Related papers: A Lepton Universality Test at CERN NA62 Experiment
KLOE has measured most decay branching ratios of Ks, Kl and K+/- mesons. It has also measured the Kl and the K+- lifetime and determined the shape of the form factors involved in kaon semileptonic decays. We present in the following a…
Recent results from the LHC's first run have revealed intriguing departures from lepton flavour universality in the semi-leptonic decays of $B$-mesons. We discuss the complementary role that rare kaon decays can provide in testing new…
In the Standard Model, lepton universality refers to the identical electroweak gauge interactions among charged leptons. The measurement of the branching ratio $R_{e / \mu} = \frac{\Gamma(\pi\rightarrow\ e…
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…
A sample of 3984 candidates of the $K^+\to\pi^+\gamma\gamma$ decay, with an estimated background of $291\pm14$ events, was collected by the NA62 experiment at CERN during 2017-2018. In order to describe the observed di-photon mass spectrum,…
A sample of 3120 $K^\pm\to\pi^\pm\mu^+\mu^-$ decay candidates with $(3.3\pm0.7)%$ background contamination has been collected by the NA48/2 experiment at the CERN SPS, allowing a detailed study of the decay properties. The branching ratio…
Precision measurements of the branching ratios (BRs) for rare kaon decays can provide unique constraints on CKM unitarity and may reveal the existence of new physics. The BRs for two of these decays, $K^+\to\pi^+\nu\bar{\nu}$ and…
Searches for heavy neutrinos can be successfully performed by fixed target experiments at the CERN SPS. New results obtained by the NA62 and NA48/2 kaon experiments are summarized in this paper. The physics potential of future projects…
We present measurements of the branching fractions for the decays $B\to K \mu^{+}\mu^{-}$ and $B\to K e^{+}e^{-}$, and their ratio ($R_{K}$), using a data sample of 711 $fb^{-1}$ that contains $772 \times 10^{6}$ $B\bar{B}$ events. The data…
The report reviews the measurements of the tau lepton parameters. The tau mass measurements at the KEDR detector as well as at the B-factories are considered in more details. The present limitations on the lepton universality are discussed.
A search for the lepton number violating $K^{+}\rightarrow\pi^{-}\mu^{+}e^{+}$ and lepton flavour violating $K^{+}\rightarrow\pi^{+}\mu^{-}e^{+}$ decays is reported using NA62 data collected in 2017 and 2018. No significant excess is…
Intriguing results for tests of the universality of electrons and muons through measurements of rates of $B\to K \ell^+ \ell^-$ and similar decays have been in the spotlight for years. The LHCb collaboration has recently reported new…
Nuclear $\beta$ decays as well as the decay of the neutron are well-established low-energy probes of physics beyond the Standard Model (SM). In particular, with the axial-vector coupling of the nucleon $g_A$ determined from lattice QCD, the…
This article discusses tests of lepton flavour universality that are carried out with the LHCb experiment. The experimental situation of \btosll and $b \to c \ell \nu$ decays is summarised.
The LHCb collaboration has very recently released a new study of $B^+ \to K^{+} \ell^+ \ell^-$ and $B \to K^{*0} \ell^+ \ell^-$ ($\ell = e,\mu$) decays, testing lepton universality with unprecedented accuracy using the whole Run 1 and 2…
A test of lepton flavor universality in B$^{\pm}$ $\to$ K$^{\pm}\mu^+\mu^-$ and B$^{\pm}$ $\to$ K$^{\pm}$e$^+$e$^-$ decays, as well as a measurement of differential and integrated branching fractions of a nonresonant B$^{\pm}$ $\to$…
The present status of universality tests of the weak couplings for quarks and leptons is reviewed, with updated information for the muon lifetime and for first-row inputs in the CKM matrix. We discuss the impact of this high-precision SM…
This is a review of new results on the Tau lepton. The lifetime has been measured with improved precision, allowing the test of lepton universality to 0.2% level. There are several new measurements of the branching ratios for the hadronic…
The NA62 experiment at CERN utilises a differential Cherenkov counter with achromatic ring focus (CEDAR) for tagging kaons within an unseparated monochromatic beam of charged hadrons. The CEDAR-H detector was developed to minimise the…
The NA48/2 experiment at CERN reports the first observation of the $K^{\pm} \rightarrow \pi^{0} \pi^{0} \mu^{\pm} \nu$ decay based on a sample of 2437 candidates with 15% background contamination collected in 2003--2004. The decay branching…