Precise measurement of Γ(K→e ν(γ))/Γ(K→μ ν(γ)) and study of K→e ν γ

We present a precise measurement of the ratio R _K =Γ(K→e ν(γ))/Γ(K→μ ν(γ)) and a study of the radiative process K→e ν γ, performed with the KLOE detector. The results are based on data collected at the Frascati e ⁺ e ^? collider DAΦNE for an integrated luminosity of 2.2 fb^?1. We find R _K =(2.493±0.025_stat±0.019_syst)×10^?5, in agreement with the Standard Model expectation. This result is used to improve constraints on parameters of the Minimal Supersymmetric Standard Model with lepton flavor violation. We also measured the differential decay rate dΓ(K→e ν γ)/dE _γ for photon energies 10<E _γ < 250 MeV. Results are compared with predictions from theory.     

Determination of the branching ratiosΓ(K L→3π0)/Γ(K L→π+ - 0) andΓ(K L→3π0)/Γ(K L→πev)

Improved branching ratios were measured for theK _L3⁰ decay in a neutral beam at the CERN SPS with the NA31 detector:

The form factors of the decays π− → e−¯veγ and K− → e−¯veγ

In the special type of the quark model we obtain the ratio=h _A/h_V of the axial (h_A) and vector (h_V) form factors for the decays ^– e^– ¯v_e and K^– e^–¯v_e different from unity. The low-energy theorem, relating the electric polarizability of the charged pion with the ratio, is analyzed. It is shown that < 1 corresponds to , calculated by accounting the contribution of the scalar meson(700) into the amplitude of the Compton effect on the pion. In the absence of the(700) contribution we have=1.Dedicated to Academician Václav Votruba on the occasion of his eightieth birthday.     

Study of the K − → e − νπ 0 decay

The decay K ^? → e ^? νπ ⁰ has been studied using in-flight decays detected with the ISTRA₊ setup working at the 25-GeV negative secondary beam of the U-70 PS. About 130K events were used for the analysis. The λ ₊ parameter of the vector form factor has been measured: λ ₊=0.0293±0.0015(stat.)±0.002(syst.). The limits on the possible tensor and scalar couplings have been derived: f _T/f ₊(0)=?0.045±0.060(stat.) and f _S/f ₊(0)=?0.019 _?0.016 ^+0.025 (stat.).     

Zum Zerfallπ→e+ν+γ

The radiative decay of the chargedπ-mesonπ→e+ν+γ is calculated using dispersion relation techniques. It is assumed that the weak interaction producing the decay has a V-A structure. The decay through the vector variant has been reinvestigated and found to be different from the result ofVaks andIoffe. The theoretical prediction of this paper is in agreement with a preliminary experiment recently performed at CERN.     

Study of K ± → e ± νπ 0 decays at the KMN setup

K ^± → e ^± νπ ⁰ decays have been studied using the KMN setup at the Institute for High Energy Physics (Protvino). The experiment has been performed in the 36-GeV/c hadron beams of the IHEP accelerator. The accumulated data allow us to select ～1.08M candidates for K _e3 decays. Analyzing the Dalitz plot of these events, we estimate the linear slope of the charge form factor to be λ ₊ = [30.44 ± 0.83(stat.) ± 0.74(syst.)] × 10^?3.     

Study of conversion decays φ→ηe+e− and η→γe+e− in the experiment with SND detector at VEPP-2M collider

The conversion decays φ→ηe⁺e⁻ and η→γe⁺e⁻ were studied by the SND detector using φ-meson production in e⁺e⁻-annihilation at VEPP-2M collider. The branching ratios of these decays were measured: Br(φ→ηe⁺e⁻)=(1.19±0.19±0.07)×10⁻⁴ and Br(η→γe⁺e⁻)=(5.15±0.62±0.39)×10⁻³. The e⁺e⁻-pair mass spectra and transition form factors were also studied.     

Probing the weak boson sector inγe→Ze

We study possible deviations from the Standard Model in the reactionγe→Ze at a 500 GeVe ⁺ e ^? collider. As a photon source we use a laser backscattered photon beam. We investigate the most generalγZγ andγZZ vertices including operators up to energy-dimension-six which are Lorentz invariant. These vertices require four extra parameters; two are CP-conserving,h ₁ ^γ andh ₁ ^Z , and two are CP-violating,h ₂ ^γ andh ₂ ^Z . We present analytical expressions of the helicity amplitudes for the processγe→Ze for arbitrary values of anomalous couplings. Assuming Standard Model values are actually measured we present the allowed region in the (h ₁ ^γ ,h ₁ ^Z ) plane at the 90% confidence level. We then show how the angular correlation of theZ decay products can be used to extract detailed information on the anomalous (especially CP-violating)γZγ andγZZ couplings.     

A new upper limit for the branching ratio of the decay K0S → e+e−

A new value of the upper limit for the branching ratio of the decay of K⁰_S into e⁺e⁻ has been experimentally obtained using a lead glass detector. The value is BR (K⁰_S → e⁺e⁻) < 1.1 × 10⁻⁴ (90% CL).     

Study of Light Hypernuclei by the (e,e′K +) Reaction

We have been performing Λ hypernuclear spectroscopic experiments by the (e,e′K ⁺) reaction since 2000 at Thomas Jefferson National Accelerator Facility (JLab). The (e,e′K ⁺) experiment can achieve a few 100 keV (FWHM) energy resolution compared to a few MeV (FWHM) by the (K ^?, π ^?) and (π ⁺, K ⁺) experiments. Therefore, more precise Λ hypernuclear structures can be investigated by the (e,e′K ⁺) experiment. ${^{7}_{\Lambda}{\rm He}}$ , ${^{9}_{\Lambda}{\rm Li}}$ , ${^{10}_{\Lambda}{\rm Be}}$ , ${^{12}_{\Lambda}{\rm B}}$ , ${^{28}_{\Lambda}{\rm Al}}$ , and ${^{52}_{\Lambda}{\rm V}}$ were measured in the experiment at JLab Hall-C. In addition, ${^{9}_{\Lambda}{\rm Li}}$ , ${^{12}_{\Lambda}{\rm B}}$ , and ${^{16}_{\Lambda}{\rm N}}$ were measured in the experiment at JLab Hall-A.     

Search for the e + e − → K ± K S π ∓ process on the VEPP-2M e + e − collider

We report on the results of the search for the e ⁺ e ^? → K ^± K _S π ^? process. Data with an integrated luminosity of 1.36 pb^?1 collected in experiment with a spherical neutral detector (SND) on the VEPP-2M e ⁺ e ^? collider in the energy range from 1.36 to 1.38 GeV have been analyzed. The upper limits of the σ < 150 pb cross sections of the sought process have been established for an energy of 1.37 GeV at a confidence level of 90%.