New measurement of the K + → π + νν̄ 1 branching ratio

The last BNL measurement of the K + → π + νν̄ 1 Branching Ratio

New results for K+→π+νν at low π+ momentum from BNL E949

The BNL E949 experiment was a successor to BNL E787 and was aimed to measure the branching ratio of the K+ → π+νν̄ decay. After detector upgrades were made, data equivalent to 1.7 × 1012 K+ decays at rest were collected in a 2002 physics run. The data were analyzed via a blind analysis with a technique called the “Bifurcation Method”. In this report we present the results of a search for K+ → π+...

Search of New Physics with Kaon decays at NA 62

the current short term phase (data taking completed in years 2007-8) we are studying the ratio RK = Γ(K→eνe(γ)) Γ(K→μνμ (γ)) of leptonic decay rates, which provides a golden probe for testing the structure of the weak interactions. In the second phase (long term) we will then focus on the measurement of the branching ratio of the very rare kaon decay K+ → π+νν̄ aiming at collecting O(100) K+→ π+...

Evidence for the Decay K + → π + νν̄

An event consistent with the signature expected for the rare kaon decay K+ → π+νν̄ has been observed. In the pion momentum region examined, 211 < P < 230 MeV/c, the backgrounds are estimated to contribute 0.08 ± 0.03 events. If the event is due toK+ → π+νν̄, the branching ratio is 4.2 −3.5× 10−10. PACS numbers: 13.20.Eb, 12.15.Hh, 14.80.Mz Typeset using REVTEX

Electroweak Corrections to the Charm Quark Contribution to K → πνν̄

We compute the leading-log QED, the next-to-leading-log QED-QCD, and the electroweak corrections to the charm quark contribution relevant for the rare decay K+ → π+νν̄. The corresponding parameter Pc(X) is increased by up to 2% with respect to the pure QCD estimate to Pc(X) = 0.372 ± 0.015 for mc(mc) = (1.286±0.013)GeV, αs(MZ) = 0.1176±0.0020 and |Vus| = 0.2255. For the branching ratio we find B...