Search

A search for the $K^{+} \to \pi^{0}\pi^{0}\pi^{0}e^+\nu$ decay is performed by the OKA collaboration. The search is based on $3.65 \times 10^9 ~ K^+$ decays. No signal is observed. The upper limit set is $BR(K^{+} \to \pi^{0}\pi^{0}\pi^{0}e^+\nu) < 5.4\times 10^{-8} ~ 90\%$ CL, 65 times lower than the one currently listed by PDG.

The $K^{+} \to \pi^{+}\pi^{0}\pi^{0}\gamma$ decay is observed by the OKA collaboration. The branching ratio is measured to be $(4.1 \pm 0.9(stat) \pm 0.4(syst))\times 10^{-6}$. The branching ratio and $\gamma$ energy spectrum are consistent with ChPT prediction., Comment: arXiv admin note: text overlap with arXiv:2310.16429

A high statistics data sample of the $K^{+}$ decays is recorded by the OKA collaboration. A missing mass analysis is performed to search for a light invisible pseudoscalar axion-like particle (ALP) $a$ in the decay $K^{+} \to \pi^{+} \pi^{0} a$. No signal is observed, the upper limits for the branching ratio of the decay are calculated. The $90\%$ confidence level upper limit is changing from $2.5\cdot10^{-6}$ to $2\cdot10^{-7}$ for the ALP mass from 0 to 200 MeV/$c^{2}$, except for the region of $\pi^{0}$ mass, where the upper limit is $4.4\cdot10^{-6}$., Comment: 6 pages, 6 figures

The paper presents a measurement of the T-odd correlation in radiation decay \boldmath $K^+ \rightarrow \pi^{0} e^{+} \nu_{e} \gamma $ performed on the installation of the 101200 candidate events of the investigated decay were identified. Measured correlation $\xi_{\pi e \gamma}$ -is a mixed product of moments $e^{+}$, $\pi^{0}$, $\gamma$ in the kaon rest system, normalized by $M^{3}_{K}$. To assess the asymmetry of the distribution by $\xi_{\pi e \gamma}$ the value used is $A_{\xi}= \frac {N_{+}-N_{-}} {N_{+}+N_{-}}$, where $N_{+(-)}$ is the number of events with $\xi$ greater than (less than) zero. For the $A_{\xi}$ asymmetry, the value is obtained $A_{\xi} = (+0.1 \pm 3.9($stat.$) \pm1.7($syst.$))\times10^{-3}$ or $|A_{\xi}| < 5.4\times10^{-3} (90\%~ CL)$

Results of a study of the $K^+ \rightarrow \pi^{0} e^{+} \nu \gamma $ decay at OKA setup are presented. More than 32000 events of this decay are observed. The differential spectra over the photon energy and the photon-electron opening angle in kaon rest frame are presented. The branching ratios, normalized to that of $K_{e3}$ decay are calculated for different cuts in $E^*_\gamma$ and $cos\Theta^{*}_{e\gamma}$. In particular, the branching ratio for $E^{*}_{\gamma}>30$ MeV and $\Theta^{*}_{e \gamma}>20^{\circ}$ is measured R = $\frac{Br(K^+ \rightarrow \pi^{0} e^{+} \nu_{e} \gamma) } {Br(K^+ \rightarrow \pi^{0} e^{+} \nu_{e})} $ = =(0.587$\pm$0.010($stat.$)$\pm$0.015($syst.$))$\times10^{-2}$, which is in a good agreement with ChPT $O(p^{4})$ calculations.

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 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 $K^{+}\to\pi^{+}\pi^{-}\pi^{+}\gamma$ decays with the energy of the photon in the kaon rest frame greater than 30 MeV. The measured branching fraction of the $K^{+}\to\pi^{+}\pi^{-}\pi^{+}\gamma$, with $E_{\gamma}^{*}$ > 30 MeV is $(0.71 \pm 0.05) \times 10^{-5}$. The measured energy spectrum of the decay photon is compared with the prediction of the chiral perturbation theory to O$(p^{4})$. A search for an up-down asymmetry of the photon with respect to the hadronic system decay plane is also performed., Comment: 9 pages, 7 figures, 1 table

A high statistics data sample of the $K^{+}\to\mu^{+}\nu_{\mu}$ decay was accumulated by the OKA experiment in 2012. The missing mass analysis was performed to search for the decay channel $K^{+}\to\mu^{+}\nu_{H}$ with a hypothetic stable heavy neutrino in the final state. The obtained missing mass spectrum does not show peaks which could be attributed to existence of stable heavy neutrinos in the mass range (220 $< m_{\nu_{H}} <$ 375) MeV$/c^{2}$. As a result, we obtain upper limits on the branching ratio and on the value of the mixing element $|U_{\mu H}|^{2}$., Comment: 11 pages, 10 figures

Recent results from OKA setup concerning form factor studies in $K_{e3}$ decay are presented. About 5.25M events are selected for the analysis. The linear and quadratic slopes for the decay formfactor $f_{+}(t)$ are measured: $\lambda'_{+}=(26.1 \pm 0.35 \pm 0.28 )\times 10^{-3}$, $\lambda"_{+}=(1.91 \pm 0.19 \pm 0.14)\times 10^{-3}$. The scalar and tensor contributions are compatible with zero. Several alternative parametrizations are tried: the Pole fit parameter is found to be $M_V = 891 \pm 2.0$ MeV ; the parameter of the Dispersive parametrization is measured to be $\Lambda_+ =(24.58 \pm 0.18) \times 10^{-3}$. The presented results are considered as preliminary.

Evidence of the $K^+\to\mu^+\nu\bar\nu\nu$ decay was searched for using E949 experimental data with an exposure of $1.70\times 10^{12}$ stopped kaons. The data sample is dominated by the backgrond process $K^+\to\mu^+\nu_\mu\gamma$. An upper limit on the decay rate $\Gamma(K^+\to\mu^+\nu\bar\nu\nu)< 2.4\times 10^{-6}\Gamma(K^+\to all)$ at 90% confidence level was set assuming the Standard Model muon spectrum. The data are presented in such a way as to allow calculation of rates for any assumed $\mu^+$ spectrum., Comment: 7 pages, 5 figures

Evidence of a heavy neutrino, $\nu_H$, in the $K^+\to\mu^+\nu_H$ decays was sought using the E949 experimental data with an exposure of $1.70\times 10^{12}$ stopped kaons. With the major background from the radiative $K^+\to\mu^+\nu_\mu\gamma$ decay understood and suppressed, upper limits (90% C.L.) on the neutrino mixing matrix element between muon and heavy neutrino, $|U_{\mu H}|^2$, were set at the level of $10^{-7}$ to $10^{-9}$ for the heavy neutrino mass region 175 to 300 MeV/$c^2$., Comment: 14 pages, 13 figures; accepted by Physical Review D

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. B

The radiative decay K->mu nu gamma has been studied at ISTRA+ setup in a new kinematical region. About 22K events of K^- -> mu^- nu_mu gamma have been observed. The sign and value of Fv-Fa have been measured for the first time. The result is Fv-Fa=0.21(4)(4)., Comment: 11 pages, 21 figures, submitted to Phys. Lett. B

Experiment E949 at Brookhaven National Laboratory has observed three new events consistent with the decay K+ => pi+,nu,nubar in the pion momentum region 140 < P_pi < 199 MeV/c in an exposure of 1.71e12 stopped kaons with an estimated total background of 0.93+-0.17(stat.)+0.32-0.24(syst.) events. This brings the total number of observed K+ => pi+,nu,nubar events to seven. Combining this observation with previous results, assuming the pion spectrum predicted by the standard model, results in a branching ratio of (1.73+1.15-1.05)e-10. An interpretation of the results for alternative models of the decay K^ => pi+,nothing is also presented., Comment: Submitted to Phys.Rev. D

The branching fraction for the decay $K^{-} \to \pi^{0} e \bar \nu$ is measured using in-flight decays detected with {\bf ISTRA+} setup working at the 25 GeV negative secondary beam of the U-70 PS:\linebreak $Br_{K_{e3}}= (5.124 \pm 0.009 (stat) \pm 0.029(norm) \pm 0.030(syst))%$. From this value the $|V_{us}|$ element of the CKM matrix is extracted, using previously measured $f_{+}(t)$ form factor: $|V_{us}|=0.227 \pm 0.002$. The results are in agreement with recent measurements by BNL E865, FNAL KTeV, KLOE., Comment: 10 pages, 8 figures

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., Comment: 9 pages, 9 figures

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- -> 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. B

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., Comment: 11 pages, 8 EPS figures, accepted by Physics Letters B

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), Comment: LaTeX-2e, epsfig.sty, 10 pages, 7 figures in EPS format

The Dalitz plot slope parameters g, h and k for the K- -> pi0 pi0 pi- decay have been measured using in-flight decays detected with the ISTRA+ setup operating in the 25 GeV negative secondary beam of the U-70 PS. About 252 K events with four-momenta measured for the pi- and four involved photons were used for the analysis. The values obtained g=0.627+/-0.004(stat)+/-0.010(syst), h=0.046+/-0.004(stat)+/-0.012(syst), k=0.001+/-0.001(stat)+/-0.002(syst) are consistent with the world averages dominated by K+ data, but have significantly smaller errors., Comment: LaTeX, 10 pages, 8 eps-figures, update of IHEP 2002-16

In the framework of scalar-vector dominance we calculate the hadronic matrix elements of scalar and tensor effective quark currents induced by virtual leptoquark interactions. Combined bounds on the product of couplings and leptoquark masses are obtained from experimental data., Comment: 19 pages, 15 eps-figures, discusion on the lepton polarization added

The first description of the experimental program "OKA" with RF-separated K+/- beam at Protvino U-70 PS is presented. The parameters of the beam as well as the potential for CP-violation searches are discussed., Comment: 8 pages, 6 figures, submitted to proceedings of International Conference on CP Violation, Sep 18-22, 2000, Italy

We show that a search for $e^+ e^- \to t \bar q$ $(\bar q = \bar c, \bar u)$ events at LEP--2 collider provide a possibility to improve significantly the modern constraints on coupling constants of anomalous $t$--quark interaction via flavor--changing neutral currents., Comment: 12 pages, LaTeX, epsfig, 4 figures. Corrected typos