The decay $K^{-} to mu^{-} bar{ u} pi^{0}$ has been studied using in-flight decays detected with ``ISTRA+ setup operating in the 25 GeV negative secondary beam of the U-70 PS. About 112K events were used for the analysis. The $lambda_{+}$ and $lambda_{0}$ slope parameters of the decay formfactors $f_{+}(t)$, $f_{0}(t)$ have been measured : $lambda_{+}= 0.0321 pm 0.004$(stat) $pm 0.002$(syst) $lambda_{0}= 0.0209 pm 0.004$(stat) $pm 0.002$(syst); the correlation $d lambda_{0}/d lambda_{+}=-0.46$ The limits on the possible tensor and scalar couplings have been derived: $f_{T}/f_{+}(0)=-0.021 pm 0.028$(stat) $pm 0.014$(theory); $f_{S}/f_{+}(0)=0.004 pm 0.005$(stat) $pm 0.005$(theory)
The decay K- -> pi0 mu- nu has been studied using in-flight decays detected with the ISTRA+ spectrometer. About 540K events were collected for the analysis. The lambda+ and lambda0 slope parameters of the decay form-factors f+(t), f0(t) have been measured : lambda+ = 0.0277+-0.0013 (stat)+-0.0009 (syst), lambda0 = 0.0183+-0.0011(stat)+-0.0006(syst), and d(lambda0)/d(lambda+)=-0.348. The limits on the possible tensor and scalar couplings have been derived: fT/f+(0)=-0.0007 +- 0.0071, fS/f+(0)=0.0017 +- 0.0014. No visible non-linearity in the form-factors have been observed.
The decay K- -> pi0 e- nu has been studied using in-flight decays detected with ISTRA+ setup operating at the 25 GeV negative secondary beam of the U-70 PS. About 130K events were used for the analysis. The lambda_+ parameter of the vector formfactor has been measured: lambda_+ = 0.0293 +- 0.0015(stat) +- 0.002(syst). The limits on the possible tensor and scalar couplings have been derived: f_T/f_+(0)=-0.044 +0.059 -0.057 (stat) f_S/f_+(0)=-0.020 +0.025 -0.016 (stat)
The rare decay K0(L) --> pi0 pi0 nu nu-bar was studied with the E391a detector at the KEK 12-GeV proton synchrotron. Based on 9.4 x 10^9 K0L decays, an upper limit of 8.1 x 10^{-7} was obtained for the branching fraction at 90% confidence level. We also set a limit on the K0(L) --> pi0 pi0 X (X --> invisible particles) process; the limit on the branching fraction varied from 7.0 x 10^{-7} to 4.0 x 10^{-5} for the mass of X ranging from 50 MeV/c^2 to 200 MeV/c^2.
The decay K- -> pi0 e- nu has been studied using in-flight decays detected with the ISTRA+ spectrometer working at the 25 GeV negative secondary beam of the U-70 PS. About 550K events were used for the analysis. The lambda+ parameter of the vector form-factor has been measured: lambda+ = 0.0286 +- 0.0008 (stat) +- 0.0006(syst). The limits on the possible tensor and scalar couplings have been obtained: f(T)/f+(0)=0.021 +0.064 -0.075 (stat) +- 0.026(syst) ; f(S)/f+(0)=0.002 +0.020 -0.022 (stat) +- 0.003(syst)
Results of study of the radiative kaon decay K-->pi0 e nu gamma at ISTRA+ setup are presented. 4476 events of this decay have been observed. The branching ratio is measured.