Related papers: Rare decay \pi^0 \to e^+e^- as a Test of Standard …

We report the observation of the rare charm decay $D^0\rightarrow K^-\pi^+e^+e^-$, based on $468$ fb$^{-1}$ of $e^+e^-$ annihilation data collected at or close to the center-of-mass energy of the $Y(4S)$ resonance with the BaBar detector at…

A search for the decay of the tau lepton to seven charged pions and one or zero pizero mesons was performed using the BaBar detector at the PEP-II asymmetric-energy e+e- collider. The analysis uses 232.2 fb-1 of data at center-of-mass…

The current status of the experimental study of the rare kaon decay K^+ \to \pi^+ \nu \bar\nu at Brookhaven National Laboratory (BNL) by the E787 and E949 collaborations is reported.

We report new experimental limits on the \pi^0 -> \gamma X decay of the neutral pion into a photon and a light boson X followed by the decay X -> e+e-. If this process exist, one would expect a flux of high energy X's produced from \pi^0's…

We present the results of a search for the rare flavor-changing neutral-current decays B --> pi l+l- (pi=pi+/-, pi0 and l = e,mu) and B0 --> eta l+l- using a sample of e+e- --> Y(4S) BB decays decays corresponding to 428 fb^-1 of integrated…

Data from the KTeV experiment have provided many opportunities for studies of fundamental symmetries in nature, not just CP. We present new limits on the lepton flavor violating decays K_L -> pi0 mu e, K_L -> pi0 pi0 mu e and pi0 -> mu e.…

In the framework of the minimal ${SU}(3)_C\otimes {SU}(3)_L \otimes {U}(1)_N$ model, the lepton-flavour-violating decay $\pi^+ \ra \mu^- \nu_\mu e^+ e^+ $ is calculated without directly invoking lepton mixing. The branching ratio for this…

We report on a search in $e^+e^-$ annihilations for new $\pi^0$-like particles produced in association with a $\tau$-lepton pair. These objects, with a similar mass and similar decay modes to $\pi^0$ mesons, could provide an explanation for…

Motivated by the LHCb measurement, we analyze the $B_s\to \pi^+\pi^-\ell^+\ell^-$ decay in the kinematics region where the pion pairs have invariant mass in the range $0.5$-$1.3$ GeV and muon pairs do not originate from a resonance. The…

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…

We have observed 1 event consistent with the signature expected of the rare decay of a positive kaon to a positive pion and a neutrino anti-neutrino pair. In the examined momentum region of 211 to 230 MeV/c in the center of mass of the kaon…

We use experimental data on $e^+e^- \to \eta (\eta^{\prime})\pi^+\pi^-$ and conservation of vector current to estimate the branching fractions of $\tau^-$ decay to $\eta (\eta^{\prime})\pi^-\pi^0\nu_{\tau}$. The obtained values are compared…

We present some recent measurements of rare flavor-changing neutral current B decays, using data collected with the BABAR detector at the PEP-II e+e- collider at SLAC. First, we search for the rare process B+ -> K+ tau- tau+ and we do not…

In a sample of 471 million BB events collected with the BABAR detector at the PEP-II e+e- collider we study the rare decays B -> K(*) l+ l-, where l+ l- is either e+e- or mu+mu-. We report results on partial branching fractions and isospin…

The problem of $\rho$- and $\omega$- mesons contributions to the background for $\eta \to \pi^0 e^+e^-$ decay and to the asymmetries in the decays $\eta \to \pi^+\pi^-\pi^0$ and $\eta \to \pi^+\pi^-\gamma$ is considered.

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…

Using 7.33~fb$^{-1}$ of $e^{+}e^{-}$ collision data collected by the BESIII detector at center-of-mass energies in the range of $\sqrt{s}=4.128 - 4.226$~GeV, we search for the rare decays $D_{s}^+\to h^+(h^{0})e^{+}e^{-}$, where $h$…

Additional evidence for the rare kaon decay K+ to pi+ neutrino-antineutrino has been found in a new data set with comparable sensitivity to the previously reported result. One new event was observed in the pion momentum region examined,…

We present an improved Standard-Model (SM) prediction for the dilepton decay of the neutral pion. The loop amplitude is determined by the pion transition form factor for $\pi^0\to\gamma^*\gamma^*$, for which we employ a dispersive…

More than 400 $K^{+}\to\pi^{+}\mu^+\mu^-$ events were observed in a rare $K^+$ decay experiment at the AGS. Normalized to the $K^{+}\to\pi^{+}\pi^+\pi^-$ decay, the branching ratio is determined to be $(9.22 \pm 0.60 (stat) \pm 0.49…