Search

On the statistics of ~1.7 × 108 interactions of positively charged kaons on copper nuclei, coherent events of the K+π0 system production are selected. The cross sections for the Coulomb and coherent strong components and their interference in the region of the K*(892) meson are measured. The partial width for the decay K*(892) → K+γ is determined. When studying the mass spectrum of the K+π0 system, an effect which can be interpreted as the interference of the chiral anomaly and the K*(892) s-channel amplitudes is found. This gives an estimate for the ratio of the observed amplitude of the chiral anomaly to the theoretical one: Aexp/Ath = 0.9 ± 0.24(stat.) ± 0.3(syst.).

Recent results from OKA setup concerning form factor studies in Ke3 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.

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.

Heavy neutrino ν h with m h ≲ 300 MeV / c 2 can be effectively searched for in kaon decays. We put upper limits on a mixing matrix element | U μ h | 2 for radiatively decaying ν h from K − → μ − ν h ( ν h → ν γ ) decay chain in the following parameter region: 30 MeV / c 2 ⩽ m h ⩽ 80 MeV / c 2 ; 10 − 11 s ⩽ τ h ⩽ 10 − 9 s . For the whole region | U μ h | 2 ≲ 5 ⋅ 10 − 5 for Majorana type of ν h and | U μ h | 2 ≲ 8 ⋅ 10 − 5 for the Dirac case.

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

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.

Results of study of the K{sup -}{yields}{pi}{sup 0}e{sup -}{nu}-bar{gamma} decay at the ISTRA+ setup are presented. We observed 4476 events of this decay. The branching ratio is found to be R=(Br(K{sup -}{yields}{pi}{sup 0}e{sup -}{nu}-bar{sub e}{gamma}))/(Br(K{sup -}{yields}{pi}{sup 0}e{sup -}{nu}-bar{sub e})) (1.81{+-}0.03(stat.){+-}0.07(syst.)) x 10{sup -2} for E*{sub {gamma}} > 10 MeV and {theta}*{sub e{gamma}} > 10{sup o}. For comparison with the previous experiment the branching ratio with cuts E*{sub {gamma}} > 10 MeV, 0.6 30 MeV and {theta}*{sub e{gamma}} > 20{sup o}, used in most theoretical papers, Br (3.06 {+-} 0.09(stat.) {+-} 0.14(syst.)) x 10{sup -4}. For the asymmetry we get A{sub {xi}} = -0.015 {+-} 0.021. At present it is the best estimate of this asymmetry.

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