Related papers: Rare decay pi0 -> e+e-: theory confronts KTeV data
The transitions $B_{s,d}\rightarrow \ell^+\ell^-$ (for $\ell=e, \mu, \tau$), although extremely suppressed within the SM, are exceptionally clean channels particularly sensitive to New Physics contributions. So far only the branching ratio…
The decay K- -> pi0 e- nu has been studied using in-flight decays detected with the "ISTRA+" spectrometer working at the 25 GeV negative secondary beam of the U-70 PS. About 550K events were used for the analysis. The lambda+ parameter of…
We analyze the most recent data for the pion vector form factor in the timelike region, employing a model-independent approach based on dispersion theory. We confirm earlier observations about the inconsistency of different modern…
I review the theoretical basis of the prediction that the decay K_L -> pi+ pi- e+ e- should show a large CP- and T-violation, a prediction now confirmed by the KTeV experiment. The genesis of the effect lies in a large violation of CP- and…
We derive factorization relations for the transverse helicity amplitudes in the rare decays B-> K\pi l+l- at leading order in Lambda/m_b, in the kinematical region with an energetic kaon and a soft pion. We identify and compute a new…
We study the exclusive decays of $B\to K^{(*)}\ell^+ \ell^-$ by the results in the perturbative QCD with the heavy quark effective theory and lattice calculations. We obtain the form factors for the $B\to K^{(*)}$ transitions in the whole…
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…
Three events for the decay K+ => pi+,nu,nubar have been observed in the pion momentum region below the K+ => pi+,pi0 peak, 140 < P_pi < 199 MeV/c, with an estimated background of 0.93+-0.17(stat.)+0.32-0.24(syst.) events. Combining this…
The OKA Collaboration has obtained a new upper limit on the $K^+ \to \pi^0\pi^0\pi^0 e^+ \nu$ decay probability which is 65 times lower than the one currently listed by PDG. However it is still about $10^{4}$ times worse than the…
We compute the branching ratio for $\Delta\rightarrow Ne^+e^-$ and $\Delta\rightarrow N\mu^+\mu^-$ in chiral perturbation theory and find that both decays should be observable at CEBAF. With sufficiently low thresholds on the $e^+e^-$…
The interplay between short- and long-distance contributions to the K_L-->mu+ mu- decay amplitude is analyzed. The long-distance piece is estimated using chiral perturbation theory techniques and large-N_C considerations, leading to a…
We present recent preliminary results from five decay channels. From the $K_L\to\pi^+\pi^-\gamma$ channel, we extract form factors for the CP violating M1 direct photon emission amplitude and the fraction of the total decay amplitude that…
We present an updated analysis of the rare decay $K_{L}\to\pi^{0}\mu^{+}\mu^{-}$ within the Standard Model. In particular, we present the first complete calculation of the two-photon CP-conserving amplitude within Chiral Perturbation…
We measured, with the KLOE detector, the spectrum of pi+pi- invariant mass in a sample of 6.7 x 10^5 e+e- --> pi+pi-g events with the photon at large polar angle (theta_g>45^o) at a centre of mass energy sqrt(s) around the phi mass. We…
We report the first observation of the rare eta->e+e-e+e- decay based on 1.7 fb^{-1} collected by the KLOE experiment at the DAFNE phi-factory. The selection of the e+e-e+e- final state is fully inclusive of radiation. We have identified…
Using 7.33 fb$^{-1}$ of $e^+e^-$ collision data collected by the BESIII detector at center-of-mass energies between 4.128 and 4.226~GeV, we observe for the first time the decay $D^{\pm}_s\to \omega\pi^{\pm}\eta$ with a statistical…
We report a search for the rare decays $B^+ \to D^+ K^0$ and $B^+ \to D^+ K^{*0}$ in an event sample of approximately 465 million $B\bar B$ pairs collected with the BaBar detector at the PEP-II asymmetric-energy $e^+e^-$ collider at SLAC.…
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…
A first observation of the rare decay $\eta$ $\to$ $\mu^+\mu^-$e$^+$e$^-$ is reported by the CMS Collaboration at the CERN LHC. The result is based on a proton-proton collision data sample at $\sqrt{s}$ = 13.6 TeV corresponding to an…
K^0 \to pi^- e^+ nu_e e^+ e^- decay is studied up to the next-to-leading order O^4 in chiral perturbation theory. It is found that the O^4 terms appreciably modifiy the shape of the invariant mass distribution of the leptons and the energy…