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^±.     

Analysis of e + e −→π+π−π+π− and e + e −→π+π−π0π0 processes in the energy range of \sqrt 2 = 0.98 - 1.38 GeV in experiments with a spherical neutral detector

The cross sections of the e ⁺ e ^?→π⁺π^?π ⁺π^?, e ⁺ e ^?→π⁺π^?π⁰π ⁰, and e ⁺ e ^?→ωπ→ π⁺π^?π ⁰π⁰ processes, as well as the e ⁺ e ^?→π⁺π^?π⁰π⁰ process with subtracted contribution of the ωπ intermediate state, are measured in experiments with a spherical neutral detector on the VEPP-2M collider in the energy range 0.98–1.38 GeV. About 41 000 events of the e ⁺ e ^?→π⁺π^?π⁺π ^? process and more than 54 000 events of the e ⁺ e ^?→π⁺π ^?π⁰π⁰ process have been selected in experiment. The statistical error in determining the cross section is 2–20%, while the systematic error is 7 and 8%.     

Lepton charge and model of weak interactions with μ-e transitions

The gauge model of weak interactions is proposed and μ^±?e^? transitions predicted by the model are discussed. Estimates are given for μ^±→e^? transitions on hadrons like K⁺→π^?μ⁺e⁺ with Γ (K⁺→π^?μ⁺e⁺) ? 10^?11Γ(K⁺ and μ^? capture on nuclei with W(μ^?→e⁺) ? 10^?12W(μ^? → ν). Single μ^± production in e^? beams with a cross section δ ～ 10^?42?10^?41 cm² is predicted.     

Multipion production below 1.1 GeV by e+e− annihilation

The production of multipion events by e⁺e^? annihilation has been measured at centre of mass energies 915,990 and 1076 MeV. Both channels e⁺e^?→π⁺π^?π^o and e⁺e^?→π⁺π^?π⁺π^? have been analysed. An energy threshold effect analysed. An energy threshold effect around 919 MeV (m_ω + m_π^o) has been evidenced for the π⁺π^?π^oπ^o channel and the cross section is consistent with the quasi two-body process e⁺e^?→ωπ^o. The cross section for π⁺π^?π⁺π^? is lower by an order of magnitude and increases with the energy.     

Effect of triple gluon coupling in semi-inclusive polarized scattering processes

We show that the gluon helicity inside a proton and a photon can be deduced from a knowledge of a special combination of cross sections of the semi-inclusive processese+p→e+π+π+... ande ⁺+e ^?→e ⁺+e ^?+π+π+... Such a measurement could thus be used to check the QCD prediction that the gluon helicity increases linearly with lnQ ².     

Production of pion and muon pairs in e±e− colliding beams. Extension of the equivalent photon approximation

The reactions e^?e^?→e^?e^?π⁺π^?(μ⁺μ^?) are considered here in the situation where only pions (muons) are recorded and k_⊥ (total transverse momentum of the pair) is not too small (roughly speaking m_e²?k_⊥²?m_π²); this domain gives the main contribution to the cross section. In this paper the differential cross sections have been obtained to an accuracy of (Ink_⊥²/me²)^?1k_⊥/m_π. The amplitudes with one scalar photon have to be taken into account in this approximation. Also the charge asymmetry appears due to the interference of the two-photon and bremsstrahlung diagrams. It is shown what information on amplitudes of the reaction γγ→π⁺π^? and on the pion electromagnetic form factor can be obtained from an experiment in the given set-up.     

Saturation of counterterms by resonances inK →πe + e − decays

The decaysK ⁺→π ⁺ e ⁺ e ^?,K _S→π ⁰ e ⁺ e ^? andK _L→π ⁰ e ⁺ e ^? are reinvestigated within the framework of chiral perturbation theory. The counterterms induced by strong, electromagnetic and weak interactions are determined assuming the resonance exchange. The weak deformation model, the factorization model and the largeN _c limit are used to create a weak Lagrangian. It is found that the results of the first two approaches depend on theH ₁ coupling, defined in the effective chiral Lagrangian of theO(p ⁴) order. The set of parameters used in the extended Nambu and Jona-Lasinio model can accommodeteK ⁺→π ⁺ e ⁺ e ^? decay rate within the factorization approach. The CP violatingK _L→π ⁰ e ⁺ e ^? decay rate is discussed.     

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.     

A global treatment of VMD physics up to the φ: II. τ decay and hadronic contributions to g−2

Relying on the Hidden Local Symmetry (HLS) model equipped with a mechanism breaking the U(3)/SU(3)/SU(2) symmetries and generating a dynamical vector meson mixing, it has been shown that a global fit successfully describes the cross sections for the e ⁺ e ^?→π ⁺ π ^?, e ⁺ e ^?→(π ⁰/η)γ and e ⁺ e ^?→π ⁰ π ⁺ π ^? annihilation channels. One extends this global fit in order to include also the dipion spectra from the τ decay, taking into account all reported information on their statistical and systematic errors. A model accounting for lineshape distortions of the ρ ^± spectrum relative to ρ ⁰ is also examined when analyzing the τ data behavior within the global fit framework. One shows that a successful account for e ⁺ e ^? annihilation data and τ spectra can be simultaneously reached. Then, issues related with non-perturbative hadronic contributions to the muon g?2 are examined in details. It is shown that all e ⁺ e ^? data considered together allow for improved and motivated estimates for the a _μ (π ⁺ π ^?), the π ⁺ π ^? loop contribution to the muon g?2; for instance, integrated between 0.630 and 0.958 GeV, we find a _μ (π ⁺ π ^?)=359.62±1.62 (in units of 10^?10), a 40% improvement of the current uncertainty. The effects of the various τ samples in the context of a global fit procedure leads to conclude that different lineshape distortions are revealed by the ALEPH, BELLE and CLEO data samples. Relying on global fits to the data quoted above, one also provides motivated estimates of the π ⁺ π ^?, π ⁰ γ, η γ and π ⁰ π ⁺ π ^? contributions to a _μ up to 1 GeV with the smallest possible uncertainties. These estimates are based on various global fit configurations, each yielding a good probability.     

The process e + e − → ωπ0 near the Φ resonance

The reaction e ⁺ e ^?→ωπ⁰ near a Φ resonance was studied with a spherical neutral detector at VEPP-2M e ⁺ e ^? collider. Both main modes of decay of a ω meson were investigated: ω→π⁺π^?π⁰ and ω→π ⁰γ. The probability of decay Φ→ωπ⁰ was obtained from the magnitude of the interference wave in the cross section for the reaction e ⁺ e ^?→ωπ⁰→ π⁺π^?π⁰π⁰: B(Φ→ωπ⁰) = (5.5 _?1.4 ^+1.6 ±0.3) ×10^?5. The ratio of the partial widths of the ω meson was obtained from the ratio of the cross sections for the two modes: Γ(ω→π⁰γ )/Γ(ω→π⁺π^?π⁰) = 0.0994 ± 0.0036 ± 0.0038.     

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.     

K+介子衰变的分枝比

The branching ratio of the following three modes of K⁺-meaon decay K⁺→μ⁺+π⁰+ν K⁺→e⁺+π⁰+ν K⁺→μ⁺+ν is calculated by using the theory of the universal Fermi weak interaction proposed by Feymann and others. Perturbation method with cut-off is used. The ratio obtained is 1:1.5:12, which is in fair agreement with the experimental value 1:1:15. It is shown, other conbinations of Fermi interactions can not give result in agreement with experiment.     

The discrepancy between τ and e + e − spectral functions revisited and the consequences for the muon magnetic anomaly

We revisit the procedure for comparing the π π spectral function measured in τ decays to that obtained in e ⁺ e ^? annihilation. We re-examine the isospin-breaking corrections using new experimental and theoretical input and find improved agreement between the τ ^?→π ^? π ⁰ ν _τ branching fraction measurement and its prediction using the isospin-breaking-corrected e ⁺ e ^?→π ⁺ π ^? spectral function, though not resolving all discrepancies. We recompute the lowest order hadronic contributions to the muon g?2 using e ⁺ e ^? and τ data with the new corrections and find a reduced difference between the two evaluations. The new tau-based estimate of the muon magnetic anomaly is found to be 1.9 standard deviations lower than the direct measurement.     

Leptonic coupling-types in K+ → π++- decays and the question of strangeness-changing semileptonic neutral currents

A study of the leptonic coupling types in K⁺→π⁺?⁺?^? (? = e, μ) provides come model-independent distinction between the various underlying mechanism: lowest order weak cum electromagnetic vs higher order weak interactions vs genuine strangeness-changing semileptonic neutral currents. This distinction is necessary in order to know the existence of these neutral currents. Pion energy spectrum for ? = e and the ratio of the total rate for ? = e to that for ? = μ is useful for this purpose, and the pion energy spectrum for ? = μ is of further help. Available data (? = eonly) are inadequate to provide the above distinction. Estimates of various coupling strengths are made from the observed ? = e rate.     

Measurement of the branching ratio for Υ(1S) state intoπ + π − andsearch for decaysΥ(1S)→π + π −,K + K −,p \bar p

In the experiment withe ⁺ e ^?-beams performed at the VEPP-4 storage ring with the MD-1 detector we have measuredB _μμ, the branching ratio for the decay of Υ(1S) state intoμ ⁺ μ ^?. We obtainedB _μμ=(2.12+0.20+0.10)%. It is shown that the continuum and resonance interference should be taken into account. For the first time the upper limits on the branching ratio for the decaysΥ→π ⁺ π ^?,K ⁺ K ^?,p \(\bar p\) have been measured: Br(Υ→π ⁺ π ^?)<5·10^?4, Br(Υ→K ⁺ K ^?)<5·10^?4, Br(Υ→p \(\bar p\) <9·10^?4 (90% CL).     

Lepton and pion pair production in γγ collisions measured near the threshold at DCI

This paper reports a complete analysis of data taken at DCI to measure lepton and pion pair production close to the threshold in two-photon processes: e⁺e⁻→e⁺e⁻(e⁺e⁻, μ⁺μ⁻,π⁺π⁻). Preliminary results have been previously published including one-half of the total statistics. Final results presented here are in good agreement with QED for lepton pair production. The measured cross section for pion pair production is twice as large as that expected from Born terms only — a two standard deviation effect.     

Measurement of thee + e −→π + π − π 0 ande + e −→ωπ + π − reactions in the energy interval 1350–2400 MeV

The cross sections fore ⁺ e ^?→π ⁺ π ^? π ⁰ ande ⁺ e ^?→ωπ ⁺ π ^? have been measured in the 1.35 ≦ \(\sqrt s \) ≦2.4 GeV range from 1900 nb^?1 collected by DM2 at DCI. The second process proceeds via a resonant state at ≈- 1660 MeV/c², ≈- 280 MeV/c² wide. The first one is larger than a VDM extrapolation from the ω-? peaks and, although does not show any clear structure, is compatible with the presence of the above resonance.     

Limits on the couplings of ϱ′ (1300 Me) and rhov;″ (1700 MeV) to the photon and to the (ππ) system

The analysis of the reaction e⁺e^?→π⁺π^? measured at the e⁺e^? colliding beam machine ADONE shows that, if ?′ and ?″ exist, the cross sections compare as follows (taking the ? as the reference point): $\text{σ(}\text{e}{}^{\mathrm{+}}\text{e}{}^{\mathrm{?}}\text{→ ? → π}{}^{\mathrm{+}}\text{π}{}^{\mathrm{?}}\text{)}$: σ(e⁺e^? → ?′ → π⁺π^?): σ(e⁺e^? → ?″ → π⁺π^?) = 1: (7 ± 4) × 10^?3: (1 ± 5) × 10^?4. The square of the product of their couplings to the photon (γ_?) and the γγ system (g_?ππ) are derived.