Related papers: Lepton flavour universality test at the CERN NA62 …
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…
Recent measurements of kaon decays provide new information about CKM unitarity, lepton universality, and discrete symmetries. KLOE-2, the proposed extension of the kaon physics program at Frascati, will extend the world data set on kaon…
Precise measurements of the tau lepton properties provide stringent tests of the Standard Model structure and accurate determinations of its parameters. We overview the present status of a few selected topics: lepton universality, QCD tests…
The ultra-rare decay $K^+\to\pi^+\nu\bar\nu$ is a golden mode in flavor physics. The Standard Model prediction for its branching ratio is below $10^{-10}$. This decay mode is highly sensitive to new physics models at mass scales up to…
The NA62 experiment at CERN targets the measurement of the ultra-rare $K^{+} \to \pi^{+}\nu\bar{\nu}$ decay, and carries out a broad physics programme that includes probes for symmetry violations and searches for exotic particles. Data were…
A new measurement of $B_{\pi e2}$, the $\pi^+ \to e^+\nu(\gamma)$ decay branching ratio, is currently under way at the Paul Scherrer Institute. The present experimental result on $B_{\pi e2}$ constitutes the most accurate test of lepton…
We study the flavor universality of the lepton couplings with the W and Z bosons. Currently, it is constrained by the electroweak precision observables. We focus on the leptonic decay of the pion. It is shown that the decay is expected to…
The final results of the search for the lepton flavour violating decay $\mu^{+} \rightarrow {\rm e^{+}} \gamma$ based on the full dataset collected by the MEG experiment at the Paul Scherrer Institut in the period 2009--2013 and totalling…
The electroweak sector of the Standard Model contains three generations of charged leptons $\ell^-\in\{e^-,\mu^-,\tau^-\}$ as exact replicas of each other, except for their Yukawa couplings to the Higgs that determine their masses. The…
A measurement of the ratio of the branching fractions, $R_{\tau/e} = B(W \to \tau \nu)/ B(W \to e \nu)$, is performed using a sample of $W$ bosons originating from top-quark decays to final states containing $\tau$-leptons or electrons.…
The ratio $R_K = \Gamma(K^{\pm}\to e^{\pm}\nu(\gamma)) / \Gamma(K^{\pm}\to\mu^{\pm}\nu(\gamma))$ provides a powerful probe of the structure of weak interactions. It is calculated with very high precision within the Standard Model, but…
At the back of succeeding measurements of anomalies in semileptonic decays at LHCb and several collider experiments hinting at the possible violation of lepton flavor universality, we undertake a concise review of theoretical foundations of…
Kaon physics can test new-physics effects in leptonic or semileptonic decays. A unitarity test of the first row of the CKM mixing matrix is obtained from the precision measurements of Kl3 widths for K{\pm}, KL, and (unique to KLOE) KS. The…
Recent measurements have revealed a number of intriguing deviations from the Standard Model predictions in $B$ meson decays, in particular in observables testing lepton flavour universality. We review their experimental status and…
The $B\to K^*\mu\mu$ decay exhibits deviations with respect to Standard Model expectations and the measurement of the ratio $R_K$ hints at a violation of lepton-flavour universality in $B\to K\ell\ell$ transitions. Both effects can be…
Soon the NA62 experiment will start looking for the rare K+ ---> pi+ nu nu bar decay. In this talk, its theoretical interests, together with those of the neutral rare decays KL ---> pi0 nu nu bar, KL ---> pi0 e+ e-, and KL ---> pi0 mu+ mu-,…
The decay rate of the neutral long-lived K meson into the e+ e- e+ e- final state has been measured with the NA48 detector at the CERN SPS. Using data collected in 1999, a total of 132 events has been observed with negligible background.…
Kaon decay studies seeking new-physics (NP) effects in leptonic (K_l2) or semileptonic (K_l3) decays are discussed. A unitarity test of the first row of the CKM mixing matrix is obtained from the KLOE precision measurements of Kl3 widths…
There are some slight tensions with the SM predictions within the latest LHCb measurements. Besides the known anomaly in one angular observable of the rare decay B -> K* mu+ mu-, another small discrepancy recently occurred. The ratio R_K =…
The NA62 experiment reports an investigation of the $K^+\rightarrow\pi^+\nu\bar{\nu}$ mode from a sample of $K^+$ decays collected in 2017 at the CERN SPS. The experiment has achieved a single event sensitivity of $(0.389\pm…