International audienceAntiproton--proton annihilation into light neutral mesons in the few GeV energy domain is investigated in view of a global description of the existing data and predictions for future experiments at PANDA, FAIR. An effective meson model earlier developed, with mesonic and baryonic degrees of freedom in $s$, $t$, and $u$ channels, is applied here to $\pi^0\pi^0$ production. Form factors with logarithmic $s$ and $t(u)$ dependencies are applied. A fair agreement with the existing angular distributions is obtained. Applying SU(3) symmetry, it is straightforward to recover the angular distributions for $ \pi^0\eta$, and $\eta\eta$ production in the same energy range. A good agreement is generally obtained with all existing data

We calculate the QED and QCD radiative corrections to the charged lepton energy distributions in the dominant semileptonic decays of the top quark t → bW + → b(+ ν) (= e, μ, τ) in the standard model (SM), and for the decay t → bH + → b(τ + ν τ) in an extension of the SM having a charged Higgs boson H ± with m H ± < m t − m b. The QCD corrections are calculated in the leading and nextto-leading logarithmic approximations, but the QED corrections are considered in the leading logarithmic approximation only. These corrections are numerically important for precisely testing the universality of the charged current weak interactions in t-quark decays. As the τ + leptons arising from the decays W + → τ + ν τ and H + → τ + ν τ are predominantly left-and right-polarised, respectively, influencing the energy distributions of the decay products in the subsequent decays of the τ + , we work out the effect of the radiative corrections on such distributions in the dominant (onecharged prong) decay channels τ + → π +ν τ , ρ +ν τ , a + 1ν τ and + ν ν τ. The inclusive π + energy spectra in the decay chains t → b(W + , H +) → b(τ + ν τ) → b(π +ν τ ν τ + X) are calculated, which can help in searching for the induced H ± effects at the Tevatron and the LHC.

Antiproton-proton annihilation into light neutral mesons in the few GeV energy domain is investigated in view of a global description of the existing data and predictions for future experiments at PANDA, FAIR. An effective meson model earlier developed, with mesonic and baryonic degrees of freedom in s, t, and u channels, is applied here to π 0 π 0 production. Form factors with logarithmic s and t(u) dependencies are applied. A fair agreement with the existing angular distributions is obtained. Applying SU(3) symmetry, it is straightforward to recover the angular distributions for π 0 η, and ηη production in the same energy range. A good agreement is generally obtained with all existing data.

Abstract:The two-photon decay widths of scalar mesons σ (600), 0

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