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Register a new userStudy of the decay $K^{+}topi^{+}pi^{-}pi^{+}gamma$ in the OKA experiment
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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 $K^{+}topi^{+}pi^{-}pi^{+}gamma$ decays with the energy of the photon in the kaon rest frame greater than 30 MeV. The measured branching fraction of the $K^{+}topi^{+}pi^{-}pi^{+}gamma$, 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.
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Results of a study of the $K^+ rightarrow pi^{0} e^{+} u 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 $cosTheta^{*}_{egamma}$. 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^{+} u_{e} gamma) } {Br(K^+ rightarrow pi^{0} e^{+} u_{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.
The first observation of the decay K^+ --> pi^+ gamma gamma is reported. A total of 31 events was observed with an estimated background of 5.1 +- 3.3 events in the pi+ momentum range from 100 MeV/c to 180 MeV/c. The corresponding partial branching ratio, B(K+ -> pi+ gamma gamma, 100 MeV/c < P_pi^+ < 180 MeV/c), is (6.0 +- 1.5 (stat) +- 0.7 (sys)) x 10^{-7}. No K^+ --> pi^+ gamma gamma decay was observed in the pi^+ momentum region greater than 215 MeV/c. The observed pi^+ momentum spectrum is compared with the predictions of chiral perturbation theory.
The KTeV E799 experiment has conducted a search for the rare decay $K_{L}topi^{0}pi^{0}gamma$ via the topology $K_{L}topi^{0}pi^{0}_Dgamma$ (where $pi^0_Dtogamma e^+e^-$). Due to Bose statistics of the $pi^0$ pair and the real nature of the photon, the $K_{L}topi^{0}pi^{0}gamma$ decay is restricted to proceed at lowest order by the CP conserving direct emission (DE) of an E2 electric quadrupole photon. The rate of this decay is interesting theoretically since chiral perturbation theory predicts that this process vanishes at level $O(p^4)$. Therefore, this mode probes chiral perturbation theory at $O(p^6)$. In this paper we report a determination of an upper limit of $2.43times 10^{-7}$ (90% CL) for $K_{L}topi^{0}pi^{0}gamma$. This is approximately a factor of 20 lower than previous results.
Using a sample of $1.3times 10^9$ $J/psi$ events collected with the BESIII detector, we report the first observation of $eta^{prime}topi^{+}pi^{-}pi^{+}pi^{-}$ and $eta^{prime}topi^{+}pi^{-}pi^{0}pi^{0}$. The measured branching fractions are $mathcal{B}$($eta^{prime}topi^{+}pi^{-}pi^{+}pi^{-}$) = $(8.53pm0.69({rm stat.})pm0.64({rm syst.}))times10^{-5}$ and $mathcal{B}$($eta^{prime}topi^{+}pi^{-}pi^{0}pi^{0}$) = $(1.82pm0.35({rm stat.})pm0.18({rm syst.}))times10^{-4}$, which are consistent with theoretical predictions based on a combination of chiral perturbation theory and vector-meson dominance.
We have performed a measurement of the K^+ -> pi^+ pi^0 gamma decay and have observed 2 X 10^4 events. The best fit to the decay spectrum gives a branching ratio for direct photon emission of (4.7pm0.8pm0.3) X 10^{-6} in the pi^+ kinetic energy region of 55 to 90 MeV and requires no component due to interference with inner bremsstrahlung.
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