Related papers: On V_ud determination from kaon decays
Pion $\beta$ decay, $\pi^+ \to\pi^0 e^+ \nu_e$, offers a pristine way to measure the CKM matrix element $V_{ud}$ in a purely mesonic system, with excellent control over the hadronic matrix elements. We review the physics goals and current…
Pion beta decay, $\pi^+\to \pi^0 e^+\nu(\gamma)$, provides a theoretically clean $\pm 0.3\%$ determination of the CKM matrix element $V_{\text{ud}}$. That value falls short of super-allowed nuclear beta decays where an order of magnitude…
The consistent matching of short-distance contributions and hadronic matrix elements is crucial for precise predictions of weak processes involving hadrons. In this Letter, we address this point for charged-current processes involving two…
We review the recent measurements of the rare pion decays: Pi+ -> Pi0 e+ Nu [pion beta, Pi_(e3), or Pi_beta decay], radiative decay Pi+ -> e+ Nu Gamma [Pi_(e2Gamma) or RPD], and Pi+ -> e+ Nu [Pi_(e2)] decay, as well as the radiative muon…
We present our study of the hadronization structure of both vector and axial-vector currents leading to decays of the tau into two kaons and a pion. The cornerstones of our framework are the large-N_C limit of QCD, the chiral structure…
Pionic beta decay \pi^+ to \pi^0 e^+ \nu_e is analyzed in chiral perturbation theory with virtual photons and leptons. All electromagnetic corrections up to order e^2 p^2 are taken into account. Theoretical results are confronted with…
Hadronization in tau -> K K pi nu_tau decays is driven by both vector and axial-vector currents that we study, guided by the following principles: The 1/N_C expansion -worked out at leading order, considering only the contribution of the…
Recent measurements of kaon decays contributing to the determination of |V_us| are summarized, and up-to-date evaluations of |V_us|f+(0) and |V_us| are presented.
If the CKM matrix element $V_{ud}$, that can be derived from superallowed nuclear decays, neutron decay and pion beta decay, is used for a precision test of the unitarity of the CKM matrix, the combination of the present world data seems to…
An event consistent with the signature expected for the rare kaon decay K+ --> pi+ nu anti-nu has been observed. In the pion momentum region examined, 211<P<230 MeV/c, the backgrounds are estimated to contribute 0.08 +/- 0.03 events. If the…
A search for additional evidence for the rare kaon decay K^+ --> pi^+ nu nubar has been made with a new data set comparable in sensitivity to the previous exposure that produced a single event.
After a decade of no measurements of pion and muon rare decays, PIBETA, a new experimental program is producing its first results. We report on a new experimental study of the pion beta decay, Pi(+) -> Pi(0) e(+) Nu, the Pi(e2 gamma)…
New results from the NA48 experiment on kaon and hyperon decays relevant to |V_us| are reported here. For charged kaons we present measurements of BR(K+- -> pi0 e+- nu) and BR(K+- -> pi0 mu+- nu). On neutral kaon decays we report the…
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 study rare three- and four-body kaon decays as a probe of light vector and axial-vector bosons coupled to non-conserved currents. We find that searches for $K_L \to \pi^0 \pi^0 (X\to e^+e^-)$ decays constrain the couplings of light $X$…
The recent results of the PIBETA experiment strongly suggest the presence of a non-(V-A) anomalous interaction in the radiative pion decay. The same interaction should inevitably contribute to the neutron decay and in particular it should…
The status of the experimental determination of $V_{us}$ from $K_{\ell3}$ and $K_{\mu2}$ decays is reviewed. Factors currently limiting the precision of the evaluation of $V_{us}$ from kaon decays and prospects for new measurements within…
In this paper I will describe the search for rare kaon decay processes $K^+\to \pi^+ \nu \bar\nu$ and $K^0_L \to \pi^0 \nu \bar\nu$. The small decay rate for these processes is considered a key prediction of the standard model. We searched…
The experimental determination of V_{ud} from neutron beta decay requires accurate values of the neutron lifetime and the ratio of the weak axial-vector to vector coupling constants of the nucleon. The latter is derived from measurements of…
Simple dynamics, few available decay channels, and highly controlled radiative and loop corrections, make pion and muon decays a sensitive means of exploring details of the underlying symmetries. We review the current status of the rare…