Estimate of the probability of K+→μ+νμγ decay

About 100 000 K⁺-decays were observed in a magnetic spectrometer with streamer chambers. The estimation for the radiative decay K⁺→μ⁺ν_μγ, R^exp = [W(K⁺→μ⁺ν_μγ)]/[W(K⁺→all)]=(5.8±3.5) x 10^?3, at E_γ ? 9 MeV was obtained and the ratio R = [W(K⁺→π⁺π°)]/[W(K⁺→μ⁺ν_μ)] = 0.328 ± 0.005 was measured.     

Observation of KS0 semileptonic decays with the CMD-2 detector

The decay K_S⁰→πeν has been observed by the CMD-2 detector at the e⁺e⁻ collider VEPP-2M at Novosibirsk. Of 6 million produced K_L⁰K_S⁰ pairs, 75±13 events of the K_S⁰→πeν decay were selected. The corresponding branching ratio is B(K_S⁰→πeν)=(7.2±1.4)×10⁻⁴. This result is consistent with the evaluation of B(K_S⁰→πeν) from the K_L⁰ semileptonic rate and K_S⁰ lifetime assuming ΔS=ΔQ .     

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.     

Observation of possible production and decay of short-living heavy neutral particles in the SKAT neutrino experiment

In the SKAT bubble chamber neutrino experiment production of a short-living neutral particle with mass (1.4?m?2.5) GeV/c² and lifetime τ≈6×10^?12 s has been detected. The event may be interpreted as production and decay of the heavy lepton M⁰→μ^?+e⁺+ν_e with mass (1.4?m_M⁰?2.1) GeV/c². It might also be the production of a charmed particle D⁰→e⁺+τ^?+ν_e (D⁰→e⁺+π^?+ν_e) with mass 1.4?m_D⁰?2.5) GeV/c² in a non-diagonal neutral current. The probability to interpret the event as other possible processes is very low.     

Search for ΔQ=−ΔS transitions in Σ-hyperon decays

In a sample of 10⁶ Σ ⁺ hyperons we have searched for the decaysσ ⁺→ ne⁺ ν andσ ⁺→nμ ⁺ ν, which would violate theΔQ=ΔS rule. NoΣ ⁺→ne⁺ ν decay was found, whereas 313σ ^?→ne^? ν decays were identified in the same film. With 90% confidence we obtain $$\frac{{\Gamma (\sum ^ + \to ne^ + v)}}{{\Gamma (\sum ^ - \to ne^ - \bar v)}} \leqq 3.10^{ - 2} .$$ Having found two candidates for the decayσ ⁺→nμ ⁺ ν and 104Σ ^?→nμ ^? ν events we obtain for the muonic mode $$\frac{{\Gamma (\sum ^ + \to ne^ + v)}}{{\Gamma (\sum ^ - \to ne^ - \bar v)}} \leqq 3.10^{ - 2} .$$ The probability that theμ ⁺-events are simulated byσ ⁺→nπ ⁺ γ with subsequent undetectedπ ⁺→μ ⁺ ν decay is less than 4%.     

Signatures of neutral heavy leptons in neutrino-induced dilepton events

The tentative indication in some experiments of μ^?e⁺ or π^?μ⁺ events with unusual characteristics revives the speculation that neutrino-induced dileptons may contain a weak signal of neutral heavy lepton (L⁰) production. We study the characteristics of dileptons expected from the production of an L⁰ through a current of the form $\text{L}{}^0\text{γ}{}_{\mathrm{\alpha }}\text{(1+γ}{}_5\text{)ν}{}_{\mathrm{\mu }}$. Both quasi-elastic and deep inelastic excitation are investigated and a comparison is made with dileptons of charm origin. As an illustration of a model with a ν_μ→L⁰ transition, we discuss the 2-2 version of the SU(2) × U(1) model and comment on the role of the Higgs particle in such transitions.     

Lepton-flavor-violating pion decay π+→μ−νμ e + e + and SU(3)C ⊗ SU(3)L ⊗ U(1)N model

Within the minimal SU(3)_C ? SU(3)_L ? U(1)_N model, the lepton-flavor-violating decay π⁺→μ^?ν_μ e ⁺ e ⁺ is calculated without directly invoking lepton mixing. The branching ratio for this rare pion-decay mode is found to be much smaller than the current experimental upper limit. If the anomalous interactions are discarded, this result coincides with the result of the previous calculation.     

Radiative Kaon decays and CP violation in chiral perturbation theory

Chiral perturbation theory is a very useful framework for testing the standard model in processes where long-distance effects are expected to play an essential rôle. We analyze the rare K decays K⁰→γℓ⁺ℓ⁻, K⁺→π⁺γ3 and K_L→π⁰ℓ⁺ℓ⁻ in the effective chiral formulation of the standard model. These processes, like the decays K⁰→γγ, K⁺→π⁺ℓ⁺ℓ⁻, K_S→π⁰ℓ⁺ℓ⁻ and K⁰→π⁰γγ discussed in previous work, have the property that the corresponding amplitudes vanish to lowest order in chiral perturbation theory. Precise predictions for decay rates and spectra are made in terms of a few coupling constants not restricted by softly broken chiral symmetry alone. Special consideration is given to various possible tests of CP noninvariance in these decays, in particular to effects due to intrinsic CP violation in the amplitudes. We find that chiral perturbation theory correlates different CP-violating observables such as the charge asymmetries in K^±→π^±γγ and K^±→π^±ℓ⁺ℓ⁻, the one-photon exchange contribution to K_L→π⁰e⁺e⁻ and the transverse polarization in K_L →π⁰μ⁺μ⁻. Detailed numerical results are shown.     

Compilation of coupling constants and low-energy parameters

The electron capture decay ${}^{163}\text{Ho}\text{→}{}^{163}\text{Dy}{}^{\mathrm{<mtext>H</mtext>}}\text{+ν}{}_{\mathrm{<mtext>e</mtext>}}$ occurs with a record low energy release, Q ～ 2.6 keV. The daughter Dy^H atom has an electron hole, H, and predominantly decays by electron ejection Dy^H→Dy^H₁H₂+e^?. We investigate the neutrino mass sensitivity of the electron spectrum in the overall process Ho→Dy^H₁H₂+e^?+ν_e. In this spectrum, the fraction of events sensitive to a fixed non-zero neutrino mass in one to two orders of magnitude smaller than in the standard case of tritium β decay. But the electron energies in ¹⁶³Ho decay are considerably smaller than in ³H decay (Q ～ 18 keV). This suggests experiments whose energy resolution could be much better than that of the magnetic spectrometers conventionally used in the tritium case.     

Signatures for neutralinos at theZ 0

We calculate the visible and invisible width for production of neutralinos,Z ⁰→χ _i ⁰ χ _k ⁰ , and all possible decay rates of the neutralinos. We systematically study their dependence on the supersymmetry parameters and work out the domains where detectable signatures occur. These are the one-sided eventsZ ⁰→e ⁺ e ^?+p _miss,Z ⁰→jets+p _miss,Z ⁰→γ+p _miss andZ ⁰→H _2,3 ⁰ +p _miss, and the two-sided eventsZ ⁰→γ+γ+p _miss,Z ⁰→γ+l ⁺ l ^?+p _miss andZ ⁰→γ+jets+p _miss.     

Probing QCD via four-jet decays of theZ boson

For a quantitative analysis of the non-Abelian three-gluon vertex a continuous parameterisation of possible deviations from QCD is highly desirable. An almost unique extension of the three-gluon vertex is provided by the dimension-6 operator Tr(F _μ ^ν F _ν ^ρ F _ρ ^μ ). The effects of this interaction term on various observables ine ⁺ e ^?→γ,Z→4 jet production are studied in detail. Presente ⁺ e ^? data are expected to give rather weak bounds on such anomalous contributions to the triple gluon vertex.     

Study of some rare decays of the K+ meson

In a search for very rare decays of the K⁺ meson we observed the K⁺→μ⁺νe⁺e^? and K⁺→e⁺ν e⁺e^? modes with branching ratios of (10±3) ×10^?7 and (2⁺²_?2)×10^?7 respectively. We also put new limits on a decay allowed by the alternate scheme of lepton conservation K⁺→π^?μ⁺e⁺, on a decay with double charged weak current K⁺→π^? e⁺e⁺ and on other forbidden decays K⁺→μ^?νe⁺e⁺ and K⁺→π⁺μ^±e^±.     

Hyperfeinstrukturuntersuchung des 6p 2 P 3/2-Terms im Au I-Spektrum durch Resonanzstreuung von Licht

From about 6×10⁶ stoppingK ^?-meson reactions in the Saclay 80 cm hydrogen bubble chamber 70Σ ^?→Λe^?¯ν and 11Σ⁺→Λe⁺ν decays have been identified. The ratio of the vector to axial vector coupling constant has been determined,f ₁/g ₁=?0.22±0.28, consistent with the predictionf ₁=0 of the CVC-theory. The branching ratios for the two decay modes are,Γ(Σ ^?→Λe^?ν)/Γ(Σ^?→ all modes)=(0.69±0.12). 10^?4,Γ(Σ⁺→Λe⁺ν)/Γ(Σ⁺→ all modes)=(0.29±0.10). 10^?4. The ratio, Γ(Σ⁺→Λe⁺)/Γ(Σ^?→Λe^?v)=0.69±0.18, agrees with the phase space ratio, 0.61, therefore a theory that includes no second class currents is consistent with the data.     

New search for T violation in the decays of the charged kaon

We report the results of the measurement of T-violating transverse muon polarization in the decays K ⁺→μ ⁺ ν _μ π ⁰ (K _μ3) and K ⁺→μ ⁺ ν _μ γ(K _μ2γ) performed in experiment E246 at KEK. The preliminary results obtained for the entire data set taken in the period 1996–2000 are consistent with no T violation in both decays.

     

K→ππγ and chiral perturbation theory

Weak radiative decaysK _L,S →π⁺π^?γ andK ⁺→π⁺π⁰γ are reexamined. The electromagnetic form factors and long-distance contributions to the direct photon emission are evaluated using the higher order effective chiral Lagrangian. We find that (1) the naive soft-pion theorem cannot be applied to the magnetic-type transition amplitude, (2) the shortdistance contribution toK _L →π⁺π^?γ is comparable to or even bigger than the long-distance one, (3) the ΔI=1/2 enhancement persists in the decayK ⁺→π⁺π⁰γ, (4) to the order of 1/Λ _χ ² (Λ _χ being the chiral-symmetry breaking scale) the direct photon emission amplitude does not receive a contribution from penguin operators, and (5) the 1/N _c expansion improves the discrepancy between theory and experiment.     

New measurements of the radiative decay modes of the φ-meson

The radiative decay models of the φ-meson have been studied: e⁺e^?→φ→ηγ→3γ; e⁺e^?→φ→π^oγ→3γ. Cross sections σ_{φ→ηγ→3γ} and σ_{φ→π^oγ→3γ} have been measured at five energies in the φ-meson energy region and clearly show the φ-resonance in the ηγ → 3γ mode as well as in the π^oγ → 3γ mode. From a Breit-Wigner fit to the experimental data the values of the branching ratios are deduced: B_φ→ηγ = (1.5 ± 0.4) × 10^?2; B_φ→π^oγ = (1.4 ± 0.5) × 10^?3.     

Exotic decays of the muon and heavy leptons in gauge theories

We have studied the decay ?₁ → ?₂ + γ for arbitrary like charged spin $\text{1}\text{2}$ leptons in a manner which is applicable to a large class of models. Our computations assume that this process is induced by one loop diagrams. When the leading effect is cancelled by a leptonic G.I.M. mechanism, we find an extremely large enhancement of O(M_W⁴/M_L⁴) in Λ(μ^?→e^?+e⁺e^?)/Λ(μ^?→e^?+γ) if the intermediate lepton is charged.     

e + e − annihilation to π 0 π 0 γ and π 0 η γ as a source of information on scalar and vector mesons

We present a general framework for the model-independent decomposition of the fully differential cross section of the reactions e ⁺ e ^?→γ ^?→π ⁰ π ⁰ γ and e ⁺ e ^?→γ ^?→π ⁰ η γ, which can provide important information on the properties of scalar mesons: f ₀(600), f ₀(980) and a ₀(980). For the model-dependent ingredients in the differential cross section, an approach is developed, which relies on Resonance Chiral Theory with vector and scalar mesons. Numerical results are compared to data. The framework is convenient for development of a Monte Carlo generator and can also be applied to the reaction e ⁺ e ^?→γ ^?→π ⁺ π ^? γ.     

Measurement of the pion axial form factor from radiative decay

The decay π⁺→e⁺νγ has been measured by detecting the positron with a magnetic spectrometer and the photon with an array of NaI scintillators. Using CVC to compute the vector form factor from the π⁰ lifetime we use our data to determine the ratio γ of the axial-vector form factor to the vector form factor. With the best present value for the π⁰ lifetime (0.897±0.022±0.017)×10⁻¹⁶ s and F_V=(2.55 ±0.05)×10⁻² we obtain two solutions: γ=0.52 ±0.06, favored by a likelihood ratio greater than 8.5 against γ=−2.48±0.06.