Speaker
Description
The talk is devoted to the latest results from the OKA collaboration. The OKA setup is using the RF-separated 17.7 GeV/c momentum kaon beam of the U-70 accelerator. The data corresponds to the flux of $2.62·10^{10}$ «live» kaons entering the decay volume.
A missing mass analysis is performed to search for an invisible pseudoscalar axion-like particle(ALP) in the decay $K^+ \rightarrow \pi^+\pi^0 a $. No signal is observed,the 90% CL upper limit is changing from $2.5·10^{-6}$ to $2·10^{-7}$ for the ALP mass from 0 to 200 MeV.
Several rare EM decays are investigated:
A new precise measurement of the vector and axial-vector form factor difference $F_V − F_A$ in the $K^+ \rightarrow \mu^+ \nu \gamma$ decay is reported. About 144K events are selected. The preliminary result is $F_V − F_A = 0.135 \pm 0.017(stat)\pm 0.024(syst)$ which differs by $\sim 3 \sigma$ from $χPT(O(p^4))$ and by 1.5 σ from the Lattice calculations.
The $K^+ \rightarrow \mu^+ \nu \pi^0 \gamma (K\mu3\gamma)$ decay is studied with the high statistics of more than 1000 signal events with the energy of the emitted photon in the rest frame of the decaying kaon $E_\gamma > 30$ MeV. Using $4.48 · 10^6$ events of the decay the ratio Br($K\mu3\gamma$)/Br($K\mu3$) is found to be $(4.45 \pm 0.25(stat)) · 10^{−4}$. From this value, using Br(Kµ3) = 3.352% we get Br($K\mu3\gamma) = (1.492 ± 0.085(stat)) · 10^{−5}$. Our result is preliminary, with systematic errors being estimated.
A rare EM decay $K^+ \rightarrow \pi^+ \pi^0 \pi^0 \gamma$ is observed for the first time on the statistics of ~50 events with $E_\gamma >10$ MeV. The branching is measured to be Br$ = (3.7 \pm 0.9 \pm 0.3 ) · 10^{-6} E_\gamma > 10$ МэВ
A super-rare EM decay $K^+ \rightarrow e^+ \nu \pi^0 \pi^0 \pi^0 $ is searched for, no events were observed, the upper limit set is: Br$ < 5· 10^{-8}$ , ~60 times better than in the previous searches.
