Search

A precise measurement of the vector and axial-vector form factors difference $F_V-F_A$ in the $K^+\rightarrow{\mu^+}{\nu_{\mu}}{\gamma}$ decay is presented. About 95K events of $K^+\rightarrow{\mu^+}{\nu_{\mu}}{\gamma}$ are selected in the OKA experiment. The result is $F_V-F_A=0.134\pm0.021(stat)\pm0.027(syst)$. Both errors are smaller than in the previous $F_V-F_A$ measurements., Comment: 9 pages, 8 figures

A high statistics data sample of the $$K^{+}\rightarrow \mu ^{+}\nu _{\mu }$$ decay was accumulated by the OKA experiment in 2012. The missing mass analysis was performed to search for the decay channel $$K^{+}\rightarrow \mu ^{+}\nu _{H}$$ with a hypothetic stable heavy neutrino in the final state. The obtained missing mass spectrum does not show peaks that could be attributed to existence of stable heavy neutrinos in the mass range $$(270< m_{\nu _{H}} < 375)$$ MeV $$/c^{2}$$ . As a result, upper limits on the branching ratio and on the value of the mixing element $$|U_{\mu H}|^{2}$$ are obtained.

A high statistics data sample of the decays of $$K^+$$ mesons to three charged particles was accumulated by the OKA experiment in 2012 and 2013. This allowed to select a clean sample of about 450 events with $$K^{+}\rightarrow \pi ^{+}\pi ^{-}\pi ^{+}\gamma $$ decays with the energy of the photon in the kaon rest frame greater than 30 MeV. The measured branching fraction of the $$K^{+}\rightarrow \pi ^{+}\pi ^{-}\pi ^{+}\gamma $$ , with $$E_{\gamma }^{*} > 30\ \hbox {MeV}$$ is equal to $$(0.71 \pm 0.05) \times 10^{-5}$$ . The measured differential branching fraction over photon energy is compared with the prediction of the chiral perturbation theory to $${\mathcal {O}}(p^{4})$$ . A search for an up-down asymmetry of the photon with respect to the hadronic system decay plane is also performed.

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 K2π branching fraction, this result leads to the measured Ke3 branching fraction of Br(Ke3) = 0.0501 ± 0.0009 and to the value of |Vus|f+(0) = 0.2115 ± 0.0021.

The rare decay KL0 → π0ν\( \tilde v \) branching ratio measurement is one of the clearest Standard Model test. Calculations based on the SM predict Br(KL0 → π0ν\( \tilde v \)) ≈ 2.8 × 10−11, but the most accurate experimental value Br(KL0 → π0ν\( \tilde v \)) < 6.7 × 10−8 (90% C.L.). We present design of a new experimental setup KLOD (U-70 accelerator, IHEP, Protvino) for KL0 → π0ν\( \tilde v \) branching ratio measurement. Sensitivity of the KLOD experiment will be enough for registration of 2.4 events KL0 → π0ν\( \tilde v \) for every 10 days of the data taking (according to SM predictions).

The future investigations of rare decays of elementary particles demand the creation of new-generation setups which can perform much greater statistics and precise experimental data. The proposed new setups at CERN, NA62 (NA48/3 (P326SPS)), and at IHEP, OKA, are planned to obtain experimental data at the level of 10−10–10−12 branching ratio. The main goals of both experimental programs are connected with the study of ultrarare kaon decays, but beams of these experiments contain 95% (NA48) and 50% (OKA) of pions. It is natural to use the pion part of these beams for study of rare pion decays. The pion program may be performed simultaneously or consecutively with the main tasks. Such problems as search for tensor interaction, measurements of branching ratio and form factors of some pion decays, effects of polarization, and search for new particles are included in this program.

Using data collected with the ISTRA+ spectrometer during the 2001 run of the U-70 proton synchrotron in Protvino, we report the first observation of the radiative kaon decay K- -->mu-pi0gammanu. We find Br(Kmu3g)/Br(Kmu3) for two regions 5

The branching ratio in the charged-pion kinetic energy region of 55 to 90 MeV for the direct photon emission in the K- --> pi- pi0 gamma decay has been measured using in-flight decays detected with the ISTRA+ setup operating in the 25 GeV/c negative secondary beam of the U-70 PS. The value Br(DE)=[0.37+-0.39(stat)+-0.10(syst)]*10^(-5) obtained from the analysis of 930 completely reconstructed events is consistent with the average value of two stopped-kaon experiments, but it differs by 2.5 standard deviations from the average value of three in-flight-kaon experiments. The result is also compared with recent theoretical predictions., Comment: 13 pages, 8 figures