[en] A long distance contribution to the amplitude for K⁺→π⁺νν(bar sign) is calculated. Its magnitude, comparable to that of other long distance effects, is three orders of magnitude smaller than the short distance effects, but the techniques involved may have other applications. (c) 2000 The American Physical Society

[en] A calculation of the semileptonic decays of the kaon (K_l3) is presented. The results are direct predictions of a covariant model of the pion and kaon introduced earlier by Ito, Buck, and Gross. The weak form factors for K_l3 are predicted with absolutely no parameter adjustments of the model. We obtained, for the form factor parameters, f_-(q²=m_l²)/f₊(q²=m_l²)=-0.28 and λ₊= 0.028, both within experimental error bars. The connections of this approach to heavy quark symmetry are discussed. copyright 1997 The American Physical Society

[en] A search for additional evidence for the rare kaon decay K⁺→π⁺νν (bar sign) has been made with a new data set comparable in sensitivity to the previous exposure that produced a single event. No new events were found in the pion momentum region examined, 211< P<229 MeV/c . Including a reanalysis of the original data set, the backgrounds were estimated to contribute 0.08±0.02 events. Based on one observed event, the new branching ratio is B(K⁺→π⁺ν ν(bar sign))=1.5^+3.4_-1.2x10^-10 . (c) 2000 The American Physical Society

[en] We report the first observation of a manifestly CP violating effect in the K_L→π⁺π^-e⁺e^- decay mode. A large asymmetry was observed in the distribution of these decays in the CP -odd and T -odd angle φ between the decay planes of the e⁺e^- and π⁺π^- pairs in the K_L center of mass system. After acceptance corrections, the overall asymmetry is found to be [13.6±2.5(stat)±1. 2(syst)]% . This is the largest CP -violating effect yet observed when integrating over the entire phase space of a mode and the first such effect observed in an angular variable. (c) 2000 The American Physical Society

[en] We report on a search for the decay K_L→π⁰νν(bar sign), carried out as a part of E799-II, a rare K_L decay experiment at Fermilab. Within the standard model, the K_L→π⁰νν(bar sign) decay is dominated by direct CP violating processes, and thus an observation of the decay implies confirmation of direct CP violation. No events were observed, and we set an upper limit for the branching ratio of K_L→π⁰νν(bar sign) to be < 5.9 x10^-7 at the 90% confidence level. (c) 2000 The American Physical Society

[en] We investigate the mechanism of K⁺→π⁺l⁺l^- (l=e, μ) decays in which a virtual photon is emitted either from the incoming K⁺ or the outgoing π⁺. We point out some inconsistencies with and between two previous calculations and discuss the possible experimental inputs. This mechanism alone fails to explain the existing experimental data by more than one order-of-magnitude. But it may show itself by its interference with other long-range mechanisms, which may lead to a better agreement between the theoretical and experimental form factors. (c) 2000 The American Physical Society

[en] We report on a search for the decay K_L→π⁰μ⁺μ^- carried out as a part of the KTeV experiment at Fermilab. This decay is expected to have a significant CP violating contribution and a direct measurement will either support the Cabibbo-Kobayashi-Maskawa mechanism for CP violation or point to new physics. Two events were observed in the 1997 data with an expected background of 0.87±0.15 events, and we set an upper limit B(K_L→π⁰μ⁺μ^-)<3.8x10^-10 at the 90% confidence level. (c) 2000 The American Physical Society

[en] Recently it has been demonstrated that large phases in softly broken supersymmetric (SUSY) theories are consistent with electric dipole moment constraints, and are motivated in some (type I) string models. Here we consider whether large flavor-independent soft phases may be the dominant (or only) source of all CP violation. In this framework, ε and ε^'/ε can be accommodated, and the SUSY contribution to the B system mixing can be large and dominant. An unconventional flavor structure of the squark mass matrices (with enhanced super-Cabibbo-Kobayashi-Maskawa mixing) is required for consistency with B and K system observables. (c) 2000 The American Physical Society

[en] An improved search for a T -violating transverse muon polarization (P_T) in K⁺→π⁰μ⁺ν decay was performed using kaon decays at rest. By means of this method, P_T was extracted with small systematic errors, P_T=-0.0042±0.0049(stat) ±0.0009(syst) , and the T -violation parameter was determined to be Imξ=-0.013±0.016(stat )±0.003(syst) . (c) 1999 The American Physical Society

[en] We report the first measurement of a structure-dependent component in the decay K⁺→μ⁺ν_μ γ . Using the kinematic region where the muon kinetic energy is greater than 137 MeV and the photon energy is greater than 90 MeV, we find that the absolute value of the sum of the vector and axial-vector form factors is |F_V+F_A|=0.165±0.007± 0.011 . This corresponds to a branching ratio of B(SD⁺ )=(1.33±0.12±0.18)x10^-5 . We also set the limit -0.04< F_V-F_A<0.24 at 90% C.L. (c) 2000 The American Physical Society