is evaluated at the next-to-leading order(NLO) accuracy in strong interaction. Numerical calculation shows that the NLO correction to this process is remarkable. The quantum chromodynamics(QCD)renormalization scale dependence of the results is obviously depressed, and hence the uncertainties lying in the leading order calculation are reduced.Comment: 14 pages, 7 figures; references added; expressions and typos ammende

Estimating Form Factors of Bs→Ds(∗)B_s\rightarrow D_s^{(*)} and their Applications to Semi-leptonic and Non-leptonic Decays

$B_s^0\rightarrow D_s^{-}$ and $B_s^0\rightarrow D_s^{*-}$ weak transition form factors are estimated for the whole physical region with a method based on an instantaneous approximated Mandelstam formulation of transition matrix elements and the instantaneous Bethe-Salpeter equation. We apply the estimated form factors to branching ratios, CP asymmetries and polarization fractions of non-leptonic decays within the factorization approximation. And we study the non-factorizable effects and annihilation contributions with the perturbative QCD approach. The branching ratios of semi-leptonic $B_s^0\rightarrow D_s^{(*)-}l^+\nu_l$ decays are also evaluated. We show that the calculated decay rates agree well with the available experimental data. The longitudinal polarization fraction of $B_s\rightarrow D_s^*V(A)$ decays are $\sim0.8$ when $V(A)$ denotes a light meson, and are $\sim0.5$ when $V(A)$ denotes a $D_q$ ($q=d,s$) meson.Comment: Final version published in J Phys. G 39 (2012) 045002 (Title also changed

Z0Z_0 Boson Decays to Bc(∗)B^{(*)}_c Meson and Its Uncertainties

The programming new $e^{+}e^-$ collider with high luminosity shall provide another useful platform to study the properties of the doubly heavy $B_c$ meson in addition to the hadronic colliders as LHC and TEVATRON. Under the `New Trace Amplitude Approach', we calculate the production of the spin-singlet $B_c$ and the spin-triplet $B^*_c$ mesons through the $Z^0$ boson decays, where uncertainties for the production are also discussed. Our results show $\Gamma_{(^1S_0)}= 81.4^{+102.1}_{-40.5}$ KeV and $\Gamma_{(^3S_1)}=116.4^{+163.9}_{-62.8}$ KeV, where the errors are caused by varying $m_b$ and $m_c$ within their reasonable regions.Comment: 11 pages, 5 figures, 2 tables. To be published in Eur.Phys.J.

Boundary Layer Stability and Laminar-Turbulent Transition Analysis with Thermochemical Nonequilibrium Applied to Martian Atmospheric Entry

As Martian atmospheric entry vehicles increase in size to accommodate larger payloads, transitional ow may need to be taken into account in the design of the heat shield in order to reduce heat shield mass. The mass of the Thermal Protection System (TPS) comprises a significant portion of the vehicle mass, and a reduction of this mass would result in fuel savings. The current techniques used to design entry shields generally assume fully turbulent flow when the vehicle is large enough to expect transitional flow, and while this worst-case scenario provides a greater factor of safety it may also result in overdesigned TPS and unnecessarily high vehicle mass. Greater accuracy in the prediction of transition would also reduce uncertainty in the thermal and aerodynamic loads. Stability analysis, using e(sup N) -based methods including Linear Stability Theory (LST) and the Parabolized Stability Equations (PSE), offers a physics-based method of transition prediction that has been thoroughly studied and applied in perfect gas flows, and to a more limited extent in reacting and nonequilibrium flows. These methods predict the amplification of a known disturbance frequency and allow identification of the most unstable frequency. Transition is predicted to occur at a critical amplification or N Factor, frequently determined through experiment and empirical correlations. The LAngley Stability and TRansition Analysis Code (LASTRAC), with modifications for thermochemically reacting flows and arbitrary gas mixtures, will be presented with LST results on a simulation of a high enthalpy CO2 gas wind tunnel test relevant to Martian atmospheric entry. The results indicate transition caused by modified Tollmien-Schlichting waves on the leeward side, which are predicted to be more stable and cause transition slightly downstream when thermochemical nonequilibrium is included in the stability analysis for the same mean flow solution

Multiple Boundary Layer Instability Modes with Nonequilibrium and Wall Temperature Effects Using LASTRAC

Prediction and control of boundary layer transition from laminar to turbulent is important to many flow regimes and vehicle designs, including vehicles operating at hypersonic conditions where nonequilibrium effects may be encountered. Wall cooling is known to affect the instability characteristics of the boundary layer and subsequently the transition location. Design considerations, including material failure and fuel chemistry, require the use of actively cooled walls in hypersonic vehicles, further motivating the study of wall temperature effects on top of the considerations of reducing heat flux, drag, and uncertainty. In this work, we analyze the stability of a boundary layer with chemical and thermal nonequilibrium on a Mach 20, 6 wedge. We investigate the effects of wall temperature on multiple unstable modes individually and on the integrated growth of disturbances along the surface. We use the LAngley Stability and TRansition Analysis Code (LASTRAC) to evaluate boundary layer stability, using capabilities implemented by the authors. Included are results that address chemical nonequilibrium with both thermal equilibrium and nonequilibrium

The BcB_c Decays to PP-wave Charmonium by Improved Bethe-Salpeter Approach

We re-calculate the exclusive semileptonic and nonleptonic decays of $B_c$ meson to a $P$-wave charmonium in terms of the improved Bethe-Salpeter (B-S) approach, which is developed recently. Here the widths for the exclusive semileptonic and nonleptonic decays, the form factors, and the charged lepton spectrums for the semileptonic decays are precisely calculated. To test the concerned approach by comparing with experimental measurements when the experimental data are available, and to have comparisons with the other approaches the results obtained by the approach and those by some approaches else as well as the original B-S approach, which appeared in literature, are comparatively presented and discussed.Comment: 33 pages, 5 figures, 3 table