The Coherent Production of the (K +π0) System by K + Beam on Copper Nuclei at the OKA Setup

Journal of Experimental and Theoretical Physics - On the statistics of ~1.7 × 108 interactions of positively charged kaons on copper nuclei, coherent events of the K+π0 system production...     

Measurement of charged kaon semileptonic decay branching fraction K^ - \to e^ - \bar \nu _e \pi ^0 using ISTRA+ detector

The ratio of branching fractions for \(K^ - \to e^ - \bar \nu _e \pi ^0\) andK ^? → π^?π⁰ decays has been measured using the ISTRA+ spectrometer. The result of our measurement is the following: $$\mathcal{R}_{Ke_3 /K_{2\pi } } = 0.2423 \pm 0.0015(stat.) \pm 0.0037(syst.).$$ Using the current PDG value for the K _2π branching fraction, this result leads to the measured K _e3 branching fraction of Br(K _e3) = 0.0501 ± 0.0009 and to the value of |V _us |f ₊(0) = 0.2115 ± 0.0021.     

<Emphasis Type="Italic">K</Emphasis><Subscript><Emphasis Type="Italic">e</Emphasis>3</Subscript> Decay Studies in the OKA Experiment

Recent results from OKA setup concerning form factor studies in K_e3 decay are presented. About 5.25 M events obtained for decays of 17.7 GeV/cK⁺ are selected for the analysis. The linear and quadratic slopes for the decay form factor f₊(t) are measured: λ'₊ = 2.95 ± 0.022 ± 0.018 × 10 ^-2 for the linear slope fit and λ₊ = 2.611 ± 0.035 ± 0.028 × 10 ^-2, λ"₊ = 1.91 ± 0.19 ± 0.14 × 10 ^-3 for the quadratic one. The scalar and tensor contributions are compatible with zero. Several alternative parametrizations are tried: the Pole fit parameter is found to be M _V = 891 ± 3 MeV; the parameter of the dispersive parametrization is measured to be Λ₊ = 2.458 ± 0.018 × 10^-2.