Related papers: The Standard model prediction for K(e2)/K_(mu2) an…

Including the recent preliminary results of BaBar and BELLE experiments, we update the currently allowed intervals for various CKM parameters: $\bar\rho$, $\bar\eta$, $\sin2\beta$, $\sin2\alpha$, $\sin^2\gamma$. We also update the SM…

Using the full data set of the NA48/2 experiment, the decay K+- -> pi+- e+ e- gamma is observed for the first time, selecting 120 candidates with 7.3 +- 1.7 estimated background events. With K+- -> pi+- pi0D as normalisation channel, the…

Measurements of the ratio of $B \to K^* \mu \mu $ to $B \to K^* e e $ branching fractions, $R_{K^*}$, by the LHCb collaboration strengthen the hints from previous studies with pseudoscalar kaons, $R_K$, for the breakdown of lepton…

A preliminary measurement of RK = Gamma(Ke2)/Gamma(Km2) at the KLOE experiment is discussed. The result, RK = (2.55+-0.05+-0.05)x 10^-5, is based on 1.7 fb^-1 of luminosity integrated on the phi-meson peak at the Frascati e^+e^- collider…

Measured ratios of decay rates for Ke3/K2\pi, K\mu3/K2\pi and K\mu3/Ke3 are presented. These measurements are based on K^+- decays collected in a dedicated run in 2003 by the NA48/2 experiment at CERN. The results obtained are Ke3/K2\pi =…

We have observed the rare decay K+ --> pi+ mu+ mu- and measured the branching ratio Gamma(K+ --> pi+ mu+ mu-)/Gamma(K+ --> all) = (5.0 +/- 0.4 (stat.) +/- 0.7 (sys.) +/- 0.6 (theor.)) x 10^{-8}. We compare this result with predictions from…

Semileptonic $b \to c$ transitions, and in particular the ratios $R(D^{(*)}) = \frac{\Gamma(B \rightarrow D^{(*)} \tau \nu )}{\Gamma(B \rightarrow D^{(*)} \ell \nu )}$, can be used to test the universality of the weak interactions. In light…

We have measured the ratio R=Gamma(K_L -> gamma gamma)/ \Gamma(K_L -> 3 pi^0) using the KLOE detector. From a sample of ~ 10^9 phi-mesons produced at DAFNE, the Frascati phi-factory, we select ~ 1.6 10^8 K_L-mesons tagged by observing K_S…

We propose a method to quantify the Standard Model uncertainty in B to K pi decays using the experimental data, assuming that power counting provides a reasonable estimate of the subleading terms in the 1/mb expansion. Using this method, we…

The long-term goal of NA62 is to measure the ultra rare K+/- -> pi+/- nu anti-nu decay with a sensitivity of 10^-12 per event. This is done by using the decay - in - flight technique which allows a signal acceptance of ~10% . The aim is to…

The PIENU experiment aims at the measurement of the branching ratio R = \Gamma (\pi -> e \nu + \pi -> e \nu \gamma) / \Gamma (\pi -> \mu \nu + \pi -> \mu \nu \gamma) at the <0.1% precision level, with which mass scales of 1000 TeV/c^{2} can…

The quantity R_K = Gamma(K -> e nu)/Gamma(K -> mu nu) studied by the experiment NA62 at CERN is known to probe lepton-flavour violating (LFV) parameters of the Minimal Supersymmetric Standard Model (MSSM). A non-zero parameter…

The present status of the ratio $\varepsilon'/\varepsilon$ in the Standard Model (SM) is summarized. In particular we stress the differences between three approaches that attempt to calculate $\varepsilon'/\varepsilon$ within the SM:…

The E36 experiment recently conducted at J-PARC by the TREK Collaboration will provide a precise mesurement of the decay ratio $ R_K = \Gamma(K^+ \rightarrow e^+\nu_e) / \Gamma(K^+ \rightarrow \mu^+\nu_{\mu}) $ with the aim of testing…

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…

We estimate B(K -> pi nu nubar) in the context of the Standard Model by fitting for lambda_t = Vtd x V*ts of the `kaon unitarity triangle' relation. We fit data from epsilon_K, the CP-violating parameter describing K-mixing, and a_{psi K},…

The LHCb measurement of the $\mu/e$ ratio $R_{K^*}$ indicates a deficit with respect to the Standard Model prediction, supporting earlier hints of lepton universality violation observed in the $R_K$ ratio. We show that the $R_K$ and…

We find that the phase appearing in the unitarity relation between $\mathcal{B}(K_L\rightarrow \mu^+\mu^-)$ and $\mathcal{B}(K_L\rightarrow \gamma\gamma)$ is equal to the phase shift in the interference term of the time-dependent…

The three precision measurements of the cross section $\sigma\big(e^+e^-\rightarrow\pi^+\pi^-\gamma(\gamma)\big)$ using initial state radiation by the KLOE collaboration provide an important input for the prediction of the hadronic…

We review some recent theoretical results on rare kaon decays. Particular attention is devoted to find Standard Model tests. This is theoretically easy in $K\to \pi \nu \bar{\nu}$, while a careful study of the long distance contributions is…