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Register a new user$K_{e3}$ decay studies in OKA experiment
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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.
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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.
The measurements of $V_{us}$ in leptonic $(K_{mu 2})$ and semileptonic $(K_{l3})$ kaon decays exhibit a $3sigma$ disagreement, which could originate either from physics beyond the Standard Model or some large unidentified Standard Model systematic effects. Clarifying this issue requires a careful examination of all existing Standard Model inputs. Making use of a newly-proposed computational framework and the most recent lattice QCD results, we perform a comprehensive re-analysis of the electroweak radiative corrections to the $K_{e3}$ decay rates that achieves an unprecedented level of precision of $10^{-4}$, which improves the current best results by almost an order of magnitude. No large systematic effects are found, which suggests that the electroweak radiative corrections should be removed from the ``list of culprits responsible for the $K_{mu 2}$--$K_{l3}$ discrepancy.
A precise measurement of the vector and axial-vector form factors difference $F_V-F_A$ in the $K^+rightarrow{mu^+}{ u_{mu}}{gamma}$ decay is presented. About 95K events of $K^+rightarrow{mu^+}{ u_{mu}}{gamma}$ are selected in the OKA experiment. The result is $F_V-F_A=0.134pm0.021(stat)pm0.027(syst)$. Both errors are smaller than in the previous $F_V-F_A$ measurements.
We report a high-precision calculation of the Standard Model electroweak radiative corrections in the $Kto pi e^+ u(gamma)$ decay as a part of the combined theory effort to understand the existing anomaly in the determinations of $V_{us}$. Our new analysis features a chiral resummation of the large infrared-singular terms in the radiative corrections and a well-under-control strong interaction uncertainty based on the most recent lattice QCD inputs. While being consistent with the current state-of-the-art results obtained from chiral perturbation theory, we reduce the existing theory uncertainty from $10^{-3}$ to $10^{-4}$. Our result suggests that the Standard Model electroweak effects cannot account for the $V_{us}$ anomaly.
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.
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