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Register a new userMeasurement of $K^+ to pi^0 pi^0 e^+ u$ ($K_{e4}^{00}$) decay using stopped positive kaons
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The $K^+ to pi^0 pi^0 e^+ u$ ($K_{e4}^{00}$) decay has been measured with stopped positive kaons for a data sample of 216 events. A comparison of the observed spectra with a Monte Carlo simulation determined the $K_{e4}^{00}$ form factor. The results are compatible with the $K^+ to pi^+ pi^- e^+ u$ data, as estimated from the $Delta I=1/2$ rule. We also established that the $K_{e4}^{00}$ channel can be used to determine the $pi$-$pi$ scattering lengths.
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The K^+ to pi^0 mu^+ u gamma ($K_{mu 3 gamma}$) decay has been measured with stopped positive kaons at the KEK 12 GeV proton synchrotron. A $K_{mu 3 gamma}$ sample containing 125 events was obtained. The partial branching ratio $Br(K_{mu 3 gamma}, E_{gamma}>30 {rm MeV}, theta_{mu^+ gamma}>20^{circ})$ was found to be $[2.4 pm 0.5(stat) pm 0.6(syst)]times 10^{-5}$, which is in good agreement with theoretical predictions.
A binned Dalitz plot analysis of the decays $B^0 to D K^{ast 0}$, with $D to K_{S}^{0} pi^{+} pi^{-}$ and $K_{S}^{0} K^{+} K^{-}$, is performed to measure the observables $x_pm$ and $y_pm$, which are related to the CKM angle $gamma$ and the hadronic parameters of the decays. The $D$ decay strong phase variation over the Dalitz plot is taken from measurements performed at the CLEO-c experiment, making the analysis independent of the $D$ decay model. With a sample of proton-proton collision data, corresponding to an integrated luminosity of $3.0,rm{fb}^{-1}$, collected by the LHCb experiment, the values of the $CP$ violation parameters are found to be $x_+ = 0.05 pm 0.35 pm 0.02$, $x_-=-0.31pm 0.20 pm 0.04$, $y_+=-0.81pm 0.28pm 0.06$ and $y_-=0.31pm 0.21 pm 0.05$, where the first uncertainties are statistical and the second systematic. These observables correspond to values $gamma$ = $(71 pm 20)^circ$, $r_{B^0} = 0.56pm 0.17$ and $delta_{B^0} = (204,^{+21}_{-20})^circ$. The parameters $r_{B^0}$ and $delta_{B^0}$ are the magnitude ratio and strong phase difference between the suppressed and favoured $B^0$ decay amplitudes, and have been measured in a region of $pm 50$ MeV/$c^2$ around the $K^{ast}(892)^{0}$ mass and with the magnitude of the cosine of the $K^{ast}(892)^{0}$ helicity angle larger than 0.4.
We searched for the $CP$-violating rare decay of neutral kaon, $K_{L} to pi^0 u overline{ u}$, in data from the first 100 hours of physics running in 2013 of the J-PARC KOTO experiment. One candidate event was observed while $0.34pm0.16$ background events were expected. We set an upper limit of $5.1times10^{-8}$ for the branching fraction at the 90% confidence level (C.L.). An upper limit of $3.7times10^{-8}$ at the 90% C.L. for the $K_{L} to pi^{0} X^{0}$decay was also set for the first time, where $X^{0}$ is an invisible particle with a mass of 135 MeV/$c^{2}$.
The structure dependent radiative $K^+ rightarrow e^+ u gamma$ ($K_{e2gamma}^{rm SD}$) decay was investigated with stopped positive kaons. The $e^+$ momentum spectra were measured with and without a photon in coincidence and analyzed with Monte Carlo simulations for acceptance and detector response to extract the ratio of the $K_{e2gamma}^{rm SD}$ and $K^+ rightarrow e^+ u$ ($K_{e2}$) branching ratios. A value of $Br(K_{e2gamma}^{rm SD}) / Br(K_{e2}) = 1.22pm0.07_{rm stat} pm 0.04_{rm syst}$ was obtained, which is significantly larger than the value inferred from a previous experimental result for $Br(K_{e2gamma}^{rm SD})/Br(K^+rightarrow mu^+ u)$.
We present the results of a Dalitz plot analysis of D^0 to K^0_S pi^0 pi^0 using the CLEO-c data set of 818 inverse pico-barns of e^+ e^- collisions accumulated at sqrt{s} = 3.77 GeV. This corresponds to three million D^0 D^0-bar pairs from which we select 1,259 tagged candidates with a background of 7.5 +- 0.9 percent. Several models have been explored, all of which include the K^*(892), K^*_2(1430), K^*(1680), the f_0(980), and the sigma(500). We find that the combined pi^0 pi^0 S-wave contribution to our preferred fit is (28.9 +- 6.3 +- 3.1)% of the total decay rate while D^0 to K^*(892)^0 pi^0 contributes (65.6 +- 5.3 +- 2.5)%. Using three tag modes and correcting for quantum correlations we measure the D^0 to K^0_S pi^0 pi^0 branching fraction to be (1.059 +- 0.038 +- 0.061)%.
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