Search for Heavy Neutrino in K->mu nu_h(nu_h-> nu gamma) Decay at ISTRA+ Setup

Heavy neutrino nu_h with m_h < 300MeV/c^2 can be effectively searched for in kaon decays. We put upper limits on mixing matrix element |U_mu_h}|^2 for radiatively decaying nu_h from K->mu nu_h (nu_h -> nu gamma) decay chain in the following parameter region: 30MeV/c^2 < m_h < 80MeV/c^2; 10^{-11}sec < tau_h < 10^{-9}sec. For the whole region |U_{mu h}|^2 < 5 x 10^{-5} for Majorana type of nu_h and | U_{\mu h}|^2 < 8 x 10^{-5} for the Dirac case.Comment: Published in Phys. Lett.

High statistic measurement of the K- -> pi0 e- nu decay form-factors

The decay K- -> pi0 e- nu is studied using in-flight decays detected with the ISTRA+ spectrometer. About 920K events are collected for the analysis. The lambda+ slope parameter of the decay form-factor f+(t) in the linear approximation (average slope) is measured: lambda+(lin)= 0.02774 +- 0.00047(stat) +- 0.00032(syst). The quadratic contribution to the form-factor was estimated to be lambda'+ = 0.00084 +- 0.00027(stat) +- 0.00031(syst). The linear slope, which has a meaning of df+(t)/dt|_{t=0} for this fit, is lambda+ = 0.02324 +- 0.00152(stat) +- 0.00032(syst). The limits on possible tensor and scalar couplings are derived: f_{T}/f_{+}(0)=-0.012 +- 0.021(stat) +- 0.011$(syst), f_{S}/f_{+}(0)=-0.0037^{+0.0066}_{-0.0056}(stat) +- 0.0041(syst).Comment: 11 pages, 8 figures. Accepted by Phys.Lett.

Study of K+ →π0e+νeγ decay with OKA setup

Results of study of the K+ → π0e+νγ decay at OKA setup are presented. 16889 events of this decay have been observed. The branching ratio with cuts E*γ > 10 MeV, 0.6 < cosΘ*eγ < 0.9 is calculated R=Brk+→π0e+veyBrK+→π0e+ve=0.574±0.010star.±0.021syst.×10−2. For the asymmetry Aξ we get Aξ = -0.009 ± 0.012(stat.

Extraction of kaon formfactors from K−→μ−νγ decay at ISTRA+ setup

AbstractThe radiative decay K−→μ−νμγ has been studied at ISTRA+ setup in a new kinematic region. About 22K events of K−→μ−νμγ have been observed. The sign and value of FV−FA have been measured for the first time. The result is FV−FA=0.21±0.04(stat)±0.04(syst)