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A. Yu. Polyarush

Publications and source records attributed to A. Yu. Polyarush.

At least 19 recordsLinked to original sources
arXiv2026

A search for the dark photon in the OKA experiment

A search for the massless dark photon in the decay $K^{+}\to \pi^{+}\pi^{0}\overline{{} \gamma}$ is performed with the OKA detector exposed to 17.7 GeV/c RF separated secondary beam of the U70 Proton Synchrotron. A high-statistics data sample of the $K^{+}$ decays is used for a missing mass search of the stable massless invisible dark photon ($\overline{\gamma}$) in the final state. In the absence of a statistically valuable signal the upper limit on the branching ratio of the decay $Br<2.0\times10^{-6}$ is obtained with a 90% confidence level based on a realistic matrix element of the process. Currently, it is the best upper limit for this hypothetical decay channel.

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arXiv2024

The upper limit on the $K^+ \to \pi^0\pi^0\pi^0e^+\nu$ decay

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.

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arXiv2023

Observation of $K^{+} \to \pi^{+}\pi^{0}\pi^{0}\gamma$ decay

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.

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arXiv2023

Searches for the light invisible axion-like particle in $K^{+}\to\pi^{+}\pi^{0}a$ decay

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 $4.4\cdot10^{-6}$.

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arXiv2022

Measurement of T-odd asymmetry in radiative K+ -> pi0 e+ nu gamma decay using OKA detector

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 $|A_{\xi}| < 5.4\times10^{-3} (90\%~ CL)$

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arXiv2020

Study of $K^+ \rightarrow \pi^{0} e^{+} \nu \gamma $ decay with OKA setup

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.

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arXiv2019

Measurement of the $K^+\rightarrow{μ^+}{ν_μ}γ$ decay form factors in the OKA experiment

A precise measurement of the vector and axial-vector form factors difference $F_V-F_A$ in the $K^+\rightarrow{μ^+}{ν_μ}γ$ decay is presented. About 95K events of $K^+\rightarrow{μ^+}{ν_μ}γ$ 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.

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arXiv2019

Study of the decay $K^{+}\toπ^{+}π^{-}π^{+}γ$ in the OKA experiment

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 $K^{+}\toπ^{+}π^{-}π^{+}γ$ decays with the energy of the photon in the kaon rest frame greater than 30 MeV. The measured branching fraction of the $K^{+}\toπ^{+}π^{-}π^{+}γ$, with $E_γ^{*}$ > 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.

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arXiv2018

Search for heavy neutrino in $K^{+} \to μ^{+} ν_{H}$ decay

A high statistics data sample of the $K^{+}\toμ^{+}ν_μ$ decay was accumulated by the OKA experiment in 2012. The missing mass analysis was performed to search for the decay channel $K^{+}\toμ^{+}ν_{H}$ 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 $< m_{ν_{H}} <$ 375) MeV$/c^{2}$. As a result, we obtain upper limits on the branching ratio and on the value of the mixing element $|U_{μH}|^{2}$.

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arXiv2017

$K_{e3}$ decay studies in OKA experiment

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: $λ'_{+}=(26.1 \pm 0.35 \pm 0.28 )\times 10^{-3}$, $λ"_{+}=(1.91 \pm 0.19 \pm 0.14)\times 10^{-3}$. 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 $Λ_+ =(24.58 \pm 0.18) \times 10^{-3}$. The presented results are considered as preliminary.

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arXiv2012

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_{μh}|^2 < 8 x 10^{-5} for the Dirac case.

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arXiv2007

Measurement of K^{-}_{e3} branching ratio

The branching fraction for the decay $K^{-} \to π^{0} e \bar ν$ 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.

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arXiv2004

Experimental study of direct photon emission in K- --> pi- pi0 gamma decay using ISTRA+ detector

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.

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arXiv2004

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).

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arXiv2003

High statistic study of the K- -> pi0 mu- nu decay

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.

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arXiv2003

High statistics study of the K- -> pi0 e- nu decay

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)

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