The KTeV E799 experiment has conducted a search for the rare decay \(K_{L}\to\pi^{0}\pi^{0}\gamma\) via the topology \(K_{L}\to\pi^{0}\pi^{0}_D\gamma\) (where \(\pi^0_D\to\gamma e^+e^-\)). Due to ...Bose statistics of the \(\pi^0\) pair and the real nature of the photon, the \(K_{L}\to\pi^{0}\pi^{0}\gamma\) 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 \(2.43\times 10^{-7}\) (90% CL) for \(K_{L}\to\pi^{0}\pi^{0}\gamma\). This is approximately a factor of 20 lower than previous results.
We report on a new measurement of the branching ratio B(KL->pi0 gamma gamma)using the KTeV detector. We reconstruct 1982 events with an estimated background of 608, that results in B(KL -> pi0 gamma ...gamma) = (1.29 +/- 0.03(stat) +/- 0.05(syst)) x 10**-6. We also measure the parameter, aV, which characterizes the strength of vector meson exchange terms in this decay. We find aV = -0.31 +/- 0.05(stat) +/- 0.07(syst). These results utilize the full KTeV data set collected from 1997 to 2000 and supersede earlier KTeV measurements of the branching ratio and aV.
We present a new determination of the parity of the neutral pion via the double Dalitz decay pi^0 -> e+ e- e+ e-. Our sample, which consists of 30511 candidate decays, was collected from K_L -> pi0 ...pi0 pi0 decays in flight at the KTeV-E799 experiment at Fermi National Accelerator Laboratory. We confirm the negative pi^0 parity, and place a limit on scalar contributions to the pi^0 -> e+ e- e+ e- decay amplitude of less than 3.3% assuming CPT conservation. The pi^0 gamma* gamma* form factor is well described by a momentum-dependent model with a slope parameter fit to the final state phase space distribution. Additionally, we have measured the branching ratio of this mode to be B(pi^0 -> e+ e- e+ e-) = (3.26 +- 0.18) x 10^(-5).
We report on a new measurement of the branching ratio B(KL -> pi0 e+ e- gamma) using the KTeV detector. This analysis uses the full KTeV data set collected from 1997 to 2000. We reconstruct 139 ...events over a background of 14, which results in B(KL -> pi0 e+ e- gamma) = (1.62 +/- 0.14 (stat) +/- 0.09 (syst)) x 10^{-8}. This result supersedes the earlier KTeV measurement of this branching ratio.
Phys.Rev.Lett.95:081801,2005 The Xi^0 muon semi-leptonic decay has been observed for the first time with
nine identified events using the KTeV beam line and detector at Fermilab. The
decay is ...normalized to the Xi^0 beta decay mode and yields a value for the
ratio of decay rates of $(1.8^{+0.7}_{-0.5}(stat.)\pm0.2(syst.))\times
10^{-2}$. This is in agreement with the SU(3) flavor symmetric quark model.
Phys.Rev.D71:012001,2005 We present measurements of R_Kl3rad = Gamma(KL->\pi\ell\nu\gamma; Egcm > 10
MeV)/Gamma(KL->\pi\ell\nu), where ell = mu or e, and Egcm is the photon energy
in the kaon rest ...frame. These measurements are based on KL decays collected in
1997 by the KTeV (E832) experiment at Fermilab. With samples of 1385
KL->\pi\mu\nu\gamma and 14221 KL->\pi\e\nu\gamma candidates, we find R_Km3rad =
(0.530 +- 0.019)% and R_Ke3rad = (4.942 +- 0.062)%. We also examine
distributions of photon energy and lepton-photon angle.
The Xi^0 muon semi-leptonic decay has been observed for the first time with nine identified events using the KTeV beam line and detector at Fermilab. The decay is normalized to the Xi^0 beta decay ...mode and yields a value for the ratio of decay rates of \((1.8^{+0.7}_{-0.5}(stat.)\pm0.2(syst.))\times 10^{-2}\). This is in agreement with the SU(3) flavor symmetric quark model.
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