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M. M. Shapkin

Publications and source records attributed to M. M. Shapkin.

5 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 $K^{+}\to π^{+}π^{0}\overline{{} γ}$ 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 ($\overlineγ$) 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.

hep-ex↗
arXiv2020

Study of $K^+ \rightarrow π^{0} e^{+} νγ$ decay with OKA setup

Results of a study of the $K^+ \rightarrow π^{0} e^{+} νγ$ 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 $E^*_γ$ and $cosΘ^{*}_{eγ}$. In particular, the branching ratio for $E^{*}_γ>30$ MeV and $Θ^{*}_{e γ}>20^{\circ}$ is measured R = $\frac{Br(K^+ \rightarrow π^{0} e^{+} ν_{e} γ) } {Br(K^+ \rightarrow π^{0} e^{+} ν_{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.

hep-ex↗
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.

hep-ex↗
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.

hep-ex↗