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.

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

The decay K − → μ − νπ 0 has been studied using in-flight decays detected with the ISTRA+ setup operating in the 25-GeV negative secondary beam of the U-70 PS. About 112K events were used for the analysis. The λ + and λ 0 slope parameters of the decay form factors f +(t) and f 0(t) have been measured: λ +=0.0321±0.004(stat.)±0.002(syst.), λ 0=0.0209±0.004(stat.)±0.002(syst.); the correlation dλ 0/dλ +=−0.46. The limits on the possible tensor and scalar couplings have been derived: f T/f +(0)=−0.021±0.028(stat.)±0.014(theor.), f S/f +(0)=0.004±0.005(stat.)±0.005(theor.).