Emission Diagrams Research Articles

Nonleptonic weak decays of bottom baryons

Cabibbo-allowed two-body hadronic weak decays of bottom baryons are analyzed. Contrary to the charmed baryon sector, many channels of bottom baryon decays proceed only through the external or internal $W$-emission diagrams. Moreover, $W$ exchange is likely to be suppressed in the bottom baryon sector. Consequently, the factorization approach suffices to describe most of the Cabibbo-allowed bottom baryon decays. We use the nonrelativistic quark model to evaluate heavy-to-heavy and heavy-to-light baryon form factors at zero recoil. When applied to the heavy quark limit, the quark model results do satisfy all the constraints imposed by heavy quark symmetry. The decay rates and up-down asymmetries for bottom baryons decaying into ${\frac{1}{2}}^{+}+P(V)$ and ${\frac{3}{2}}^{+}+P(V)$ are calculated. It is found that the up-down asymmetry is negative except for ${\ensuremath{\Omega}}_{b}\ensuremath{\rightarrow}{\frac{1}{2}}^{+}+P(V)$ decay and for decay modes with ${\ensuremath{\psi}}^{\ensuremath{'}}$ in the final state. The prediction $\mathcal{B}({\ensuremath{\Lambda}}_{b}\ensuremath{\rightarrow}J/\ensuremath{\psi}\ensuremath{\Lambda})=1.6\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}4}$ for $|{V}_{\mathrm{cb}}|=0.038$ is consistent with the recent Collider Detector at Fermilab measurement. We also present estimates for ${\ensuremath{\Omega}}_{c}\ensuremath{\rightarrow}{\frac{3}{2}}^{+}+P(V)$ decays and compare with various model calculations.

QCD corrections to the production of a heavy quark pair plus a hard photon in e+e− annihilation

We present complete results for the O( α s ) corrections to the production of a heavy quark pair plus a hard photon, in e + e − annihilation, including both photon and Z intermediate states. Virtual corrections are calculated analytically in 4 - 2ϵ dimensions, together with the soft approximation to the real emission diagrams. After cancellation of infrared divergences, real and virtual contributions are combined numerically to obtain the cross section for the production of two heavy quark jets plus a hard photon in next-to-leading order. The resulting fully differential cross section can be used to construct arbitrary distributions with the desired experimental cuts.

Finite-temperature radiative corrections to Compton scattering.

We calculate the finite-temperature ${\mathrm{\ensuremath{\alpha}}}^{3}$ corrections to the differential and total Compton scattering cross sections. We find that it is necessary to include soft photon absorption and emission diagrams to cancel the infrared divergences in the cross section. The cross sections are evaluated for the case where the initial electron is at rest.

Polymérisation de monomères organiques dans des plasmas froids —3: étude du rayonnement u.v. émis

The polymerization of low vapour pressure acrylic monomers may be carried out under partial vacuum in reactive vessels under electric discharges. Incorporated radical initiators increase the reaction rates, in well defined experimental conditions. The efficiency depends on the natures of the initiator and the ambient gas, the power of radio emission, and the substrate temperature. Two radiation emission diagrams have been established in the u.v. range.